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Cylinder Head Fastener Torque (Read 116 times)
hotrod
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Re: Cylinder Head Fastener Torque
Reply #15 - 12/13/19 at 19:30:25
 
Is it safe to say that the base gasket failure had nothing to do with the crankcase check valve ?  This opens the possibility of more check valve experiments without fear of hurting anything.
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Armen
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Re: Cylinder Head Fastener Torque
Reply #16 - 12/14/19 at 11:18:09
 
This shows why a lot of manufacturers use 'torque angle' instead of a torque spec in Ft/Lbs. Maybe set up the stud with the suggested lube, torque to spec, measure the stretched stud, then put on whatever goop you like, and torque til the same length using a torque angle gauge, and use that angle as your new way of torquing the fasteners?
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DragBikeMike
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Re: Cylinder Head Fastener Torque
Reply #17 - 12/14/19 at 12:21:26
 
Batman, I agree there are six studs restraining the cylinder head to the cylinder, but there are only four restraining the head and cylinder to the case.  I think we can ignore those two 6mm studs on the side of the cylinder base adjacent to the cam chain channel.  Either way, its pretty evident that stressing those studs up to only 37.6 ksi isn't going to cut it.

Armen, the acorn nut depth was on my mind when I did the quench project.  That's why I stacked the copper washers.  You will note from this post that I ditched the .090" copper washers and replaced with .220" steel washers.  The steel washers are .130" thicker than stock.  That compensates for the .130" I machined off the cylinder.

Using the degree method to tighten up the nuts is certainly and option, but it would require testing all four studs.  Each stud is a different length on this engine.  The longer the stud more nut rotation is necessary to achieve the same stress.  It is a more accurate method.  

Hotrod, I can't rule out the check valve entirely, but it sure looks like it was not the cause of my gasket failure.  I'm thinkin maybe the check simply set up the right conditions to push the gasket over the edge.  I've been testing the KrankVent, riding around with a vacuum/fuel pressure gage installed on the crankcase.  I haven't observed any vacuum/pressure in excess of 2 psi.  That's not enough to cause a gasket failure.  I have a copper base gasket in there now and its 100% oil-tight.

I have a big problem with the test, the gage was not intended for high vibration application.  I broke the gage.  I didn't note any major pressure or vacuum spikes so I'm pretty sure vibration did the gage in.

The failure was so weird that it would be difficult to explain.  I have it on a series of videos.  If any of you are willing to review the vids and comment I would certainly appreciate it.  I can post links to the vids so you can see for yourself what took place.  I have observed a lot of gages in my career and have never seen one behave like this.  Shocked
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Armen
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Re: Cylinder Head Fastener Torque
Reply #18 - 12/15/19 at 15:27:22
 
Hey DBM,
Maybe instead of measuring stretch of each stud, just use the assembled motor with the nuts coated in your fav juice, and a torque angle gauge below an indicating torque wrench. Just see how many degrees it takes to reach the stock spec? Then use the degrees after gooping up the nuts with your fav magic juice?
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DragBikeMike
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Re: Cylinder Head Fastener Torque
Reply #19 - 12/16/19 at 18:05:56
 
That's an interesting suggestion Armen.  I will have to ponder it for awhile.  The tests I'm doing correlate stud stress-level to friction.  I determine the stress level by how much the stud elongates.  Regardless of stud length, the friction should remain consistent for the desired stress level.  Using your proposed method might be an option.  It would be cumbersome when you consider that you want to pull up the fastener in at least four increments.  

Degrees of rotation generally determines elongation based on thread pitch.  These studs have a pitch of 1.25mm, so for every quarter turn the stud is elongated .31mm (.012").  That would be every quarter turn past the point where the stud first starts to stretch.  That's the real tricky part.

There's a head gasket in there, and it's also crushing as the nut is turned.  I just received a set of four studs so now I have one of each length.  Maybe I'll see if I can figure something out.  As I recall, my Evolution Harley had a spec that was something like torque to 7 ft-lbs, then tighten 90 degrees.  But all four studs were the same length.  I would have to figure out the correct torque necessary to achieve the "just starting to stretch" condition.  Then I imagine I would end up with four different rotation values in degrees.  The shortest stud requiring the least rotation, and the longest stud requiring the most rotation.  Argh!!!!  Too complicated.  Maybe I'll just stick with torque.
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