Meltdown Motorsport - In the bleak midwinter

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Re: Meltdown Motorsport - In, out, in, out, shake it all abo

Post by ImpManiac » Wed Mar 21, 2012 5:42 pm

On the plus side, at least you noticed the problem and shut the engine down quickly, Meltdown. I'd say you averted what could have been a really bad blow up rather than just a really nasty snag. :wink:

IM 8)
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Re: Meltdown Motorsport - In, out, in, out, shake it all abo

Post by apeximp » Sat Mar 24, 2012 3:19 pm

Any further news on your car Nick ?
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Re: Meltdown Motorsport - In, out, in, out, shake it all abo

Post by Meltdown » Sat Mar 24, 2012 7:30 pm

As yet no, haven't had the time. Tomorrow is the big strip-down day.
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Re: Meltdown Motorsport - In, out, in, out, shake it all abo

Post by apeximp » Mon Mar 26, 2012 8:03 pm

Nothing to tell after yesterdays strip down ?
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Re: Meltdown Motorsport - Come in number three your time is

Post by Meltdown » Tue Mar 27, 2012 9:25 pm

As predicted, big end bearing on number 3 cylinder has indeed given up...in fact when you see the photo I'm sure you'll agree it was moments away from total disaster :shock: I've seen flanges before but not to this extent, plus the locating tang (?) has gone so the shell has rotated within the rod :shock: The end cap shows some blueing - I presume as a result of the faliure rather than the lightening process, what thinks you?

Image

BSK not revealing much so out it came.

Image

Image

Image

To my knowledge the engine has just done the miles I've driven since Harry rebuilt it, 100 very gentle road miles, an afternoon on a rolling road where it spent more time off than on, plus 7 very soggy laps of Donington. I'm struggling to see how the bearing could wear so quickly and am open to ideas. As stated before, I've used good oil, was on track with a good sump by all accounts and the track was way too slippery to generate surge. Does the rod need changing?

No 3 was the only rod that I could move on the crank by hand. I've not had time to inspect the others or the crank itself as yet. The shell you see here is so worn I can't even read the size markings. The drained oil shows plenty of metal particles as you'd expect.

All help and advice gratefully received.
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Re: Meltdown Motorsport - Come in number three your time is

Post by Dave ' Linwood ' Lane » Tue Mar 27, 2012 9:43 pm

jeez that got hot :shock: , oil starvation i would guess given its only done 100 miles or so , is that sump baffle something to do with it maybe
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Re: Meltdown Motorsport - Come in number three your time is

Post by Meltdown » Tue Mar 27, 2012 9:47 pm

Noddy wrote:jeez that got hot :shock: , oil starvation i would guess given its only done 100 miles or so , is that sump baffle something to do with it maybe
Looks like one of Stuart Brownsey's judging by his excellent website so I hope not.
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Re: Meltdown Motorsport - Come in number three your time is

Post by CMGBW » Tue Mar 27, 2012 10:02 pm

Having said that, I've witnessed a bottle part company from its mount in a rally car that came second best to a tree stump as it landed...backwards...at around 100mph The force was sufficient to break the co-driver's grp seat in half
I too remember that day hubby darling, as we were backing at speed into the trees to see the under carriage of the aforementioned car fly past us!!

Hmmmm that was the day I was given a brolly by a friend of the chap you were crewing for - only to end up working for the company the brolly was from 2 weeks later... and now 20 days short of 17 years later I shall be leaving them! Redundancy... it's a wonderful thing!!
:roll: :)
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Re: Meltdown Motorsport - Come in number three your time is

Post by CMGBW » Tue Mar 27, 2012 10:14 pm

Personally - I think the big end let go because it knew Nick hadn't painted PTO on the underside so it saved him the embarrassment of flipping with no instructions... Love ya really honey! x
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Re: Meltdown Motorsport - Come in number three your time is

Post by Meltdown » Tue Mar 27, 2012 10:23 pm

Piccies of the car (and cake) on the Donington thread btw :D
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Re: Meltdown Motorsport - Come in number three your time is

Post by Lotus-e-Clan » Tue Mar 27, 2012 10:52 pm

Here comes the Voice of doom and gloom (I know, I know :roll: ), but the following is just my opinion ... :|

I would not use a strengthening plate like that. Even if others told me they used the same design "without problems" ... I'd have my fingers in my ears singing la la la la, and I still wouldn't risk it.

