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Twin cam head bolts

19K views 22 replies 15 participants last post by  claydbal 
#1 · (Edited)
Why the torque to 12to14 ft. lbs. then a 1/4 turn? why not a final torque # ? Do you need to replace studs each time?
 
#2 ·
That technique is called "torque to yeild". It's more accurate, and sets the "stretch" of the fastener.
 
#3 ·
This is quite often done away with and a set torque used instead. Both stretch the studs. Studs can handle a few cycles of reuse and the engine pros on this site will know better than I do and likely respond to that question.
Ron
 
#4 ·
everyone has there own way. as Ron indicated.
mine is 42 ft-lbs. final reading.
tighten in sequence @5 ft lbs increments until 35 ft lbs then 7 ft lbs.
I have also screwed up my sequence and went to 40 ft lbs in 5 ft lbs increments then did a 2 ft lbs increment.
never had a head warp or blow a gasket yet.
 
#6 ·
It has to do with the way the stock gaskets are constructed. If you were to run a plain copper gasket, be sure to use the specs that come with the gasket.
 
#8 ·
Studs are usable several times. The OEM stud is a very stong item. If you have an engine that has been apart many times then a new set would not be a bad idea. Or if you are pulling the stud and for whatever reason you need to use a pipe wrench and it gets gouged then replace them. I just pulled a set out of a early engine and they where a mother to get out. Heat double nutted, JIMS stud puller nothing worked. Pipe wrench did get them out with heat but they are toast.
 
#10 ·
There are times when we have damaged threads on the studs or head bolts such as a burr or anything else that would cause extra friction or resistance as the two where be bolted together. This extra force caused by the problem threads will cause the torque wrench to give a false reading....ie....the final torque will be lighter than the wrench says it is. The 1/4 turn method eliminates the reading of the torque wrench and disregards the extra drag of the problem threads and you end up with a truer final torque.
The auto industry has been doing this method for years, Harley adopted this 1/4 turn method when the EVO was introduced.
Doc
 
#13 ·
I check things out as well, but as you know, torquing a fastener is not always as simple as waiting for the click, to get all 4 equal. Assuming the threads are perfect, those flanges on the head nuts can create considerable variations in torque readings between them. Some stick and drag more than others, especially when sneaking the torque up in increments, even when lubed, since that gets squished out quickly. The tighter it gets the more deviation could happen. With the initial 12-14 or whatever any deviation will be negligable. This small amount, with the extra 90* will not multiply into gross amounts of unequal readings when done. Only pointing out the way I see it, but honestly havn't used the method, yet.
Obviously both methods work.
Ron
 
#15 ·
I dont like the 90 deg method because to be honest I am a dumbazz and the first time I tried it I stripped a stud in the case.
90 deg that's 1/2 turn RIGHT LOL.
probably would have stripped using 5 ft lbs method also but I like knowing it's there not wondering if it's to tight or not tight enough.
just me everybody has there theories.
 
#16 ·
Head bolt torque

what relation is there between head bolt torque, cylinder finish bore/hone in torque plates and crankcase deflection? How does this affect the cylinder roundness?
Crankcases deflect more on parting line that thick torque plates.....need this explained!
 
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