valve piston clearance

[raycemon]

I'd like to check the clearance between my valves and pistons. I fly cut the 2.0 pistons for more clearance for the larger valves installed. I am using hydraulic lifters so how can I rotate the engine by hand and have the valves open up properly with no oil pressure? I was planning on putting a little clay on the top of the piston to check the clearance

I still have the solid lifters if they could be used.

thanks for your Help, Bill

[wrench459]

You could pump up the hyd lifter so thats its at zero lash or use a solid .
Place the lifter in a container of oil I would use a drill press to pump it up. Pump it dude get it on!!
The tensioner is not involved in the equation because its on the slack side of the chain.

[jeff denton]

Easy, just substitute a solid lifter for the hydraulic on the valve of which you are checking the clearance.

[N61WP]

NEAT TRICK!

I used Play Dough when I built my engine. It was a real PITA to be sure I didn't mess up the measurement by mashing it or by leaving some behind while peeling it off the top of the piston. I repeated the measurement several times to be sure.

Last Saturday I was watching HorsePower TV on Spike. They had a neat trick....use small Tootsie Rolls! You could put one under each valve.

Warm the Tootsie Rolls in your hand (leave wrapped). The wrapper stops it from sticking to the piston. After you bolt the head down and turn the engine over, gently remove the Tootsie Roll and stick in the freezer for a few minutes to harden it up. This helps assure you don't mash it with your mic and get a good measurement. Much firmer then Play Dough.

Then, when finished, have a well deserved snack!

James

[Gordy]

I used the play dough method. It takes just a small piece on each butterfly cut. I was a little worried because the exhaust valves were cutting it close but was told not to worry too much because as that piston is flying upward the exhaust valve is closing. On the otherhand, as the piston is flying up the intake is opening towards it so there is less room for error. All went together 2.0 OGTS pistons with Bob Legere instructed 1.84 /1.50 sbc valve setup with Cam Techniques cam. Runs awesome. Happy engine building!

[wrench459]

A very light layer of wd-40 across the eyebrows of the piston works nicely.
Then with a razor blade slice 1/8 or so segments of the radius and measure away.

[raycemon]

thanks for your suggestions. I'll give them a try this weekend. Bill

[GTJIM]

The first thing you need to ask yourself is: "What happens if there is not enough clearance when I start this test?"

Scary, Huh?

Got to start with a test that will not bend valves if there is not enough clearance - ie: less than none!

1) With pistons #1 & #4 at TDC set the cam at overlap on #4 chamber.
2) With play dough in the piston notches carefully lower the head onto the block with a used head gasket in place. (a pair of studs in a couple of the head bolt holes will ensure easy alignment)
3)Lift the head and check the play dough thickness.

This will give you some idea of the clearance and certainly show if there is not any without bending things ... as long as you do not drop the head!

Of course this is just a rough and ready check as TDC with split overlap on the cam is probably not where the valves are closest to the head - but it gives a good 'first guesstimate' - however, if there is no clearance at this positon things are too close and the 'eyebrows' need deepening in the pistons before going much further.

Now place the head on with new play dough and all 4 pistons and with the weight of the head alone holding it down connect the cam chain and carefully turn the motor over twice. Not bolting the head down will allow it to lift if the valves contact the pistons.

If all is well it is time to replace the play dough and bolt the head down with about 4 head bolts and go through two complete revolutions again.

If you have .100" on exhaust and .080" on intake - or more - then you are pretty safe.

This lengthy procedure is why custom engine building cost a bit .......

[jeff denton]

My preferred method uses very light springs instead of the regular valve springs. Start with lots of valve lash, make sure your cam timing is where you want it. As the piston is coming to TDC you can push on the valve against the light springs and "feel" the valve hit the piston. A dial indicator on the retainer will tell you how much clearance you have.
Yes, you'll have the head on and off the engine many times. I wrote a story about this once.
Remember the slightest change in cam timing will change your clearance. You'll find yourself doing cam timing adjustment and valve clearancing simultaneously as you get the process refined.