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#488441 05/02/13 7:10 pm
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koan58 Offline OP
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I've found discussions about torquing vs bolt extension topics for con rod bolts illuminating.
It has made me think again about the head bolt tightening on my pre-unit T120 8-stud.
Would the recommended torque figure be based on dry or lubed threads?
As in this instance its not possible to measure bolt extension, it must be based on torque value.
I would hope its meant to be lubed threads, 'cos you wouldn't want to wear the bolt/cylinder threads surely?
Your wisdom appreciated Dave

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Open that can or worms, will yah clap

The basics:
All of Triumph torques figures are given dry.

Let the fun begin :bigt

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Torque recommendations are made for new bolts, new threads etc.
Bolts are cad plated from new and have a certain property of lubrication from the plating. A couple of times in and out of the threads and this is gone. Then you would apply lubrication to the thread to get proper torque. The torque figure of 18 ft/lbs seems too low for most, but remember that the bolt must retain it's elastic properties in a throughout a range of temperatures and stresses.
You must run a cleaning tap through the threads before you can achieve proper torque. I run the bolt ALL the way in and out with only my fingers to ensure that the threads are clean and that the bolt is not stretched. If there is any stretch in the bolt, it will happen at the weakest point and that is at the threads. The bolt will not thread in all the way and needs to go in the garbage.
Since I started doing it this way, I've had no problems with head gaskets blowing or any other such problems. I don't use gaskets on the rocker boxes either, and that means that when I check torque later on, I almost never find a loose bolt.
That's how I do it, but other have their own methods, too.
Bill


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koan58 Offline OP
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Thanks John and HT,
Somehow I wasn't expecting a simple answer!
The bolts do wind in and out easily, so hopefully ok to use.
Guess I'll stick to my lubed and arbitrary 25ftlbs on old bolts, which seems to have done ok, though the 1st 20 years of 30 were done without torque wrench at all!
And Bill, belated thanks for the ATF in chaincase info!
Many thanks Dave

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The dry torque should be 18 ft-lbs.The 25 ft-lb figure was revised in the mid-'60s.
With lubed threads,it would be more like 15 ft-lbs.

Do you find the washers crushing into the head at 25 ft-lbs?Does the head then find its own "happy" torque,after it got hot and crushed?

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Has anyone who has worked on these non-unit 8 bolt bikes relate over torquing the head bolts with all of the cracks that develop in these heads, or is it just me? Structurally the rocker boxes, and especially the heads, are pretty close to the edge of what will work. Additional stress, from over tightening the head bolts, is not going to do them any favors. 25 foot pounds wet would be like nearly 30 dry depending on what you are using for a lubricant.

The Triumph Workshop Manual for Models 1945 to 1955 lists the head torque at 18 pounds with a warning that "if tightened beyond this figure distortion may take place." Even the old No. 17 Triumph Instruction Manual (for non-unit) lists the head bolt torque as 18 pounds.

Using 3/8 in. bolts in this application, and a rather fragile aluminum head and rocker box, there would be no way that you could get any bolt stretch before the aluminum was compromised.

As threads mate to each other with use, you get more clamping force for a given amount of torque. Get out the old ARP hardware technical guide and read about retightening hardware numerous times before the final torque is taken. ARP has you tightening the rod bolt nuts 6 times, and each time for a given torque the bolt stretch increases until it settles down on about the 5th or 6th tightening. So over time, as these bikes are rebuilt and the reads worn in, the 18 pounds of torque will provide more clamping force than the first time the head was torqued. No need for lubrication. And no, you are not wearing out those 3/8" head bolts as they are over kill for the application.

Bill, we have come a long way with rocker box gaskets. You need to try one of our new ones! It's like running no gasket, but they are a gaskets. Go figure! PM me and I will send you a sample... you'll like them!
John

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Originally Posted by John Healy

Bill, we have come a long way with rocker box gaskets. You need to try one of our new ones! It's like running no gasket, but they are a gaskets. Go figure! PM me and I will send you a sample... you'll like them!
John


They ARE excellent!

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koan58 Offline OP
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John, thanks for the detail - most helpful.
What's different about these gaskets? and are they available in the UK?
and a happy birthday to boot!
Dave

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Based on the accuracy of most torque wrenches, head bolt tightness must vary considerably. Maybe that's why the factory relied on the assemblers "feel" when they assembled the heads. It was likely very consistent.
The outer head bolts almost never relax their torque due to the fact that they are very short and have only a couple of inches of head to hold down. Those center one have a tougher job holding the head and the rockers. Running a Triumph hot will see the center bolts stressed more than the outer bolts and this can cause a leak between the cylinders that is exacerbated by often too tight push rod tube seals.(except iron head models)
I've often wondered why the factory didn't do something to balance the head bolts by using smaller diameter outer bolts or perhaps hollow bolts. By '71 they did, but only for another reason related to the BSA frame they started using. I think that's just plain lazy and weird.
It's a compromise at best, but it can work under the right circumstances.
I have seen a few stretched long head bolts over the years. I attribute that to HD mechanics that tighten everything as tight as they can get it.
Their motos are: Cross thread is better than no thread and tighten until it starts to strip, then back off 1/4 turn.
Bill

Last edited by HawaiianTiger; 05/03/13 7:26 pm.

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Bill that is too funny, I will have to use that in the future. Makes my one click of the elbow torque setting sound better laughing


Regards

Grant

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