Will it fit and how will it go?

Side valve, 803, 948, 1098., 1275 and Vizard mods

Will it fit and how will it go?

Postby imagoodbloke » Wed Feb 13, 2019 11:17 am

Hi guys, I know there are a few experts out there who’ll know the answer, so here goes.........I have purchased from different people a 12g295 head, and a HS4 carb on cast manifold ( off a 1000cc Mini, I believe.) The plan is to fit them onto my 1098cc engine, is it a simple bolt on job or do I need to skim the head etc? And roughly, how much extra bhp will I achieve. Any advice, hints, comments would be appreciated. Thank you Pete
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Re: Will it fit and how will it go?

Postby Panky » Wed Feb 13, 2019 2:02 pm

If the new head hasn't been skimmed then the compression ratio will be down (295 head has a chanber volume of 28.3cc where the standard 202 head has 26.1cc) so that will need to be sorted. It will bolt straight on but the gains wont be that much without a better cam and decent inlet/exhaust manifolds.
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Re: Will it fit and how will it go?

Postby plastic orange » Wed Feb 13, 2019 3:22 pm

I ran a 1098 with 295 head and a single 1 1/2 carb and car performed better than it did before. As this was almost 40 years ago, I can't remember how much was skimmed off the head, but it was certainly skimmed to up compression. Car bent the speedo needle against the stop frequently, and even did so with a 3.7 diff.

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Re: Will it fit and how will it go?

Postby Panky » Wed Feb 13, 2019 4:16 pm

Crikey, didn't expect it to make that much difference without the other mods. Would be a little fire breather with a decent cam and exhaust :twisted:
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Re: Will it fit and how will it go?

Postby MM » Wed Feb 13, 2019 10:33 pm

Indeed, a 1098cc engine with the 12G295 head (as fitted to MG Midget 1098s) should give around 55bhp, compared to the standard Minor's 48bhp, though you may also need to fit a better exhaust system (e.g., Maniflow) and possibly twin SUs or a single 1.5" HIF 38 to achieve this figure.
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Re: Will it fit and how will it go?

Postby imagoodbloke » Thu Feb 14, 2019 3:24 pm

Thank you guys for your comments/advice. I’ve scoured previous posts about the subject and have come away with a stewed brain, so many differing opinions.
How do I know by how much to skim the head ? Also I read that the exhaust valve rocker clearance should be 15 thou. but my workshop manual says 12 thou.
More help needed. Thanks again.
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PostThis post was deleted by Panky on Thu Feb 14, 2019 4:31 pm.
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Re: Will it fit and how will it go?

Postby Panky » Thu Feb 14, 2019 4:49 pm

After a bit of research on the other side it looks like you will need to take .060" off an un-skimmed head to get the comp ratio to where it should be. You will need to measure the thickness accurataley with a micrometer or venier callipers to make sure before you get it skimmed. An un-skimmed head measures 2.75" from face to face.
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Re: Will it fit and how will it go?

Postby philthehill » Thu Feb 28, 2019 2:29 pm

Skim the 12G295 head by 0.060" if not already skimmed from the standard 2.75".

The reason for the 0,015" exhaust valve clearance is to allow for regression of the valve into the head if unleaded seats are not fitted.

From experience the 'A' Series does run better with both inlet/exhaust gaps of 0.015" but rocker noise is louder.

I would advise that the damped crankshaft pulley should be fitted to damp out any crankshaft vibrations to which the 1098cc engine is prone.

Having run a 12g295 head on my 948cc/998cc engine with a Cooper camshaft, LCB and twin 1.5" SU carbs it certainly made a difference to overall performance.

12G295 head - a very good performance mod but getting a bit expensive these day - the last one I bought cost me £12.
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