Small end Reaming

[chappers1962]

Got a new JP piston for my 56 G3LS to replace the last one (also a JP piston) which has bad scoring marks (although the barrel is ok). The gudgeon pin is a tight fit in the new piston, but won't go through the small end bearing. Therefore planning to ream out using an adjustable reamer. Question is will the relatively cheap reamers on eBay/ amazon (£20) do the job or is it best to have an engineering firm do it? The pin measures in at .875 which is in the range of a H10 adjustable reamer.


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[Greybeard]

I used an adjustable reamer when I did the bushes in my Ariel single and the B31. Theyve been fine since. Increase the reamer diameter in tiny stages, keep it square to the rod and never turn it anticlockwise as youll dull the cutting edge. Chances are youll find that you dont need to remove much at all if youve not fitted a new bush. Aim for a nice sliding fit in the bush. Warm the piston before fitting the pin and youll find it slides through the pison easily.
Dont forget to stuff the crankcase mouth with plenty of rags to stop any debris dropping in there and avoid pushing sideways on the conrod.

Steve

[chappers1962]

Many thanks Steve


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[Andy51]

Over 40 years ago I scraped a G80 small end bush in with a Stanley knife blade held one hand either side of the small end (engine in frame and crankshaft in engine, just a few rags to stop bits falling in and save knocking conrod against crankcase) to give even pressure, making sure I did it evenly all round to keep bush hole as circular as possible. It went together perfectly afterwards and was still going strong many miles and years later when I sold it. Cheers, Andy

[chappers1962]

Thanks Andy - bought a £17 adjustable reamer from eBay safe in the knowledge that it will do the job ok provided I take my time. I trained in the aircraft industry and therefore was a bit sceptical whether a cheap tool would do a precision job,; also didn't want to buy a quality tool that cost more than the piston.


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