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Evo Big Twins
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  #1  
Old 27-11-2009, 09:42 AM
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little bill little bill is offline
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can head bolts stretch on evo,s

i am still haveing trouble with blowing head gaskits on my 94 fat boy 1340 evo,can head studs stretch,?
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Old 27-11-2009, 09:47 AM
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Re: can head bolts stretch on evo,s

Head studs can stretch, even pull out, but if they reach the required torque figure, they should be OK, I would have thought.

Another couple of reasons are: over advanced ignition, and wrong pistons tapping the head.
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Old 27-11-2009, 11:35 AM
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Re: can head bolts stretch on evo,s

It could be one of several things Bill, this is not an exhaustive list:-

Torque wrench needs calibrating.

Torque sequence not correct.

Heads laid on gaskets without torquing down (gone home for tea syndrome).

The heads might need skimming.

The head bolts could be bottoming before the "real " torque setting has been acheived usually as a result of the crankcase studs not set at the correct length (too long).

Dirt in the head bolt threat or crankcase stud can give a false torque setting.

Does this affect both cylinders or just one?

Do a compression check and see what figures you get.
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  #4  
Old 27-11-2009, 12:36 PM
Kiwi
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Re: can head bolts stretch on evo,s

evo's rely on themal expansion to take up the head gasket torque

if you don't warm it up before riding off and giving it full noise they will blow quite easily
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  #5  
Old 27-11-2009, 02:28 PM
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little bill little bill is offline
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Re: can head bolts stretch on evo,s

answers to question phil,
brand new snap on torque wrench
both gaskits have blown
cylinder studs are all the same depth and ping when flicked
torqued down in three stages in correct order
cylinder head mopped and checked perfect
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  #6  
Old 27-11-2009, 02:32 PM
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Re: can head bolts stretch on evo,s

no muck in all eight nuts
just under half inch sticking out of barrels on all 8 studs
cant do affective comp test till engine is warm,cold test is no good
got to rebuild again to do test
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Old 27-11-2009, 02:34 PM
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Re: can head bolts stretch on evo,s

ive always warmed her up before moving off and i dont give her the beans till oil tank is warm
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  #8  
Old 27-11-2009, 09:15 PM
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Re: can head bolts stretch on evo,s

Bill and myself will check this one out. As recommended, after boring, the case/barrel mating faces where skimmed,and if it wasnt the first rebore, (although I doubt it) and the faces skimmed before then this could be the problem. However Im not quite sure of this shoulder thing.What does it achieve? and as Ive heard the trick of turning the studs over how will you get the studs down full depth into the case with this shoulder down the bottom. I fail to see why they're there in the first place. Is there a minimun barrel length stated anywhere?
Thanks for all your replies
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Old 27-11-2009, 09:43 PM
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4valve 4valve is offline
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Re: can head bolts stretch on evo,s

Have you or a previous owner replaced the head bolts & or the washer/spacer that goes under them ? some after marketstuff is not as accurate as it could be.
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Old 27-11-2009, 09:57 PM
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Re: can head bolts stretch on evo,s

We havent, cant answer for previous owner/s
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