Measuring Piston to Valve Clearance

[Cuzzo]

Hey,

How do i measure the clearance distance between piston and valves on my 4agte.

Do i need to CC the chamber?

Or is there an easier way?

The reason im asking is that i was currently using a copper head gasket at 2mm.

However i want to use a cometic mls item which stands at 1mm.

I want to make sure its safe before starting her up.

thanks,
Adam

[gianttomato]

Plasticine on the piston crown.

[abently]

Plasticine on the piston crown.

+ 1

Usually with an old Headgasket or no Head gasket at all so that you can leave a fair gap to account for temp and stretching.

[oldcorollas]

to add to that, put glad wrap/cling wrap over the plasticine so it doesn't stick to valve.

[Cuzzo]

thats a good idea cheers.

So whats ideal? How far away from the piston should the valve travel?

Will it travel further under hard accel?

[oldcorollas]

stretch is based on rpm...
will depend on your rods and the rpm you aqre planning (or might accidentally get to )

4A's are non-interference with stock lift.... how much lift do they need to get interference when the belt breaks?

if the head is off already, you can make a good rough measurement by setting cam to position at TDC (and also +- whatever) and measuring clearance to the face of the head...
if that is a few mm, then should be fine..

but if you are worried abotu belt breakage, set cam to max lift on intakes, and measure clearance to bottom of head.. (as a first step before torquing up with plasticine etc)

[Cuzzo]

I just install some playdoh inbetween the piston and the head, then install the head complete and rotated the engine a few times.

I have this nicely shaped playdoh but now what?

What am i suppose to see with it?

[oldcorollas]

carefully slice the playdough in half with razor blade, through the thinnest area, and then measure the thickness

sorta like

[Celica RA45]

easy way is to set the cam shafts at the tdc lifter rise as you would set up your cams .when you have done that then care fully take cam belt off the top cam pulleys and with dial indicator measure how much further you can move the inlet cam towards the exhaust and if you have more than 80thou before the valve hits the piston you will be safe any less then you would need to fly cut the valve reliefs more

[Billzilla]

to add to that, put a little engine oil over the plasticine so it doesn't stick to valve.

Fixed ...

[oldcorollas]

maybe my plasticine was stickier than usual
(plus is easier to reuse if it is not covered in oil )

[rolleraction]

What Glenn RA45 says is the go. AND you dont have to pull the head off to do it.

[abently]

What Glenn RA45 says is the go. AND you dont have to pull the head off to do it.

+1

Unless you are cutting valve reliefs into pistons with none, like me.....

In most cases though, if you are measuring the P2V clearance then chances are your going to need them cut deeper. 80thou is way on the safe side though, half that is fine and 30thou is on the limit.

[rolleraction]

+1
80thou is way on the safe side though, half that is fine and 30thou is on the limit.

I used 40 thou in 3SGE race engine and spun a big end.. piston kissed valve ever so slightly (only a feint mark. no bending but couldnt have been closer to total disaster if I tried..) so I personally wouldnt go less than 40 and maybe 60 (or more) would be better if possible, depending on the cam specs/profiles/timing used of course..

I guess the material used for rods/pistons also changes this a bit re: stretch and expansion etc....

I ran Aries & Argo in the above example..

[Celica RA45]

race guy always told you need 80 thou minium as if you buzz your motor or miss a gear it can stretch that much