Cylinder Head

·         MartinHands

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Hi Matt,
I have just had the cylinder heads of my 2200a overhauled and am now trying to refit them. As you know the head bolts pass through the Aluminium heads and scerw into the cylinder barrells. I was having trouble getting the bolts to go into the threads in the barrells then I saw that the holes in the ally heads were also threaded so as I screwed in the bolts they were not entering the thread in the barrells but tending to push the head away from the cylinder. I can see no reason for the holes in the heads to be threaded as I would have thought the bolts should just pass cleanly through them.
Are the threads in the aluminium head holes there by design or hve the steel bolts which don't have a smooth shank, imprinted a thread in the softer aluminium over the years due to expansion and vibration.
Hope you can help
Thanks
Martin

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·         Doug Smith

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Hi Martin,
First, apologies for taking so long to reply: it's been exceptionally busy lately.

The holes in the heads are not threaded by design so what you're looking at is imprinting from the previous bolts used. The holes can be cleaned out... the easiest way I could suggest would be to fully fit a bolt into the head on the bench and turn it with a spanner: it should pull the imprinted material out pretty easily. If you have one available, using a drill or similar to spin the bolt should make it all a bit faster.

From memory the current heads use screws that have a shank and are only threaded where they go into the cylinder, but it's still not uncommon to get a burr or similar in the hole which can snag the bolts.

Regards,

Doug.