10 replies to this topic

[THedooBZ]

iv been doing a bit of searching and have found out that you can fit a 1275 head to a 998 engine with a bit of work..i have aquired an aeg163 cooper head and wondered if it is possible to fit this or not??

my questions are;
1) what exactly is block pocketing as i could possibly get the machining done at work???
2)is their any other modification to do???
3) will the oil/ water galleries match up or not???

cheers

[mike.]

The valves on a 1275 head are much bigger than in any 998 head. It means that when the vavles open they hit the block just around the bore. So basically you have to cut a little pocket in the block for the vavles to fall into so they don't hit the block.

It pretty simple machine work really - Jetblick did his with a dremel and the grinding stone attachments - Details in his project thread.

[THedooBZ]

how do you know how much needs machining??? is there any adverse effects of doing as obviously it cannot be made back to normal once done???

[minipac]

iv been doing a bit of searching and have found out that you can fit a 1275 head to a 998 engine with a bit of work..i have aquired an aeg163 cooper head and wondered if it is possible to fit this or not??

my questions are;
1) what exactly is block pocketing as i could possibly get the machining done at work???
2)is their any other modification to do???
3) will the oil/ water galleries match up or not???

cheers

block pocketing is done to make room for the exhaust valves if you place the head on a 998 block with the valves loose the you will find the inlet valve will drop in to the bore and the exhaust valve will sit on the block. you will need to use a 1275 head gasket.
some people say you need to pocket and some say you don't

[mike.]

Not an adverse effect as such but if the machining was done on the cheap like jetblicks your hand could quite easily slip and damage the bores - but if getting the machining done professionally then that shouldn't be an issue. I can't think of any other adverse effects pocketing the block has really - possibly trouble getting the headgasket ti seal? Although i've not heard of any probs.

To work out where needs machining i think jetblick placed bluetac around the bores, rested the 1275 head in place and pushed the vavles down into the bluetac. Then when you remove the head you'll have bluetac templates of where to cut. As to how deep the pocket needs to be i'm pretty sure there about 5mm.

By the way there not just solid, harsh edged pockets - They're smoothed curved shape pockets - To assist flow i'd imagine.

[dklawson]

Correct me if I'm wrong but I think there was another thread running within the past two months talking about putting big-bore heads on small-bore blocks. In that thread I remember everyone saying that while it was possible, there were other issues that surfaced after the engine was started. Specifically, the chamber volumes of the big-bore head were larger so the compression ratio dropped. It was implied that some of that can be improved upon by shaving the head... but not all of it. I seem to remember that the discussion went on to point out that after fitting the big-bore head, extensive dyno tuning and experimenting with carb needles was required to get anything approaching normal running. In short, it didn't sound like a good idea.

As I mentioned in your other thread, the AEG163 head was the original big-bore Cooper-S head. It breaths very well but it has two serious problems. Over time the valves recess into the head. There is NO room in the head for seat inserts. So, once the valves sink, the head is toast. The "no room" for inserts issue is associated with another problem. The web between the inlet and exhaust ports is relatively thin and unfortunately... subject to cracking.

In your other thread I pointed out that the AEG163 head is valued by vintage racers who are often regulated on what cylinder heads they can run. My suspicion is that IF the head you've just received is in good shape, you could sell it and get most (if not all) of the money you need to buy a completely built performance small-bore head.

[THedooBZ]

is this head really worth something then,, i mean i dont really know loads about engines, so for me buying something ready built would be easier,, i may put it up for sale on here then or on ebay just dont really know what it is worth? it was more of a passing idea than i want to deffo do this to my engine.

Edited by THedooBZ, 20 March 2008 - 09:52 PM.

[dklawson]

My engine came with the AEG163 head but its valves seats have sunk. I decided that I would put the big-valve 12G940 on as part of the engine rebuild. When a couple of vintage racer acquaintances learned I'd replaced the head on my car they wanted to buy my AEG163 even knowing the seats had sunk. I have no idea what the head is worth in the U.K. However, if you have a shop inspect it and they determine it's in good condition then you stand a very good chance of selling the head. Yes, having the head inspected will cost money up front, however, when you're selling something that you can certify is in good shape it will command much more money. For example, I wouldn't offer you $200 for any used A-series head UNLESS you could certify for me that the seats were in good condition, no cracks, and hopefully with good valve guides.

[minipac]

is this head really worth something then,, i mean i dont really know loads about engines, so for me buying something ready built would be easier,, i may put it up for sale on here then or on ebay just dont really know what it is worth? it was more of a passing idea than i want to deffo do this to my engine.

if you want to add performance to a 998cc engine you cant do much better than putting a 12g295 or 12g206 head on skimmed to get the right cr as the valve are as big as you can put on a 998 without pocketing.

[THedooBZ]

ahh cool,, cheers for the advice doug..

[JetBLICK]

To work out where needs machining i think jetblick placed bluetac around the bores, rested the 1275 head in place and pushed the vavles down into the bluetac. Then when you remove the head you'll have bluetac templates of where to cut. As to how deep the pocket needs to be i'm pretty sure there about 5mm.

To answer our PM doobz... thats /\ exactly how i did it. 5mm deep will clear for most applications. You grind the head with a carbide tool, or just a grinding stone in a dremel, doesnt take longer thanan hour. Just take your time and get it right first time. and then re-check afterwards.