'66 T120R bent rockerbox head bolts - Triumph Forum: Triumph Rat Motorcycle Forums
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Classic, Vintage & Veteran For Coventry and Meriden Models. Anything pre-Hinckley goes.

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Old 12-06-2012, 04:53 PM   #1 (permalink)
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'66 T120R bent rockerbox head bolts

Today as i was assembling the head to the engine, as I turned one of the head bolts that passes thru the rockerboxes, I could see the head of the bolt wobble as I turned it. I checked the rest of them and 3 of the 4 are bent. I never in a million years expected bent head bolts.

I suspect this is from additional stress caused by the upper engine mounts, although they appear to be bent at mid span of the bolt. Another thought is over torqued and they were twisted. But I am doubtful about this.

Is this common? I can straighten them, but am reluctant to use them after straightening them.

Any thoughts from those who have worked on these engines more than the average rider?

Thanks,
Rob
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Old 12-06-2012, 07:36 PM   #2 (permalink)
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Rob,
When you first removed these bolts- did you notice anything wrong then?

It would be tough to bend one by over-torquing going in without damaging something else.

Easier to twist/bend on removal if the threads were rust or corrosion bound?

Err on the safe side and use new hardware - check and or chase the corresponding threads. . . .

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Old 12-06-2012, 08:02 PM   #3 (permalink)
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No, Morris. The engine came apart without a hitch and I never noticed the runout in the bolts since I was probably using a wrench versus turning them with my fingers.

Called Lance and he said in 45 years he's never encountered a bent head bolt during a rebuild. And he's lost count on rebuilds long ago.

They are not really bad. Maybe a total of less than 1/16" at the mid span for the first one I checked. Have not looked closely at the others yet.

As much as I try to come up with a scenario that would put a slight bow in those bolts, I cannot. It would take a big wrench to twist a 3/8" bolt and I'd expect to find damage elsewhere. The hexes on the bolts are nearly perfect. Even if the engine were severly misaligned in the frame because they are already in tension when the upper motor mounts would be installed, I cannot see any bending stresses put on the long shank of that bolt. Maybe the short shank that attaches to the mount, but not the long.

Maybe it is just creep or stress relieving after many years under stress and at operating temps.

I hear you about replacing them. But I'm leaning towards straightening them in my press and using them. I'm using 1/8" thick hardened washers on all head bolts and I've already spotfaced the head and rocker boxes to restore the faces of the bolt holes. I think it will be okay.

But, we'll see if anyone else pipes up and has seen this before. I've posted an identical inquiry on the Britbike Triumph forum.

Thanks,
Rob
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Old 12-08-2012, 04:43 AM   #4 (permalink)
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My 66 had the same problem. On my bike at least, the rocker box head bolts go very very close to the frame rail when fitting. If you fit & tighten the rocker box bolts in the wrong sequence, the last long bolt can jam on the frame rail.

I think a previous owner might have slightly misaligned the rocker box by tightening the smaller bolts first & then had difficulty in getting the large bolts home and whacked them with a hammer.
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Old 12-08-2012, 08:58 AM   #5 (permalink)
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That's probably as good a theory as any, Rev. If old bikes could talk you could probably make a couple of horror movies based on how they were treated over the years.

regards,
Rob
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