Racer eating distributors: rotors and caps?

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Racer eating distributors: rotors and caps?

Postby knutspeed » Mon May 12, 2014 9:02 am

Another feature on the Bevan tribute car: it eats rotors/distributor caps. This all started after we had a new engine built. It was fitted with a brand new race-dizzy, but quickly started snapping rotors. It seemed like the rotor would dig into the cap until it broke, and this would happen after a lap or two. After trying many combos of caps/rotors (including the good ones from Swiftune etc) over the last couple of years, we ditched that dizzy for a brand new one fitted with an electronic kit. To our surprise, the same thing keeps on happening.

This weekend I modded a rotor by filing off a couple of mm, and the car ran the entire race after we had two rotors snap during testing and qual, but there was hints of trouble the last few laps with a starting misfire. And sure enough - post race the cap and rotor were yet again close to death.

Dad's car had a differential failure post race 1, so for race two we borrowed the complete and pristine dizzy from his car. It ran fine for 4 laps of warmup, and one lap of the race before it started misfiring at high rpm, throttle response was bad etc. I never got to do more than 2 laps anyway as the gear lever snapped in 4th, but it would have been a matter of a couple of laps before the car would stop anyway.

So - anybody take a guess at this? Can there be something related to the drive off the crank, or the block itself that leads to this?
We assume the dizzy axle starts to move at high RPM sending the rotor crashing into the cap and eventually snapping off. We've now tried 3 new complete units, and probably 10 caps and 30 rotors...all with the same results.
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Re: Racer eating distributors: rotors and caps?

Postby The Nun » Mon May 12, 2014 11:10 am

The only way the rotor arm can contact the cap is if there's too much side to side play in the distributor shaft bearings or the distributor shaft has too much end float allowing it to ride up too far under high revs?
The distributor/oil pump drive gears are supplied in matched pairs so if you mis match them that might be a reason?
Does it have the bronze drive gear for it?

Once youve had a failure is there play in the shaft and bearings or is it still the same as when you fitted it?
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Re: Racer eating distributors: rotors and caps?

Postby knutspeed » Mon May 12, 2014 12:25 pm

Thanks, yeah we looked at that - but since we've tried 3 different new distributors we are scratching our heads. I think it has the bronze gears - will have to check with Doc. The drive gears (missing dictionary here...) are fitted in the block? That was our next step - to see if anything there could cause it to jump up at high revs.

The strangest thing is that I shift at about 8000-8200 RPM in my car, but Doc's car running a different cam runs 9500+, and had no marks or problems in the distributor - even after several races. As soon as we bolted it to my car, problems after only 2-4 laps, sometime it would even snap the rotor after 1 lap.

The car would be very driveable, even in the paddock with a brand new rotor and cap, but as soon as it was revved a few times or after a lap, it would sputter and misfire and have poor throttle response at anything but 5000 RPM+ and full throttle.
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Re: Racer eating distributors: rotors and caps?

Postby knutspeed » Mon May 12, 2014 12:29 pm

the play in the bearings/shaft is more or less as it was. No noticeable difference. We could fit a new rotor, and the car would run again for X laps before a new one snapped. Last year we even managed to snap one in the pits while tuning the carbs - but a new dizzy since then.

I've been driving with a spare rotor in my pocket since last year so I can drive back rather than get a tow :)
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Re: Racer eating distributors: rotors and caps?

Postby The Nun » Mon May 12, 2014 12:32 pm

Could it be the actual rotor arm itself thats causing all your problems? some of the new ones arent made like they used to be the quality is a bit duff? It might not be able to cope with your high revs as normal cars dont go much above 6000 do they.
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Re: Racer eating distributors: rotors and caps?

Postby knutspeed » Mon May 12, 2014 12:43 pm

Very possible (Chinaware perhaps) - but this still doesn't explain why there was no problems on one car revving more than the one that keeps breaking them?
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Re: Racer eating distributors: rotors and caps?

Postby The Nun » Mon May 12, 2014 12:59 pm

Try putting the distributor from the one engine that revs without any problem into the one that breaks them and see if that works?

If that breaks that too its something with the drive or distributor housing in the engine I would think??
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Re: Racer eating distributors: rotors and caps?

Postby knutspeed » Mon May 12, 2014 1:05 pm

That's exactly what we did for race #2, and it broke after 3 laps, so yes, we'll dig in and see what we find in the engine itself.
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Re: Racer eating distributors: rotors and caps?

Postby The Nun » Mon May 12, 2014 1:45 pm

knutspeed wrote:That's exactly what we did for race #2, and it broke after 3 laps, so yes, we'll dig in and see what we find in the engine itself.


