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Head Bolts


I'm having to get the cyclinder helicoiled as the 2 holes near the exhaust valve are shot , by the look of it the last owner has put the shorter nuts in them so they havent had enough thread yo grip.

Am I correct the coil kit I need is 3/8 20 tpi BSF ?

The other question which bolts goes where and do they which ones need washers. I know it's quite obvious but I just want to make sure I get it correct the washers I am not too sure about.

email (option): chriscool@sky.com

Re: Head Bolts

Yes 3/8 BSF. there are 5 long and 5 short and 10 washers.(10 long bolts for an ally head) It's obvious where the long and short go. This page from Drags might help. I think it gives lengths.

https://draganfly.co.uk/product-category/bsa/sparesparts-for-bsa-a710-b3133-c101112-m202133/engine-gaskets-gearbox/cylinder-head-barrel/pre-unit-m-group-head/

Ron

email (option): ronpier@talk21.com

Re: Head Bolts

I'd recommend using class 3 'heavy' washers at least for the head bolts...I usually make up thicker ones for the job...

I also found that the stated bolt lengths aren't ideal (IMO)....I worked out the lengths to give the most thread engagement with the barrel...Also remember that in a perfect world the bolt that secures the head steady should have a little extra length...

Finally, I've bought zinc plated bolt sets in the past that snap at the end of the thread with little force applied..It may be that they have become more brittle after plating. Fasteners of this type should be 'debrittlised' after plating.....Make sure you are buying high tensile fasteners....

Tap out all the holes before fitting new fasteners and apply a little light machine oil only when torqueing down...Fasten to the tightening sequence in the manual and torque down to 28-30 ft. lbs.

I'd also recommend a solid copper head gasket if you don't already have one...Modern composite gaskets are pretty unreliable.....Ian

email (option): ian@wright52.plus.com

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