Author Topic: conrod bolts  (Read 2244 times)

Offline olev

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conrod bolts
« on: 15.02. 2009 01:57 »
Gday,
The star twin's small journal crank and rods should be back from the grinders some time soon (I hope)
I have all the information and parts required to rebuild the bottom end except for conrod bolts.
The general concensus is to buy new bolts and nuts. The internet forum searches I've done has only put the wind up me. I haven't found a recommended bolt and nut set anywhere. Even SRM gets bagged and nobody gets a tick. which is a worry considering the cost of the things.
They talk about rolled and machined threads and different steels. I know..Iknow I read too much and should spend more time in the pub.
The motor will not be travelling huge kilometers, and there is a temptation to just buy anybodys or use the original bolts with new nuts. however I'd prefer to do things right and do them once.
Has anyone had trouble with conrod bolts stretching??
Is there a quality set available out there??
Is the whole saga a load of manure??
Will Elizabeth eventually find true love??
 ........anyone??
cheers

Richard

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Re: conrod bolts
« Reply #1 on: 15.02. 2009 19:49 »
 Definately fit new bolts and try to find bolts that have had a rolled thread as these are less prone to fracture problems
At least that is what the experts have told me.
I secured mine from Kidderminster Motorcyles (UK) who are knowledgable and extremely helpful
Richard

Offline beezalex

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Re: conrod bolts
« Reply #2 on: 16.02. 2009 16:39 »
Olev,

I disagree about the new nuts and bolts.  Under normal running conditions, there is no reason the originals should wear out.  I know they're old, but a)they never see enough heat to change material properties and b)they are under CONSTANT tension unless they've seen a catastrophic bearing failure.  I DEFINITELY would not put a generic bolt in there, even if it's supposed to be high-tensile (grade 8).  As long as the threads are OK on the stock items, I re-use them on street bikes (and cars, for that matter) and I have not had a problem.
Alex

Too many BSA's


Richard

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Re: conrod bolts
« Reply #3 on: 16.02. 2009 18:58 »
olev
I can not agree with your view on this as it is not a case of them wearing out
1) the nuts are the locknut type and once undone one could argue that they may not lock securley

2) the bolts are torqued up so therefore it is reasonable to say they are already stretched so when reused they are stretched some more as they are retorqued up.

Of course if reused they may never fail but it only takes one to fail and ruin the motor.
Most  dealers that know anything about engineering should only stock high quality bolts
Richard

Offline A10Boy

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Re: conrod bolts
« Reply #4 on: 16.02. 2009 19:42 »
When I re-build [comparatively] high revving engines I always use new big end bolts, I would never use "generic" bolts. I would have thought that items supplied by SRM would be top quality and am surprised to hear an opinion to the contrary.

Where did you hear that ?

Regards

Andy

1960 A10 - Black Golden Flash
Plus
1974 Kawasaki Z1a
Yam XJR 1300

Offline beezalex

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Re: conrod bolts
« Reply #5 on: 16.02. 2009 20:53 »
Richard, with all due respect, I realize your two points represent the conventional wisdom, but that conventional wisdom conforms neither to engineering principles or what I have heard from others.  I have not personally heard from one person who re-used good stock conrod bolts in a street application and had them fail.  I've personally heard from two people who have had failures with aftermarket replacements.  I realize it's not statistically significant, but it is the data I have.

Also,
1)We're still talking about the bolts, right?  I said nothing of nuts, but in this case, the original nuts are not locking, so it doesn't matter and there is no problem re-using them.
2)The bolts are preloaded and torqued to be elastically deformed ONLY.  That is what they are designed to do and to stay under constant tension regardless of external load.  Therefore, unless there is a catastrophic failure of some sort, there is not reason the bolt should plastically (irreversibly) deform.  I suppose that there's a remote possibility that the bolts may have been overtorqued by some ham-fisted mechanic without damaging the threads, and I guess that is a concious risk I'd be willing to take over an un-tested bolt of dubious origin.

