mini 1275 head

Post by **bmcecosse** » Wed Dec 02, 2009 12:06 am

For a 1098 engine - best to use the smaller inlet valve version of the 940 head - unless going for a Full Race engine - in which case it will break within the week! As well as assuring exhaust valve clearance (and a steel rule will NOT do!) you may need to take some metal off the water pump casing - and a set of 1275 rockers are required, or spend time carefully re-aligning the existing 1098 rockers on the shaft so they act directly over the valve stems.

Post by **RogerRust** » Wed Dec 02, 2009 8:21 am

This picture is very interesting, it looks as if the mark the valve has made is not the same on the two cylinders. Do you think that this is the case. If so its something we need to be aware of because misalignment of the head could be the cause of other problems.

Post by **stuart_k** » Wed Dec 02, 2009 11:49 am

It is academic for me now Roger. I replaced the head and the engine had a full stage 2 rebuild with lightened flywheel, balanced components, fast road cam, yada yada. Here is a pic of the corresponding area on the head. I can't imagine there is a misalignment or these heads wouldn't be used by so many. It was more than likely caused by the head being slightly warped, probably needed skimming. <br>

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Post by **bmcecosse** » Wed Dec 02, 2009 5:25 pm

I don't think the heads are all that well located - they slide up and down he head studs quite easily - and there is some 'slop' from side to side and end to end. These marks are very slight. My 'racing' 998 engine had a full Cooper S head - with the larger exhaust valves. It had deep pockets in the block - yet every time I lifted the head - despite further deeping each time - there was further evidence of contact. But then - it was getting run up to maybe 9000 revs -and the valves were definitely 'bouncing'! The easiest thing to do is to sink the exhaust valves into the head by 40 thou - with a standard lift camshaft this will give plenty of clearance for normal use. Don't forget to add a 40 thou packer (ie a thick washer) under the exhaust valve springs to make up for the extra 40 thou the valve stem is now showing through the guides!