checking valve to piston clearance

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racingsnake440

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can anyone tell me how many degrees before and after TDC I should check for valve/piston clearance issues?

thanks
 
Not sure what you mean by "number of degrees". It's recomended that you turn the engine round the clock twice to get both readings on int. and exh. Be sure the cam is dialed in first, or as installed.
 
probably didn't explain very well - I don't have a cam at the moment and want to check how far the valves can be opened (by hand with checking springs in place of regular valvesprings) before they hit the piston so that when I order a cam I know I won't have any problems. Obviously when the piston is at or near BDC there will be no problems and it's only around TDC and/or max valve lift that I need to be concerned about. I seem to recall reading that if you checked from 20 degrees before TDC to 10 degrees after 10 TDC that would cover the area in which interference was most likely

Can anyone confirm/deny this?
 
Actually tdc is not where your valves are closest to the piston. Awfully hard to check ptv without a cam. Do your pistons have valve notches? If so you can usually go pretty big (.600) without problem. If not, well..... What is your engine package?
 
Sounds like you are going to fall victim to the too big of cam thing. It sounds like you want to to put the biggest cam you can in the motor so it sounds nasty. Don't do it, we have probably all been down that path and it sucks. Like dusterdon is saying match your cam to your package. It may not sound as nasty but it will run much harder.


Chuck
 
racingsnake440 said:
probably didn't explain very well - I don't have a cam at the moment and want to check how far the valves can be opened (by hand with checking springs in place of regular valvesprings) before they hit the piston so that when I order a cam I know I won't have any problems. Obviously when the piston is at or near BDC there will be no problems and it's only around TDC and/or max valve lift that I need to be concerned about. I seem to recall reading that if you checked from 20 degrees before TDC to 10 degrees after 10 TDC that would cover the area in which interference was most likely

Can anyone confirm/deny this?
Click to expand...

Set #1 piston at TDC. Then as you said check from 20* before to 15* after
in 2-3* increments will give you the info you want.

As for leaning towards the smaller of two cams - good advice.
 
hi, at TDC/overlap stroke is where you need to check clearance. on the exhaust, 20 deg before to TDC. on the intake, TDC to 20 deg, after. this is where the valves will be the closest to piston. for accurate results, degree cam in motor. when you line up the two timing marks, you are on #6 TDC firing. rotate motor one full turn will bring you up on #1 TDC firing. now you can degree cam in and check P/V clearances by rotating crank over.
 
thanks! I don't think I'll have any clearance issues because I'm only planning an XE268 cam with stock pistons but not sure how much my magnum heads have been milled so just wanted to check everything out first.
 
Always good to check. But really, the way to "know" is to use the cam you are using, and check after the cam is degreed properly.
 
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