Con Rods

So, kind of new to Norton bottom ends (there's a first time for everything), but as I've been mulling this over recently I noticed that the con rod bolts are located on the underside as assembled - so when rebuilding is the procedure to attach the rods and then assemble cases around the completed crankshaft/rod assembly? Otherwise, you would not have access to the nuts that secure the con rods, yes? Seems like an odd approach - any thoughts on why didn't the design reverse the direction and have the nuts face up where they would be accessible? Seems it would allow more clearance below this way...

Thanks,

-kjo

bostonkevino said:

I noticed that the con rod bolts are located on the underside as assembled - so when rebuilding is the procedure to attach the rods and then assemble cases around the completed crankshaft/rod assembly?

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Yes.

bostonkevino said:

Otherwise, you would not have access to the nuts that secure the con rods, yes? Seems like an odd approach - any thoughts on why didn't the design reverse the direction and have the nuts face up where they would be accessible? Seems it would allow more clearance below this way...

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It's reasonably standard practice for many conrod assemblies to have the nuts at the bottom.

As L.A.B. says its standard practice in fact I don't think I have ever seen in done differently.

If you did have the nuts on the rod side of the cap you would have to remove piston for access to nut which would not be possible on engine that didn't have removable cylinder (not issue with commando i know but with other engines). Also once rods are in crankcase it is much harder to verify they move freely on crank unlike when they are assembled outside the cases first.

I agree with both posters and would add that the engine designers probably figure that any engine requiring big ends to be changed probably requires the crank to be at least properly checked for re-grinding / polishing a d to have the sludge trap cleaned.

i think they'd also say that if big ends have reached the end of their service life, main bearings and cams will probably have also reached the end of their service life.

In short, the bottom end would be seen as a combined 'system' that requires many things to be done at the same time once sufficient use has deemed the big ends unserviceable and thus the bottom end needs splitting anyway.

For the new motor for my bike.

Nice rod. Did you ask of it to by made that way or did it just come supplied like that?
I have seen steel rods with no nuts but a bolt or stud screwing straight in the rod before with the reasoning behind it to lose the weight of the nut. Your cap looks very light so was that the idea over the normal design? Plus it looks to benefit from increasing the clearance between the lower area of crankcase.

toppy said:

Nice rod. Did you ask of it to by made that way or did it just come supplied like that?
I have seen steel rods with no nuts but a bolt or stud screwing straight in the rod before with the reasoning behind it to lose the weight of the nut. Your cap looks very light so was that the idea over the normal design? Plus it looks to benefit from increasing the clearance between the lower area of crankcase.

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The reason is simply that with my 92mm stroke and 2 inch rod journal there was no room for a bolt head down below.
They are a custom design. Jim

comnoz said:

The reason is simply that with my 92mm stroke and 2 inch rod journal there was no room for a bolt head down below.
They are a custom design. Jim

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Assuming the motor of them is of the Norton twin type what will be it displacement?

toppy said:

comnoz said:

The reason is simply that with my 92mm stroke and 2 inch rod journal there was no room for a bolt head down below.
They are a custom design. Jim

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Assuming the motor of them is of the Norton twin type what will be it displacement?

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It will have the same bore/stroke as my present motor. 924cc

Jim will those rods require a small end bush or will you use a coated gudgeon pin?

Brooking 850 said:

Jim will those rods require a small end bush or will you use a coated gudgeon pin?

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I use a small end bush. It makes the rod re-build-able.

I will also use a dlc coated pin with the bushing. Jim

comnoz said:

For the new motor for my bike.

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Leave it to you... Are you ready for my motor? Happy New Year.
When I saw this I you made me laugh.

Jim - nice rod. - Are Carillo easy to communicate with when they are supplying custom-made rods ? And have you considered Arrow titanium rods ?

acotrel said:

Jim - nice rod. - Are Carillo easy to communicate with when they are supplying custom-made rods ? And have you considered Arrow titanium rods ?

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Yeah, They are pretty easy. You just fill out a custom design form and hope they follow it. It took a couple times to get these right...

I ordered up Ti rods from Swanson Machine in Ohio a couple years ago. They got my money but I never got my rods.
No reply to e-mails, phone calls or letters. I should have stuck with Carrillo.

I have not talked to Arrow. Jim

toppy said:

As L.A.B. says its standard practice in fact I don't think I have ever seen in done differently.

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Standard practice but not exclusively. Check out a Triumph Tiger Cub con rod.

I have often wondered about titanium rods - the low mass is attractive. What concerns me is the loss of dimension when titanium components are subjected to repeated impact. Have you heard of anyone using them in a Commando motor ?

The Commonwealth Norton, for which I once rebuilt the engine (878 cc), and which I later bought, used custom Crower titanium rods. It was run several times at Daytona, and the rods were still good the last time I tore it down. I also have a set of extended length Crower titanium rods that I had made for a short stroke 750 with shorter pistons, which I never built. The problem I've seen with the Crower rods, is that the small end weight, which is where you gain most of the advantage of light rods, is only slightly less than standard Carrillo steel rods, significantly more than Jim Schmidt's light weight Carrillo rods, and way more than the stock aluminum rods. The big end weight on the later Crower rods is less than either the Carrillo or the stock rods, but that's rotating weight, not reciprocating, so isn't as significant. To gain the real benefit from titanium rods, they would need to be properly designed using FEA to optimize the design, not just copied from old steel rod designs, as the Crowers appeared to be. That's what the factory guys do for their titanium rods, and probably what Carrillo does for it's rods. It would be interesting to see how the weights would turn out for a Carrillo titanium Norton rod vs. their standard steel rod, but someone would have to cough up the cash to have some made, and it certainly won't be me.

Titanium rods for Norton's have been around for a long time. I used to have a titanium rod for my basket case Manx project that was made here in Southern California back in the '60s. It went with the project when I sold it.

Ken

acotrel said:

I have often wondered about titanium rods - the low mass is attractive. What concerns me is the loss of dimension when titanium components are subjected to repeated impact. Have you heard of anyone using them in a Commando motor ?

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Norman White used them, and was able to set a very tight squish....very expensive exercise...

When I was collecting components for my 920 I called Arrow to enquire about a pair of Titanium rods. They suggested that having a limited lifespan they would not really be suitable for a road going engine & also the price was twice that of Carrillos. I chose a pair of JS rods which are almost as light at the important end.
I was working on a friends RC30 a while ago & that bike has done 40,000 miles + on its Titanium rods so I think the lifespan issue isn't really a problem. The Honda rods have a special surface coating to prevent galling as they run in pairs on the same crankpin .

Martyn.