25 replies to this topic

[Nu2mini]

Interesting article which covers this subject.

Some may wish to agree or disagree with Mr Calvers view on the state of the diminishing stock of 12G295 (which must have got considerably worse since he wrote the article 10 years ago) v his suggested alternative

Calver Article 998 Tuning Further options

[Cooperman]

Ebay linky

Buy these, no skimming required. (OR find some that are sensibly priced!)

Without gudgeon pins they are not worth a lot really. A better buy would be the currently available flat-tops.
If building an engine properly the volumes should still be measured, the calculations done after the 'trial-build', then any machining done to get the C.R. correct.
Those D-tops are standard, so if needing to re-bore, as you would with any new engine build, it would be necessary to sleeve back to standard bore. So it would not be cheap.

[stickycreambun]

Thanks for all the ideas guys

Sadly not a rebuild by any means, more just after bolt-on extras.

[MRA]

There is an oil feed hole which goes downwards from the top of the 295 head. You measure the depth of this hole with a digital vernier and subtract the depth from the thickness of the head as you also measure that. The difference should not be allowed to go below 0.050", although i've known it to go to 0.040". The problem now is that most 295's have been skimmed once or twice during the past 40 years, so standard it probably won't be.
It is almost always possible to get an acceptable C.R. even on a 998 with dished pistons. I once skimmed 0.070" from a 295 to get 10:1 CR.

Said it before, that is a standard head NOT a 12G295 !
A 295 has approx half inch before you touch the drilling...................

I have just measured a standard 12G295 and the oil way is 2.588" with a toal thickness of 2.751" which leaves me with 0.163" before it leaks...

[MRA]

Ebay linky

Buy these, no skimming required. (OR find some that are sensibly priced!)

Without gudgeon pins they are not worth a lot really. A better buy would be the currently available flat-tops.
If building an engine properly the volumes should still be measured, the calculations done after the 'trial-build', then any machining done to get the C.R. correct.
Those D-tops are standard, so if needing to re-bore, as you would with any new engine build, it would be necessary to sleeve back to standard bore. So it would not be cheap.

What currently available flat tops ??? (AE) Federal Mogul have stopped making them .. never come across such a crappy company in my life... especially after the Manager in charge of aftermarket sales Europe told me this would never happen

[bmcecosse]

ALL heads start life at 2.750 " - I guess there must be some variation in that oil way - and it may not be drilled horizontally in the head. I've never dared to take more than 80 thou off a 295. We did once take 120 thou of a 202 head - and the deck was then so thin it could be flexed by hand between waterway holes. The oil hole was not exposed - but I never dared to use the head. The 940 head is a far better head - and no 'skimming' worries. My understanding is that the MG Metro cam has same lift as all the standard BMC cams - up to and including the 731 - the 544 has more lift and the 649 a bit more again. An MG cam should be fine with the 940 with the exhaust valves sunk by 40 thou - but DO measure it all up first.

[MRA]

Just for info - the 998/1098 engines NEVER had the spider drive oil pump - they were only for the 1275 (and yes 970/1071S) engines.

Oh yes the 998 did have a spider drive fitted.....

998 & 1098 Auto's did because the pin drive (alternative) wasn't up to the job

Edited by mra-minis.co.uk, 29 June 2011 - 09:08 PM.

[Cooperman]

Ebay linky

Buy these, no skimming required. (OR find some that are sensibly priced!)

Without gudgeon pins they are not worth a lot really. A better buy would be the currently available flat-tops.
If building an engine properly the volumes should still be measured, the calculations done after the 'trial-build', then any machining done to get the C.R. correct.
Those D-tops are standard, so if needing to re-bore, as you would with any new engine build, it would be necessary to sleeve back to standard bore. So it would not be cheap.

What currently available flat tops ??? (AE) Federal Mogul have stopped making them .. never come across such a crappy company in my life... especially after the Manager in charge of aftermarket sales Europe told me this would never happen

Not tried to buy any lately. The last set I bought were Hastings at +0.080" which gave 1061 cc. Good quality pistons it seemed.
Mini Spares list their own 998 flat tops at +0.020" upwards, P20950-20, -40, -60 and -80 at about £42 each inc VAT.

Edited by Cooperman, 29 June 2011 - 09:22 PM.

[bmcecosse]

Re spider drive - not ever considered an auto - know nothing of them - but I learn something new every day! Thanks MRA....

[MRA]

Are you saying that the drillings on yours are less than 2.59 (ish) or that yours are thicker (taller) than 2.75" ??

I was only adding the dimensions that I measured on one of the 295's in my unit....

[stickycreambun]

This is pretty interesting actually, learning a lot just following!

Talking of the 940 head, does 'sinking' the valves literally mean just sitting them further into the head? (and if needed at the same time I guess fitting hardened valve seats?) And does that then have no effect up top, springs rockers etc?

Also does a 940 head not have a larger chamber volume in the same way as a 295 would if fitted (if both were standard)?

Edited by stickycreambun, 30 June 2011 - 05:42 PM.