The main issue for me is the lack of oil return to the sump under braking at high revs on the over-run, and just the lack of consideration for oil return full stop ...basically the strengthening aspect is over engineered. The type that is open (and gives access to the BEs without removal ) is man enough to give the block rigidity AND the oil return is unobstructed. I worked out the oil volume of a high capacity oil pump (like yours) and then calculated that it can pump nearly 1 litre per second @ 10,000 rpm, so even allowing for error in the calc, pumping losses, the bypass valve and a lower peak rpm it will not take long for the sump to empty it's contents to all regions above the BS plate and those holes in those locations won't cope with the oil return IMO.

It's much safer to deal with oil surge by using baffles in the sump pan ALONE and Mr Hanna's sump IS a proven anti-surge design. But to belt and brace using such a sump PLUS effectively partitioning off the crankcase from the sump via the BS plate means oil return has to be compromised at some point at high revs and/or under braking. For sure those holes and their location in the BS plate will impede oil surge from the sump so logically the reverse flow will be impeded also.

I'd be thinking that if the cap is that overheated then the BE was binding for SOME TIME BEFORE it span the shell.... so could be either out of round or over tightened enough to bind.

EDIT: OR the BS plate /baffled sump / poor oil return issue I suspect has caused chronic oil starvation at high rpm (no surge necessary!)...and as often is the case, No 3 is the one that suffers most following oil starvation. :(
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Re: Meltdown Motorsport - Come in number three your time is

Post by apeximp » Tue Mar 27, 2012 11:44 pm

Nick if you read thro my Fraser imp thread I had a almost identical blow up with my 998 after only 120 road miles , it never saw the track !!!
Was never resolved and Dennis Ault replaced the engine !
That engine was then after my second Silverstone race sold to a guy I Scotland who was going to put it in a side car !
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Re: Meltdown Motorsport - Come in number three your time is

Post by Dave ' Linwood ' Lane » Wed Mar 28, 2012 6:52 am

Lotus-e-Clan wrote:I would not use a strengthening plate like that. Even if others told me they used the same design "without problems" ... I'd have my fingers in my ears singing la la la la, and I still wouldn't risk it.

The main issue for me is the lack of oil return to the sump under braking at high revs on the over-run, and just the lack of consideration for oil return full stop ...basically the strengthening aspect is over engineered. (
I didnt want to say it like that as Nick wouldnt speak to me again , baffle was my first thought though
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Re: Meltdown Motorsport - Come in number three your time is

Post by Lotus-e-Clan » Wed Mar 28, 2012 7:11 am

He's deffo not gonna speak to me. :(

Something else to consider.

IF chronic oil starvation @ high rpm due to poor oil return IS the problem,.... when the supply from the pump resumes, the extra long circuit from oil pump; filter block; Laminova; Mocal oil rad; then back to filter block BEFORE reaching the main oil gallery may well add to the oil starvation time. And you said it took a while for that circuit to fill when you first started the engine from new, so not difficult to imagine something similar in a chronic oil starvation scenario.

