"Cocked" rod bolts

[Truckedup]

Cocked as in not straight..I'm working on a modified vintage BSA motorcycle . Had a difficult time removing the connecting rod caps Ths engine last ran many years ago, history unknown..
Like many old British bikes, the rods are forged aluminum with bolts and nuts for the cap.It's an I beam style. These rods when newer were quite sturdy and used for racing.....The rod bolts appeared bent inward at the threaded end about .010. Removed the bolts, the cap appears to fit square on the rod. I had some NOS bolts and installed them..the bolts still are closer together at the end by .005. So I checked 4 other used rods, all the same.
I have experience with these old aluminum rods.If the big end hole goes out of round by .001, the rod is junk, this is the only hint before it breaks. Can't be fixed by resizing...But I have never seen ones like this....
I can assume no rod would be manufactured with cocked bolts? Can't tell if the rods were resized in the past but anyone have an idea what is going n here.?

[BCjohnny]

Big end has simply deformed and taken a set, despite the cap sitting 'square'

Aluminium, even forged, remains quite malleable ..... despite the substantial age

Other Brit manufacturers went over on some models to an Alum rod with a forged steel cap, which would suggest the caps however designed in Alum didn't have the rigidity required ...... puling the bolt thread ends in would surely be a symptom of this .....

[Truckedup]

Thanks....Best to consider the rods as scrap...New aftermarket aluminum or steel rods are available from the UK and USA...$400 a pair....Less expensive than risking sawing the engine in half from a broken rod

[PackardV8]

I have experience with these old aluminum rods.If the big end hole goes out of round by .001, the rod is junk, this is the only hint before it breaks. Can't be fixed by resizing.

Is this true for all forged and billet aluminum rods or only for those found in old Brit bikes?

[Truckedup]

Jack, it's true for the original forged alloy rods on the vintage British bikes when the engine is used in anger.
I have no idea if it's true for the aluminum aftermarket car rods.

[modok]

I would guess it has been re-sized. Check length.

I agree they "should" not be re-sized, but I do lots of things that "should" not be done. sorry.
people have different opinions on the matter, and that's fine.

[hoodeng]

The problem with all early British stuff [and American] is that the history is lost to time. These bikes on the whole were butchered to keep them running by people with no idea of what they were doing. When i got my first British bike in the late 60's there were people i held in awe of their ability's, after owning a number of bikes and having seen the outcome of some of their handy work, their highly elevated on pedestal status slipped to the level of someone i would not let put blades on my lawnmower.

I can still remember one guy touted as guru, honing rods with emery wrapped around an diagonally cut steel bar mounted in a lathe that could be expanded into a shape not used by any manufacturer, this was a vast improvement over emery wrapped around a wooden mandrel that operated on the same principal, it was not until i saw the workings of an engine reconditioning section using a Sunnen horizontal hone, that i came to understand the butchery that was passed as hand fitting skills.

I reluctantly do British bottom ends for this very reason,,if i do,, it will be, on a plain bottom end, hard chrome crank journals and a decent quality rod. If it is roller, an Alpha shaft and insert then size to clearance. A lot of British bottom ends can use American pinion rollers IE; 350/500 B31/33 BSA's can use a .250" x .600" Pan pinion roller, same applies for a large number of British roller bottom ends.

Alpha got a bad name undeserved by them when people would fit a rod insert then wind it over the rod rollers and pin, consequently the bottom end would fail in short notice. They surmised that because the kit was supplied with the insert over the rollers and pin that it was ready to go,, It wasn't, once the insert was installed in the rod it would mostly go out of round. I have shown a number of owners how rods are sized on the Sunnen, some still go away with the idea the pin kit is ready to go as supplied and that Alpha is junk.

After all that, new rods.

Cheers.

[Truckedup]

Most riders never push on these old turds so as long as the bearing inserts don't fall out all is good. If you like to use all the performance a suspect rod can have an unscheduled disassembly..

[turbo camino]

Well if it couldn't have been damaged in operation, and it couldn't have been machined wrong when it was made, what the hell is left to explain it? It has to be one of those two things, however unlikely you think either one to be.

[Truckedup]

Well if it couldn't have been damaged in operation, and it couldn't have been machined wrong when it was made, what the hell is left to explain it? It has to be one of those two things, however unlikely you think either one to be.

With age, 60 years, these rod bottom ends go out of round 90 degrees to the parting line. The usual explanation say the aluminum has been stressed beyond it's design limit....The cocked bolts must be caused by the rod "ears" that the bolts pass through getting distorted...Or something else..