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WLA head bolt torque

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Frankenstein

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Post Thu Apr 11, 2013 5:43 pm

Re: WLA head bolt torque

I've been a good and tight man myself, started with the OHV's cause I didn't have the equipment to measure their torques.
On the flatheads, when reusing copper gaskets, which I always do, retorquing usually isn't necessary.
DD
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knucklebolt

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Post Sun Apr 14, 2013 6:29 pm

Re: WLA head bolt torque

I would re-enforce using anti-seize or grease on the threads. I always make sure my bolt threads are squeaky clean also, clean them good with a wire brush. I also lightly lube the washers where they contact the bolt, guess that would be the "top".

I wouldn't think that going over 55 pounds would be necessary...especially with old and tired threads. And as someone mentioned above/earlier, if the gasket did start leaking, there's no oil or water involved, or even leaking between cylinders, and changing head gaskets is pretty simple and easy.

I would also think that it depends on how much of a fire breathing dragon your motor is. I'm pretty sure my stock gently driven 76 inch UL wouldn't even leak if I went with even less than 55 pounds of torque...but maybe a 88" or bigger highly modified and hard run engine might...??

My 45 never leaked or blew a head gasket, and I used to torque them down very gently...but that was before I ever owned a torque wrench, so I don't know how many pounds I actually used, but I do remember it wasn't much.
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knucklebolt

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Post Sat Apr 27, 2013 9:33 am

Re: WLA head bolt torque

Had a strange thought, thinking about this the other day.

Just spit-balling here again, obviously I have too much time to think of things, but I was wondering, are torque plates usually used on flathead cylinders when they are bored and honed? And if so, wouldn't the torque used on the torque plates, whatever that was, be the correct torque?

On the other hand, if they are not commonly used, would not the least torque possible be "best", to avoid, or minimize any cylinder distortion?

Or, on a flathead Harley, does any distortion of the cylinder bore take place when the head bolts are torqued/tightened? With the way the head bolts are spread out around the cylinder and valves, and all the cooling fins which must make the cylinder pretty rigid, perhaps cylinder bore distortion is a moot point???

Just a thought.

???

ken.
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X-WLCH

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Post Sat Apr 27, 2013 2:53 pm

Re: WLA head bolt torque

A BOLT IS TORQUED TO PREVENT THE BOLT FROM STRETCHING IN OPERATION. ( NOT TO CREATE A SEAL ) AS LONG AS YOU EXCEED THE STRETCHING FORCE FROM COMBUSTION ON THE BOLT IT WILL MAINTAIN ITS SEALING FORCE.
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knucklebolt

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Location: Six miles East of Cheney, Wa.

Post Sat Apr 27, 2013 8:23 pm

Re: WLA head bolt torque

But are you familiar with head bolts on engines distorting the roundness of the bore? Which in turn, causes the piston to not seal the bore as well....nothing to do with sealing the head to the cylinder. ?? That is the purpose of torque plates when boring and honing cylinders on a small block Mopar, or big block, Chevy, Ford engines etc. And that is what I was getting at: (obviously not very well) cylinder bore distortion.

Also, wouldn't you say that a bolt is tightened, to a specific torque value? Not just "torqued". It does seem that the purpose of tightening the head bolts would be to seal the head to the cylinder, or have I been missing something all these years and countless engines later? :) ?? Are you saying that if a bolt is not tight enough, or tightened to a specific torque value, it will stretch and compress with combustion chamber pressure? I think I really missed your point there. !!! :)

On stretch, I don't know a lot about that, but it's my understanding that the torque value would be just before the bolt begins to stretch, or possibly just at the point where it begins to stretch...but I will gladly stand to be corrected on that. On some aircraft engines, are not the bolts discarded once they have been "torqued", for that reason??

And why are you yelling at me? Do I sound that dense? :)

ken.
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Pa

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Post Sat Apr 27, 2013 8:45 pm

Re: WLA head bolt torque

Head bolts on flatheads are torqued to seal not to align. Flathead cylinders do the aligning.
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Frankenstein

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Post Sun Apr 28, 2013 8:18 am

Re: WLA head bolt torque

All bolts stretch on torqueing. The inclined plane of the thread is forcing the bolt to lengthen, once gaskets are fully compressed, etc. So, torque spec's are given for bolts so as not to exceed their ability to stretch without deformation. There are tables everywhere on bolt size and grade and corresponding recommended torques. On old flatheads, I think the important points are not to pull the threads out of old cast iron, put enough pressure on the head gasket so it won't "pass gas" and your job is done. That's why I use "good and tite" rather than a book figure. Heilicoiling a headbolt thread is a bitch on a cylinder in a frame.
In a sense, I think that's what Harley came up with on torqueing evo's and twinkies. Tighten the bolt to a certain spec, insuring gasket crush, then further tighten, not to a torque, but to a certain amount of stretch, i.e. 1/4 turn. won't exceed the elasticity of the stud, but maintain maximum sealing pressure on the head/cylinder joint. Just speculation, of course.
DD
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woody

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Post Sun Apr 28, 2013 11:22 am

Re: WLA head bolt torque

I think that the proper scientific terminology for all this is "1/4 turn before it breaks." :)
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37ULH

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Post Sun Apr 28, 2013 11:29 am

