6 replies to this topic

[rob mini]

right, ive got a spare 998 head ove aquired so im thinking of having a go modifying it. I've got the vizard book of how to modify your mini but can only make sense of a few of the diagrams. Was just thinking if any of you have tried doing your own heads, how sucessful has it been? All im looking to do is enlarge the areas around the valves to increase valve lift, any help would be greatly appreciated!

thanks, Rob

[siggy]

The only way you can increase valve lift is to fit 1.5 rockers or a high lift cam.

Siggy

[Bluemini]

998 heads are hard to port because they are so small, you'd be better off getting a 1275 head and putting that on instead.

When you do port a head, you want to aim to take the shoulder off that the valve stem comes thru, so that it is one nice smooth flowing curve around that corner. I normally aim to take the neck of the port out to the size of the exhaust gasket or the manifold, tappering in so you dont break thru the push rod holes, then opening out again int to big area behinde the valve. The back of the valve seat can be shaved off a bit to give it a nice smooth curve too. When you are happy with you finnished head, then you need to make sure all the ports are the same volume...

The pics in the 'Bible' are the best way of figuring out what to do, or try and get a look at a head thats allready been done. There is loads of metal that can be taken out of the head, but it needs to be in the right places. Dont rush doing it either, the last one I did took my about 3-4 days solid to finnish using a die-grinder and diamond tipped burrs.

[siggy]

Rich you can not fit a 1275 head to a 998 unless you pocket the block.

Siggy

[Bluemini]

Taken from The Mini Encyclopedia, Click Here to read the full article.

When I did this I had to keep the std cam because of cost. I was literally swapping heads. In my case the std cam didn't have too much lift. If you are keeping the std cam then there is a pretty good chance that the 12G940 head will go straight on however I suggest you check to see if you have enough clearance as tolerances of the rockers etc are poor and the amount of actual valve you get varies. I did this by attaching a lump of blutack to each exhaust valves and bolting the head onto the block with no gasket and 0 valve clearance. Then I turned the engine over by hand and pulled the head off and looked to see how much the blutack had been squashed. The other way to do it is again bolt the head on with no gasket and 0 valve clearance then turn the engine over until an exhaust valve us fully open then winding the adjuster until the valve touches the block. If it takes about 1mm of extra valve lift then you will be ok.

[siggy]

There is not a lot of point of fitting a 1275 head with a std cam. And the last time I tried it guess what happened.

Siggy

[Tucker SP]

f**ked Valves?