Lost cylinder head nuts!

Well, after a fairly high speed run (75 - 90mph) for about an hour and a half, on my '74 Commando, I noticed a little oil on the lowermost fin of the cylinder head in front. I assumed it was time to re-torque the heads (done 3 times after a re-build, about 3000 miles ago) and started the process when I got home. I was stunned to find out that not one but both of the bottom front cylinder-type nuts were gone! I suppose that vibration can loosen anything, but I've never come across this before. Has anyone?
I'm not in the habit of Loctiting cylinder head bolts, but should I when I replace them?
Thanks in advance,
Paul.

see page 3-4 of this thread about locktite and cylinder head nuts/bolts

born-again-bikes-experience-t14169.html

To turn loctite into a lube it should be heated to a couple hundred degree's F. Head at front easy excedes 300' F. Once cooled down again, such as might be when undoing them the loctite become like sand grains to over come. If threads ok then sounds like ya skipped one re-torque about 2000 miles prior.

Thank you, Mike, for pointing me in the direction of that discussion on tread-locker use. I've never used it before on a cylinder head - have never thought it to be a good thing for the reasons described. Yet here I am with two nuts gone and I'm not keen on it happening again, so thought I'd ask if there were differing opinions. Hobot, I re-torqued three times after replacing the head-gasket and I'm pretty anal with using the correct sequence and appropriate torque on all bolts/nuts so I very much doubt I missed those two. Anything's possible, I suppose....
Paul.

Further to the bit about no locktite on the cylinder head nuts, it's important to get proper washers installed with the nuts for proper torque.

I have never heard of the cylinder nuts coming loose to the point of falling off. Most likely the result of poltergeists in the garage.

I have heard of too large a washer bowing und allowing a cylinder base to become loose.

Any chance you have damaged or pulling studs?

Dances with Shrapnel said:

Further to the bit about no locktite on the cylinder head nuts, it's important to get proper washers installed with the nuts for proper torque.

I have never heard of the cylinder nuts coming loose to the point of falling off. Most likely the result of poltergeists in the garage.

I have heard of too large a washer bowing und allowing a cylinder base to become loose.

Any chance you have damaged or pulling studs?

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It would be very possible the studs have pulled the threads from the head. I have seen several lost front nuts without pulled studs- it means they were not retorqued often enough. Jim

Re: rther to the bit about no locktite on the cylinder head nuts, it's important to get proper washers installed with the nuts for proper torque.

I have never heard of the cylinder nuts coming loose to the point of falling off. Most likely the result of poltergeists in the garage.

I have heard of too large a washer bowing und allowing a cylinder base to become loose.

Thanks, but these are the front nuts on the cylinder head, not barrel, and should not, I'm fairly sure, have any washers.
Jim, how often should I re-torque the head, do you think? The third and last time I did it, there was no movement in any bolts or nuts. Should I be re-torqueing every thousand miles, or so?

Gosh Paul non of us seem to know what went wrong, just that loctite ain't the solution here. All I know is if I only apply torque factory manual states then I can expect leaks after I thought I had done em often enough with a few 1000 miles fooling me. Forgive me for implying you were slack attention, Who'd re-torque just for fun if the cycles prior had worked so well. Still as no one else has reported those 2 nuts disappearing, makes me wonder about horizontal resonance, which makes me wonder about piston/rod mass or stuff I don't know about yet. Your report is so unusual I'd suspect threads worn or something else weird un-discovered yet. There is a saying that everything that falls off Brit Iron was a quality British product.

phsDommie said:

Re: rther to the bit about no locktite on the cylinder head nuts, it's important to get proper washers installed with the nuts for proper torque.

I have never heard of the cylinder nuts coming loose to the point of falling off. Most likely the result of poltergeists in the garage.

I have heard of too large a washer bowing und allowing a cylinder base to become loose.

Thanks, but these are the front nuts on the cylinder head, not barrel, and should not, I'm fairly sure, have any washers.
Jim, how often should I re-torque the head, do you think? The third and last time I did it, there was no movement in any bolts or nuts. Should I be re-torqueing every thousand miles, or so?

