13 replies to this topic

[mini_matt_106]

hi, ok have done some searching and reading but i am still soo confused!!!

i have just bought a 1275 head (12G940) to go onto a 998 engine for that little bit extra! but i am unsure what needs to be done! do i need to pocket is the first thing? if so how much do i need to pocket it by, anyone got a how to?
compression ratio is the other main issue, what will i need to do to get the correct CR? skim? if so how much?
other than these points will it fit straight on? pulleys etc. any help will be much apriciated and il put up a how to with pics when i fit it!
many thanks, Matt.

[minipac]

hi mate you will have to strip the engine back to bear block and have it pocketed about 2mm is enough. at the same time it would be worth having the main bearing straped. if you take the valve springs of the exsaut valves on your head and paint them while the piant is still wet place head on block and let valves touch block this will mark where you need to have cut out .any decent machine shop will be able to do this, cost my £60 last year. as for pulleys water pump will have to be ground flat to the block so the head can be torqed down.
not home at the moment but when i get home i will take some photos of my engine .

[mini7boy]

hi mate you will have to strip the engine back to bear block and have it pocketed about 2mm is enough. at the same time it would be worth having the main bearing straped. if you take the valve springs of the exsaut valves on your head and paint them while the piant is still wet place head on block and let valves touch block this will mark where you need to have cut out .any decent machine shop will be able to do this, cost my £60 last year. as for pulleys water pump will have to be ground flat to the block so the head can be torqued down.
not home at the moment but when i get home i will take some photos of my engine .

an alternative to pocketing the block is to sink the exhaust valves slightly into the head. Keith Calver wrote an excellent article that used this technique. Lots of details and power results provided.

I know for sure that it is published in a one-off(so far) special edition of Mini Magazine named Mini Expert published in August 2006.

The article is something like 8-10 pages with a heap of photos, dimensions, flowbench results and rolling road results.

If you really want to put a 1275 head(12G940) on a 998, this is the article for you. See if you can beg, borrow or steal a copy of Mini Expert.

He also has another article on 998 tuning that is about 7 pages in length.

You may be able to buy one from Mini Magazine, but they were nearly out of it some time ago.

[Pooky]

You'll also need to use a 1275 radiator bracket and source a small water pump pulley, the standard one will foul the cylinder head.

Does anyone know what push rods you should use?

[RONNIE]

IM WITH POOKY

[mini_matt_106]

have read you dont need to pocket the block if you are using 1:3:1 rockers, could i use the rockers from my 998 1275 rockers are 1:5:1 i believe??? not sure tho? seems to defy the point by fitting lower lift rockers!
oh yeah push rods, im guessing the 998 ones would be ok??
grind the pulley or get a smaller one?
cheers for the quick responsis

[Pooky]

I wouldn't risk not pocketing the block to be honest, could be an expensive mistake!

Get a smaller pulley, turning down the standard one will cause it to slip off!

[mini_matt_106]

ok so so far iv got: pocket the block and get a small pulley and rad strap
how much do i need to skim the head to get the CR to decent levels? what sort of results should i expect anyone?
guessworks must know lol
iv got the visard book but cant find about this in it, if its in there can someone tel me a page number please! cheers
thanks for the replies guys! much appriciated!

[minipac]

hi cant get camra to work i have been using 1.7 roller rockeer on this engine fine as long as you dont want to go to wild you should be ok. standard as long as the head has'ent been skimmed to much should be ok with out pocketing.

[mini7boy]

hi cant get camra to work i have been using 1.7 roller rockeer on this engine fine as long as you dont want to go to wild you should be ok. standard as long as the head has'ent been skimmed to much should be ok with out pocketing.

I re-read the Calver piece last night and he said that very low-lift cams are the only ones which can be used, even with standard rockers, without either sinking the exhaust valves in the head or pocketing the block.
What this means is that unless you sink the valve in the head or pocket the block, you would be unable to use either high-lift performance cams or 1.5 rockers.

You really need to read the article to understand all of this.

[mini_turbo_pete]

you can use a standard unskimmed 1275head on a 998 block without clearance issues of the exhaust valves (i have built quite a few so talking from experience.

You will need to run a small water pump pully, you will also need to grind the top of the water pump off as this will foul the head.

Use 1000cc pushrods

When you are bolting the head on, undo the tappets and slacken them all right off before bolting it down.

With compression ration a 1275cc head will hire it slightly as the combustion chamber is less volume so no skimming needed.

[mini_matt_106]

you can use a standard unskimmed 1275head on a 998 block without clearance issues of the exhaust valves (i have built quite a few so talking from experience.

You will need to run a small water pump pully, you will also need to grind the top of the water pump off as this will foul the head.

Use 1000cc pushrods

When you are bolting the head on, undo the tappets and slacken them all right off before bolting it down.

With compression ration a 1275cc head will hire it slightly as the combustion chamber is less volume so no skimming needed.

hmmm seems mixed views then, everyone talking from experience? as il go with pepl that have act done this themselves! cheers much!

[mini7boy]

you can use a standard unskimmed 1275head on a 998 block without clearance issues of the exhaust valves (i have built quite a few so talking from experience.

You will need to run a small water pump pully, you will also need to grind the top of the water pump off as this will foul the head.

Use 1000cc pushrods

When you are bolting the head on, undo the tappets and slacken them all right off before bolting it down.

With compression ration a 1275cc head will hire it slightly as the combustion chamber is less volume so no skimming needed.

hmmm seems mixed views then, everyone talking from experience? as il go with pepl that have act done this themselves! cheers much!

and then if the head needs to be skimmed significantly ???

you'll then have to pocket the block, causing engine disassembly and reassembly, or you'll have to sink the exhaust valve in the head.

[mini7boy]

you can use a standard unskimmed 1275head on a 998 block without clearance issues of the exhaust valves (i have built quite a few so talking from experience.

You will need to run a small water pump pully, you will also need to grind the top of the water pump off as this will foul the head.

Use 1000cc pushrods

When you are bolting the head on, undo the tappets and slacken them all right off before bolting it down.

With compression ration a 1275cc head will hire it slightly as the combustion chamber is less volume so no skimming needed.

hmmm seems mixed views then, everyone talking from experience? as il go with pepl that have act done this themselves! cheers much!

and then if the head needs to be skimmed significantly ???

you'll then have to pocket the block, causing engine disassembly and reassembly, or you'll have to sink the exhaust valve in the head.

If you can get ahold of and read the Calver Mini Expert article, he provides dimensions on the head to check to see if you'll have problems using the head as-is.

Unless you measure the head and the exhaust valve's depth within it, , you won't know if it is suitable or not.

Then you have to consider how much cam lift you will be limited to as well.

This is definitely one of those cases before you measure it twice before you cut it once.

Why build an engine that is going to limit your cam and compression ratio options?