Torquing camshaft holder bolts


RE5Guy
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Torquing camshaft holder bolts

Post by RE5Guy »

Hi all,

I have had a good search on the site, but can't find an answer to my question. Apologies if I have missed it.

Last weekend I was reassembling my head and despite being very careful I managed to snap two of the camshaft holder bolts. In both cases the bolts were originals to the bike and I was re-installing them in the same cap and place they where in when it was dissasembled (although 2 different caps). The torque wrench is of good quality, was set correctly and I was following the assembly instructions in my genuine shop manual and torquing for 9.5 ft-lbs. The recomended torque is 9-10 ft-lbs. In both cases the bolt sheared well short of this amount. I had just previously successfully torqued 2 others to this spec.

I managed to get one end out, but the other was stubborn. There is now a helicoil in there as a result. Yes there was a lot of swearing.

What is the wisdom of the forum on what happened? Was I just very unlucky and had two damaged bolts or is 9-10 ft-lbs to much?

The reason I pose the second theory is because I went to a specialised fastner shop today to see if they could supply replacements. They could provide high tensile bolts the right size and out of curiosity asked what was the recommended torque limit for them. The helpful salesman went away and got the distributor to fax through an info sheet. The info provided stated 7 ft-lbs.

The bike is a '79 and has 13,000 miles up.

Thanks

Tony

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Post by Terry »

My first guess would be that having just two, thirty year old super heated over and over bolts, break on you was pretty good luck!
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Post by cbxtacy »

Yep, old bolts. I have a few spare engines (in real bad shape) so I have a lot of spare bolts. I always make sure the threads are clean and put a dab of grease on the threads when assembling. I'll snap one off occasionally and the grease makes it easy to remove the remnants. Some people say it makes them too tight lubricating the threads but I've never had a problem with that.
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Post by alimey4u2 »

I had the same problem & found 3 sheared bolts when I did a valve shim job. Luckily they spun out when I drilled them with a left hand bit. They are known to fail so check them regularly. I replaced all mine with higher grade bolts from Summit Racing... These bolts weren't exactly the same length ( a tad longer in the unthreaded portion) & couldn't be rethreaded with a die as they had rolled threads. I then fitted thicker hard precision washers (from McMaster Carr.) Had to Dremel the inside of the cam cover for clearance at the oil supply pipe banjo's but it worked out just fine...

Don't forget that the torque values are dry, so back off a bit if lubed...
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Post by alimey4u2 »

Two lengths are involved, these are some left over in my tool box. The un-threaded portion on these is wider in diameter than the stock bolts which are slimmed ( hence the problem compounded by lube) to improve oil flow. However, I did several checks & found the oil flow to the cams to be more than adequate... As I said, these cannot be re-threaded as they are "rolled" threads to improve strength, so adequate spacers must also be incorporated.

OH! I forgot, slipping the cam cover on whilst the engine is still in the frame was a challenge. Bit more of a challenge after this mod but entirely possible with the assistance of some foul language.. :wink:


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Post by Terry »

..."Bit more of a challenge after this mod but entirely possible with the assistance of some foul language.."

:lol: :lol: :lol: :lol: :lol:
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Don #6141

Post by Don #6141 »

cbxtacy wrote:Some people say it makes them too tight lubricating the threads but I've never had a problem with that.
It does throw off the torque wrench readings - Fairly standard practice to reduce the torque by 25% or so if you've lubricated the threads

If he's snapping old bolts torquing them dry, I would imagine the problem would only get worse if he tries torquing them lubricated

Don

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Post by EMS »

Don #6141 wrote: If he's snapping old bolts torquing them dry, I would imagine the problem would only get worse if he tries torquing them lubricated

Don
:?: :?: :?: Why would that be? The torque is reduced by 25% :?:

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Post by Terry »

My guess is he meant to say this,

"If he's snapping old bolts torquing them dry, I would imagine the problem would only get worse if he tries torquing them lubricated (w/o reducing the torque recommendation).
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Post by EMS »

Ahaaa! :thumupp:

Don #6141

Post by Don #6141 »

Yup - Torquing them 'wet' should leave them about 25% tighter than if he hadn't lubed them . . . . and if he's snapping bolts at about 75% of the desired torque now when he's doing them dry, he should have nearly twice the torque on them as what it'a taking to break them now if he torques them wet

(Don't scratch your head on that one too long or you'll go bald!) ;)

Don

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Post by RE5Guy »

Thanks for all the comments guys...best I do buy some new bolts I think!

I think I will grease up the replacement bolts and back off the torque 25% just in case I snap another one. Sounds like a good tip. Thanks.

One question, one of the comments mentions that the original bolts are slimmed to aid oil flow. Whilst I am not sure about the longer ones, I can't see how this is so for the shorter ones because surely oil doesn't flow around them?

Just trying to get all this straight in my head....

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Post by alimey4u2 »

Good point, only the 4 bolts on the banjo connections flow oil, still plenty of orifice for flow, even with a full bolt... :wink:
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Torquing Camshaft Holder bolts

Post by Larry Zimmer »

Honestly, I don't remember the markings on these bolt heads. However, as general info, if it is something like 8.8 or 9.8, I believe these are 'common' steel with an industry recommended torue of 5-6 ft-lbs. If they are 10.8, 8 ft-lbs. If they are marked 12.8, then 9-10 ft-lbs. I know the manual says 9 - 10. This just to give some general info. Keep this in mind when using replacement bolts. You want them to have a 12.8 (or at least 10.8) on the head if you're going to try to do 9 - 10 ft-lbs. Also, hope they go into the head at least 10mm so they don't pull the head threads. That's a real pain in the butt.
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Post by EMS »

The bolts have no marking as to the strength or quality. There is a raised marking on the heads that looks like a 10. They are 6mmx48 and 6mmx62.
Funny thing is, the parts list calls out for only 30 bolts ( 28 x 48 and 2 x 62). Where are the other two?

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