Navigator connecting rods

All Lightweight conrods have a plain, un-bushed, hole in the small end for the gudgeon pin.

Often damaged by forcing rusty or burred gudgeon pin through on piston removal.

Heavyweights of the era had same diameter gudgeon pin but brass brush in the conrod small end. These bushes, which need shortening for Jubilee, perhaps Navigator/Electra, make a good repair. Need reaming to final bore size after pressing in, as you have noticed. Take care to keep parallel to big end.

Lubrication is via the hole through top of conrod small end. Countersunk slightly to catch a bit more oil. Any bush obviously needs drilling to restore lubrication hole.

I think it would be very unwise to put an undersize bush in a conrod to compensate for a worn gudgeon pin. The unworn parts of the pin, that go in the piston, have to pass through the conrod eye/bush on assembly.

Hoping all goes well for you John.

Peter 

Check out the attachments.........

The 500 & 600 motors used conrods that had bushed small ends.  Whereas the 650 and 750 end used rods with un-bushed small ends.  The Gudgeon pins for these rods ran in the plain Aluminium small end.

If you are going to bush the rod end, I recommend that the rod eye itself should be grooved in relation to the oil hole in case the bush turns and covers the source of lubrication.

Peter, bushed with Brass? are you sure? I would have thought phospherbronze? and the bush would be 'oversize'.

With regard to the 'worn gudgeon pin'  Peter points out that forcing the unworn part of the gudgeon pin through the bush is not the best way to go. Ie the worn gudgeon pin has become 'waisted'.  Better to fit new pins.

We get the same issue with wear in the 18D2 distributor shaft when the bush in the 18D2 body wears and then gets replaced, but the wasted shaft then has to 'push' its unworn part through the oversize new bush. But the 18D2 is a bit less critical than con rods and pistons!!

Al, you are right, bronze (copper zinc alloy) would likely be better than brass (copper tin alloy)

I recovered a pair of Jubilee conrods using the Dominator bush from RGM. They know more about materials than me. I used a light/medium interference fit and then had to ream the bores which shrink on fitting.

Peter 

Surely with this problem-The pins are too tight for the bushed rods so I have decided to re-bush (with aluminium) to suit the new pins.  Then you ream the bush that you have?

So now we learn about small end reaming -or NOT. But then we do not all have Mills and Hones in our work shop!

Just to clarify.

Bronze Composition Bronze consists of around 88% copper with about 12% tin and other metals (e.g., aluminum, zinc, nickel, manganese, lead) and sometimes other metalloids or nonmetals (arsenic, silicon, phosphorus).

Bronze minus tin but replaced with zinc is classed as brass.

I don't know but I suspect the grade of aluminium (7075?) in the small quantity that you require to be used as a small end bearing would be quite expensive than readily available bronze.

Hi JC.

         I'm intrigued through ignorance as to what areas of the "JP" pistons lend themselves to be lightened?

50 odd, plus years ago when I was tuning Villiers 9E's for Go Karting I would take a thou or two off the outer diameter of the piston 1/4" below the bottom ring land to 3/8" above the bottom of the skirt, this was done to reduce friction in that area not to reduce weight specifically although weight was reduced at the same time.

As for body weight I could do with putting some on, preferably the muscular kind as an aid to kick my twins over in a dignified manner.

Our Atlas came with Commando pistons that were considerably heavier than the orriginal fitment. . In an effort to reduce the horrendous vibration  i spent a few hours removing metal from inside the crown and knife edging the skirts . It was also clear that the gudgion pins had  considerably thicker walls than  those of other twins i have worked on. I did not have the engineering facilities to alter the pins but managed to get the weight down much closer to the orriginal fitment . With the knowledge that the Atlas was not going to be used hard I accept that there is a risk with such  modifications. Its possible that orriginal fitment pistons were much lighter and you could research this and perhaps find some used lighter pistons and get the bores machined to suit. You may have to look for some time. The Atlas still vibrates plenty enough  though , but is bearable with raised gearing and a compression plate under the barrel.

My Tuppence-worth....

1) Peter H's idea of using existing 500/600 bushes from RGM (other suppliers exist) sounds like the way to go. Ensure you are at the exact centre line and at 90° to the rod.

2) For sizing, the gudgeon pins should be a sliding fit in the rod, and tight (released by heat) fit in the pistons. Likewise, to fit, you must heat the pistons. I use a Heat Gun. Dims are: Gudgeon Pin = 0.6868"/0.6866" and the small end bore = 0.6878"/0.6873"

3) The oil hole, as Peter says, is lightly countersunk at the top to 'catch' oil. The rods originally WERE NOT scrolled - wiser heads than me, need to advise you about scrolling replacement bushes.

4) Care must be taken that the bush cannot rotate & block the oil hole. There are bearing retainer Loctite products out there - much stronger than Thread Lock. thread lock!

Hi John. Looks like you are having fun with your Navigator removing precision swarf from the pistons! 

Had you ridden the bike prior to this work so as to be able to assess your labours?

In deed some clarification re metals being used. Time and again people note they use Aluminium, yet 98% of the time it is not pure ally. As said here the Ally we have and use is often of unknown composition. Just remember that REAL Aluminium is very soft and we hardly ever come across it/use as such.

Removal of metal from Pistons to lighten, yes it is taken from inside the crown. Have done this with Reliant engines (think 850 Robin, but NOT used in the Robin) with some sucess in the past.

Hi Al. You should open a new topic on Norton & Reliant owners' stoicism.

I owned a "C" reg' Reliant van for 9 months in 1973. We called it "The Death Trap"!

I'm guessing that you were into sidecar racing against the likes of Florian Camathias?!!!