Oh well theres your answer on that bit, nothing wrong with the distributors or components then in any way, got to be the drive to it or its mounting, theres nothing else to go wrong, its a fairly simple set up.
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Re: Racer eating distributors: rotors and caps?

Postby Lotus-e-Clan » Mon May 12, 2014 2:10 pm

Sounds like you have too much end float in your OIL pump so the gear is rising and pushing upwards on the dizzy shaft?

The oil pump gear is fitted to the pump shaft with a roll pin ...competition pumps are fitted with a bronze gear so maybe whoever drilled the gear to shaft has fitted it too far up the shaft?

Take off the sump remove the oil pump ...you might even find the pump rotor has chewed the pump body too - especially if a high capacity pump with a 1/4 inch spacer ..hopefully the spacer is the correct thickness and with NO Gasket between the spacer and pump body.

Is your oil pressure good - or has it changed since first used from new?
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Re: Racer eating distributors: rotors and caps?

Postby benwick3 » Mon May 12, 2014 2:12 pm

From your tests it would appear that the problem lies with the drive for the distributor on the oil pump. It could be that the slots for the drive to the dizzy are worn or even that the oil pump shaft is bent/not running true. Could be worth changing the oil pump.

Have you tried the distributor from the 'low' rev engine in the 'high' rev engine? If so were there any problems?

How is the fit of the distributor bodies into the timing case? Could the hole be worn?

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Re: Racer eating distributors: rotors and caps?

Postby Lotus-e-Clan » Mon May 12, 2014 2:17 pm

Also check the the crank pulley is fully on and not binding on a displaced Woodruff key allowing the tuffrided oil gear (worm) to move back and forth on the end of the crank...which in turn could make the oil pump gear oscillate in sympathy?
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Re: Racer eating distributors: rotors and caps?

Postby bks974c » Mon May 12, 2014 7:08 pm

See viewtopic.php?f=33&t=26984&p=255851&hilit=irish+clan#p255851

My problem seems to have been a one of apart from the time I checked it and didn't put the clip back on properly :oops: -
what dizzy are you using 23/25 or 43/34 ?

I was going to cut out a section of the cap so I could see what was going on but as its been OK never followed it up.

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Re: Racer eating distributors: rotors and caps?

Postby doc knutsen » Mon May 12, 2014 8:54 pm

Lotus-e-Clan wrote:Also check the the crank pulley is fully on and not binding on a displaced Woodruff key allowing the tuffrided oil gear (worm) to move back and forth on the end of the crank...which in turn could make the oil pump gear oscillate in sympathy?
Clan004


Many thanks to all who have offered helpful suggestions. It seems like the problem has to be with the oil pump/distributor drive assembly. The blocks are new and the distrubutors are new also, so no wear on any parts at all. Yesterday we swapped distributors from my car (out of Sunday's race due to worrying graunchy sounds from the diff) which looked perfect, yet inside a few laps on Matt's car the rotor arm had started eating into the contact points inside the distributor cap, indicating that there is movement of the rotor arm at high revs. As there is just nominal movement in the distributor shaft inside the dizzy body, it seems likely that the shaft must move longitudinally at high revs, probably exacerbating the lateral movement of the dizzy shaft. Which, when running the Swiftune red rotor arms, enables the rotor arm to physically touch the contacts inside the dizzy cap and start machining them...not very healthy!
I am going to drop the sump and remove the oil pump/bronze drive assy, and replace that with another oil pump....

While I love a technical challenge, this is a pain as Matt has lost at least four wins over last season and this, while we have been diagnostically barking up several wrong trees.
But at least we proved how quick the Imps can ! To see Matt head the field on the pace car lap, in an Imp, in pole postion yesterday - ahead of a Galaxie and a Mustang - was a memorable sight!
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Re: Racer eating distributors: rotors and caps?

Postby benwick3 » Tue May 13, 2014 9:33 am

As an aside can you upload a picture of the rotor arm you are using? I use an arm from another car which is better at high revs as it is evenly balanced, Unfortunately it's only usable as a replacement for one of the standard rotor arms and cap.

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Re: Racer eating distributors: rotors and caps?

Postby knutspeed » Tue May 13, 2014 10:13 am

We've tried several different rotor arms, but by far the most reliable has been Swiftune's variant: http://www.swiftune.com/Product/669/rotor-arms.aspx (the long one in the picture)
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Re: Racer eating distributors: rotors and caps?

