connecting rod
- Thread starter zenand
- Start date
- Status
- Joined
- Aug 21, 2006
- Messages
- 748
zenand said:
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.
- Joined
- Aug 21, 2006
- Messages
- 748
ludwig said:
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!!
- Joined
- Oct 19, 2005
- Messages
- 18,978
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
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
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.
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.
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.
- Joined
- Nov 6, 2008
- Messages
- 502
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
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.
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.
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.
lcrken
VIP MEMBER
- Joined
- Mar 15, 2009
- Messages
- 5,035
RennieK said:
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
- Status
