Valve and piston clearance question

S

Skalabala

Member +
Hi members.

For 4EFTE

Can anybody tell me what the clearance is like when intake valves are max open with stock cams?
If you had pistons with no valve cut outs will the pistons hit the valves?
Or will the timing cause it not to? But if timing belt snaps then you will be in trouble?

Thanks :)
 
Texx

Texx

Super Moderator
No idea how much clearance there is in a stock engine, but considering there's supposedly no piston to valve contact with a valve fully open and the piston at TDC, I wouldn't think the pockets in the piston crown would be necessary as long as the valve timing is set correctly and the timing belt doesn't slip or snap.
 
1

123*stumpy

Untrusted Seller
as far as i know these engines are non interference which means when the piston is at TDC and the valve is open it wont hit unless youve had your head skimed loads of times, not sure about if it had no cut outs tho..
 
S

Skalabala

Member +
Where is the piston when intake valves are max open?
Am I right if I say the intake valves can not be max open when piston is at TDC?
Piston might be 10mm+ away from the block deck when intake valves are max open in a running engine?
So the Valve cut outs on the piston might only be there to make it non interference if a belt snaps?
Thanks Texx and 123 :)
 
A

AdamB

Member +
If you have the engine open, get yourself some play doh and place it on top of the piston, measure it first with a micrometer. Then turn the engine over with the cylinder head on and then measure the thickness of the play doh again, the difference is the clearence you have.
When the intake valves are open max will probably be just after TDC as the piston is on the intake stroke as its moving back down the cylinder. To know for sure you would need the valve opening and closing angles and place them on a degree disc :)
 
weeJohn

weeJohn

Lifer
I have a head off a block at the minute, I will turn the cam so the valve is fully opened and see where it is in relation to the face of the head.
 
J

jam35

Member +
the valves when fully open do not pass the face of the head, so if you have pistons with no cut outs and the belt snaps you should be fine :)
 
Texx

Texx

Super Moderator
jam35 said:
the valves when fully open do not pass the face of the head, so if you have pistons with no cut outs and the belt snaps you should be fine :)
Click to expand...

The exhaust valves would possibly be OK, but the inlet valves pass the face of the head after approx 1mm of lift. With a piston that has no inlet valve pockets sat at TDC, the inlet valves would contact the piston crown after approx 3mm of lift.
 
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