connecting rod

zenand · Feb 9, 2010

I'm a newbie to forums 1st question so be kind!! I'm installing commando rods in my atlas cafe racer and the small ends have a little ply in them and show alittle scoring. Can they have bushings installed? where do I find these bushings? THANXS!!!

tpeever · Feb 9, 2010

zenand said:
I'm a newbie to forums 1st question so be kind!! I'm installing commando rods in my atlas cafe racer and the small ends have a little ply in them and show alittle scoring. Can they have bushings installed? where do I find these bushings? THANXS!!!

Most of the Commando parts dealers should sell them. You will need to press out the old ones and press the new ones back in. You will also need to size them to your wristpins. I had this done by a specialty machine shop for my recent Dominator restoration as I do not have the proper equipment to do it myself. You need to make sure the bushings are reamed perfectly square and with the proper clearance for your pins.

RennieK · Feb 9, 2010

Also if they weren't designed for bushings and you enlarge the small end bore for bushings will there be enough strength left on the top end of the rod? It might be better to go for .010 over size wrist pins which shouldn't be too hard to do.

tpeever · Feb 9, 2010

ludwig said:
Commando conrods don't have small end bushings .
Probably it is possible to install them , but is it worth it ?

Had the pistons off my Commando two years ago and I could have sworn they had bushings!! I certainly remember my Matchless G12 not having them as at the time I thought it was odd not to have any sort of bearing there. Memory ain't what it used to be. Getting old sucks!!

RennieK · Feb 9, 2010

tpeever said:
[I certainly remember my Matchless G12 not having them as at the time I thought it was odd not to have any sort of bearing there.

I think many of us had that feeling when we fist saw our Norton rods.

pbmw · Feb 9, 2010

I was pretty shocked years ago to discover my Atlas didn't have bearings in the little end. Kinda chuckled about it ever since.

Hobot · Feb 9, 2010

While Norton rods thread is on,
can someone set me straight on orientation refitting them.
Where should rod oil jet face, to inside or outside of bore?
Is there any mark or issue for which way rods should face camshaft?
I was asked this but don't remember now for sure but will need
to this spring.

BTW oil holes are left over useless solution to early siezures
that turned out to be bad piston batch. There is not
nearly enough oil flow for signifcant cooling and many
racers block off oil jets and Carrilo rods don't have them.

hobot

RennieK · Feb 9, 2010

The oil jet faces outwards and the lock tabs on the shells are on the same side across from each other when assembled but it doesn't matter otherwise which way the rods face as long as you are using new bearings of coarse. Caps are scribed to the rod on one side.

Flo · Feb 10, 2010

While on the subject of rods & small end bushes. I believe that (or used to) be able to buy thin walled bronze bushes for Commando rods. Bore the rods out, press then in & resize them. Commando rods are made from L77, the forged equivelent of L168 bar. I would use bushes made from L168, same expansion rate. I have done this a couple of times.
Matchless singles use similar Al.Alloy in their steel rods, when they should be using bronze.
Boring the small end out will not weaken it to any degree, a substantual amount of material can be removed from the top of the small end for racing. All the force is downwards.

chris plant · Feb 11, 2010

flo, all the force is not downwards,when a race engineer measures con rods for spec he is more concerned with stretch as opposed to compression {basically rods dont compress with the force above them but they do stretch with the force of stopping the pistons at tdc } however i agree with with your other comments regarding bushes.it can be done successfully and a lot cheaper than new rods

kommando · Feb 12, 2010

In modern diesel engines the small end bushes are truncated, they are wider at the bottom than at the top. Cummins Ford Volvo to name a few have gone this way.

RennieK · Feb 12, 2010

I'm not sure where stock con rods fail under race conditions but they are a commonly substituted part. I don't think the original design was overly robust so alterations to the design other than overall polishing are risky business. I would think the neck below the small end would be typically the 1st. place for stretching to begin. Given the same rods are used on the much heavier 850 pistons and cranks you may get away with thin bushings on the 750 but is this work worth it on used rods in the 1st place as Ludwig mentioned above.

Flo · Feb 12, 2010

A lot of rods that have broke have gone just above the big end, due to lubrication failure. The big end can sieze & just rip the lower half of the con rod off. I had a small end sieze on an Ariel Huntmaster once at high speed ( yes, a whole 100mph), again an Ally. rod, luckily it just ripped the small end bush away from the aluminium.
I just steer clear now from a certain make of oil, one which a lot of people recommend, but I won't go into that.
Is it worth renewing the small end? Well maybe if you can do it yourself or if somebody can do it at a reasonable cost, but it is worth checking the rod all over first & for ovality in the big end.

RennieK · Feb 12, 2010

Carrillo makes lighter wrist pins for Nortons so it would be simple if they could supply a .010 oversize and just enlarge the rod and piston.

lcrken · Feb 12, 2010

RennieK said:
I'm not sure where stock con rods fail under race conditions but they are a commonly substituted part. I don't think the original design was overly robust so alterations to the design other than overall polishing are risky business. I would think the neck below the small end would be typically the 1st. place for stretching to begin. Given the same rods are used on the much heavier 850 pistons and cranks you may get away with thin bushings on the 750 but is this work worth it on used rods in the 1st place as Ludwig mentioned above.

I've never broken a stock rod, but have found several with cracks after racing use (yes, I replaced them!). All were cracked at the pin end, below the pin bore. Typically the bad ones looked like a spiderweb. I've seen broken stock rods in other racer's bikes that broke at the big end. Years ago, my magnaflux guy found a crack on one of my steel caps, but he said that was really unusual. I've also had a couple used rod bolts rejected for cracks, so maybe replacing them regularly isn't such a bad idea.

I've never tried to bush a stock alloy rod, but I have run them with the small end bored out for a larger pin (the old Fair Spares 920 pistons), and had no problems with them.

Ken