HEAD BOLT CAUTION

This may be helpful to those planing on plating there engine bolts. I had various bolts & nuts nickle plated. One head bolt snapped like a carrot. I had already torqued the head down, run the engine and was re tensioning the head after an overnight cool down. After carefully backing off all bolts and nuts in reverse order I re torqued, 30 ftlb for the 3/8 bolts and latter in the day my son asked how come one head bolt was lying next to the spark plug. Bugger, that ruled out the promised shakedown run that afternoon. After some deliberations overnight, I decided to have a go extracting the offending broken off section of the bolt, without removing the head. I armed myself with a 1/4" long drill bit, machined up a 3/8" to 1/4" clearanced sleeve, this was used to protect the head and centralise the 1/4" drill bit. And carefully bored a hole through the centre of the broken off bolt, then with a partly broken Ezi-out I was able to carefully unwind the broken section out. Bit of compressed air and a 3/8" cycle thread tap to clean out and ALL-GOOD!

I was very happy to get away without having to pull the head.

So moral is replace your head fastenings, as the consequences are not worth considering, I think I got off lightly?

Cheers Richard

I worked in a plating place for a year as soon as you plate any metal it will weaken it, we had a barrel line that we used for zinc plating nuts and bolts a lot better than nickel and chrome plating, best to stay with all oginal head bolts...

Ashley

My understanding is that Cadmium plating will not degrade fasteners.

Any science nerds have the "poop" on this?

I've heard the term "hydrogen embrittlement" used frequenly around here...

I had some hardware cad plated when I restored my 750 and the plating shop baked the parts in an oven after plating to mitigate possible hydrogen embrittlement. Haven't had any broken bolts but I didn't have any head bolts plated.

When I built the 850 I bought new head bolts but ended up reusing the old ones because the threads were so poorly formed on the new bolts. It appeared to be plating buildup in the threads that was causing the problem. I guess one needs to invest in a complete British tap/die set so you can clean up the parts before use.

Debby

Good alert and salvaging post Stockie1. A shame old stock Cadmium plated fasteners ain't as shiny as chrome or SS and rusts up fast if wire bushed, but old stock is what I'll use on my stock Combat, polished up 'shiny' then nipped up, then clear paint coated. Or buy a couple extra sets of new, to send back the set whose threads don't match- ugh - like I found in barrel nuts last week. P/n is right but not the thread form. Alas even the good structural grade SS tends to darken-blacken- by time oxygen, moisture and heat, even in a few seasons in Peel's case.

FYI

I have been using the same stainless four head bolts for the last 12 years and 28K miles with no issues. In that time the head has been off probably half a dozen times. The torque setting for the head bolts is relatively low at 30lbs/ft.

I have been using the same stainless four head bolts for the last 12 years and 28K miles with no issues. In that time the head has been off probably half a dozen times. The torque setting for the head bolts is relatively low at 30lbs/ft.

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And I pulled the head off a friends 'S' model with all shiny new SS bolts to find the head bolts beginning to neck at the threads. Might be the alloy used as I know a couple others that have the same experience as illf8ed. I would suggest critical fasteners in stainless come from reputable sources.

My meager understanding is the more Stainless it is the weaker it is and visa versa.
Please correct me if I'm wrong and missing out on shiny hi strength stuff.
Peel was hot tuned, ran almost 1400' F EGT and almost 400' F CHT, and had a few bad timing events that turned header red to the silencer, so her example may not apply to normal engine usage. Only saw those temps a few times as hard to find places to stay WOT for long out here. SS was sourced via Rocky Point Cycle and glad of it after what Peel went through on stuck throttle.

hobot said:

My meager understanding is the more Stainless it is the weaker it is and visa versa.
Please correct me if I'm wrong and missing out on shiny hi strength stuff.

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Not necessarily, 304 and 316 are two grades of stainless i deal with. 316 is the more durable in food processing applications but has the same design strength as 304 - both of which are approx 80% the strength of mild steel.

Ron L said:

And I pulled the head off a friends 'S' model with all shiny new SS bolts to find the head bolts beginning to neck at the threads. Might be the alloy used as I know a couple others that have the same experience as illf8ed. I would suggest critical fasteners in stainless come from reputable sources.

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One of the tricks with stainless is that even if it has the same (so called) strength as a carbon steel it has quite a different stress/strain curve.
Mild steel, and carbon steels in general, behave elastically all the way up to a reasonably defined yield point. For stainless the curve becomes non linear much sooner, and it does not have a well defined yield point.
So in a high stress use the choice of stainless grade is important to make sure permanent stretch doesn't happen at in service loads - reputable sources is good advice.

