info on checking valve clearances needed (not tappets)

[ChaosAD]

Can anyone point me in the direction of some websites or explain to me how to to check valve/piston clearances when installing high comp pistons or high lift cams.

Thanks

[ChaosAD]

Surely someone must know

[ATAl]

The only way I know to do it is to use play-do / putty etc on the top of the piston (just a thin layer). Then assemble the engine and hand turn the engine over, if you feel anything catch back off.

When this is done pull the head off again and look for marks in the play-do, if you can see metal or something was catching there is not enough clearance.

Be very careful with this method, I've never tried it and it could bend a valve if you put pressure on it if anything catches.

[TrouserFxGt]

Look at cam specs. They should say at what degree maximum lift is and what maximum lift is. Factor in any rocker multiplication or nothing for buckets and shims.

Get depth micrometer or calipers and measure depth of piston from top of block at the cams max lift degree. Add head gasket thickness to this.

Subtract this measurement from the valves maximum lift. If you have a positive number then it should be good. Negitive number = bad

Off the top of my head but should work.

[RedMist]

Trouser, I think your talking about an attempt to make a non interference engine. And you still haven't allowed for rod stretch. Large duration cams this isn't possible, unless you run very low compression.
The PlayDo Clay method is one of the best I've heard of. There are programs that will mathematically model your engine and give you correct cam timing, however it would probably be quicker to torque down your head and rotate the engine as already stated. Ensure you allow something for rod stretch.
4 stroke performance tuning G Alexander Bell.

[ChaosAD]

Thanks, but how do you actually measure the clearance? do you pull off the playdough after and measure the thickness with a mic or something?

[ATAl]

I think the idea with the playdo is just to see if there is any contact, not to measure clearance.

You could try and find the thinnest part of playdo where the valves have pushed on it then push something thru the playdo and measure how far in it goes - might work.

[atmosports]

Doing it with playdough/plasticene is the only way we've done it for years, put it in there, torque it all down with a gasket in place, bearing in mind that a new gasket when torqued down will squash, carefully turn the engine over(never turn it backwards), if nothing hits then take it all off & see if any indentations are in it, if so measure up the distance from the edge of that srface to the bottom of the indentation to get your clearance, as stated above remember that things stretch as your rev them & also as temperature increases so err on the safe side.

[kingcorolla]

yep i just used blu-tac!

I tourqed the head down on a stock gasket, and wound it over a couple times slowly. Clearences seem to all be good with the increased duration cams, but i am soon to get an 8.0mm TRD gasket so will have to check it again.

I also plan to run the motor in with stock cams for approx 500k, then run the cams in seperatly with different method.

how big are ya cams Chaos?

[ChaosAD]

8.8mm cams. I decided to run-in the engine with standard cams too. Will be good to see how much of an increace they make.
What size u runnin?

[kingcorolla]

272deg in
264deg ex

[craigt]

You could always do the check with no headgasket in place.
That way if the valves dont touch the pistons then you know
you have a shitload of room to play with!
Also its easier to cut the playdough through the middle with
a sharp knife and measure that way than to try and peel it off.