SOHC.co.uk Forums > CB350/400
400 - “elasticity†in headnuts
K2-K6:
--- Quote from: Erwin83 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.
--- End quote ---
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.
K2-K6:
Tensile load failure looks like this
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Classic failure of too much loading by over tightening.
royhall:
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.
400 Cafe Racer:
--- Quote from: Erwin83 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)?
--- End quote ---
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
McCabe-Thiele (Ted):
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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