17 replies to this topic

[Oh Dear]

Well, I have stage one'd my 998 and have a hif 38, uprated coil etc....I now have a 12g940 to go on. This has already had it's waterways appropriately blanked and is soon to be skimmed. It has also been ported . I am also going to have the block pocketed. (see pic}
I have a few questions for you experienced types:

1. Am I to fit an ordinary 1275 gasket.
2. Who makes the best gaskets.
3. Will the 998 rockers be any good or should I replace them with 1.5 (rollers)
4. Will I need a different rocker cover (1275)
5. Will I need a smaller pulley wheel (just under the thermostat).

Any other advice would be very much appreciated and yes, I have used the search feature but without success.

Thanks for any help,

Attached Files

•  pockets_12g940.jpg   24.85K   23 downloads

[Pie]

1. yes
2. Minispares do all the gaskets, and the supersticky is regarded as the best, but a copper one does the same job.
3. In my personal opinion 1.5rockers are a waste of money, cooper S are fine, an cheaper.
4. rocer cover will be the same, the heads were all the same size.
5. you dont NEED a smaller pulley wheel but itll make the fan turn quicker/faster.

Hope tha helps some how lol

[panelbeaterpeter]

I belive THIS is the best head gasket you can get, I bought one for my 998 when I did this conversion, although I've not driven it yet..

Edit: link not working, try http://www.minispare....aspx?pid=35695

Edited by panelbeaterpeter, 20 January 2008 - 10:26 PM.

[Pie]

Also, why do the waterways need to be blanked on the 12G940!?!??

[1984mini25]

you dont NEED a smaller pulley wheel but itll make the fan turn quicker/faster.

YOU DO NEED THE SMALLER PULLY as the underside of the 12g490 head around the thermostat end is a lot larger, and as the 1275 blocks are 10mm taller than the 998 ones, the top of the water pump needs shaving down or else the head simply won’t touch the top of the block on that side.

[Oh Dear]

I thought some of the water channels needed plugging like this pic!

Attached Files

•  12g940_mods.jpg   7.48K   4 downloads

[1984mini25]

Some of the waterways do ideally need plugging and re-drilling to suit the 12g940 head on a 998 block, although there’s only really one that might cause problems with the head gasket and that’s the second water hole along on the front right hand side, the rest you “should” get away.

[Oh Dear]

MANY THANKS for the advice. I am really getting into this mini stuff..but where does it all end. Am I to be destined for 1380, a fast road 998 or Mk1 850 and 50mph. It's all so addictive because every drive is fun.

Wishing you all well.

[Sprocket]

Its not the head that needs plugging its the block. It needs plugging at number one cylinder, if you place a 1275 gasket on the block, you can see which hole needs plugging. It needs to be a black iron taper threaded plug so that it has a posative location and wont fall out, the block then needs a skim, as the fire ring of the gasket sits on this plug.

Dont waste your money on any sort of high lift rockers as you wont get any benefit, the 12g940 head is more than up to the job!

I wont use anything other than the Payen AF460 head gasket, but at a push, the Payen BK450 would be second on my list. The BK450 is the one all the turbo guys use. If its not Payen or Cometic, dont touch it!!

Rocker cover is a rocker cover, there is no difference.

You may or May not need the rocker cover, depends on the head. Some clearance can be ground out of it, but dont go to far, lol.

[Oh Dear]

I have just come back from talking to some workshop people who sort out grasstackers. I was shown the rolling road results for various set-ups, including 998's with 12G940 heads. The average was a gain of 4bhp...therefore not really worth doing.

As this 998 is running great...pulling smoothly right through the rev range and driving well, I have decided to leave this engine as it is and buy a 1275 engine which I can overbore and build up from scratch at my leisure..possibly fitting a supercharger.

Nuts. I was becoming a victim of Mini magazine articles and starting to believe things which are more to do with marketing than with creating good driveable cars.

Thanks for the advice though.

[Ethel]

I would expect a 12g 940 to make a lot more than 4hp on a 998 - even though that is 10% up on standard. Class regulations for grassers can be pretty strict so it could be exhaust, carb or even restrictor plates could be responsible for the low gains. though, if you intend building a 1275 you may as well put your money in to that.

[Oh Dear]

Well, one or two were 5-6bhp (at the wheels)..which is reasonable I suppose. But this 998 is sweet as a nut with it's lcb, hif and one box exhaust. (AAL needle) I would change the cam maybe but only if I could find a way to do it without taking the engine out.

[stardude]

i beleive you can with a 998.

i think you may need to remove a bit of the inner wing?

[samwell]

i would say its the restrictions in the grass track engines that limit the improvements fromt the head, plus its fun to do anyhows. You don't have to take the engine out to fit a came, just need to remover or bend one of the inner wing "ribs" and lift the cam followers out through the tappet covers in the back. AFAIK you need the head off to time the cam up so might as well change the head while you're there. And you will need the smaller pulley wheel.

[Pie]

I have just come back from talking to some workshop people who sort out grasstackers. I was shown the rolling road results for various set-ups, including 998's with 12G940 heads. The average was a gain of 4bhp...therefore not really worth doing.

Who told you that?!! Dan (JetBLICK) added a 12G940 head and a 286 cam and got something like 64 bhp, think this was at the fly. But even still standard 998s wernt 60hp at the fly!!