14 replies to this topic

[chris2009]

I think I have warped my head on my 1986 998 Mayfair. I've got an old Austin healey 1100 a series engine knocking about and was wondering if i could use that same head as its a series to a series. Only question is will the valves clear and run properly and what head gasket will I have to use? Also any other mods that i might have to do.

Cheers Chris

[BoboGib]

what's the casting number of the head. It will fit but might need skimming.

[chris2009]

Not sure on the casting number as its not currently at my house but can find out shortly. Which code will fit and which code will fit but needs skimming?

Also would it need to be skimmed to bring the compression ratio back up?

[lrostoke]

http://www.somerford.....nd 1098cc.pdf

12g202 should only need a light skim

12g295
12g206 will both need skimming to raise compression

http://www.calverst......sting_ no.htm

[chris2009]

Brilliant will check out the codes and get back to you guys. I can skim the head at college but i have no idea by how much so if anyone has any previous experience with these type of heads would be brilliant

[bmcecosse]

202 head would need 40 thou if going to be used with flat top pistons - the 206/295 would need 60 thou off. Both will give a performance advantage - the 206/295 much better than the 202. But if it was an AH engine - it should have the 295.

[chris2009]

Cheers bmcecosse, Im having a real trouble finding the head code tho. Have looked by the thermostat housing and all around but cant seem to find it. Am i blatently missing it somewhere as the twin carbs, manifold and heat shield are still attached. Will my stock push rods be able to put up with the stiffer double valve springs? Another quick question if i was just to skim my other head as i think its warped how much would i need to take off?

[blacktulip]

you have to take the rocker cover off to check the number. it should stamped on the head somewhere.

[Cooperman]

Don't just randomly skim it, as you don't know whether it's been skimmed before.
You MUST take the old head off and do a proper compression ratio measurement & calculation. Then you will skim the correct amount off to get the comp.ratio you want. A good C.R. to go for is about 10:1. If you don't know how to do this, come back on here and one of us will help you.
To do the measuring you need a set of feeler gauges, a 6" steel straight edge, a 5 ml shrynge from Boots-the-Chemist, a piece of flat perspex about 3.5"square, a digital vernier caliper and a pocket calculator.

[Udo]

If you have the machines etc to skim the head etc why not just skim the minimum off your existing head and use that?

Yes it will up the compression slightly but unless its really badly warped then i'm sure it will be fine

[ado15]

you have to take the rocker cover off to check the number. it should stamped on the head somewhere.

Not stamped, but cast into the area under the rockers.

If it's an Austin Healey Sprite 1098 head, it should be a 12G295, the same casting as used on most 998 Coopers. It was also used on the equivalent MG Midget along with MG1100's and VDP 1100's.

[Cooperman]

you have to take the rocker cover off to check the number. it should stamped on the head somewhere.

Not stamped, but cast into the area under the rockers.

If it's an Austin Healey Sprite 1098 head, it should be a 12G295, the same casting as used on most 998 Coopers. It was also used on the equivalent MG Midget along with MG1100's and VDP 1100's.

And the 295 head is a super head for all 998's so long as the CR measurements and calculations are done, plus the correct machining to get the CR correct.

[chris2009]

Cheers for all the replies guys, i've been told the theory on how to check compression ratio but never actually done it. I have most of the things you said Cooperman apart from the vernier and piece of perspex. If you could give me a run down on how to check the compression ratio that would help a lot! I will do it for both heads and find the best ratio it will give me. I have a feeling its the 295 head. Im guessing at it was used as cooper head then I will see a good power increase also with twin carbs attached im hoping for quite a tidy improvement.

[Cooperman]

I'll PM you with the details of how to measure and calculate as soon as I get the time, which will probably be tomorrow as I have some bodywork to do on a '97 MPI this afternoon/evening.

[chris2009]

No worries i cant get the head actually skimmed until next Wednesday so any time in the next week would be brilliant!