R21 cam timing
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R21 cam timing
Hi all, I have lost my data sheets on cam timing & need to set up an R21 I have it in my memory its 135 thou lift ATDC but not sure, frankas site does not list the R21 lift for some reason, this one is a BB cam cheers in anticipation Roger
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Re: R21 cam timing
is this any good:
http://www.revilo89.freeserve.co.uk/Cam ... vilo89.htm
thanks to adrian oliver for his website
http://www.revilo89.freeserve.co.uk/Cam ... vilo89.htm
thanks to adrian oliver for his website
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Re: R21 cam timing
Guys, in relation to R21 timing, does valve size impact on setting? I am using a 1.4 inlet valve and its on a 998.
Thanks
John
Thanks
John
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Re: R21 cam timing
Valve size should have no impact, apart from the sizes of the valve cut-outs in the crowns of the pistons. Are they sized appropriately?
It would be worth doing a dry build of your engine and checking that you have sufficient clearance between pistons and valve heads. You can do this using weak springs in place of valve springs and physically pushing the tappets down at various points close to TDC to take up valve head-to-piston crown clearance and read the measurement off using a dial test indicator (dial gauge). Make sure you run at least the minimum clearance (I think 0.100" is recommended at minimum BUT CHECK THIS).
IM
It would be worth doing a dry build of your engine and checking that you have sufficient clearance between pistons and valve heads. You can do this using weak springs in place of valve springs and physically pushing the tappets down at various points close to TDC to take up valve head-to-piston crown clearance and read the measurement off using a dial test indicator (dial gauge). Make sure you run at least the minimum clearance (I think 0.100" is recommended at minimum BUT CHECK THIS).
IM
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Re: R21 cam timing
On valve to piston clearance, the valve head diameter needs room to flutter a little so the diameter of the cut outs need to account for this. I've had 175 thou lift @ TDC with the valve head nowhere near the piston top in terms of depth of large valve cut-outs, but the 1.4 inch heads just clipped the sides of my DIY cut outs due to a little flutter and piston rock - which is difficult to account for on a static trial build for minimum clearance and maximum squish.
BTW. You can increase some the quoted R series cam timings by about 5 to 7 thou for a bit more power. So an R17 quoted @ 100 thou is better @ 107 and an R20 works well @ 118 -120 thou. So on that basis an R21 should be OK @ 135 thou.
Alternatively, find the rock-point of the cam (lift when both inlet and exhaust valves are open same distance @ TDC) and then add 10 thou to that rock-point figure and you won't be far wrong. It's a good idea to do this anyway to check against the published lift figures and confirm you haven't got a cam that's been messed with or mislabelled.
BTW. You can increase some the quoted R series cam timings by about 5 to 7 thou for a bit more power. So an R17 quoted @ 100 thou is better @ 107 and an R20 works well @ 118 -120 thou. So on that basis an R21 should be OK @ 135 thou.
Alternatively, find the rock-point of the cam (lift when both inlet and exhaust valves are open same distance @ TDC) and then add 10 thou to that rock-point figure and you won't be far wrong. It's a good idea to do this anyway to check against the published lift figures and confirm you haven't got a cam that's been messed with or mislabelled.
74 Clan Crusader 1040 Red 190 bhp/ton
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Re: R21 cam timing
Guys,
Thanks for the info. When I last ran my engine the R21 was timed in at 110 thou at TDC which was the information I was given when I bought the cam. I'm looking forward to a bit more power which will be interesting as the car previously went well! Whilst I can build an engine (to settings detailed) as an electrical engineer I've never got to grips with the reasoning/advantages/disadvantages for various settings.
Again thanks for the help on this front.
John
Thanks for the info. When I last ran my engine the R21 was timed in at 110 thou at TDC which was the information I was given when I bought the cam. I'm looking forward to a bit more power which will be interesting as the car previously went well! Whilst I can build an engine (to settings detailed) as an electrical engineer I've never got to grips with the reasoning/advantages/disadvantages for various settings.
Again thanks for the help on this front.
John