Postby doc knutsen » Sun May 18, 2014 8:00 pm

knutspeed wrote:We've tried several different rotor arms, but by far the most reliable has been Swiftune's variant: http://www.swiftune.com/Product/669/rotor-arms.aspx (the long one in the picture)


Well there's no end to the fun and games...removed the oil pump this afternoon, and there appears to be nothing wrong with it. The bronze drive gear is the prescribed 2.5mm from the oil pump body, and there is no slack anywhere, nor any marks of misalignment on any of the components...Oil pressure was a steady 50lbs running hot, and the engine proved to be clean as new inside, once I removed the sump. I am really scratching my head over this one... I am going to get another oil pump mit bronze gear from one of our other engines, and compare them. The only component that I have not checked is the Tufftrided gear on the crankshaft itself, unfortunately the crank has to come out for this to be changed and it's a major operation with another meeting coming up in ten days.

Incidentally, the clutch problem that caused headaches last season was due to one of the little springs that secures the (heavy) clutch release bearing to the release fork popping out, leaving the release bearing secured on one side only...some safety wire has got that sorted.
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Re: Racer eating distributors: rotors and caps?

Postby bks974c » Sun May 18, 2014 9:28 pm

Had a look at my old Lucas caps and the new ones and the fit of the new ones is not as good as the originals - you can move then slightly back and forth around the locating lug.
The running clearances are very small and it might just be enough with vibration to cause them to clash.

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Re: Racer eating distributors: rotors and caps?

Postby cov_climax » Sun May 18, 2014 10:00 pm

For the arm to be wiping out caps there's got to be a mis match of components or radial movement in the shaft.

I would remove the points and bench test it, when turning by hand can you feel any hint of the arm clashing with the contacts, is there any play in the main shaft, or where the split upper part joins on, if possible spin it with a drill, or better still a motor- ideally a high speed one that can replicate the distributors 4500rpm (9k engine speed), does it smash the contacts .

You could put bluetack on the contact in the cap, spin it by hand and see what clearance is achieved.


Can you get a dial gauge on the oil pump drive where the distributor engages and measure the radial run-out while cranking, (it will spin over quicker with plugs out). There could be a few things to check is the drive gear on the same centerline as the hole in the timing chest where the distributor slots in?

Good luck
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Re: Racer eating distributors: rotors and caps?

Postby bks974c » Sun May 18, 2014 10:36 pm

I've seen witness mark on Karen car running a 45DM4 set up and the Clan problem running a similar set up but only since I started using new stock caps and red rotor arms so I'm heading towards mismatched or out of spec components. Never seen similar marks on the 25D's

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Re: Racer eating distributors: rotors and caps?

Postby Lars Hagermark » Sun May 18, 2014 10:45 pm

Long shot but... Have you checked if the screw (under the rotor) holds the upper "cam-part" firmly to the lower half of the shaft (part with gear on it)?
EDIT: I re-read the thread and saw you have tried another distributor with the same result. Makes my long shot a total miss. :oops:
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Re: Racer eating distributors: rotors and caps?

Postby Lotus-e-Clan » Mon May 19, 2014 12:28 am

With the sump off is there any movement of the oil gear on the crank?

And is the pulley fully seated on the oil gear+ timing gear cluster?
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Re: Racer eating distributors: rotors and caps?

Postby knutspeed » Mon May 19, 2014 6:29 am

Keeping all options open here while dad (Doc) gets his hands dirty.

Cap: It doesn't sit firmly in place when clipped on. You can wiggle it a fair bit by hand.

Mismatch: not impossible: but why does the complete unit have no issues on one car for several races - no marks, and last 4 laps on the other car as a direct replacement?

Can there be vibrations simply because of different engine spec/chassis/mounts/whatever which makes a violent vibration move the cap around? nothing specific felt in car, but it did run 12 laps with a new cap and a filed-off swift rotor. It did start misfiring after about 8 laps. Typically when hitting the throttle (just like fuel was cut), and at high revs. After the race, the cap was junk.

However: the "bad" car has always been a dog to drive around in the pits. Runs on 3 cylinders until you rev it up, has rather poor throttle response etc. When we fit a brand new cap and rotor, it's smooth and "gentle", but this only lasts until it's run a lap in anger. We always thought this was down to a carb setting issue, but it now seems likely that it is down to the distributor-mystery.

There is evidence on the top of the rotor arm that it has been riding high and making contact with the cap that way as well, so it seems to be oscillating up and down as well as sideways.

Last year, while adjusting the carbs in the paddock, we managed to break a (swift) rotor arm while revving. So this also makes things seem rather random. It might of course be that the problem is staring us straight in the eye without us seeing it. Has happened before :)

Thanks for all help in this investigation, guys!
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Re: Racer eating distributors: rotors and caps?

