I just recently bought a 355 engine kit with .125 dome pistons and 6" rods! I'm curious if anyone thinks I will have piston to valve clearance problems with this combination! The lift of my cam with the 1.52 roller rockers is going to be .470/.476!! Other specs are in my signature! Any input on this would be greatly appreciated!

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1986 Trans AM
305 TPI
Well over 200,000+ miles (speedo/odometer non-funtional! Odometer reads 142,000)
4 Wheel Discs
9 bolt Borg Warner Rear (2.77's....oh joy) :P
Completely Stock
Current Project: upgrade to a 355 TPI, 6" rods, 9.5:1 Compression, Stock TPI ported, 24#/hr LTI injectors, Hedman Shorty Headers, SBC Stock Casting heads pocket ported, Comp Cams XE262-14 TPI Cam, Ed Wright Fast Chip, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Box, proform hot coil!!

 

Two words - modeling clay...

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Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

You want at least .100 clearance between the piston and the valve. I think that's what happened to my engine when I broke a valve.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

Best ET on a time slip: 11.242 altitude corrected to 10.69
Best MPH on a time slip: 121.52 altitude corrected to 127.76
Altitude corrected rear wheel HP based on power to weight ratio: 504.5
Best 60 foot: 1.546

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

Thanks for the replies guys! I was aware of the .100 clearance and also of using modeling clay to check the clearance!! However, I have never checked piston to valve clearance with modeling clay and would appreciate it is someone could give me step by step instructions on how this process is done! thanks in advance!

 

First of all you need 2 solid lifters. Hydraulic lifters won't give an accurate reading.

With the head off, put the modeling clay on top of the piston in the valve reliefs. You can coat the piston with something like vasoline so the clay doesn't stick and is easy to remove. Install the head and torque the bolts down snug. Full torque isn't required but you don't want the head loose. A head gasket isn't required but subract the gasket thickness from the results. Using solid lifters, adjust the 2 valves to zero lash. Rotate the engine by hand 2 full revolutions. Remove the head and measure the thickness of the clay.

If there isn't enough clearance you need to mark the pistons where the exact center of the valves are and have the pistons fly cut for more clearance.

 

never mind

[This message has been edited by Z_Ghost (edited May 28, 2001).]