Having said all of that, a totally separate possibility for the No 3 failure, not related to oil starvation, is that the fillet radius on the BE journal is out of spec (Pete Richards had this ....and it can be measured at least) ....plus maybe wide shells have been used?
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Re: Meltdown Motorsport - Come in number three your time is

Post by Mike Hanna » Wed Mar 28, 2012 8:25 am

Hi all. Perhaps this being a"spare engine" sitting unused for a period of time the bearings dried out and together with the extra long route to fill up to get pressure the damage may have started before the engine was run. Might be the system got an air lock Perhaps an electric oil pump should be employed to get the oil circuit filled before the engine is turned over.I presume standard size rod bolts were used and not over tightened? Cheers. Mike
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Re: Meltdown Motorsport - Come in number three your time is

Post by benwick3 » Wed Mar 28, 2012 8:36 am

For once I'll agree entirely with my fellow Clan owner. Failure is due to oil starvation at moderate to high revs. Design of strengthening plate is preventing adequate oil return to the sump and hence inadequate oil feed to the bearings. The holes are in the wrong place for an engine that is tilted over. The direct route for the return is along the lowest edge where there are only two small slots. Despite what some of the so called experts tell you the original open strengthening plate provides adequate rigidity and does not impede the return oil flow to the sump. I don't know the type of sump used but from reports it has performed satisfactory on other cars over the years.

For a wet sump installation I add volume to the bottom of the existing sump with the original base forming a horizontal baffle and extend the pick up to the lower area. Works with no problems as confirmed by Michel Chapel in his Clan which has completed two successful years in the Maxi 100 series in France. winning his class both years, without any problems on the oiling front whatsoever. Also he uses soft Yoko A0048 tyres which have more grip than the teflon Dunlops used in the HSCC Historic Saloons.

Getting back to the Meltdown Motorsport problems as the rod has blued due to overheating then it's definately a case, in my opinion, of replacement being necessary. Similarly a replacement crank should be used as it's a fair bet that apart from the journal requiring regrinding that the crank will be bent.

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Re: Meltdown Motorsport - Come in number three your time is

Post by impmann » Wed Mar 28, 2012 9:28 am

Nick,

If you need a crank, let me know - I have one in the shed that will need a clean up but came from a good running engine (corrosion damage to the water jacket/top of liner). 8)
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Re: Meltdown Motorsport - Come in number three your time is

Post by stuartbrownsey » Wed Mar 28, 2012 9:42 am

Seems everyone has their own ideas on sumps, baffels etc. Its all being tried before but it still
appears Imps suffer from big end bearing faliure. I've even got an engine on a dry sump setup
that lost no3 bearing last year.I think Pete has also a lost big end in his dry sump setup.
David Heale is using one of my plates in his engine with no problems at all last season as are many others.
There could be a possible conflict in baffle arrangement betweem Mikes sump and my plate.

My thoughts are the bearing width is very marginal when under high loads so its always going to be an issue.
Oil selection is critical and for that reason I only use Joe Gibbs XP6 in all my race engines, Its much more shear stable
than many other including Valvoline VR1 which I wouldnt put in my lawn mower. Also oil temp should be kept to 80 degs
max. If you warm an Imp block to 80 degs and measure the main bearing journels they're around .002" bigger. Andy Jones
makes a neat water/oil heat exchanger that works well.(I'll collect my commision later Andy) I'm wary of laminova's. I've had
an issue with oil frothing on a hyabusa and it was found to be the laminova causing the problem for some reason.

Keep the faith

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Re: Meltdown Motorsport - Come in number three your time is

Post by Lotus-e-Clan » Wed Mar 28, 2012 10:20 am

Yep to be fair to Stuart, somethings work in combination and somethings don't....and too much of something can be bad obviously.

And whilst we are on the subject of oil return, I've been thinking about improving the oil drain from my head. I even ran through the possibility in my head, of an electric oil pump triggered @ high rpm (by th shift light output from the Canems). But once I thought about the frothing that could occur and then the complication of using intermediate swirl tanks to control the frothing, I came to the conclusion I might just optimise the oil drain bore diameter and be done with it for now.