BTW, EVERY mass-produced bolt has its threads rolled, but I would not put a grade 5 bolt from the hardware store on a con rod.
Alex

Too many BSA's


Richard

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Re: conrod bolts
« Reply #6 on: 16.02. 2009 22:16 »

 Firstly my second post was meant for beezalex not Olev

Beezalex
I can see your point of view regarding using old bolts, BUT one may not know how many times these bolts have been used for instance if you obtained a bike and stripped it down and the shells were 20 thou oversize it may mean that the crank could have already have had two regrinds (unless you knew the complete history of the engine) and the bolts could also, if the engine was being rebuilt by some one with your view, have been refitted twice more since new also they could well have been over tightened.

I have the view that having bought new bolts and nuts with rolled threads from a decent supplier with a reputation to uphold I would be a lot happier than if I was trusting old fatigued bolts and nuts.

We both have different opinions and may not have helped Olev with his original question, and for that I must apologise but hey this is life and it would be a boring world if we all agreed 100% of the time!!
Sorry Olev I hope someone else wades in and it makes it a bit easier to decide
Richard

Offline olev

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Re: conrod bolts
« Reply #7 on: 10.03. 2009 12:14 »
I've received a set of conrod bolts and nuts for the A7's small journal crank.
The suppliers (MCA) use part number 67-1535 which doesn't match anything in my books.
Maybe its for a small journal crank after 1952 where my parts book stops. I don't really care but would like to use the correct torque setting for the particular bolt. They look good quality which is comforting as they cost an arm and a leg. The new ones have a finer thread and locknut rather than the castellated nuts and pin.
The service sheet reckons 10 ft/lbs for the early ones, 8.5 ft/lbs for the later type and 22 ft/lbs from 1956 on. MCA are a bit slack answering emails so my guess is 22 ft/lbs.
Anyone know where the 67-1535's come from and/or their torque settings??
cheers

Online bsa-bill

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Re: conrod bolts
« Reply #8 on: 10.03. 2009 13:08 »
 Draganfly list this as
   

67-1535 - Big-end bolt, small journal - A7/SS -1960-62
Suprceded to - 10419-54Anut

The year seems a bit funny I thought small journals were an early thing - perhaps not or maybe just a typo

22 lbs is correctI think

All the best - Bill
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline BSA500

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Removing con rod bolts
« Reply #9 on: 26.05. 2016 21:34 »
A hopefully easy one. How do you remove the con rod bolts from the con rod without any damage occuring. They appear to be a tad tight-heat and a light tap ????

Online chaterlea25

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Re: conrod bolts
« Reply #10 on: 26.05. 2016 23:30 »
Hi,
No heat,
They should move when tapped with a  mallet
Make sure to align the eccentric  bolt head when fitting the new bolts
Search the forum for ARP rod bolt tightening, You should get some of their thread lube with the bolts

John
1961 Super Rocket
1963 RGS (ongoing)

Offline BSA500

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Re: conrod bolts
« Reply #11 on: 27.05. 2016 08:31 »
Thanks I just like to be careful when waving a mallet/hammer near a con rod  *smile*

Offline bikerbob

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Re: conrod bolts
« Reply #12 on: 27.05. 2016 14:11 »
I would never knowingly buy anything from MCA I have had push rods that were too short valve adjusters that were very brittle and magneto brushes that were too soft this was admittedly about 20 years ago but once bitten or three times bitten in my case maybe they have improved their quality but I will avoid if possible. I am not surprised that you have communication problems with them I had the same problem 20 years ago before emails. In the case of the push rods they denied there was anything wrong even though I provided them with a BSA original rod they just told me that if not satisfied with their products to go elsewhere.

Online edboy

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Re: conrod bolts
« Reply #13 on: 27.05. 2016 19:36 »
 i have found that the conrod bolt holes burr easily and the conrod bolt becomes too tight. as already posted the bolts should be easy to move when tapped so i ream out the conrod. 22ft.1b with no friction thanks. i reuse the conrod bolts if they look in good condition and not bent.i also clean up the oval part where the conrod bolt sits- no burrs or swarf wanted there either. nuts are cheap and best to renew.

Online bsa-bill

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Re: conrod bolts
« Reply #14 on: 27.05. 2016 19:57 »
I dare to question wiser heads but I understood the critical thing with bolts was how much they had stretched during  torquing.
If the bolts stretch and stay stretched when removed are they still allright to torque and stretch further or do they once removed revert to their original length (before torqued )
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco