Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Torque and threadlocker on con rod bolts?

Do I put threadlocker on con rod bolts? If so, which one? Loctite blue? I've seen a variety of opinions on the interweb and am now not sure. Hughie Hancox does but lots of folk say 'use engine oil and forget the Loctite'. Any opinions?

Also, what are the correct torques for OEM con rods?

Cheers.

Forget the torque, use bolt stretch measurement to determine the correct tightness from first principles which is more accurate than a derived figure which can be distorted by lubrication etc

I have never measured bolt stretch. Is this straightforward (I do have a micrometer)? Where do I measure from on con rod bolts? The whole bolt or portion that's proud of the big end?

Whole bolt length using a micrometer, smooth/polish the ends so you can be sure of an accurate measurement.

This has been covered in previous threads ( excuse the pun ), but from 1970 B/E nut torque for 650/750's was amended to 22ft lbs.JB Nicholson, in his book,"Modern Motorcycle Mechanics ", sayys that thiswas with the change to the bonderised("grey finish ) nut. Also, the change to UNF thread form was an influence in the reduction of torque from 28 ft lb of the earlier thread form.
In his book " Triumph Tuning", Stan Shenton advocates using loctite onB/E nuts. On OEM, I've always used loctite blue.
When I fitted Carrillo conrods to my T140, during a rebuild 1993, I followed the instructions given by Carrillo then, and securing the conrod in a conrod vice, tightened a bolt in increments of 2 ft lbs, and at the requisite strech, measured with a micrometer, it corresponded with their recomnended torque. Back then, they recommended the bolts be lubed with 50/50 moly and 50 wt oil!
I now have aJeggs conrod bolt stretch gauge. The top echelon conrod manufacturersnow always advocate stretch measurement preferable to torque.
Hope this is of some help.

Nuts can be self securing nuts.
On my conrods the nuts have saw cuts so the last turns are "heavy", like with nyloc nuts.
This means that with these nuts the reading of a torque wrench does not tell you anything about the pulling strength on the bolt.

They have to an adequate flat area to give repeatable results...they may have to be spot faced properly...
Bolt stretch is the best way, but 1000's of Triumphs running around with bolts tightened by a torque wrench that are perfectly fine..

I vote for:
True the ends of the bolts, tighten till correct stretch and Loctite blue on thread as insurance/peace of mind.

Yes, and because most "mechanics" do not adjust the torque down for lubricated threads: oil or Loctite, most of them are over over stretched... For example Loctite recommends you reduce torque by 20% for torque figures given for dry threads.

Sometimes reading threads here I can't but help but wonder why the world isn't full of exploding triumph engines caused by misguided backyard mechanics.

davy

I know, I know, If it was only backyard mechanics...

...my story regarding con rods and torque is:
-with my heavy modified 48 I needed to put newer pre units rods so the shells situation was very different; however, I used the same torque as previous rods (that had shells too but those were the old ones, transformed to fit them)

-Then, with a 79 STD crank, new original rods and new shell bearings I used the same torque than my 500; I tried less torque but I did not got a free rod, then with more torque somehow they released and moved perfectly free and light.

So a Triumph engine is disassembled and rebuilt by a knowledgeable hobbyist.Now it's time to tighten the rod nuts by using bolt stretch...How can you be sure the bolts haven't been stressed in the past by over tightening? Spot facing old bolts and measuring may be a waste of time. Do you replace the bolts with known quality bolts to be safe?
I don't see the purpose of using Loctite on rod nuts..
I suppose if it's a sedately ridden machine it may not matter about rod bolts like it will if the the rider uses it in anger...

I find if bolts have exceeded their elastic limit in the past they start to move a lot as they approach the correct stretch/tension.
Same time as I built my Daytona motor a couple of years ago I built a Ducati superbike motor and the brand new bolts moved far too much for not much effort/torque at the required stretch... I re-used the old tried and tested ones instead as they felt completely solid as they approached the right numbers and I didn't trust the new ones.

davy

Yes, and it's been my experience wrenching on cars,trucks tractors and such some bolts get "stiff" or work hardened from past over torquing. You can feel it as the bolt is tightened and does not give a "feedback" (stretch)

Can you tell which one of the after market rod bolts was made from bar stock?

Can you tell me which one was made in India?

Can you tell me which one has the proper radius under the head?

Can you tell me which one has the face of the head that is not square with the shaft?

Can you tell me which after market supplier is using proper forgings to make his bolts (originals were made by Unbrako)?

Can you tell me which one, other than the stock one that is in the rod, would I use on a rebuild?