Postby Lotus-e-Clan » Mon May 19, 2014 6:45 am

One other small detail to consider is the timing chain cover GASKET thickness. The OEM gasket is 'paper-thin' for good reason. you don't want a thick card gasket covered with silicon on both sides because the distributor hole will be offset. That said, until you verify the oil skew gear is unworn and properly clamped by the pulley, my money is still on the skew gear.
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Re: Racer eating distributors: rotors and caps?

Postby The Nun » Mon May 19, 2014 7:14 am

Sounds a little like the meshing of the oil pump drive and the crank drive is too tight then? as the engine gets hot this is causing more tightness between the gears causing excessive binding, so to speak, between the gears and it pushing up on the distributor as they are trying to ride out of each other??
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Re: Racer eating distributors: rotors and caps?

Postby knutspeed » Mon May 19, 2014 7:21 am

Lotus-e-Clan wrote:One other small detail to consider is the timing chain cover GASKET thickness. The OEM gasket is 'paper-thin' for good reason. you don't want a thick card gasket covered with silicon on both sides because the distributor hole will be offset. .


We could see that three of the points inside the cap were more worn than the last one. in which direction would a too thick gasket make the hole offset?
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Re: Racer eating distributors: rotors and caps?

Postby The Nun » Mon May 19, 2014 7:26 am

knutspeed wrote:
Lotus-e-Clan wrote:We could see that three of the points inside the cap were more worn than the last one. in which direction would a too thick gasket make the hole offset?


A thicker gasket would move the timing case cover towards the rear of the car.
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Re: Racer eating distributors: rotors and caps?

Postby leadfoot » Mon May 19, 2014 4:18 pm

Hi Mathew
I agree with the others it has to be related to drive from the oil pump, end float or bronze gear movement.
On the gear lever problem I would give Mike Dent (Moose) a call he has developed a very good modified one, I think some guys on here have them? ideal for racing ,rallying.
good luck keep us informed how you get on
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Re: Racer eating distributors: rotors and caps?

Postby Andy Hillman » Mon May 19, 2014 9:32 pm

I had a similar problem once, drove me round the bend. in the end i change the bronze oil drive as the offset drive slot had been machined in the wrong position.
simple test is slacken off the dizzy take the plugs out and crank the engine over, if you have a clock guage then set it up on the side of the dizzy and watch for a wobble on cranking,
i assume that on my car the bad vibe been put into the dizzy shaft was causing the rotor arm to vibrate off the top, then catch the roof of the cap and break its little drive peg inside.
Hope this helps Andy
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Re: Racer eating distributors: rotors and caps?

Postby ImpManiac » Tue May 20, 2014 3:39 pm

Andy Hillman wrote:I had a similar problem once, drove me round the bend. in the end i change the bronze oil drive as the offset drive slot had been machined in the wrong position. Simple test is slacken off the dizzy take the plugs out and crank the engine over, if you have a clock guage then set it up on the side of the dizzy and watch for a wobble on cranking


That's interesting and very helpful, Andy. :idea:

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Re: Racer eating distributors: rotors and caps?

Postby knutspeed » Tue May 20, 2014 5:11 pm

Andy: that souns very much like our problem - thanks! Will be investigated tomorrow...
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Re: Racer eating distributors: rotors and caps?

Postby doc knutsen » Sun Sep 21, 2014 4:47 pm

ImpManiac wrote:
Andy Hillman wrote:I had a similar problem once, drove me round the bend. in the end i change the bronze oil drive as the offset drive slot had been machined in the wrong position. Simple test is slacken off the dizzy take the plugs out and crank the engine over, if you have a clock guage then set it up on the side of the dizzy and watch for a wobble on cranking


That's interesting and very helpful, Andy. :idea:

IM 8)


Well, good to relate that the bronze oil pump drive was indeed the culprit, so thanks ImpManiac, you were spot on!
We only managed two more races this season, with my yellow car still being hors de combat from a broken diff, Matt did the two last races in the blue car, but was dogged by a misfire that cropped up after a couple of laps and persisted. Of course, we assumed yet more distributor woes and were tearing our collective hair out, but Matt mentioned that the engine appeared to die on him during gear-changes, which made me wonder about the car possibly having a fuel problem as well...and a quick look in the tank revealed no sign of the mandatory safety foam at all! The tank had sat on the shelf for some years before being fitted, and on removing the fuel pump filter the awful truth was revealed: The tank foam had dissolved into a load of grainy material, about the same consistency as rock salt, which had completely blocked the tank exit and the fuel pump inlet side, it is a great wonder any fuel made it into the carburettors at all!