And yes, I'm a great believer in controlling oil temp too. But to control it you need to know how a newly designed system is behaving....so an oil temp gauge (with the sensor in the return line from oil cooiler/heat exchanger that feeds the main gallery) is a "must-have" for any new installation design, water temp does not reflect oil temp unless heat exchange is optimised.
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Re: Meltdown Motorsport - Come in number three your time is

Post by Dave ' Linwood ' Lane » Wed Mar 28, 2012 4:56 pm

Cant tell exactly but purple in heat treating is about 270 - 280 degrees C ,
OUCH :shock:
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Re: Meltdown Motorsport - Come in number three your time is

Post by ChrisBenoy » Wed Mar 28, 2012 7:29 pm

There are two things I can think of here that might possibly help the situation, these are things i've pondered while being in a similar situation to how you are now (looking into an engine damaged by lack of oil)

Firstly, very well done for stopping it before it went bang, that has obviously saved you a lot of money and extra hassle. When imps blow, as i'm sure everyone here is aware of it tends to be no.2 or usually no.3 big end that ultimatly lets go. Now this is obviously down to the fact that 2 and 3 share an oil supply so when the system overall has low pressure these two big end bearings will suffer badly. Now this is only speculation and theory but the fix to this generally, as used on other cars that have a shared oil supply, is to crossdrill the crankshaft, this is to equalise the pressure across the crank and give improved oil flow to the shared big ends. I believe the downsides to this are that firstly its quite hard to do so is a job for a good machine shop or engine builder and secondly as that it can cause weakness in the crank although I believe this only happens if its done wrong. I've seen this done on long stroke cranks by a well regarded imp engine builder so it has been done and might be a good idea in the competition environment.

Secondly, the general concensus here is that either dry bearings on startup or surge due to lack of oil is what would have caused this sort of damage. Its not unreasonable to think that both of this problems could be avoided with an accusump. For those that are not aware of what this is - Its essentially a sealed hydraulic oil reservoir that can pressurise the system when necessiary. This can give oil pressure and lubrication to an engine prior to cranking which would sort out the dry bearing issue. Also when the oil pickup cannot get a supply of oil the accusump releases its oil to keep the oil pressure up. Once the oil pressure rises again the accusump refills ready for the next surge. How long it can supply an engine with low oil pressure for depends on the size of the accusump and how large the engine is/ how fast its going but it should be able to cope with the couple of seconds of surge a race imp suffers from. The main downside of these being the price, which is not insubstantial.

Once again I haven't actually tried one of these (although i'd like to at some point funds permitting, more for the pre-lubrication than anything but surge protection seems good too) although the theory is sound and I know of several people with high grip kit cars that do a lot of trackdaying and they swear by them. Its generally considered to be the next best thing to a dry sump system and is considerably easier to install.

Anyway just some random musings :)
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Re: Meltdown Motorsport - Come in number three your time is

Post by Meltdown » Wed Mar 28, 2012 8:01 pm

Well, the above comments are precisely what I need, plenty of thoughts and ideas will help so please keep them coming (don't worry LeC & Noddy, I haven't blacklisted you).

The design of Mike Hanna's sump, from what I can see, would have no ill effect on oil flow through the plate but I understand that the slots MIGHT possibly be restrictive (Stuart, I'm not having a go, especially as you've proved the design in other engines - I'd be interested to know whether others have the same plate/sump combination, I'll call you tomorrow if that's ok. I'd rather solve the problem than point a finger at anyone). The notion that the shells might be too wide is interesting, too.

To bring you up to speed, I've been taking ancillaries off the engine ready for removal, the camshaft lobes are good as new but haven't taken a cap off yet, followers are good too. I'll take the head off next as with the large amount of movement of no3 piston I fear it may have become over-familiar with the head. It seems that my main priority is to establish whether the oil starvation is localised or widespread. Rod bolts are ARP and were not, in my opinion, over-tight.

LeC, thanks for letting on where the oil temp sensor should go, that was on my question list :D
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Re: Meltdown Motorsport - Come in number three your time is

Post by bks974c » Wed Mar 28, 2012 8:45 pm

I have an engine sitting awaiting a new bottom end that suffered pretty much the same fate except the blueing in the rod. This engine had done a few thousand road and competition miles since its rebuild.