I agree with Deb about the Andover bolts, I have had to run a 3/8" cycle thread die over the new head bolts I procured , otherwise they would bind in the cylinder barrel threads. I suspect the plating build up was excessive. Also now I have to suffer the indignation of using a 13mm socket as Andover were unable to locate hex stock in a 1/4 whitworth dimension, or even 12.7mm (1/2") for AF sizing. Cor blimey.
Well as long as they keep the head eleastically attached I will be gratefull?

Cheers Richard

ludwig said:

You should think of of a bolt like a spring .
Tightening any bolt is stretching it out , like tensioning a spring .
It is the elasticity of the bolt that provides the clamping force .
like ntsc8 says , it is not just about strength ..
lots of info on the web , like here :
http://www.boltscience.com/

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And this is why chrome plating weakens the fastener; chromium plating is a very stiff, hard, brittle outer coating. At the points where the bolt would normally stretch and flex, the plating prevents this. Soon, a crack in the plating will propagate and this crack will spread to the base material. Nickel is softer and will flex more than chrome. Years ago, they used to nickel plate flat track frames to better resist the ravages of the nasty chemicals in the dirt which were put there to promote faster drying and discourage plant life. Chroming the frames would cause them to crack at the stress/flex points in the same manner. The chrome was too stiff to flex and then cracked and the crack would spread to the underlying metal, ruining the frame.

I see that several places,(British Cycle Supply, Commando Specialties, etc.), are offering stainless front axel and nut. Should one stay away from these?

Blue noser said:

I see that several places,(British Cycle Supply, Commando Specialties, etc.), are offering stainless front axel and nut. Should one stay away from these?

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I wouldn't have any reservations, I recently bought one from a bit closer to home for my 16H.

There are suitable, high strength, stainless alloys that are a great material for things like head bolts. ARP makes some head bolts out of their A286 stainless alloy, with 170,000 psi yield strengh and 200,000 psi tensile strength (UTS). That's considerably stronger than the material in most motorcycle head bolts. They'd be happy to make a batch of Norton head bolts in A286, or any of their other exotic materials, but I'm not sure there's a large enough market for expensive Norton fasteners to make it profitable. Also, it's possible to make them too strong, so you don't have enough elastic stretch to maintain the clamping force needed over an engines temperature range. As several others have pointed out, it all comes down to knowing your supplier, or at least knowing the material he uses. There are plenty of stainless fasteners out there that are just fine for holding your license plate on, but you might not want to use the same material for your disk brake carriers.

Ken

Ken, I spoke to ARP about doing Norton head bolts. They were not real keen about doing them in stainless but suggested a 180,000 psi stud that was waisted in the center according to their formula for the correct stretch. Then use a stainless nut. Their price quote put a stop to the idea, but I have had good results using their standard black studs with stainless nuts and their hardened washers.
I have also used many of Rocky Points stainless head bolts on standard engines without a problem. I do stay away from stainless for the engine to cradle bolts anymore though. Nothing but ARP studs there. Torque them once and forget them. Jim

Should one stay away from the original steel studs and new stainless nuts for the motor, gearbox and iso mounts?

Dave
69S

Naw, factory bolts and studs were made for their tasks. Mainly just need to watch out or avoid long items in SS fasteners. SS shear failure leads the reports of twist or pull apart by 10-1.
Nuts are not under the same stain, even though their threads wear-give out so may require renewing every few motor rebuilds. If your as scardy cat as me to really stretch by nuts and bolts in alloy cases, reline with Timserts and worry more about wrench jaws. Anit-seeze is next subject to learn on using SS threads.

DogT said:

Should one stay away from the original steel studs and new stainless nuts for the motor, gearbox and iso mounts?

Dave
69S

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I have not had problems with oem engine to cradle bolts if they are in good shape. This is one place where the design was a little borderline and loosening of these bolts is fairly common. I like to upgrade to good studs for the three engine to cradle bolts and then I don't have to worry about them. If the bike gets ridden very long with loose engine to cradle bolts it makes a mess of the cases. So if your using stock bolts there check them once in a while.
The two front iso.mount to engine bolts are not under much load and anything seems to work there. The trans mount bolts and long isolastic through studs are good in OEM but I avoid stainless there. Jim

Factory though bolts just don't fit real snug and bores on small size for Al to bare the shock loads. Peel had them all replaced by slight interference fit 7/16" bolts from Aircraft Spruce. Very satisfying to see and feel their robustness tapped home then nipped up and staying put though thick and thin, in and out a half dozen times and still feels and fits same as first time. Same bolts but new holes will hold Maney cases together to cradle in new Peel, done a few years ago.