Can't stop the engine pinking!

Post by **matt993fod** » Wed Dec 17, 2008 9:32 am

I am running a 1098cc midget motor in my moggy, which was fitted with stupidly high compression pistons when rebuilt years ago. When my last engine wore out I put this one in, but had to use the only cylinder head I had in stock, which had the hell skimmed out of it. Naturally, this means I can't stop the bugger pinking, no matter how much I retard the ignition.

I have to cure it, as this is a really sweet engine, and had only done 20000 miles when I put it in. I don't want to break it.

What I was thinking, is maybe use a thick shim head gasket to lower the compression, or perhaps use two head gaskets together, but don't know if the latter is physically possible. Has anyone ever heard of this being done successfully? Would anyone know where to look for shim type gaskets for the A series?

Thanks in advance.

Matt.

Post by **Cam** » Wed Dec 17, 2008 10:40 am

Try using octane booster and super unleaded. I have to use this combination on my 10.5:1 compression 1380cc engine.

Any idea what compression your engine is now?

I personally would not consider trying two gaskets and I have never seen a shim piece personally. If the above does not cure it I would look for a lower compression head!

Ratbag · Post by **Ratbag** » Wed Dec 17, 2008 1:24 pm

Try colder plugs, multiple head gaskets, or porting/polishing the combustion chambers!

Post by **matt993fod** » Wed Dec 17, 2008 3:44 pm

The compression is at least 11.5:1, maybe even 12:1.

I'd rather not use another head as this one is a beauty. Plus its the only 12G295 head I own, and the cam I have is to high lift to go for a 12G940 head without the valves hitting the block. Maybe I could try to source another 295 head, but I could never get it as nicely ported as this one I already have.

It was suggested that I try multiple gaskets, but I'd never seen it actually done, so wasnt sure if it would work. Has anyone actually ever seen it done?

Post by **bmcecosse** » Wed Dec 17, 2008 11:02 pm

Best bet will be to open up the chambers in that head to drop the CR - with best fuel and possibly octane booster it should be ok. Otherwise - you could quite simply skim the piston tops which will also drop the CR. But 11.5 : 1 is not especially high - it should be ok. What advance is built-in in the dizzy ? And NO - don't use two head gaskets ! Turbo lads sometimes use a steel spacer - with gaskets either side - but to me it seems easier and more reliable long-term to just skim the pistons.

Post by **Matt** » Wed Dec 17, 2008 11:09 pm

How much is the head skimmed by? I have 2 bare 12g295s and would consider a swap. I dont think either has been skimmed at all, but would need to check.

Failing that use a 12g202 and port it a bit!

Post by **matt993fod** » Thu Dec 18, 2008 5:54 pm

This is all academic now it seems. A compression test revealed that the existing head gasket is gone between 3 and 4.

Sod it, I'll whip it apart, shim it up and try again.

Thanks for chipping in though, guys.

Post by **bmcecosse** » Thu Dec 18, 2008 7:42 pm

If the head is coming off -take the chance to open out the chambers. DO NOT use a shim !! For the record - all heads start at 2.750" thick - so measure yours and you will know how much it has been skimmed. The 12G940 head is a MUCH better head - so that's the way I would go - indeed I have already!

Post by **twincamman** » Fri Dec 19, 2008 11:38 am

Might be worth trying Ferriday Engineering. They can make up Bi-metal and Multilayer Steel(MLS) head gaskets from a pattern.

Go to www.ferriday.co.uk

EDIT:- They can make them in various thicknesses as well.

Post by **matt993fod** » Fri Dec 19, 2008 3:14 pm

Many thanks for the link.

Post by **Dean** » Fri Dec 19, 2008 4:18 pm

Matt, as well as the above, try working on the moggy while wearing a pair of leather studied hot pants. Not sure my advice will completely cure the problem though.