Author Topic: 400 - “elasticity” in headnuts  (Read 3533 times)

Offline K2-K6

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Re: 400 - “elasticity” in headnuts
« Reply #15 on: July 09, 2020, 09:19:21 AM »
We're back to this oil don't oil the threads debate. If you did a full rebuild the threads would be dry on assembly, if you did the head on a bike that's run all the threads will be oiled and there's not much you can do to remove it. What's the correct torque for oiled threads because I suspect we are all doing it wrong on repairs?

You're right Roy,  in that you'd have to have them all clean or all lubricated to firstly make them even,  and secondly take account of the difference.  Best case data indicates that dry to oiled gives 10 to 15% more tensile loading for the same rotational torque.

In effect if you went for maximum spec torque number dry and take off 10% for lubricated,  it would essentially pull the stud to the same loading.  How close it is to material yeald we don't know.

It's a problem illustrated by occurrence in other places.  The stud often used to hold cam belt tensioners in place is a good example because of this variance.  Most tensioner are now supplied with a new stud (because they just don't know what's happened to the last one) and then they torque the nut to a very low figure around 5 ft lb , they then turn the nut 90 or180 degree to get the loading they require.  You in effect get low error total from the torque setting (even if completely cocked up) followed by exactly the correct elongation from prescribed angle.

Offline royhall

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Re: 400 - “elasticity” in headnuts
« Reply #16 on: July 09, 2020, 09:38:59 AM »
Just wondering if the nuts were oily on the gasket replacement, the torque would be too much with the wrong setting plus 10 to 15% and that's caused the stretching.
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Offline Erwin83

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Re: 400 - “elasticity” in headnuts
« Reply #17 on: July 09, 2020, 11:51:58 AM »
Well, this was truly only a head gasket replacement, done in a single evening. So everything was a bit greasy, but the nuts themselves... not so much I would say. However there is definitely oil on the copper washers.
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Offline MCTID

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Re: 400 - “elasticity” in headnuts
« Reply #18 on: July 09, 2020, 04:49:20 PM »
Mmmmm this thread has got me thinking........when the Factory assembles Engines, they usually don't use any lubricants on the fasteners........they don't have the time - or the inclination - and bollox to the poor sods down the line who have to take them apart later.

Some years down the line poor sods like me often use some kind of grease/ oil/ copper paste etc etc etc on fasteners so that they will come apart more easily in future, especially where dissimilar metals are bolted together such as a steel stud in an alloy casing or a stainless nut on a steel stud. Where components are subjected to the heat cycles of the engine, this criteria is also important. The use of washers (of various materials) may also pose potential Torquing discrepancies, but I suppose if the Parts diagram shows a particular washer, then the Factory has allowed for that in their recommended Torque settings.

So the question is........how accurate or critical is the Torque setting if a lubricant has been employed, and is there a rule of thumb be used when determining the Torque setting that is used in a rebuild with regard to lubricants being used ?
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Offline Erwin83

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Re: 400 - “elasticity” in headnuts
« Reply #19 on: July 07, 2022, 09:33:46 AM »
So, couple months (and just a few kilometers, really) later. I'm back at square one.
Again, Cilinder 2 is smokey. I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.

I'm going to retorque the head again, first without changing the gasket. Remember last time I found 'loose' head nuts.
Could there be anything wrong with my Studs, or Head?
Is there any harm in using an extra ring under the head nuts, just to make sure the nuts are not bottoming out on the studs (because of the aforementioned elasticity)?
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Offline K2-K6

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Re: 400 - “elasticity” in headnuts
« Reply #20 on: July 07, 2022, 10:12:44 AM »
So, couple months (and just a few kilometers, really) later. I'm back at square one.
Again, Cilinder 2 is smokey. I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.

I'm going to retorque the head again, first without changing the gasket. Remember last time I found 'loose' head nuts.
Could there be anything wrong with my Studs, or Head?
Is there any harm in using an extra ring under the head nuts, just to make sure the nuts are not bottoming out on the studs (because of the aforementioned elasticity)?

I can't immediately remember but someone on forum had one of these head with crack in casting allowing oil to leak into exhaust port to smoke on #3 I think ?

It was long convoluted chase through all the other possibilities, but ended definitely with this outcome.

Offline Erwin83

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Re: 400 - “elasticity” in headnuts
« Reply #21 on: July 07, 2022, 10:20:49 AM »
Well I'm hopefull it's not that. Afterall, replacing the headgasket and (re)torquing the head nuts stops the smoking completely.
It appears to come back only after riding hard (full throttle up to red-line).

I think my issue is with the studs/nuts, as I have this 'elasticity' on torqueing, and headnuts that appear to come loose after a short while of riding (couple 100 km).
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Offline royhall

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Re: 400 - “elasticity” in headnuts
« Reply #22 on: July 07, 2022, 11:25:22 AM »
So, couple months (and just a few kilometers, really) later. I'm back at square one.
Again, Cilinder 2 is smokey. I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.

I'm going to retorque the head again, first without changing the gasket. Remember last time I found 'loose' head nuts.
Could there be anything wrong with my Studs, or Head?
Is there any harm in using an extra ring under the head nuts, just to make sure the nuts are not bottoming out on the studs (because of the aforementioned elasticity)?

I can't immediately remember but someone on forum had one of these head with crack in casting allowing oil to leak into exhaust port to smoke on #3 I think ?

