M21 cylinder head coming loose /blowing gaskets

[bill shortall]

The head on my M21 keeps coming loose  ,it has an alloy head  which has been tightened down  three times  and blown two gaskets . I have now managed to strip one of the threads on a bolt  .
Is there a difference  between the bolts on a alloy head and a iron head as the bike came in  bits  and i am not sure if the head bolts are correct , or  are  the threads are tyred in the barrel 
Has anybody  got any suggestions as i am running out of head gaskets   

[berniej]

Hi Bill,

Yes, the bolt sets are different as I found out recently when I changed my alloy head for a cast iron lump.

I can't remember the precise difference but think that the bolts in the alloy head are longer.
I believe I read about them on the draganfly site which might be worth a visit to get a better idea.

I also had another M21 on which the threads in the barrel were stripped and I repaired these pretty easily with a thread repair kit that I got on eBay for around £30. If you go that route then just check that you are sure which thread to specify and also the length of the thread inserts which are often quoted as 'D' values which can seem a bit confusing. In fact it relates to the diameter of the thread being repaired so for example a 5/16 2D insert would be 2 * 5/16" i.e. 5/8" long.

Cheers,
Bernie

[Pete C]

The bolts are longer on the alloy heads.

I recommend you follow the advice on the WM20 site here:   http://wdbsa.nl/bolt%20torque%20values.htm   

Also use a solid copper gasket. If you seach on the WM20 site you will find a source for these. You will only need the one then as you can anneal it. The composite gaskets are not really any good!

Cheers

Pete

[TTJOHN]

Solid copper head gaskets can be obtained by me at £15 plus p+p they are soft copper that does not need annealing, lazer cut. contact me by pm  and I will get back to you.

[bill shortall]

Brilliant how do i get sorted   

[berniej]

I thinks the bolts you need are 10 off, part number 36-0011 which are 1 3/4" long 3/8" BSF.

You might find you can get good quality bolts cheaper by checking at bolt suppliers by size rather than shopping by BSA part number.

Cheers,
Bernie