Small end bush

[john]

As I progess my latest project (18MS) I have got to the stripping down the engine stage. All as gone well so far, apart from when I separated the piston from the conrod.

The piston is a factory wire wound one, on standard size. Which gave me a good feeling that the engine maybe a good one and that it has not been messed about with too often. The problem is that when I took the gudgeon pin out I found that the bush to conrod fit was looser than the gudgeon pin to bush fit. As there is an oil hole through the conrod and bush that should line up I think we can make the assumption that the bush should not move.

Is it acceptable to lock tight the bush in, or does the bush need replacing.

Thanks for the help.

[paul knapp]

G'day John, while I always maintain Loctite was invented to hold the old British bangers together, I don't think that in your case it would be appropriate.
Heat destroys the mechanical properties of Loctite.....Fit a new bush.

Paul

[Don Madden]

A simple job. I have a special made bush install tool but a large, preferably fine thread bolt & nut, with two large washers & a spacer a little larger than the bush & longer than the small end bush does as well.

Scribe a mark or use a pencil across length of the bush in line with the oil hole. Place a large washer followed by the new bush on the bolt. Line the scribe mark with the oil hole in the small end & place the spacer, large washer & nut on the bolt. Run the nut down finger tight & verify the oil holes line up & the spacer will not foul the old bush. As you tighten the nut, the new bush will displace to old, pushing the old one out. Only push enough to line up the oil holes & remove the tooling.

You may have to ream the new bush when done. The pin must push in by thumb but with no play. A reamer is best for this. While some have used abrasive paper, I recommend against it.

Cheers, Don.

[GSAX1]

Using abrasive paper is very bad practice. It will leave particles embedded in the soft material that will cause wear forever after.

Michael

[wilko]

Whilst it sounds like a simple replacement job, i have had the experience of a sloppy bush in a BSA M20 and ordered a new replacement which also was a crappy fit. So i measured up and found the little end eye had worn to an oddball taper so had to junk the new bush and get the little end trued and an oversized bush made to suit! So make sure it has'nt been abused in the paste and measure accurately.Douglas

[john]

I have looked through my tool collection which I inherited, borrowed, stolen and in the worst case bought; and I have 7/8” machine reamer.

So the plan is that I press a new bush in assuming that there is enough metal in the conrod to allow an interference fit and ream out the bush using the back of the reamer where there is a little tapper to square the reamer.

Do I trust this will give the right fit or do the experts use an adjustable reamer to fine tune the fit?

Thanks again for the help.

[itma]

put the new bush in, then check the fit of the pin,
genuine bushes were machined to allow contraction when fitted, so often reaming was hardly needed.
Depending on the source of the new bush, a 7/8 reamer may be too tight to go in or too slack after,
In the manual you will see that all AMC dimensions had a plus minus factor.
Is the old bush white metal or brass?
It is very important that it goes in Square.

[john]

The bush is not white metal, what I think your saying is that I am over thinking the problem and I should just get on with it.

[paul knapp]

...and use an adjustable reamer in preferance to a machine reamer to... 'fine tune the fit'

[itma]

Its always worth asking for a second opinion...
Reason I asked is that the white metal bushes are 99% sure to be genuine AMC
Pattern bushes, are normally brass/bronze, its these that will have the greatest variation in tolerances.