So now the whole system has been cleaned out, the tank has had new foam fitted, and we are due to go testing along with the Corsa Italiana lot who have their end-of-season meeting next week-end. Hopefully, both the Imps will be working sufficiently for us to have a meaningful sorting session, preparing for a proper attack in 2015!
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Re: Racer eating distributors: rotors and caps?

Postby ImpManiac » Sun Sep 21, 2014 9:49 pm

^^ Not my diagnosis! Andy "Hillmanator" Jones got it spot on. :wink:

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Re: Racer eating distributors: rotors and caps?

Postby doc knutsen » Tue Sep 23, 2014 5:53 pm

ImpManiac wrote:^^ Not my diagnosis! Andy "Hillmanator" Jones got it spot on. :wink:

IM 8)


Oops, sorry about that! Credit where due, and all that. Thank you Mr Hillmanator, Sir!
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Re: Racer eating distributors: rotors and caps?

Postby benwick3 » Tue Sep 23, 2014 6:45 pm

Reading through the posts I think credit is due to all who posted. A number mentioned the pump/dizzy drive as the possible culprit, myself included very early on in the discussion.

Pete Richards
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Re: Racer eating distributors: rotors and caps?

Postby ImpManiac » Tue Sep 23, 2014 9:43 pm

^^ Correct, as ever, Pete. :)

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Re: Racer eating distributors: rotors and caps?

Postby doc knutsen » Wed Sep 24, 2014 6:29 pm

benwick3 wrote:Reading through the posts I think credit is due to all who posted. A number mentioned the pump/dizzy drive as the possible culprit, myself included very early on in the discussion.

Pete Richards


You are right, of course. Many thanks to all those who cared enough to post helpful suggestions, much appreciated.

Please see my post of May 12th and Matt's post of May 19th, both expressing our gratitude for all the help we have received.

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Re: Racer eating distributors: rotors and caps?

Postby doc knutsen » Sun Sep 28, 2014 10:18 am

News update: We enjoyed a very fruitful day of testing yesterday, at long last. Both cars ran sans problems all day, and we even used one session for swapping cars, ie Matt got to drive the yellow one, while I had a go in his blue car. Matt was over the moon over my car, he says it handles beautifully and has tons of grip,after one lap he threw it it smoothly and quickly around the hilly Rudskogen circuit. He was revelling in its handling and the smoothness of the engine, which runs a RP 410 cam, and yet is so flexible that you feel you could drive down to the supermarket in it. Only fly in the ointment is the fact that it is late September, and no more races until May 2015. :(
Matt's blue car, I thought, had great grip, and brakes that "bite" much more confidence-inspiring than mine. It runs fatter ACB10s than mine. But the carburation is way too rich all the way up to about 7k, making it misfire and not pull very well until right at the top of its rev range. This engine was set up on a dyno locally, but the people who did the job had no spare parts for Dell'Ortos, so set to with their reaming tools using what was fitted to the carbs already. Obviously, not an ideal set-up, even of it did see 117BHP at the top end. So, next step is to fit a pair of DCOE Webers, for which spares are readily available here, and with jetting the same as the Webers on the yellow car.
On hearing me describe the carburetion problems on his car, and having tried mine, Matt said somewhat sheepishly that the difference was huge, and he had assumed Imps really were supposed to be like that... And he has won races and taken numerous podiums, in an Imp that was, to my mind, really difficult to drive, due to ist power delivery. What it must have been like with the fuel tank debris clogging up the fuel system in addition...
Hopefully, we may be excused for feeling a tiny bit confident about finally doing justice to the cars next season. We have shown the speed of the Imps very clearly for some time, but time to sort out problems and do some development has been at a premium.
Next season should see another locally-built Imp out, Geir Opoien having purchased a shell and relevant parts from me, should have his car out by the time 2015 kicks off. Cannot wait!
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Re: Racer eating distributors: rotors and caps?

Postby Andy Hillman » Sun Sep 28, 2014 7:44 pm

What a lovely way to end the season ! I will look forward to seeing your in car footage in 2015.
If you decide to stay with the Dellorto carbs their is a mail order website called "green spark plug company" they stock dellorto parts and post all over the world
cheers Andy
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Re: Racer eating distributors: rotors and caps?

Postby ImpManiac » Mon Sep 29, 2014 4:00 pm

That's brilliant news, Doc! :mrgreen: :mrgreen: It sounds as though you both had great fun and the Imps were flying.

The Green Spark Plug Company sounds like a helpful outfit, Andy. Depending on my carburettor choice (DCOEs or DHLAs) when I put the car back together, I might look them up too. Thank you! :wink:

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