The V8 Owners Forum -

Hi
I gather from Ian's "tins" thread that it is possable to run flat top forged pistons at zero deck height and tin gaskets, this to my reconing is about 18 to 20 thou piston to head clearance.

Ian, am I correct in what I have gathered from what you have said?

Is anyone else running piston to clearances in this region?

How tight has anyone gone on piston to head clearance successfully?

I was going to go run 24 to 25 thou piston to head clearance on cast flat tops and thought that is tight (that is if I can track down the head gaskets at the right price).
Best regards
Mike

I will have a good measure tomorrow, But I ran tins for 5 years, I think they are 15thou, and Im fairly sure the piston is at zero deck height,, I also rev the nuts off the engine, 7k regularly, the rods are standard HRCs and the pistons are Omegas, I dont know how much strech there is, but nothing seems to be hitting

your getting me very tempted to go to 18 thou gaskets (I'm running 1/2 thou out the block on all eight pistons) If I can I will get the compression up a bit (about 11.7 to 1) which I think will be a good thing I'm planning a redline of 7800 so its good to know you have reved yours a healthy amount
Has anyone else experiance of clearance this tight?
Mike

seen 8250 on a missed shift, when I fubered up the rev limiter.

Just got down from the Garage, and the pistons are below deck height, about 20tho

Hi Ian
many thanks I'll keep searching for 25 thou head gaskets, I read an article in car craft a while back where a small block 302 ford had been built with 20 thou piston to head clearance, but obviously only 3" stroke, 25 thou should be safe on the longer stroke of this engine. Just got to find a suplier who charges sensible postage ($11 for 1 gasket, $45 postage ....for 2 its $22 and $65 postage )
Thanks again
Mike

Just read some information from Keith Black Pistons, relating to piston to head clearance.

For their pistons they recommend not less than 40thou as a total of piston to deck + gasket to allow for heat expansion and the growth of components at high RPM. They are probably erring on the safe side but it's made me re-think what I can safely remove from the decks.


Link to information.

http://kb-silvolite.com/article.php?action=read&A_id=35

Kevin

CastleMGBV8 wrote:Just read some information from Keith Black Pistons, relating to piston to head clearance.

For their pistons they recommend not less than 40thou as a total of piston to deck + gasket to allow for heat expansion and the growth of components at high RPM. They are probably erring on the safe side but it's made me re-think what I can safely remove from the decks.


Link to information.

http://kb-silvolite.com/article.php?action=read&A_id=35

Kevin

Hi Kevin,

That is what I was saying earlier so cheers for backing me up!

20 thou is too close, 40 thou is about the minimum but it does depend on many, things such as conrod material, crank whip, bearing clearance, piston rock, etc.


Pete

sidecar wrote:

CastleMGBV8 wrote:Just read some information from Keith Black Pistons, relating to piston to head clearance.

For their pistons they recommend not less than 40thou as a total of piston to deck + gasket to allow for heat expansion and the growth of components at high RPM. They are probably erring on the safe side but it's made me re-think what I can safely remove from the decks.


Link to information.

http://kb-silvolite.com/article.php?action=read&A_id=35

Kevin

Hi Kevin,

That is what I was saying earlier so cheers for backing me up!

20 thou is too close, 40 thou is about the minimum but it does depend on many, things such as conrod material, crank whip, bearing clearance, piston rock, etc.


Pete

Pete,

I did read another article by some Harley Davidson race engine builders and they do build their engines with the squish down to 25thou and they reckon the pistons are just about kissing the heads, and they couldn't do that unless the engine were frequently being rebuilt as just a little carbon build up would be enough to cause problems.

Anyway it's a lovely day and I'm going to get the MGB out of the garage and give it a bit of TLC and have a rest from engine design.

It's become a bit of an obsession in the last few weeks worrying about getting it right as it's quite a mixture of parts, Buick 300 heads,Chevy 5.85" rods Chevy 305 pistons and of course a Rover 3.9 block with 4.2 (77mm.) crank to make 4355cc. so I needed to make sure I'd got my maths right and it would all fit together!

Regards,

Kevin.