Once the big end has picked up for whatever reason and starts to turn it demise is sealed as the oilway is now blocked and its running without any lubrication.

Scott
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Re: Meltdown Motorsport - Come in number three your time is

Post by Meltdown » Wed Mar 28, 2012 9:20 pm

bks974c wrote:
Once the big end has picked up for whatever reason and starts to turn it demise is sealed as the oilway is now blocked and its running without any lubrication.

Scott
That makes sense. From then on it would happen quickly as was the case...on song braking into the chicane then suddenly off kilter coming out onto the straight.
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Re: Meltdown Motorsport - Come in number three your time is

Post by bks974c » Wed Mar 28, 2012 9:55 pm

There has been a number of comments on the oil return being through the slots at the bottom of the BSK but seem to have missed the fact that the oil level at rest is pretty much at the top of the oil pick up mount ie two allen capped bolts in the pics. Any oil above this level during running will be able to return through to the sump side through the round holes.

Whether the holes are sufficiently large to allow adequate flow I'm not qualified to comment, long time since I did any fluid dynamics.

Most of the oil that is being sucked up by the pump will be being returned via the Pressure relief valve in the oil filter housing straight to the sump - would it make sense to pipe this directly to the sump rather than spraying out on the wrong side of the baffle or taken a step further and piped directly to the pick up.

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Re: Meltdown Motorsport - Come in number three your time is

Post by benwick3 » Wed Mar 28, 2012 10:32 pm

Meltdown wrote: The notion that the shells might be too wide is interesting, too.:D
I think you will find that what Stuart actually said is that he believes that the width of the bearing is marginal, i.e, not wide enough. This confirms an analysis on the rods and bearings from one of my blown engines some years ago by a manufacturers engineering division that came up with the same opinion that at the power and torque being delivered the width of the bearing was marginal. Consequently, as some of you know, I have been using slightly wider bearings in my race engines. Whilst this would appear to have helped the situation it has resulted in other minor problems which I believe to be currently under control.

On the Accusump front whilst it would appear that this could provide a solution, someone I know did look into it several years ago and whilst using it on another type of engine came to the conclusion that in practice the reaction time was too slow. Perhaps, however, someone would be willing to spend the considerable amount of money required to purchase one and give it a try. In the mean time I think I'll stick to using a dry sump where I can.

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Re: Meltdown Motorsport - Come in number three your time is

Post by Mike Hanna » Wed Mar 28, 2012 11:20 pm

HI. I think the clue to the problem could be the length of time it initially took to get oil circulation in the first instance.. Perhaps the oil used is too thick when cold and the pump is struggling to get the oil round quick enough on initial start ups thus doing "minor " damage to the shells. Mike
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Re: Meltdown Motorsport - Come in number three your time is

Post by Meltdown » Thu Mar 29, 2012 6:06 am

benwick3 wrote:
Meltdown wrote: The notion that the shells might be too wide is interesting, too.:D
I think you will find that what Stuart actually said is that he believes that the width of the bearing is marginal, i.e, not wide enough. This confirms an analysis on the rods and bearings from one of my blown engines some years ago by a manufacturers engineering division that came up with the same opinion that at the power and torque being delivered the width of the bearing was marginal. Consequently, as some of you know, I have been using slightly wider bearings in my race engines. Whilst this would appear to have helped the situation it has resulted in other minor problems which I believe to be currently under control.


Pete Richards
Ah I see. Not much one can do about that then.
Mike Hanna wrote:HI. I think the clue to the problem could be the length of time it initially took to get oil circulation in the first instance.. Perhaps the oil used is too thick when cold and the pump is struggling to get the oil round quick enough on initial start ups thus doing "minor " damage to the shells. Mike
I did wonder that, but I didn't connect the ignition until the pressure was up. What's the best way to prime things once I've rebuilt it? Would it be worth blanking the oil take-offs at the filter block until running, then switch off, fill the cooler/laminova circuit and reconnect?
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Re: Meltdown Motorsport - Come in number three your time is

Post by Lotus-e-Clan » Thu Mar 29, 2012 7:12 am

bks974c wrote:There has been a number of comments on the oil return being through the slots at the bottom of the BSK but seem to have missed the fact that the oil level at rest is pretty much at the top of the oil pick up mount ie two allen capped bolts in the pics. Any oil above this level during running will be able to return through to the sump side through the round holes.

