Info/ID on 12G940 Head

[NCT1111]

Good day,

I am hoping someone can provide me with a bit of info or ID on a head I have here in New Zealand. The valves are slightly inclined so I am suspecting Longman but I don't know if the stamped numbers confirm this?? Also, does any one have any idea why there are punch marking fully around where the rocker cover gasket sits, all punched at even spacing, I am totally baffled? And lastly, the inlet valves are 37.7mm and exhaust 29.3mm but where the inlets have a flat profile, the exhausts look more tapered, are the exhausts correct for this type head or should I be looking for a profile more in line with the inlet?

Any advice or ideas would be greatly appreciated!

Cheers, Neil

[InimiaD]

At a guess I'd say the "punch" marks are there to act as extra grip for the gasket.
That's a fairly large combustion chamber. Maybe for use with a turbo.

[InimiaD]

There's some more info here.

http://mk1-performance-conversions.co.uk/longman.htm

[NCT1111]

Cheers for the replies. Helping to hold the gasket in place was the only thing I could think off but I cannot imagine it would add a lot. I have never seen this method before.

[ivor badger 2]

If it's an angle valve head, it does have large combustion chambers. They use flat top pistons, though I think the pistons are a result of the combustion chamber rather than the other way round. Is the inlet valve bent or photo illusion?

[NCT1111]

Re. the bent valve, it is just a illusion but I am sure I want to replace the exhaust valves anyway. I need to double check the chamber cc. I have a Mk2 block that has been decked to match Datsun pistons (apparently a period mod in this part of the world?) and the these pistons have been modified to accept mini gudgeon pins. They are not quite flat top so again I need to do some careful measurements and calculations. Has anyone heard of this Datsun/Nissan mod?

Cheers, Neil

[mk1]

Hi Neil,

As I am sure you have gathered by now, your head is probably a Longman GT17 inclined valve head, the only oddity is that I would have expected the exhaust valve to be 31mm not 29mm. The little punch marks round where the rocker cover gasket sits are typical of the care that was taken over Longman heads of this period. Its a fairly old one, but looks to be in brilliant condition.

With a job number as low as 619 there is every possibility that this head was done by George Toth himself!

If you measure you should find the valves are inclined at 3.5°

[Jim1071]

Cheers for the replies. Helping to hold the gasket in place was the only thing I could think off but I cannot imagine it would add a lot. I have never seen this method before.

we use the same method to keep the base gaskets on the RD 350 LC two stroke bike

[NZmember]

A lister, do you know how to modify the rocker geometry for these heads? I've asked Steve Harris but no response.

[NCT1111]

Hi Mark, thanks for the info. I have the head in getting crack tested at the moment so fingers crossed! The valves are not offset as with 29.3mm exhausts the inlet/exhausts are pretty much touching so 31mm will not fit this head. The valves are certainly inclined. It does seem odd to have such large inlets with standard exhausts.

The porting is incredibly smooth and consistent, someone certainly new what they were doing!

Cheers, Neil

[mk1]

The 29mm inlet is pretty much all that is ever needed for any A series application. Right back in the mid 1960's Daniel Richmond of Downton was arguing that the 31mm exhaust was too large & would create reliability problems.



http://mk1-performance-conversions.co.u ... _index.htm

[NCT1111]

Very interesting Mark! Thanks. I have posted a photo of the valve types on the first post. The exhaust valve looks very standard in shape (most like because it is standard, I know), in your opinion do you think I should try and source a valve profile more like that of the inlet to help the flow of exhaust gases due to 'only' having a 29.3mm valve.

Cheers, Neil

[mk1]

I wouldn't worry too much about the exact valve profile as long as they are the correct size.

If you want really good advice, it may be worth contacting Brett Sims http://www.brettsimsmotorsport.co.uk/ who cut heads for Richard Longman more recently.

[Cammsjb]

Further to the previous discussions about the cylinder heads which are believed to have been modified by Richard Longman identifiable by the indented number sets on the flat face of the cylinder head, is it likely that Richard Longman could have also carried out modifications to A series engine blocks at the same time and if he did, would there have been a number set added anywhere on the block as with the cylinder heads to indicate this?

Has anyone any knowledge of this occuring?

[mk1]

Longman didn't to my knowledge stamp blocks with info or job numbers.