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With a new flame ring gasket I would retorque it at least 5 or 6 times in the first 5000 miles. They give a lot until they get settled in. After that you should check them at least once a year. I lost one of the front nuts on my bike a few years back after getting lax about checking them. I had to borrow one from a guy who was taking his bike home in a truck. Jim

If you're referring to the hex studs under the front (7 + 8 in the torque sequence) they are 3/8" studs and need 30 ft-lb of torque. The newer versions (your '74 should have) are stepped down to 3/16W (7/16"). It's hard to get 30 ft lb on a short 7/16" spanner. I have an adapter that lets me get my 3/8 torque wrench on them.

Any torque critical fastener should have a washer. The AISC (American Institute of Steel Construction) refers to a washer as a lubricant. I take that to mean a washer provides a surface that has the least friction and is consistent. Keep in mind it's tension of the fastener that we are interested, torque is only a relative indicator.

phsDommie said:

Thanks, but these are the front nuts on the cylinder head, not barrel, and should not, I'm fairly sure, have any washers.

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According to a few exploded views and instruction from the Clymer manual you are apparently correct. My bad. I am mostly working with alloy barrels where steel washers in these positions is a must. I suppose steel nuts to cast iron barrel is not too bad and they call for washers elsewhere in the barrel. I would use them.

If you lost the barrel nuts, do you suppose the studs had backed out, were too long or otherwise not seated and you were bottoming out the barrely nuts when torquing?

Re torqued bolt's, the pressure on the bolt [stretch] let's go when the head heats up,the head being alloy will expand twice the rate of the bolts.and as an effect of over stretching the bolt, once cooled down the bolt stays over stretched and becomes loose.
Re-torque imparts more stretch and the head re-heats and starts the proccess all over again, Measure the bolt length after 4-5 tightening, quaility bolts usally have rolled threads, machine cut threads could mean the steel is not best quaility ... :roll: All truck engine head bolts are rolled from top grade steel...who knows what norton spares are made from :?: looking for andover to chime in here.

john robert bould said:

Re torqued bolt's, the pressure on the bolt [stretch] let's go when the head heats up,the head being alloy will expand twice the rate of the bolts.and as an effect of over stretching the bolt, once cooled down the bolt stays over stretched and becomes loose.
Re-torque imparts more stretch and the head re-heats and starts the proccess all over again, Measure the bolt length after 4-5 tightening, quaility bolts usally have rolled threads, machine cut threads could mean the steel is not best quaility ... :roll: All truck engine head bolts are rolled from top grade steel...who knows what norton spares are made from :?: looking for andover to chime in here.

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With due respect, unless the bolts are initially over torqued, there should be ample elastic range left for the bolts to retract. Even if the bolts were tightened a little past their yield point they would still retract (spring back) but not to the like new condition.

I think what is happeneing is that during break in and bedding in the gaskets and sealed surfaces may be inelasticly yielding/compressing and upsetting due to the thermal induced loading and viibration. When the engine cools, the bolts are no longer as tight as they should be due to the inelastic yielding and upsetting of the gaskets and sealants.

Yes i would agree if the bolts to start with are the correct steel,some venders offer stainless bolts as a replacement? which are not hy-tensile
Another "if" is the head gasket type being constantly compressed ? I suppose the start -finnish thickness as not been measured?
I know Norvil re -torques 3 times on their New Commandos...so for the moment i will go allong with your head gasket compression theory..

Here's my 2 cents as I'm currently dealing with similar issue:

If the oil is appearing on the 'lower most fin of the cylinder HEAD', head rather than cylinder block, the oil is more likely coming from the rocker covers rather than the head gasket. I've got a very small amount of oil appearing on the upper most fin of the cylinder block. This is probably coming from the push rod tubes and corresponding holes in the head gasket. At any rate, I've re-tightened the head gasket and have to talk myself through the 'righty tighty, opposite upside' down when tightening the inverted nuts that have gone missing on your machine. Further, I've ditched the torque wrench and just reef on the damn things. I set the torque setting originally and can still get a 1/4 turn onto them. I've also used thick washers similar to the ones on the head bolts either side of the spark plugs on the underside studs. Even though the nuts fit against cast iron, I wanted to get an even seating so as to hopefully eliminate this oil leak.

BC