Suspected Low Compression Engine

Post by **jaguar68** » Wed Oct 21, 2009 12:06 pm

Hi Guys,

I'm looking for some information on a suspected low compression 1098cc engine. The engine in question is a "Genuine" BMC Gold Seal Engine (the transfer on the rocker cover tells me so). However, when stipping it down for rebuilding, I find that it has deeply dished pistons and a 12G1456 cylinder head fitted. According to Vizards book, these heads were fitted to the 803cc and 948cc Minors (amongst others)

Would this be correct for a low compession engine? It seems odd otherwise, and I can't believe BMC would rework lower spec heads to a higher spec.

I intend to fit new pistons and rings to the engine. Should I have the block rebored or would glazebusting be a better option? I can't feel any ridge at the top of the piston travel, but that's not a guarantee that there isn't one.

What do you suggest?

Also, what size is the camshaft securing nut?

Regards

John

Post by **mike.perry** » Wed Oct 21, 2009 4:36 pm

The compression ratio was in the pistons. The l/c engine had a deeper bowl in the pistons. Can't comment on head nos. because I don't know anything about them.

Post by **bmcecosse** » Wed Oct 21, 2009 7:12 pm

Are you sure it's not a 948 engine ? Check the bore sizes. That head is certainly useless on a 1098! Cam nut I think is 1 5/16" AF or near enough 33mm if you are 'metric'.

Post by **billlobban** » Wed Oct 21, 2009 9:01 pm

Dont know much about the numbering of Gold Seal engines but I have a genuine low compression 'van' engine that I am rebuilding as a high compression engine replacement for Matilda
My engine number is 10V/451E/L 5621 I think the clue is in the L as in low compression instead of H
Quite easy to tell when you have the head off it has pistons like soup bowls
If you dont have access to a micrometer take the block to your local machine shop and ask them to check it for ovality

Post by **mike.perry** » Wed Oct 21, 2009 9:06 pm

The 948 engine has 950 cast on the side of the block below the front tappet chest. The 1098 has a plate with 1100 on it in the same place.

Post by **bmcecosse** » Wed Oct 21, 2009 9:20 pm

Good point MP! Just because the rocker cover sports a 'transfer' - dosn't necessarily mean the engine has been 'reconditioned' !