Thanks for the input Graham.

In my case I’ve already locked in the 70mm stroke crank which is the 12G2827 casting from South Africa. These are 1.75” journals, and give essentially the same stroke as the 1071 and are apparently pretty bulletproof


Edit: ignore this bit below, I misread Graham’s earlier post
In regards to the 202 head, I’ve got the current head on the small bore 1098 with 1.26”/1.07” valves which you modified. Would this need any different modifications to suit the big bore block?

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Timmy, I won't answer for GR but I would consider a modded 1275 head. We will need a lot of air/fuel at the top end.

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

Hi TK
Placing a light fly wheel on the motor will have nothing to with the mass you are trying swing on the crankshaft,why do we try to get the lightest rods/ pistons we can get to reduce the mass we are trying to turn at RPM.
Yes you can run a 1275 head on a small bore but it will perform better with a 295 head,( you don't think I have already done this testing on the dyno)
When I had Ivan Glasby's 970 on the dyno which runs a MK1 AEG163 head we took it off and put a 1100S head on just cleaned up and the seats cut 3 angle it made 3 to 5 ft lb of torque more through the range, once again smaller ports and smaller valves.

The motor you refer to is called an XSP there were only 9 to 13 of these engines made (have a look at my website) I had to rebuild one for Queenslander
Don Thallon who had a 1959 cooper with one of these engines in it.
I talked him out of running the motor in case he broke it an the value of this car would go right down, so I built him a replica engine based on a 998 engine running a 295 head dry sump and all it made 113HP at 9000 RPM and 89 ft lb of torque.
I have all the photo's of one of these engines in pieces including the 11 stud head they run a one off(on my website)
Graham Russell

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"It's better to be not informed than ill-informed"

HI Timmy
No don't run a small bore head on a 1275 bore the chamber shape is all wrong for the big bore, but yes it would work there is enough air following through that head to make a lot of HP.
I don't know what TK means by we need all the air/ fuel we can get I don't think he understands velocity in a head.
I would run an 1100S head on your motor with 1.3 inlets (std) an just clean it up in the ports.
When Ivan run his 970 at Oran Park on the short circuit he held 3 gear all the way down the straight just on 10000 RPM because he recons it was to slow when he pulled top gear, yes they do rev.
Good luck with your build your doing well, if I can be of any help as well as parts just give me a ring.
Graham Russell

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"It's better to be not informed than ill-informed"

Thanks Graham, got a bit confused with some of the posts there.

The head I've got aside is a small valve 12G940 (1.33" & 1.15" valves), I think it'll just need a clean up. I'm still yet to decide on unleaded inserts and whether I'll get it drilled for 11 studs, but that is a long way down the track.

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Hi Timmy
That head will be fine, if you want it drilled bring it up and I will do it for you.
Graham Russell

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"It's better to be not informed than ill-informed"

I remember Don Thallon. I really wanted to buy his Chevy Nova.

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

I think he is still with us in QLD...last raced a Cooper T53 F1 in 2018???

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"Show me the Mini!"

Hi Mike
Don is still with us he sold the cooper to a guy in New Zealand and now runs an MRC22 ford formula junior.
Graham Russell

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"It's better to be not informed than ill-informed"

Thanks GR...nice little jigger

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"Show me the Mini!"

yep... I think you'd need to melt it down and recast it

pretty sure small bore heads won't go on big bore blocks

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did I tell you that I won a trophy?

Sorry I got a bit confused there with some of the posts - we were talking about big bore & short stroke then all of a sudden the talk changed to not putting 1275 heads on small bore blocks, which I got mixed up with small displacement short stroke blocks.

So, I'm sticking to the original plan of the 12G940 head from the first post which will get a clean up

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Good lad!!!

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

Good luck with the project, I too some 20 odd years ago went a bit silly on a 1098. If you push the boundaries to far it won't last more than 100,000 Kms. My learnings were, just because it hits 9000rpm without any valve bounce doesn't mean you should. Started off with twin SU's followed by a downdraft 28/36 weber before settling on a 40mm weber. It happily revved out to 7500rpm which took it's toll on the standard crank which I had tufftrided. The biggest failing however was going 60 oversized pistons on the standard block, the lack of meat/metal between the bores led to its demise. I believe the 1098s has thicker walls between the bores. My block developed a hair line crack between cylinder 3 & 4, it kept blowing out copper head gaskets every 5000kms. Eventually it took out a chunk of cast iron from the head between cylinder 3 & 4. The only thing left worth keeping was the 557 cam

Interesting experience there Stefano! Cracking the block doesn't sound very fun at all.

Was yours a small bore 1098 or a big bore based engine?

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