Except for rods that came with ARP rod bolts, I have never used anything other than the original bolts that came in stock rods, even in 750 race motors that were making competitive hp. In racing since 1959 I have never experiened a rod bolt failure with a Triumph rod bolt. Even in the later years where we actually did find some real horsepower. We also reved teh 500's to well over 9,000 even on tracks like Daytona where the engine sits at red line for a very long time. We have also never used anything other than stock rods except on large journal Nourish 750 crankshafts and never experienced a failure. On the later UNF Triumph rod bolts used for racing I have gone to using clevloc nuts and bolt stretch (recording the length for checking for elongation later).

JH, so you feel comfortable reusing rod bolts from a 50 year old engine with an unknown history over torqued bolts... ?

...also, I add that in the past with those needle torque wrenches was not possible to torque exactly to 18 or 22 or whatever torque set.
Do a test with one of those and compare the fine results with the other type of torque wrenches

Basically, yes. Triumph rods and their rod bolts, even though 50 years old, have not been themselves a problem. I don't see any more failures than I see with any other rod - and yes, God's own rods also fail. They are generally not failing because of any defect in the rod or its hardware, but because of other causes, but that is another subject.

I am in a different position than most. I know where my suppliers get their parts and get so see their offerings. Besides ARP, to date there is only one supplier who's rod bolts I would use, and I wouldn't race with them. As well as not knowing the history of the bolts in hand, I know more about the ones supplied as spares.

While not a scientific study, I base my opinion having walked over burlap bags full of Indian rod bolt blanks, seen rod bolts turned from bar stock with machine marks that looked like they were made by "bucky beaver". Measured rod bolts to find the shoulder on the head isn't square to the shaft. None of them have rolled threads. They may be "new", but are they better than an 50 year old original. If I was able to buy "factory" original forged Unbrako with rolled threads I would change the bolts every time. But, and yes it is a big but, sometimes the devil you know is better than the one you don't know.

Even the aftermarket rod bolts that I would use are not finished to a standard that pleases me. The rod bolt blanks are forged by Unbrako, but are not finished as well as original.

Of course there are ARP rod bolts. Thanks to the efforts of Paul Ackerman and Eddie Mulder they now come with recommendations for torque tightening. Getting them to give up torque figures was a battle. Ten odd years ago they were having nothing to do with torque wrenches and stubbornly held out giving only stretch figures. This was not accepted by dealers, who for what ever reason, only wanted torque figures. Then there is the issue of resizing the rods once the new ARP bolts are torqued. With increased clamping the big end of the rod will no longer be round. To finish the rods at the factory they were finished honed after the rods were torqued. Because the ARP bolts distort the big end more than the original bolts this needs to be repeated. Although they have been available, from us and other suppliers, for the 650 for more than ten years, they have not really caught on. I base this on my sales and discussions I have with dealers about their reluctance to use them.

Why don't you just tell us?

I think I have when I answered Hillbilly...

i've never measured con rod bolt stretch, just used a torque wrench. but i also always bought new stock bolts whenever i had the caps off. not all that often, but often enough.

it seemed really wasteful, so now i have little plastic drawers with rod bolts that i won't use but can't bring myself to throw away.

nuts too

Great info. Always great to hear especially about the racing. Really gets me going. With regard to the nuts, I recall a number of different types on the bikes. One case of a '73 Trident comes to mind c1976. One conrod's nuts unscrewed with disastrous result. I saw the pieces, the nuts had no self locking power! Please share your thoughts on this, were there bad ones, etc.?

Another story comes to mind of someone using nyloc nuts. The tale went that the nylon melted with yes, another disaster.

In my misguided past I rebuilt a A65 BSA and used Triumph rod bolt nuts.The nuts were too long and the locking section didn't make proper contact with the bolt .So I used Loctite...this was 1974 when I was even more stupid than now...I sold the bike before finishing it and the buyer got it running and rode about 1000 miles when the nuts got loose. He heard the knock and fixed the problem before a rod exited the crankcase.
And my usual hot rod stories....The powerful V-8's have a connecting rod like a Triumph but all steel. No locking devices,just a nut and bolt. They never come loose. I believe the olded Honda 750's also had just plain nut ?
The after market rods in my Triumphs have the bolt screwed into the rod, no nut, no locking device...
So...Triumphs need a locking nut because of vibration? Or the rods flex? Or the bolts flex ?. But since a Triumph rod and bolts can handle racing stresses they must rugged enough not to flex...
And what about the Triumph ARP rod bolts...I have only pictures but it appears the nut is non locking...

very interesting

Interesting indeed Tony, and remember the 3 piece Triumph cranks were held together by six high tensile 1/4" bolts with non locking nuts. I never heard of problems in that area, at least not for road bikes...