It was long convoluted chase through all the other possibilities, but ended definitely with this outcome.
That was me on the 350F. It was a real head scratcher problem. I ended up rebuilding the top half three times. In desperation I took the head to an NDT place who gave it to a chap called Eddie Current. He was good, he found a crack next to a valve guide that was invisible cold but opened up when hot. I replaced the head with a really good low mileage one off eBay and problem solved. It's never smoked since.

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Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline 350Simon

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Re: 400 - “elasticity” in headnuts
« Reply #23 on: July 07, 2022, 01:09:35 PM »
When I rebuilt my 125s I torqued the head down properly (circa 16ft lb iirc) and I distinctly remember looking at the manual multiple times thinking is that it?! Is that the correct figure, have I misread something? That torque seemed way to low to me after having worked on car engines with aluminium heads countless times when your generally over 50ft lb on head studs.

However the 125s studs are on the small side so I thought OK that must be correct and duly proceeded to finish off the build. After about 400 miles of riding I noticed oil seeping from the cylinder base gasket. So I duly re torqued the studs and noticed exactly the same as what you did, the stud would turn with the nut for a couple of degrees, then go tight allowing the nut to turn on its own. I put it down to everything just settling in.

Only for it to happen again at about 1000 miles. This time I thought, this is really strange I've never known this to happen before so I approached one of the engine builders at work and asked him for advice. He said the torque spec does seem very low but if that's what honda specified then it must be correct.

We work on vintage/pre war cars so are used to dealing with worn out and re used parts. He suggested that perhaps the threads in the crankcase were stretching / already stretched and the studs and nuts likewise. Therefore although torqued to the correct setting they were able to fret loose with engine vibration due to the wear on each component. I had after all re used my studs and nuts which were original.

So I asked what he would do and he said come here my boy....... and pulled out a 12mm spanner from his drawer. Go home and tighten those nuts as hard as you can with the ring end of this spanner. I suggested that I might run the risk of over tightening them if I did that, to which he replied you can't, this 12mm spanner is this length for precisely that reason.

So I did what he said and a few thousand miles later hey presto all was well. I'm not suggesting that you do this to your engine, merely sharing my similar experience!

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« Last Edit: July 07, 2022, 01:12:48 PM by 350Simon »
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Offline Erwin83

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Re: 400 - “elasticity” in headnuts
« Reply #24 on: July 08, 2022, 07:48:34 AM »
Took the valve cover off last night and found that the 2 nuts on the intake side of cil 2 (the smoking cilinder) were indeed a bit loose again.
I've tightened them up, but one would not stop with the 'elastic' feel once torqued. So I added another ring and that helped (for the feeling of stretch at least). Maybe this nut is binding on the threads or binding in the dome of the nut?
No idea, but I'll put everything back together this weekend and see what happens.
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Offline K2-K6

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Re: 400 - “elasticity” in headnuts
« Reply #25 on: July 08, 2022, 09:48:32 AM »
Took the valve cover off last night and found that the 2 nuts on the intake side of cil 2 (the smoking cilinder) were indeed a bit loose again.
I've tightened them up, but one would not stop with the 'elastic' feel once torqued. So I added another ring and that helped (for the feeling of stretch at least). Maybe this nut is binding on the threads or binding in the dome of the nut?
No idea, but I'll put everything back together this weekend and see what happens.

I see it as one of two reason, either the nut is backing out by rotating to release load or the stud has been stretched beyond it's normal elastic point of integrity and now in a failure state. If it's stretched beyond normal limits it will keep getting longer each time it's tightened until it snaps, indication of this is that the stud is getting higher than the other examples on the engine. 

Offline K2-K6

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Re: 400 - “elasticity” in headnuts
« Reply #26 on: July 08, 2022, 09:51:43 AM »
Tensile load failure looks like this

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Classic failure of too much loading by over tightening.


Offline royhall

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Re: 400 - “elasticity” in headnuts
« Reply #27 on: July 10, 2022, 01:02:01 PM »
Just been out on the 350F (not used it for ages) and noticed when I got back an oil weep from the head gasket that wasn't there before. Also it's blowing fumes out of the breather tube. It is slightly overfilled with oil, could that be causing the fumes. The oil weep is probably time for a head re-torque I guess, I will also take some oil out of it at the same time. Runs really well though.
Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline 400 Cafe Racer

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Re: 400 - “elasticity” in headnuts
« Reply #28 on: July 12, 2022, 09:29:05 PM »
So, couple months (and just a few kilometers, really) later. I'm back at square one.
Again, Cilinder 2 is smokey. I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.

I'm going to retorque the head again, first without changing the gasket. Remember last time I found 'loose' head nuts.
Could there be anything wrong with my Studs, or Head?
Is there any harm in using an extra ring under the head nuts, just to make sure the nuts are not bottoming out on the studs (because of the aforementioned elasticity)?


 I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.

Hi Erwin,

There may be some oil overheating/thinning occuring, which will promote oil burning.
If you have a 466 bored out engine you would be running hotter than normal and definitely need oil cooling.

On a standard engine you will maintain about 90 to 105 degrees C oil temp with normal riding - give it the beans and you will soon be up to 120 C, with oil thinning. I think this causes oil degradation and probably why Honda specified 1500 miles oil changes.

Just another factor to consider. FWIW

Dennis
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Offline McCabe-Thiele (Ted)

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Re: 400 - “elasticity” in headnuts
« Reply #29 on: July 13, 2022, 10:10:47 AM »
At the risk of sounding daft I have felt this sensation decades ago when tightening Helicoiled threads back in the early days of Helicoils.

Are all the head stud threads in the block as per original ?
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