david rosenthal wrote:
Just looking at the pics posted here and people's comments I wonder if there could be more a problem with the cylinder heads expanding [IE lifting] from thermal expansion on the small area.
If the small bore engines are blowing thru 1-2 and 3-4 and the big bore engs are going thru 2-3.
It may not be the compound of the metal but if there is some lifting then no matter what metal is there it will eventually track thru.
The other day I was looking at some pics of 2 stroke diesel engines with stellited valves and seats but both had suffered from sulphur vanadium hot corrosion where is cut thru the stellite like it had been cut with a plasma cutter. This was usually caused from a slight clearance when the valve was not seating.
The fire rings are the problem not the rest of the head that just needs sealing for the water pressure.
May be the fire rings need more pressure at the narrowest point. Its something I found with my honda head conversion where I use a annealed copper ring but with .4mm compression above the rest of the plate.
The cylinder heads may be perfectly flat but if lifting is a problem with higher compression then maybe the head might need a thou or two taper from the centerline to the outer edges to give more compression in the center.
Just another mad idea.
It is true, that on most of the big bore motors I've pulled down that they do have signs of breach between 2-3... even with perfectly machined blocks/heads, even with out ANY sign of gasket failour...
But I must say, that people have been running high comp ratios in these engines since they first came out (granted with varried results)....
But it seems odd that even if there is an inadiquecy in the way which these engines are machined.... that some fail where others don't?
They're all snow ground, flat,,,,,, so even if YES they should have a slight kanter from either side towards the centre, a lot of them don't blow or stuff up, while some do..... the only varriable is the gasket.... (well that and the preassembly checks that are MEANT to be carried out)