SOHC.co.uk Forums > CB350/400
400 - “elasticity†in headnuts
K2-K6:
--- Quote from: royhall on July 09, 2020, 07:12:41 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?
--- End quote ---
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.
royhall:
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.
Erwin83:
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.
MCTID:
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 ?
Erwin83:
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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