HELP...valve/piston clearance problem!!!
This is a discussion on HELP...valve/piston clearance problem!!! within the Internal Engine forums, part of the LSx Technical Help Section category; Hey Guys, I need all the advice I can get. Heres what I got: 1999 Camaro SS, doing the heads, ...
02-04-2006, 06:02 PM #1
HELP...valve/piston clearance problem!!!
Hey Guys, I need all the advice I can get.
Heres what I got:
1999 Camaro SS, doing the heads, and cam package this winter. I bought Patriot Stage 2 heads with 1.57/2.02 valves, dual springs, and 59cc combustion chambers. The cam is Thunder Racing's 230/236 with .595/.602 lift with 111.5 LSA. I bought a adjustable timing chain and had a local engine mechanic degree the cam to make sure that it was in perfect. I wanted to double check valve/piston clearance, though I was told I shouldn't have any issues. I put the gasket on and put the cylinder head on with only 2 valves with the check springs (so I would not collapse the lifters) and put 4 bolts in (I tightened but did not torque). I spun the engine around and everything felt ok. Then I go to check the piston and son of gun, it has two tiny spots where you can tell the valves smacked into the piston, not hard but enough to make tiny notches. So I know I'll be in trouble when I torque the head down all the way and lose another couple thousandths of an inch of clearance. I called Thunder and they seem to think somehow I checked the clearance wrong, they thought that maybe the lifter was holding the valve open. ??? beats me. They said they use a solid lifter to check clearances, but I used check springs, shouldn't that be just as good?? By the way I also bought new lifters, the stock type from Comp (not the R's just the stock replacement), the 850's, but that shouldn't matter should it?? When a hyrdraulic lifter is at temp does it operate at full length?? Or is it somewhere in between?? I really don't want to have to buy pistons with valve reliefs but I will if I have to. Tell me what you think. Sorry this is so long. I'm really my head. Thanks so much!!!!
02-04-2006, 07:32 PM #2
- Join Date
- Nov 2005
- Port St. John, FL
Red & Dk Gray
- 2002 WS6, '08 G8 GT
I think you are heading for trouble there. Get some clay to verify that it is in fact valve to piston contact. Use a solid lifters and adjustable pushrods*, and use a set of throw away head gaskets of the same comp thickness you intend to use. Torque 'em down and check clearance again, SLOWLY. If you encounter resistance bringing the piston to TDC overlap with solid lifters, then STOP! You risk bending the valve! Ensure Cam was installed properly, not 180 deg out.
*(used for checking pushrod length, and to set the proper zero lash for this test with the solid lifter only. "Do Not Run Them")
Rule of thumb is minimum clearance of .080" for Intake and .100" Exhaust.
Especially with checking springs, if the valves are contacting the piston while using hyd lifters, the piston will contact and push the valve up and compress the lifter.
On a conventional (Stock) Gen1 Small Block Chevy the normal Hyd Lifter pre-load is about .060" or one full turn past zero lash when when adjusting valves. Not sure what the set pre-load is on the non-adjustable LSX engines. Normally Hyd Lifters will remain slightly depressed at idle through low RPM and pump-up as RPM increases.
Are you using the stock Rocker Ratio? If not, go back down to stock 1.70:1, check clearance again.
Included a Link from WISECO Pistons, check out #5 & #8;
Other Jee-wiz Info Links;
Let us know what you find out!
Last edited by RainMan; 02-04-2006 at 07:54 PM.
02-04-2006, 07:33 PM #3
- Join Date
- Aug 2005
- Thornton, CO
Red Tint Jewelcoat
- 2008 Trailblazer SS
Who told you you wouldn't have any P/V clearance problems?
Timing right??2008 Trailblazer SS
Yank PTB3600, Kooks 1 7/8" LT's, 4" intake, E-fans, Magnaflow, Sonnax kit, tranny cooler, tune.
Lowered, HID's, tinted.
1999 Pontiac Trans Am WS.6 #1747 SOLD
531.1 RWHP 481.3 FT/Pounds all motor.
02-05-2006, 06:50 AM #4
you more than likely wouldn't be having the piston to valve issue if it wasn't for the heads. in order to get 59cc, PP wouldv'e had to cut the heads about .040". that is if they didn't weld up the chambers to achieve this. check with TR about the P to V clearance.
you can get a flycutting tool and notch the stock pistons.
02-06-2006, 02:48 PM #5
DO NOT check the P/V clearance, [or lack of], with the roll it over, and see what happens approach.
The correct method is to use a dial indicator, checking springs, a solid lifter set, and a degree wheel.
02-07-2006, 11:41 AM #6
Thanks for all the help guys, I talked to Jason over at Thunder and the problem I was running into was the fact that the valves were being held open during the entire cycle due to the fact I was using hydraulic lifters (instead of solid lifters) and checking springs. The hydraulic lifters were at full deflection holding the valves open. I'm going to have my local engine builder come and check the clearance for me with the solid lifters, dial indicator, and degree wheel. I think I'll be a-ok. Thanks for all the help.
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