Whether the holes are sufficiently large to allow adequate flow I'm not qualified to comment, long time since I did any fluid dynamics.

Most of the oil that is being sucked up by the pump will be being returned via the Pressure relief valve in the oil filter housing straight to the sump - would it make sense to pipe this directly to the sump rather than spraying out on the wrong side of the baffle or taken a step further and piped directly to the pick up.

Scott
I think that's a "static view" and certainly is the case when the engine is not running or at low revs. At high revs running a high capacity pump, the sump level will drop dramatically if oil return is poor. Crank rotation will flay the oil around the crankcase and keep it moving around the crankcase unless there is unobstructed access to the sump. Due to the direction of rotation probably it's best route of return would be down the lower side of the crankcase but that's where the obstruction is highest. A large pool of oil will accumulate at the bottom of the BSK and the rotating crank will pick this up and throw it around the crankcase again. I assume the holes in the BSK are positioned under the crank webs or rods but not both so unfortunately the crank can't aim all of the oil out through the few holes in the BSK.

And if the dip stick is loose the excess oil above the BSK will be forced out of the tube (how do I know this? :lol: ).

BTW one of the advantages of a polished knife-edged crank (and rods) is that they pick up less oil, so less is retained in the crankcase, thus facilitating it's return to the sump.

If you use this design of BSK with a large capacity full length sump the oil return issues would be offset, but better not to carry excess oil if you can avoid it for reasons we've discussed before on this forum.

Also worth checking that the cam box oil return tube isn't compressed (they often are after bending them away to remove the head).

Andy Chesman once said to me with a knowing look and a stare.."You don't want too much oil in the cam box or you'll have problems". As a seventeen year old ex Chrysler apprentice I had no idea what he was talking about ...but that "knowing look" has stuck in my head forever ..I think that stare was perhaps telling me he had learned by experience.
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Re: Meltdown Motorsport - Come in number three your time is

Post by bks974c » Thu Mar 29, 2012 8:00 am

Lotus-e-Clan wrote:
bks974c wrote:There has been a number of comments on the oil return being through the slots at the bottom of the BSK but seem to have missed the fact that the oil level at rest is pretty much at the top of the oil pick up mount ie two allen capped bolts in the pics. Any oil above this level during running will be able to return through to the sump side through the round holes.

Whether the holes are sufficiently large to allow adequate flow I'm not qualified to comment, long time since I did any fluid dynamics.

Most of the oil that is being sucked up by the pump will be being returned via the Pressure relief valve in the oil filter housing straight to the sump - would it make sense to pipe this directly to the sump rather than spraying out on the wrong side of the baffle or taken a step further and piped directly to the pick up.

Scott
I think that's a "static view" and certainly is the case when the engine is not running or at low revs. At high revs running a high capacity pump, the sump level will drop dramatically if oil return is poor. Crank rotation will flay the oil around the crankcase and keep it moving around the crankcase unless there is unobstructed access to the sump. Due to the direction of rotation probably it's best route of return would be down the lower side of the crankcase but that's where the obstruction is highest. A large pool of oil will accumulate at the bottom of the BSK and the rotating crank will pick this up and throw it around the crankcase again. I assume the holes in the BSK are positioned under the crank webs or rods but not both so unfortunately the crank can't aim all of the oil out through the few holes in the BSK.

And if the dip stick is loose the excess oil above the BSK will be forced out of the tube (how do I know this? :lol: ).

BTW one of the advantages of a polished knife-edged crank (and rods) is that they pick up less oil, so less is retained in the crankcase, thus facilitating it's return to the sump.