Re: WLA head bolt torque

At least some of the Triumph repair manuals have specs for measuring stretch on rod cap bolts rather than torque values.
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X-WLCH

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Joined: Wed Apr 30, 2008 12:16 pm

Post Sun Apr 28, 2013 11:54 am

Re: WLA head bolt torque

Hi Ken
I APOLOGIZE IF YOU THINK I WAS YELLING. I WOULDN'T YELL AT YOU FOR SOMETHING LIKE THIS. I JUST TEND TO SPEAK LOUDLY, SPELL POORLY, AND AM SOMETIMES JUST WRONG. :oops:

I UNDERSTAND YOUR IDEA ABOUT THE TORQUE PLATES. PERSONALLY I THINK THEY ARE OVERKILL ON AN ENGINE WITH .004" CLEARANCE AT THE CYLINDER WALL. I THINK THAT DURING THE BREAK IN PERIOD OF A FRESH ENGINE THE RINGS CONFORM TO THE SHAPE OF THE CYLINDER WALL AND EVENTUALLY SEAL. :D

AS FOR HEAD SEALING. THE HEAD IS SEALED LONG BEFORE YOU REACH THE TORQUE VALUE FOR THE SPECIFIC BOLT SIZE. IF NOT TORQUED BEYOND THE WORKING STRESS, THE BOLT WILL STRETCH AND RELAX WITH THE COMBUSTION PRESSURE. THIS CYCLING WILL FATIGUE THE BOLT AND CAUSE IT TO LENGTHEN AND BE LOOSE. WE ALL KNOW WHAT HAPPENS WHEN YOU RUN WITH LOOSE HEAD BOLTS. :(

ALL BOLTS STRETCH WHEN YOU TENSION THEM. THE BOOK TORQUE VALUE OF A BOLT RELATES TO THE MAXIMUM TENSION, "STRETCH" ( TENSILE STRENGTH ) OF THE BOLT. IF YOU EXCEED THAT POINT YOU WILL FEEL THE BOLT GIVE ( THAT SICK FEELING WHEN YOU KNOW YOU JUST WENT TOO FAR ) :x

BOLTS ARE TORQUED SO THAT THEY ARE ONLY STRETCHED ONE TIME AND THE WORKING PRESSURE WONT KEEP WORKING THEM. REPEATED STRETCHING OF STEEL WILL FATIGUE IT AND LOWER IT'S TENSILE STRENGTH. THEREFORE " ALL " BOLTS SHOULD BE DISCARDED ONCE THEY HAVE BEEN TENSIONED " STRETCHED " TO THERE UPPER LIMIT. AIRCRAFT AND SOPHISTICATED ENGINES USE THE SMALLEST " LIGHTEST " BOLTS THAT WILL HOLD THE REQUIRED TENSION. THEY GET TORQUED TO THE MAX WHEN USED. YOUR FLAT HEADED AMERICAN ENGINE CAN EXCEED THE WORKING FORCE (COMBUSTION FORCE) ON THE BOLT AND KEEP IT FROM WORK FATIGUING LONG BEFORE IT APPROACHES MAX TORQUE.

TORQUE IS A MEASURE OF ROTATIONAL FORCE BUT BECAUSE A BOLT HAS A KNOWN PITCH YOU CAN CALCULATE THE APPLIED TENSION ON THE BOLT WHEN TORQUED TO A SPECIFIC AMOUNT. HOWEVER FRICTION UNDER THE HEAD OF THE BOLT AND BETWEEN THE THREADS WILL ALTER THE RESULTS. :cry:
THE EVO METHOD 1/4 TURN (SAY A 32 THREAD PER INCH STUD) THE STUD WILL STRETCH .0078" - DIRECTLY RELATED TO TENSILE FORCE AND ELIMINATING THE MISREADING CAUSED BY FRICTION.

HOPE THIS HASN'T BEEN TOO RAMBLE, IT WAS A LONG TRIP BACK FROM OLEY AND I COULD USE A BREW.
AND AS ALWAYS I MAY BE JUST FULL OF :mrgreen: OR MISTAKEN .
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knucklebolt

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Location: Six miles East of Cheney, Wa.

Post Sun Apr 28, 2013 2:54 pm

Re: WLA head bolt torque

That was a great ramble and I guess you can talk loudly if you want....I'll just move back from the screen a bit. !!!

Okay, well then I'm going to postulate that the combination of the relatively low torque value used on these engines, and head bolts, the way the head bolt pattern is spread over a large area, and the fins probably giving great rigidity to the cylinder, that indeed torque plates would not be needed, and the cylinder does not deform when the bolts are tightened, as happens with a lot of other engines.

Or in other words my theory that the ideal torque setting would be whatever was used on the torque plates kind of goes up in smoke if torque plates are never used!!! I didn't know that head bolts actually stretched and relaxed, other than from going from cold to hot, thought it was all about clamping force.

Thanks.

ken.
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X-WLCH

Posts: 111

Joined: Wed Apr 30, 2008 12:16 pm

Post Mon Apr 29, 2013 7:12 am

Re: WLA head bolt torque

I'm not suggesting that the cylinders don't deform when the bolts are tightened, they do. However they deform much more when they heat up and are constantly changing. what is perfect at rest won't be perfect in operation. It's amazing that something so imprecise designed in the 20s works so well. I guess that is why we like them.
:D
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