[Tigers] Tiger's 289 Piston to Valve Clearance Check Mistake

[Tom Witt]

Question? How will the modeling clay get into place without disassembling the motor? And how will it come out without distorting its shape and size? The fastest way I can think to measure piston to valve clearance is to set the piston at top dead center, then remove the valve spring. With a fixed dial indicator measure the travel distance from the valve pulled up tight against the seat then moving it downward until it touches the piston. A light weight spring in picture #3 makes that safer.  Compare that distance with the rating of your cam lift (factoring the rocker ratio IF not stock). DO NOT ROTATE THE ENGINE IN THIS SITUATION if you don’t use the light weight spring! Make sure the regular springs are reinstalled before rotation. Picture #3 shows the process but uses the mentioned very light weight spring. That is best as it will prevent the valve from dropping though I have gone without it in a pinch. But in either case you will know exactly how far it is from the valve being seated until it hits the piston at TDC.

In most cases the valve should not drop too far into the guide that the stem still can’t be touched. I have used rubber bands to hold the valve up while reinstalling the springs and then use a curved pick to break it and remove the broken band with tweezers. There are numerous tools available to remove the valves spring. I’d use the type in picture #1 as it avoids solely pushing the valve downward (if the locks hold) and that could cause the valve to move the piston (picture #2 No!) which as stated above is something you don’t want to do.

It might be helpful if we know the reason why you suspect the clearance is an issue. Cam lift, rocker ratio, deck height, piston surface to wrist pin height and gasket thickness are all factors.



From: Rob Hogan via Tigers 
Sent: Tuesday, January 23, 2018 5:51 PM
To: Tiger's List 
Subject: [Tigers] Tiger's 289 Piston to Valve Clearance Check Mistake

If approximately a 1 sq. in. small flat of modelling clay is placed (not near the piston's periphery) where it is in the squish area of the piston instead of only under the head's combustion pocket, can rotating the assembled piston and rod cause the piston to cant in the cylinder bore enough to crack a piston skirt?

Is there any other potential weak area that could be cracked by piston to head interference with clay in between?

I hesitate to disassemble the engine to search for possible part cracking if the clay interference is really incapable of causing something to crack.

     Virus-free. www.avg.com  



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