Modification to big end shells

I potentially have the need to modify a set of big end shells to reduce their width to suit my application. They are being used on a NRE Weslake crank and I need to reduce their width by about .060in.
They will be fitted to a Carillo con rod but are otherwise similar to what’s in a Commando.
I’m wondering if any of the resident custom engine builders on the forum here have had to do this in the past and what techniques they've used. I have a small mill and a lathe and could conceivably make a jig for machining them. I am concerned however about any burring that might be raised on the machined edge and if something as simple as hand scraping the edge would be OK.
I’d also be interested in how the manufacturers make the shells and what process they use for taking them to the finished width ( perhaps a question for Kommando?)

I've seen shells modified simply by filing (or grinding) them - in all sorts of dimensions.
This used to be a common bodge to get more life out of old shells,
when they were simply unavailable - or new ones were unaffordable.
Matchy twins reportedly had to use an "adjusted" mini shell in the centre bearing, until quite recently.

I think they are always filed/ground away (direction) from the inner surface, to avoid your burring upwards.
And the triple layer type shells must on no account be scraped on the working surface,
the outer working layer can be exceptionally thin.
What you mention wouldn't involve this though.
Have fun !

Are spares not available for these ?
That seems like an oversight by someone .

The usual method for narrowing rod bearings is with a fixture to hold them in a lathe. This is a picture of one from another forum.



Ken

My, bodging has been developed to a fine art !

Thanks for the replies Ken & Rohan
I did hear from an auto machinist here in Seattle that he could do the job on his mill if I supplied a sacrificial conrod to use as a quick and dirty jig. I do have just such a conrod lying around – it’s now about half the length of a standard one but the big end is still intact. (never throw anything away)
Since the machinist can’t get to it for a couple of weeks I’ll probably have a go myself. I am leaning towards chucking a mandrel in the lathe and then clamping the shells to it using the scrap conrod. Then facing the edges of the shells using a boring bar.

Is this topic a result of continuing problems with Noursh Engineering? Are they unable to supply?

Sadly I can't recall the details, so what I'm about to say ain't much help, but, I am pretty certain that Nourish did not design his own shells and that they are actually off the shelf items commonly fitted in Brit cars from the period. Trouble is, I can't remember which one!

If you have a shop near you that specialise in MGs or Triumph cars or similar, it may be worth asking.

SeeleyWeslake said:

Thanks for the replies Ken & Rohan
I did hear from an auto machinist here in Seattle that he could do the job on his mill if I supplied a sacrificial conrod to use as a quick and dirty jig. I do have just such a conrod lying around – it’s now about half the length of a standard one but the big end is still intact. (never throw anything away)
Since the machinist can’t get to it for a couple of weeks I’ll probably have a go myself. I am leaning towards chucking a mandrel in the lathe and then clamping the shells to it using the scrap conrod. Then facing the edges of the shells using a boring bar.

Click to expand...

Take it over to Robert Seymour in tukwilla. He's a retired machinist who is also a renoun motorcycle guy. He's done a bunch of work for me when I modified my commando to use yamaha cast wheels. He goes by the nickname of "The great seymour".... because he's not some guy who's fooling around with some harbor freight milling machine. I WISH I grew up being his apprentice so I could learn from him. He's got a machine shop in the 6 car garage behind his house packed with industrial quality machinery. He's retired, so he'll likely tell you to stop by with your parts and he'll do what you want done in a day or two...

robert seymour
14452 56th Ave S
Tukwila WA 98168-4511

206 244 4563

You can tell him Frank (who's norton he did work on) recommended you call him... One look at his shop and you'll know you're in the right place.

A better answer is always to find existing shells of the right dimensions. Years ago a friend was working in a company which specialised in after-market rings bearings and pistons. He was able to do a search through the various catalogues for something which would work correctly.

Fast Eddie,
I did get these shells from the new Nourish and did contact them about it. I was looking to see if I could modify them myself just to save time. Chris at new Nourish did confirm that the batch he has were modified, but incorrectly, and is going to replace them with the correct size. Your recollection was the same as mine in that Dave N used a standard or catalog shell and modified the width to suit.
To Alan’s point, Dave N had already searched the catalogs and this solution was the best/most cost effective he came up with. I have never had a problem with his big shells in the 28 years I’ve been running this engine
o0norton0o,
Thanks for the info on a local machinist. It is becoming harder and harder to find local auto machinists who can do traditional reconditioning/machining work. It sounds like he could be a good resource since although I can do simple machining myself, if it involves precision engine components twirling around at 9K+, I prefer to have an experienced professional doing it.

It is never a good option to use non-standard or modified parts. If you machine the crown of a piston, every time you fit a replacement you have to replicate the modification. The Japanese never work on that basis. All you do is buy their bits and fit them. I think if I was using a Nourish shaft, I'd buy rods which were in common usage, even if I had to lengthen or shorten the barrel and I would modify the journals to accept commonly available shells.
Especially if you are racing - if you have to modify every time you fit a replacement part, it becomes a real pain.

There is one bike which is particularly bad with this sort of thing. With Vincents, everything is a special. It puts you completely at the mercy of the manufacturers' agents.

acotrel your reply left me somewhat fuming, let me explain, I have a Jap single where pistons and rings have become unobtainable no thanks to the Vincent boys who appear to have pinched the lot of them :!:
I now have fitted another Jap brand bike’s single piston, which I have had to modify to make everything fit- :?

acotrel said:

It is never a good option to use non-standard or modified parts. If you machine the crown of a piston, every time you fit a replacement you have to replicate the modification. The Japanese never work on that basis. All you do is buy their bits and fit them. I think if I was using a Nourish shaft, I'd buy rods which were in common usage, even if I had to lengthen or shorten the barrel and I would modify the journals to accept commonly available shells.
Especially if you are racing - if you have to modify every time you fit a replacement part, it becomes a real pain.

There is one bike which is particularly bad with this sort of thing. With Vincents, everything is a special. It puts you completely at the mercy of the manufacturers' agents.

Click to expand...

Strange logic from a racer...

What is race preparation about if not modifying parts to a greater or lesser extent...?!

I have modified BSA 350 pistons to fit in a Triumph 650 to create squish bands in the head. If one gets dinged, replicating the modification is a pain in the arse. However the pistons were much lighter than standard and gave a performance boost. It depends on how often you race. These days it would not be a problem for me. But when I was a kid, I used to race every month. In those days a Japanese bike with lots of throw-away parts was always a better option. This is the reason that the two-strokes killed off the manxes, plus they were faster.