Honing motor cycle small ends

I need to hone two new small end bushes that I have just made and fitted to the con rods of my 1920's motor cycle. Bushes are phosphor bronze and have an oil grove straight across the bore. They were reamed in the lathe to size (3/4" and then pushed in with the normal bolt and tube method. OK, so far so good, but the expected reduction in bore size has happened and I now need to remove approx 0.003". An expanding reamer might work but as the con rods are still in the engine, it may well end up with a slightly out of line bore. I am now thinking on the lines of making a hone for my electric drill. Simplest one would be a piece of round brass a fraction under size with a slot cut in it to take fine emery paper. Anyone got a better idea ? I do have a set of hones that are used for brake cylinder reconditioning, but they do not remove that much metal.

Mike.

Can you not just put the reamer back through them ?

I would not use emery paper in a drill myself, it would end making them bell mouthed which is not good.

Phil

The reamer will not produce a good enough finish and chance of getting it off square to the cylinder barrel.

Mike.

Start again, making allowance for this three thou. when making the new bushes?

I always clamp the con rod to the bed of the miller and bore the small end to size, knowing it is now square and parallel.

Colin

To do it in the mill is fine if you have an engine that is easy to strip down and easy to get out of the frame. I am changing the pistons in an engine that has been re-built, so this has to be done in situ.

Mike.

I've been doing this same job for years on Harley engines. I usually use an adjustable reamer. I hold the rod still by clamping it with two pieces of wood about 3/4" thick and 3" x 4" or so with two bolts through them so one each side of the rod and sit the the wood on the crankcase mouth and do up the bolts. With the rod held firm like this you can incrementally ream out the bushing. Reamer will usually follow the hole so it ends up square to the rod. Take multiple light cuts. Ream until the gudgeon pin is just a light push fit through the bush by thumb pressure. If in doubt make it a bit loose so it will not seize in operation. As Mr Harley said to Mr Davidson, a little extra clearance never got in the way.

Can check alignment afterwards by putting two pieces of 5/8" square key steel across the crankcase mouth and put the gudgeon pin in place and check it touches both sides.

I would not try to remove three thou with a brake hone etc as the hole could end up bellmouthed etc as that is a lot of metal to remove with a hone. And the piece of sandpaper flapping around works for small bore master cylinders on bikes where the rubber seal will take up any irregularity but is not suited to this job at all.

I sometimes finish off the last couple of tenths of a thou with a brake cyl hone just to give a good finish but definitely not much more than that.

Edited By Hopper on 10/05/2019 09:11:56

A hone for lapping car brake cylinders would be better than using emery paper. Available from car accessory and parts outlets.

Paul.

As Mr Harley said to Mr Davidson, a little extra clearance never got in the way.

I doubt that Mr Honda ever said that !

Nigel B

Good idea Hopper !! The bike is an Indian, so very similar design. I will steam out to the workshop and hopefully progress now !!

Mike.

Last time I did this was in 1974, but I used a plain purchased 3/4" reamer with a lead-in taper of a few thou on it and ran it through by hand, and the little end was still OK when I sold the bike 30k miles later. It was a BSA A10.

3 thou is a helluva lot to take out with emery, and as well as the bell mouth you've the potential of embedded grit gnawing away at your gudgeon pin to worry about.

Even if the reamed hole ends up a thou out of line, I'd think that's a good deal less of a problem.

Ream it, and if need be lap it the last few 1/10th of a thou with the right grade of Time Saver lapping compound, if you use ordinary grinding paste it would tend to become embedded in the bronze and finish off the steel crank pin in a fairly short time.

Ian S C

Indian, nice. What model?

But it was not until 50 years later that Mr Honda started bolting surplus military generator motors on to push bike frames.

Edited By Hopper on 10/05/2019 12:55:04

Thanks for advice Hopper,

all done now, as per your photos and pin is a nice sliding push fit.

Mike.

I have done little ends with an adjustable reamer for the last 50 years, still doing my pre war stuff in the same way.

Good result! Happy riding. If you don't try to keep up with the Harleys your Indian's little ends should last for many years.

The good thing about the old stuff, as Chris Evans points out, is that it is so over-engineered for such low horsepower that primitive old workshop methods work just fine. That's how they did it back in the day and it still works.

Hi Hopper, the bike is a 1929 101 Scout. Had it three years and nearly got it back in one piece. It will be nice to hear it running.!! Pretty scarce in UK, can't be more than half a dozen over here. The sidecar is a mixture of Harley and Indian and I had to modify the sidecar frame to fit the Indian location points. Not easy.

Mike.

Totally agree. The small ends really need to be bored parallel to the big ends. While a good (sharp) reamer will produce a size/plus hole with good repeatability it may not be the right size for the pin or a good enough finish. My preferred method is to bore a small end bush to within a couple of thou and then on to the (Delapena) hone to finish.

Velocette made some of their small ends neither metric or imperial in diameter to discourage the use of a reamer to finish the bore of the bush. Problem was that it was easy enough to get a reamer ground to the size required......

I good attempt to encourage getting the job done properly.

John

Nice one. Will make a handsome looking outfit. Enjoy.