Commando conrod

This is what happened to one of my conrods last weekend whilst racing at The Ridge in WA.

I was flat out in top gear at the end of the front straight when the rear wheel locked up.

I will divulge more when I've investigated the cause of the problem.



Please see my other posting for pictures of the Maney crankcases.

Does anybody have a spare Commando conrod (or set) they have hanging around that they could sell me?

Please contact me personally, off the forum listing.

Thanks

That is the most unusual rod damage I've seen especially with the bolts still holding on. Looks like crank flex might of put a bind on the big end. Need more info to make sense of this. What rpms were reached? TC ran Norton rods in 150 hp engines to 8000+ w/o issue, so I stiil highly suspect something else did the rod in but of course don't know if that's so yet. I suppose its possible your engine can exceed rod capacity but thatds sure be permanent history of bragging rights.

hobot said:

That is the most unusual rod damage I've seen especially with the bolts still holding on. Looks like crank flex might of put a bind on the big end. Need more info to make sense of this. What rpms were reached? TC ran Norton rods in 150 hp engines to 8000+ w/o issue, so I stiil highly suspect something else did the rod in but of course don't know if that's so yet. I suppose its possible your engine can exceed rod capacity but thatds sure be permanent history of bragging rights.

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Insightful guesswork on hobot's part.

Pouchy(!?) you need to tell the whole story.

It looks like it might be broken .

Cases & Crank o.k. ? doingwell , if so .

Looks like the big end shell / bearing has picked up & spun .

Whadus the oil look like , may need a clean out .

Spun rod shell piling up to expand apart the big end makes some sense but I've seen a few of my own and they all tore up the shells to chewing gum pieces, so still mystery how an almost intact shell remains in this case.

I have a spare complete with bolts and cap factory rod in great like new un-re-touched condition and appearance for $75 + shipping if needed.

Rod is bent in fore/aft direction and would imply to me that the big end seized first for whatever reason, lack of oil? Does this make sense? Mark

With addition of your good observation of the rod shaft bent and the big end popped open, both proves the innate strenght of Norton factory rods and the weakness of everything else affecting them, like journal oil or distortion hang up kaboom, not at all the fault of the rod itself.

I wonder if other similar era brands have such fragile expensive engine failures.

hobot said:

That is the most unusual rod damage I've seen especially with the bolts still holding on. Looks like crank flex might of put a bind on the big end. Need more info to make sense of this. What rpms were reached? TC ran Norton rods in 150 hp engines to 8000+ w/o issue, so I stiil highly suspect something else did the rod in but of course don't know if that's so yet. I suppose its possible your engine can exceed rod capacity but thatds sure be permanent history of bragging rights.

Click to expand...

Saw a race Commando at Brands Hatch a long time ago with 2 snapped con rods and the barrel hanging up in the air :!:
Sorry, I don't have pictures.

That looks more like an Atlas conrod to me . I thought that the Commando Rod was thicker and stronger where it widened to accommodate the big end .

Fred

Commando era rods have a useless oil jet hole as left over useless siezure solution to what turned out to be a bad batch of pistons. I am not saying Norton rods don't break but by golly after what I've seen mine endure and survive and the more detailed exams of blow ups here and other forums, I remain of firm opinion that old Norton alloy rods only break After something else does first.
I used to think the Z-plates were the toughest part, not no more. Of course a unknown damaged Norton rod may well break first but then so do bolts and cranks if hidden damage lurking. One of the most dramatic of engine blow ups I've read of was a 850 just at warm up idle in drive way that damaged a car and home insides across the street. In the end you know I think all mc-ing is wasteful dangerous risk taking so if can't take the damage and injury - its not the best hobby for ya. I'm pretty sure I screwed up long term getting back into Norton after 3+ decades off any cycle.

Looking at the dark area on the piston crown.
Is there any indication of piston seizure near the bottom of the stroke?