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Advice on valves hitting piston
bikecarbfred - 18/10/15 at 12:24 AM

When installing bigger valves and performance cams together how can you take into account how close the valves would be to the piston.

Performance cams have higher lift and the bigger valves because facing diagonal would mean thier closer to the piston.

I know I was off a tooth on the cambelt a year ago and it did not do any damage so does that mean there's lot's of clearance.

bi22le - 18/10/15 at 03:33 AM

Timing or profiled pistons?

AntonUK - 18/10/15 at 07:22 AM

Blue tack on valve, turn engine over slowly, any resistance stop. Dismantle and check thickness of squashed blue tak.

bikecarbfred - 18/10/15 at 08:04 AM

Pistons are standard with a recess dip in them.
The cams are for the car but performance 264 schricks
The valves would be 1.5mm bigger in diameter.

I just wanted to know in an average sports car setup what tolerance should there be. 2mm from piston? or more.
p.s Noob here.

CosKev3 - 18/10/15 at 09:30 AM

So the cams have been supplied for the application with the pistons etc you've got fitted?

Unless you've decked the block/skimmed the head a lot/using a much thinner head gasket to raise compression the cams should be 'safe' to fit.

If in doubt ask Shrick, pretty sure they will know what mods will risk valve to piston contact.

[Edited on 18/10/15 by CosKev3]

MikeRJ - 18/10/15 at 10:46 AM

quote:
Originally posted by CosKev3
So the cams have been supplied for the application with the pistons etc you've got fitted?


He's also got bigger valves, so larger cut outs may be required in the pistons.

I would contact Schrick to get their recommendations on clearance. The safe value depends on numerous parameters, but 0.060-0.080" (1.5-2.0mm) is fairly typical.

There are two ways to measure clearance, but both require a dry build, i.e. head fully torqued down to block, cams timed in etc. The first is using small lumps of clay (or blutack) on the tips of the pistons, the second is to fit very light valve springs so the valve can be pushed down further by hand until piston contact is made, and the clearance measured by a DTI.

NigeEss - 18/10/15 at 10:48 AM

quote:
Originally posted by AntonUK
Blue tack on valve, turn engine over slowly, any resistance stop. Dismantle and check thickness of squashed blue tak.


Blu Tack has a degree of elasticity, Plasticine is better, Plastigauge is even better.

britishtrident - 18/10/15 at 11:03 AM

The other way is to trial assemble the head on the block without a head gasket and time the cams up. Then gently rotate it through 2+full turns by hand.

rusty nuts - 18/10/15 at 11:33 AM

Plastigauge is made for the job but I have done it by putting a thick length of soldering wire through the plug hole but that was on a few 8 valve engines

redturner - 18/10/15 at 08:51 PM

I prefer to dry build without gasket and a couple of short pieces of core solder on top of piston, then slowly crank by hand..............