Head compatability

[owenmorris]

Hi, my Morris Minor 1000 is fitted with an A+ engine,is the cylinder head off a 948cc series A engine compatable.
Thanks, Bernard.

[philthehill]

What size 'A' plus engine is fitted to your Minor?
The 948cc Minor cylinder head (see details in chart below) will physically fit a 1275cc 'A' Plus engine but it would be a mighty retrograde step.
The 940 head (see details in chart below) fitted to 1275cc 'A' Plus engine has bigger valves and has better gas flow for both inlet and exhaust gasses.
The question has to be asked why do you need to consider fitting a 948cc Minor cylinder head?
Phil

[owenmorris]

Thanks for the information.
Bernard.

[ampwhu]

i cant find an answer for this, even though I have gone through vizards book.

does the 12G940 head fit a 1098 engine? I know the 12G202 comes with the 1098.

looks like the exhaust and inlet valves are slightly larger on the 12G940 head.

I have the chance to swap the heads you see....

[philthehill]

The 940 head will fit the 1098cc engine but you will have to either recess the valves into the head or pocket the block as the valves overlap the bores.
See picture below of pocketed block.

[ampwhu]

ok, i see. a guess that any reputable engine shop would know this if you showed them this picture and the head in question?

[philthehill]

The easiest (and cheapest) way is to recess the valves further into the valve seats by cutting the seating face of the valve seats deeper into the head.
Some even face of the face of the valve to provide clearance.
If you decide to pocket the block you must ensure that the bottom of the pocket is well away from the top of the rubbing path of the piston top ring.
Use the search facility on here to provide more details before you make a final decision.
Here is one to be going on with.
https://www.mmoc.org.uk/Messageboard/vi ... ust+valves

[ampwhu]

ok Phil, thanks. i'll discuss with my mate whose got a machine shop. head valves seem the easiest option if i go that route.

that way i could return to a 12G202 head at a later date on the 1098 block.

thanks again as always. your better that the Samaritans, did anyone ever tell you this.

[paul 300358]

I looked at sinking my 12G940 head exhaust valves myself but decided that by the time I had obtained a large 45 deg countersink I could get a machine shop to do it. I took it to a company in Stoke who sunk the exhaust valves and then lapped all the valves in for £60 ish.

[Declan_Burns]

Some get away without any machining. Before doing anything measure the distance from the face of the valve to the base of the cylinder head.
You need 8mm to be safe.
Regards
Declan

[philthehill]

Also measure the thickness of the head which should be 2.75".
If less than 2.75" the head in all probability has been skimmed.

[edd_barker]

Read through my engine rebuild thread before you spend any money! I machined cut-outs into the block, can't remember what my clearance is from the top ring.

Sinking valves is definitely easier, although it then throws your rocker geometry off, so adjustment may be needed there. As soon as you go away from standard it gets plenty more complicated.

However, the result is worth it. Mine is 1150cc, HIF38, standard cam, 12G940. Plenty more pull than a 1098. Once it has got 3000 miles or so on it I will stick it on a rolling road to set it up properly.

Good luck!

Edd

[ampwhu]

does the CAM4810 head fit the 1098 engine?

[philthehill]

The CAM4180 cylinder head will fit the 1098cc Minor engine and it has unleaded seats.

Normally fitted to 998cc Mini 'A' Plus engines and is coloured yellow.

'A' Plus engines are usually fitted with 3 collet groves in the valve stem.

It has smaller inlet valves than the standard 1098cc 12G202 Minor head.

12G202.....................inlet valve 29.36mm ex valve 25.4mm combustion chamber 26.1cc

CAM4180..................inlet valve 26.99mm ex valve 25.4 combustion chamber 25.5cc.

Unless you are desperate to fit a CAM4180 cylinder head I would give it a miss.

https://www.ebay.co.uk/itm/Classic-mini ... SwDVtaadxK

Phil

[ampwhu]

I did think this and looked in the vizard book and didn't see it listed. I know it was unleaded as well.

cheers as always Phil.

[philthehill]

https://www.calverst.com/technical-info ... ng-number/

[ampwhu]

just another question regarding heads.

ive had a 12G202 head skimmed 0.060" and its currently fitted to my 948 engine in the car. it runs great.

i'm building a 1098 engine that's standard and want to know if this 12G202 head that's been skimmed, will be ok fitted to the 1098 block when I swap engines.

Alan

[philthehill]

The 12G202 cylinder head is a straight fit onto a 1098cc block and is the standard fitment for a Morris Minor 1000 1098cc 'A' Series engine.

[liammonty]

The 12G202 cylinder head is a straight fit onto a 1098cc block and is the standard fitment for a Morris Minor 1000 1098cc 'A' Series engine.

Yes - but not with 60 thou removed from it. I'd suggest calculating what the CR will be, as it's already fairly high on a standard HC 1098 (relative to the older engines). It will have been skimmed for use on the 948 to compensate for the fact that the head volume is lower on the 948 (around 24cc vs. 26 cc on the 12G202 if I remember correctly?), so skimming it will have retained the standard compression level on the 948 block. You want to ensure the static CR isn't too high, otherwise you'll struggle to avoid pinking and associated concerns.

[philthehill]

Consider it this way:-
If a 940 head with a combustion chamber of 21.4cc will fit a 1098cc engine and run without problem a 202 head with a 26.1cc combustion chamber and subsequently skimmed by 0.060" will run without problem.
By all means check the combustion compression ratio if so desired but the very slight increase in compression ratio will be of benefit.
The standard combustion chamber of the 948cc engine head is 24.5cc.
Phil