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+--- Thread: Filling a low-comp head (/showthread.php?tid=669)
Filling a low-comp head - cardiffrob - 10-01-2018
Has anyone heard of a low compression head being 'filled' to raise the compression ratio? I have been asked if it could be done with a Mo**is head and thought that A7s would probably have already explored this option in the past. It is a Sidevalve head, similar to the A7.
I can TIG weld but it is an expensive job to play with if it doesn't work.
Thanks.
Rob
RE: Filling a low-comp head - Alan - 10-01-2018
I've never done it, but I believe the thing to do was melt brazing rod into the combustion chambers.
RE: Filling a low-comp head - Phil Kingdom - 10-01-2018
I would have thought skimming a few thou off the head would be the cheapest and best option, welding cast iron or indeed brazing is a specialist job and will require the whole head being heated up evenly and even then it may distort and still require skimming not to mention the smoothing of the combustion chamber afterwards.
RE: Filling a low-comp head - Ruairidh Dunford - 10-01-2018
I have seen a couple of low compression (A7) heads skimmed at an angle (thinner on the piston side) - I have been told this can increase the compression over and above that of a standard H/C head.
Others will know for sure.
I also noted that the studs had required some adjustment for the above to work...
RE: Filling a low-comp head - Alan - 10-01-2018
Yes, I've done a few like that. It does seem to work. You can take quite a lot of metal off an early head, more than you can a late Ruby one. The problem is the transfer area between cylinder and valve chamber starts to get a bit congested. Cutting the head at an angle helps with this. Angled heads like this have, of course, been discussed here before.
RE: Filling a low-comp head - cardiffrob - 10-01-2018
Sadly, that won't work on the Morris since the head is flat above almost all of the bore. It is the transitional area between bore and valves that needs filling in a bit.
RE: Filling a low-comp head - Chris KC - 10-01-2018
Perhaps I'm a simpleton but that doesn't look too bad to me - not sure how much more compression you expect to get but it will most likely be at the expense of something else.
RE: Filling a low-comp head - Speedex750 - 10-01-2018
It looks pretty good to me as well, good chamber shape and the plug near the exhaust valve. Maybe the chamber roof is a bit high, it's hard to tell from the photo (I wonder what the alloy one is - that looks good as well!). I'd try a modest skim of the face, maybe 30 or 40 thou just to tickle the compression up. If the whole engine is in bits it may be worth decking the block as well to get the pistons a few thou proud. I'd avoid welding or brazing into cast iron heads, it can be done but cracks very easily - plus there's no obvious 'dead' areas to fill.
Dave
RE: Filling a low-comp head - cardiffrob - 10-01-2018
The iron version is maybe 5.5:1 and the alloy one about 8:1 so actually they are quite different. If you skim it too much you get valves slapping the roof of the head.