33 replies to this topic

[Spider]

Did you fit the head gasket?

 

 

no but it hits the block no where near its full lift so I don't think that will cure it, and I would rather it didn't touch the block like the rest of the valves, it is only about 20 thou (0.5mm) to big and just clips the very edge of the valve...

 

 

The Head gaskets are around 0.040" (1 mm) thick. If it's only just kissing without the gasket, good chance that's all that it will need. You will of course need to check what the fitted thickness is of the gasket you intend to use.

 

I've built up a few engines where the pistons actually come out proud of the block deck, but up to 0.014" in one case and the gasket provided enough clearance.

 

If you do end up pocketing the block, really, all cylinders should be pocket so as to maintain the same CR between cylinders and gas flow characteristics.

Edited by Moke Spider, 14 June 2015 - 05:31 AM.

[sledgehammer]

sounds like it will need a very shallow pocket anyway

[kyle9832]

 

Did you fit the head gasket?

 

 

no but it hits the block no where near its full lift so I don't think that will cure it, and I would rather it didn't touch the block like the rest of the valves, it is only about 20 thou (0.5mm) to big and just clips the very edge of the valve...

 

 

The Head gaskets are around 0.040" (1 mm) thick. If it's only just kissing without the gasket, good chance that's all that it will need. You will of course need to check what the fitted thickness is of the gasket you intend to use.

 

I've built up a few engines where the pistons actually come out proud of the block deck, but up to 0.014" in one case and the gasket provided enough clearance.

 

If you do end up pocketing the block, really, all cylinders should be pocket so as to maintain the same CR between cylinders and gas flow characteristics.

 

when I say toucking I mean the valve is touching the edge of the bore by thou across the valve not length, the side of the bore clips the side of the valve, and this is when the cam is at less than 1/2 of full lift, none of the other valves touch

[carbon]

'Just touching' would be very bad news when it's running...

 

Remember that exhaust valves get very hot, and hot metal expands. You also need to allow for rock of the valve in the guide, and when you fit/replace the head it will not always end up in exactly the same place.

 

I wouldn't be comfortable with less than 20 thou clearance between the edge of the valve and the inside of the bore, but others may have experience in running tighter tolerances.