28 replies to this topic

[crazirob]

what are the advantages/ dissadvantages ? is it worth doing ?


cheers guys

[Pooky]

Advantages - significant power increase when coupled with other mods (Stage 1 kit, sportier cam etc)

Disadvantages - takes quite a bit of work to fit. Block will required 'pockets' to be machined into the face of the block so that the exhaust valves in the 12G940 head don't impact with the block. This is really a job for a professional machine shop and will require the engine to be removed from the car. Some people have sunk the valves further into the head to avoid this issue but I've not done this.

You'll also need to modify the top edge of the water pump to avoid it fouling on the head (can be done yourself with a file/grinder if you're careful), and you'll need a new smaller size water pump pully. Then you'll need a new top radiator bracket and top hose.

Have a look/chat with Martin at MRA Minis (he's a member on the forum and has a website at mra-minis.co.uk) about his conversion gasket. It's a special gasket specifically designed for this conversion.

I have a 1062cc, with Morspeed PH3 cam and standard 12G940 on top. It's great Small bore all the way

[datsun100a]

no pocketing required with standard cam... and it makes an excellent cheap performace boost.

[sm@rty]

I Have A 998 Block with ligthened krank and con rods which has already been pocket for a 1275 head it was part of a slark hillclimb engine which i'd bought from a friend went he decided to put something a bit more driveable its was an animal but the 998 block is now for sale? i also have straight cut drop gears that were on in if you know any one who would interested. sm@rty

[leaky]

I have a 1275 head on a 998 block. Its not as great as everyone makes out. I only did it as when I bought my car it had a 1275 head on the 998 block but wasent pocketed. I sent it off for slarks to have it all pocketed and cost just over £600. to be honest it was a complete waste. Your best to just go with a stage 3 head. No need to pocket the block and is dam cheaper.

[jchomme]

after much consideration, I find this quit interesting!

 

Cheers

[liirge]

I have a 998 that's been over bored and has a 1275 MG head on it, race cam, roller rockers, lightened flywheel and crank.

The car really really flies; great fun. Problems: idle is appalling and has to be set very high. Lots of times it stalls when the clutch is engaged and decelerating.

Still fun though!

[mattcave]

Warning, zombie post, brought back from the dead!!

 

I built a 998 with a 12G940 head and a SW5 cam a few years back. It was a fair amount of work to build, but it was cheap and the end result was driveable, it revved out nicely, and it made 65bhp at the flywheel which exceeded my expectations. It kept up with standard 1275s OK, and it had the novelty factor of only being a 998.

[markus82]

sorry for bringing back an old post.. so iv looking in to this and i have a 998 block 12g940 head iv test fitted it and it work's fine the valve's clear the block but what i need to kinow is what gasket do i use? 

 

regards mark 

[Turbo Phil]

You need to use a 1275 gasket.

Phil.

[markus82]

thank you phil 

[Gr4h4m]

You will also find that a couple of the water holes are very close when you over lay the gasket. I plugged these with small grub screws and locked them in place with some thread lock.

[markus82]

thank you graham... ill have a look out for those

 

regards mark 

Edited by markus82, 03 September 2016 - 04:05 PM.

[JonnyAlpha]

Just picking up on this thread.
Just to confirm can you YES or NO fit a 1275 head onto a 998 without any extra work?
If so on a 998 HLE 1000 can it be done and what head do I need?

[JonnyAlpha]

Sorry on my phone - double post

Edited by JonnyAlpha, 05 September 2016 - 07:57 AM.