Cylinder Head Nuts

[philward]

One for the Metallurgists out there! I'm just about to re-zinc the cylinder head nuts ready for engine reassembly.
I have some Stainless Steel A2 DIN 6923 non serrated flange nuts and was wondering as to whether these would be suitable for the stress' put on these head nuts - I don't know the standard nuts tensile properties to be able to research a comparison table.
I don't want to fit the SS nut if the threads 'give' a little and affect the head seating
Whats your thoughts? (its bloody cold in the garage to be in there zinc plating!)

[Skoti]

I find myself nodding my head as I read Oddjobs footrest bar experience.

I also discovered to my expense that stainless A2 grade stuff is bad for thread galling as it's easy to overtighten because you just don't get the same feel as you do with normal steel fasteners.
Of course it's just when you try and undo them again, that's when the shit hits the fan...

Anyway A4 grade stuff is the way to go for high stress applications such as footrests and engine mounts etc, A4 has a higher nickel content and most importantly contains molybdenum so no more swearing when trying to undo stuff.

Hope this helps

Skoti

[Skoti]

This may or may not be that relevant regarding the question Phil has about A2 head nuts.

Some time ago I fitted a set of stainless head bolts to my 850 Commando which had been previously oil tight in the cylinder head area. I struggled with oil weeping in the pushrod area at the front of the head for ages after that, away to cut a long story short I had the original steel bolts re-zinced and fitted them back on -  problem solved.

   

[K2-K6]

A useful discussion here http://www.volksbolts.com/faq/basics.htm specifically about A2 bolts.

As oddjob points out,  it's the stud on these engine that is stretched to tensile load as the nut is compressed. 

I was trying to find a definitive comparison, but getting the rating of the Honda originals is not easy.

Something nagging says I wouldn't use them unless I could find more about rating.

[Trigger]

Not advisable to use S/S nuts on any head 

[mickwinf]

following with interest as i fitted stainless nuts to my 550 head.

[philward]

Good to hear everyones views! Done a bit of research myself and general consensus seems to point to issues. I am a fan of SS generally as just seems logical to avoid re-plating - I always use copper grease though, as everyone seems to suggest (read that bonding between SS and other contact material is to do with a electrolysis process). I have generally not used SS in load bearing area's to date - hence my original question?

[philward]

A useful discussion here http://www.volksbolts.com/faq/basics.htm specifically about A2 bolts.

As oddjob points out,  it's the stud on these engine that is stretched to tensile load as the nut is compressed. 

I was trying to find a definitive comparison, but getting the rating of the Honda originals is not easy.

Something nagging says I wouldn't use them unless I could find more about rating.

Thats a really interesting article - especially the part about tensile strength comparisons and 'Galvanic Corrosion' and confirms that if a barrier used (copper grease), most uses should be ok

[K2-K6]

Notice the shift in torque they give when using nickel grease?  Approximately 10%.

[K2-K6]

I was trying to find a link for the 8 identification bolts used by Japanese vehicle manufacturers and if if related to any structural specification,  but seems indistinct. 

http://sanei-screw.com/strength a little more discussed on here,  and looks to be something of reference to  8.8 material specification, but that's by looking at more wide ranging variable and so more an impression than fact.

The bolts and studs do seem to have a competent tensile capacity that could tally with the numbers around for expected torque ratings used in their applications,  with things like the studs having that high tensile "ring" to them if you tap them with something metal when they are left exposed on bare crankcase.  They have a spring like quality to them that is signature of heat treated and tempered steel.

[philward]

Rather than re-zinc the nuts or use those SS flanged nuts, I looked into original Honda nuts - CMSL 1.2O euro  (but postage expensive), and DS were £2.40 each! Found these on ebay
https://www.ebay.co.uk/itm/Metric-Zinc-Plated-Steel-10-9-Grade-High-Tensile-None-Serrated-Flange-Nuts/112818931348?ssPageName=STRK%3AMEBIDX%3AIT&var=413246378350&_trksid=p2060353.m1438.l2649

I think they will be good enough?

Did read something on the net (but can't find it now) about rolled and cut threads affecting quality/effectiveness

[K2-K6]

"Did read something on the net (but can't find it now) about rolled and cut threads affecting quality/effectiveness"

Yes, true. The Honda (and most load carriers) are ordinarily rolled.  The difference is that rolling is effectively forging the thread shape by compressing the metal into the groove shaped from that process. As opposed to "cut" which uses a tap to remove metal and create the groove.

Compressing the steel into it's formed shape just makes it stronger compared to metal removal,  also frictional torque can be different between the two as rolling usually leaves a refined/polished surface that's going to slide more easily at peak loading.

Each thing impacts the torqued procedure.  Honda,  with both stud and nut rolled I believe, state torque for this and dry (unless specific lubrication is noted) with a cut thread likely to measure higher but giving lower clamping pressure (pulls the stud less into tension before torque wrench clicks) and lubrication making it easier to turn the nut,  so putting more load onto the stud before the wrench clicks.

[Skoti]

M8 cylinder head flange nuts with 12mm heads here on Ebay:-

 eBay item number:171567437209

https://www.ebay.co.uk/itm/M8x1-25-12mm-Hex-Head-Smooth-Metric-Flange-Nut-Cylinder-Frame-Ahrma-Elsinore/131186557034?epid=679345657&hash=item1e8b54006a:g:2OoAAOxyA4ZRLOKM

[philward]

Skoti, great price but postage too high @ £24 (works out same total price as new Honda from Silvers)
Ken, good point, wasn't bothered about 12mm originality but never thought about the socket issue.
I think in light of all the variants in the nut make up/design/strength/etc as discussed in this thread, I'm going to re-zinc the existing nuts to be on the safe side. Good debate though and learned a lot - hopefully been beneficial to other members too. Thanks for all the input and advice.

[Trigger]

Just get out in the cold and re plate  And don't forget to do the stud washers