If you use this design of BSK with a large capacity full length sump the oil return issues would be offset, but better not to carry excess oil if you can avoid it for reasons we've discussed before on this forum.

Also worth checking that the cam box oil return tube isn't compressed (they often are after bending them away to remove the head).

Andy Chesman once said to me with a knowing look and a stare.."You don't want too much oil in the cam box or you'll have problems". As a seventeen year old ex Chrysler apprentice I had no idea what he was talking about ...but that "knowing look" has stuck in my head forever ..I think that stare was perhaps telling me he had learned by experience.

For the purpose of debate only as your comments make a lot of sense. I was correcting the statements that the slots at the bottom were the intended return to the sump for the oil while its the holes etc that are.

1. The higher the oil on the wrong side of the baffle the more holes are exposed
2. Most of the oil from the head actually returns via the great hole called the timing cover but under braking/downhill the oil drain comes into its own
while the opposite is true uphill or under acceleration very little oil will exit via the drain
3. The hole around the oil pump is fairly large but under braking and left handers the oil will have a hard job getting back to the sump,

4. My main point was the majority of the oil returning to the sump is via the PRV and down the casting near the oil pump rather than leakage from the bearings etc so by piping directly towards the oil pick up it has several advantages namely quicker return to the sump - not effected by surge as long as the pick up pipe is immersed - cooler as not splashing about picking up heat along the way (its last port of call before the PRV was the oil cooler)

What we need is a perspex window cut into the sump to see what is actually happening.

Comments please
Scott
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Re: Meltdown Motorsport - Come in number three your time is

Post by apeximp » Thu Mar 29, 2012 8:36 am

Hope this is not tempting fate ! As I have a hanna sump and Rodwell Motorsport 1040 with sandwich plate ! Ran at donnington and Silverstone last year with no problems ! :shock:
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Re: Meltdown Motorsport - Come in number three your time is

Post by Lotus-e-Clan » Thu Mar 29, 2012 9:41 am

apeximp wrote:Hope this is not tempting fate ! As I have a hanna sump and Rodwell Motorsport 1040 with sandwich plate ! Ran at donnington and Silverstone last year with no problems ! :shock:
Hey! This is an academic debate about oil return so keep facts out of it! :lol: (joking :roll: )

But taking the p out of myself aside, I really think that ultimately it's likely that Melty's problem was caused by a build, possible installation,issue rather than oil return problems per se. And too much oil in the crankcase impacts on performance regardless of the potential for oil starvation SHOULD a number of the operating conditions (braking, high revs, gradient, lateral surge) co-inside in total or in combination - plus the long cooling route has to be factored in as long circuits can cause pressure drops of their own making. As ever the devil will be in the detail.

So again, to be fair to Rodwell's (BTW. they have NO control over HOW their engineering solutions are implemented) , their BSK can obviously function without issues but instinctively, and it is just my instincts, I would choose another solution to minimise the risks discussed and co-incidently, reduce drag on the crank for performance reasons. This wouldn't stop me buying from Rodwells, on the contrary, Stuart has a very good reputation by all accounts....but mind you, Rodwells could exercise their right not to sell their good stuff to me ...... :lol:
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Re: Meltdown Motorsport - Come in number three your time is

Post by Mike Hanna » Thu Mar 29, 2012 10:46 am

Hi. Of course we could all be barking up the wrong tree! We mustn't loose sight of the fact that the centre main bearing has to feed 2 bigends. Perhaps this area needs work..But I do know that the engine I blew up at Donnington was due to oil surge and with my sump with a Ben Boult alloy BSK (similar to Rodwells) I had no further problems. But perhaps if I could have driven as quick as the current HSCC Impers I might have had!! Cheers. Mike
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Re: Meltdown Motorsport - Come in number three your time is

Post by Lotus-e-Clan » Thu Mar 29, 2012 11:22 am

I agree Mike. All it needs is one BE cap to be nipped beyond it's resistance to ovality or some other build fault and bobs your uncle.

