R21 cam timing

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imp-racer
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R21 cam timing

Post by imp-racer » Sat Mar 31, 2012 6:05 pm

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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cov_climax
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Re: R21 cam timing

Post by cov_climax » Sat Mar 31, 2012 8:06 pm

is this any good:

http://www.revilo89.freeserve.co.uk/Cam ... vilo89.htm

thanks to adrian oliver for his website
imp-racer
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Re: R21 cam timing

Post by imp-racer » Sat Mar 31, 2012 10:24 pm

Yes thanks for that link just the job cheers
ststown
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Re: R21 cam timing

Post by ststown » Sun Oct 07, 2012 9:58 pm

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
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ImpManiac
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Re: R21 cam timing

Post by ImpManiac » Mon Oct 08, 2012 10:14 am

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. :idea: 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). :!:

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Re: R21 cam timing

Post by Lotus-e-Clan » Mon Oct 08, 2012 10:35 am

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.

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ststown
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Re: R21 cam timing

Post by ststown » Tue Oct 09, 2012 11:26 pm

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
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