A long time ago Si thingy (Rootes on here) suggested that the high instances of BE3 failure maybe due to the bias in the oil feed septum (the divider in the crank for BE 2 & 3) inside the centre mains, He thought the septum looked slightly biased toward BE2 rather than BE3. But it was difficult to tell from his photies.
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Re: Meltdown Motorsport - Come in number three your time is

Post by ChrisBenoy » Thu Mar 29, 2012 12:13 pm

It is the high failure rate of no.3 that I was thinking about earlier in regards to crossdrilling. If you will all excuse the fairly basic diagrams i've made up. In simple terms as far as i'm aware the oil system of the bottom end works a little bit like this -

Image

Now the obvious problem here is that 2 and 3 effectivly have half a supply compared to 1 and 4 so whenever there is a drop in pressure these two suffer badly first. If as LeC suggests from Si Trickett's findings that the split in the crank oilway favours number 2 then this would suggest why number 3 is the one that tends to go before number two (as seems to usually be the case)

Now in the case of a crossdrilled crankshaft the oilways look more like this, with the two extra drillings that connect the oilways between big ends 1 and 2 and big ends 3 and 4, giving presumably, pretty equal pressure oil to all 4 bearings. Now this doesn't help the underlying problem of not enough oil pressure, if you have periods of low oil pressure then the engine is still going to expire fairly swiftly. It might however give slightly more protection on the basis that presumably with the shared oilway on the centre main this drops the pressure lower than the overall oil pressure and if this is equalised then the pressure might not get low enough in some cases to cause damage, I think i'm right in saying that often even when 2 and 3 have seen wear 1 and 4 are in a much better condition if not exactly mint.

Image

If i'm talking complete drivel then feel free to point that out. :lol:
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Re: Meltdown Motorsport - Come in number three your time is

Post by Lotus-e-Clan » Thu Mar 29, 2012 12:58 pm

All food for thought Chris! :D

Another of my own "superstitious speculations" maybe, but I never use the centre mains gallery for oil pressure take offs any longer 'cos I feel ANY pressure aberration that MIGHT compromise that central feed should be eliminated. And your first diagram re-enforces my faith in that decision.

I wonder who bought the NOS 850 cross-drilled crank off ebay last week>

Wasn't YOU or your Dad was it Chris? :wink:
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Re: Meltdown Motorsport - Come in number three your time is

Post by ChrisBenoy » Thu Mar 29, 2012 1:07 pm

Nope, we have used a short stroke 998 before that had a very similar crank throw to an 850 but sadly an 850 one brings the capacity out at about 1002 which would put the race car into a higher minimum weight group.

I also avoid using that area for an oil take off, I use the tapping on the cylinder head, although if I can ever afford to try out an accusump I would attach that to the centre tapping, that way it would flow straight into the main bearing area, particularly the centre one.
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Re: Meltdown Motorsport - Come in number three your time is

Post by benwick3 » Thu Mar 29, 2012 1:34 pm

Heres one for the theorists.

My first attempt at dry sumping used the centre tapping as the feed into the block from the pressure side of the pump. Result was failure of No 3 big end bearing due we believed to the restriction inthe size of the oil gallery. System was modified to feed into the gallery via the oil filter gallery as normal. = problem solved.

By the way Chris I think you've got your crank the wrong way round. No 1 big end is nearest the oil pump.

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Re: Meltdown Motorsport - Come in number three your time is

Post by Lotus-e-Clan » Thu Mar 29, 2012 2:01 pm

Also, the natural resistance and large surface area of the oil filter matrix would act as a pressure regulator smoothing out pressure pulses from the pump? Coarse pressure pulses direct to the centre gallery might give odd feeds to the centre mains with knock-on effects through to BEs 2&3? (apart from the restriction you identified).
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Re: Meltdown Motorsport - Come in number three your time is

Post by benwick3 » Thu Mar 29, 2012 2:16 pm

OIl filter not present in normal position, feed through oil filter gallery in side of block.

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