How to ream a small end bush?

[thornebt]

I've got a small engine that will probably need a rebore and a new small end bush reamed in. It could possibly not need reaming but I'm just thinking ahead. I can see that adjustable reamers are available on Ebay very cheaply - about £8.00. I could use a wooden dowel with soapy wet and dry and I wonder if that would be a gentler way of doing it so more likely to keep nice and straight. The conrod is fitted to the crankshaft so not easy to put in a vice etc.

Clearly it's important to do this job very carefully and slowly but I'd welcome any advice from people who have done this job before.

Cheers. Bruce.

[Mick D]

Hi

Not something I'd attempt in situ but if you're determined I'd suggest you use an expanding reamer - place it in the bush and expand it to just nip, rotate carefully, adjust to be free and remove, try the gudgeon pin in the bush - repeat as necessary. Turning the reamer the bare minimum of times will help to maintain the bore perpendicular to the con rod.

Regards Mick

[Ozmadman]

And block up any gaps around the con rod/crankcase!!

[Andy51]

Many years ago, as very much a tyro mechanic, I scraped in the small end bush of my G80 with a Stanley knife blade (no handle) held one hand either side of the bush to provide a tolerably even pressure. It worked and the bike gave me many thousands of miles of service before I eventually sold it to buy a K******i - as you did in those days! I am not recommending this method, but it worked then! Andy

[Expat]

You probably know this so apologies if needed in advance.

Keep rotating the reamer in the same direction ie clockwise when you withdraw it.

Steve

[JimFitz]

Many years ago, as very much a tyro mechanic, I scraped in the small end bush of my G80 with a Stanley knife blade (no handle) held one hand either side of the bush to provide a tolerably even pressure. It worked and the bike gave me many thousands of miles of service before I eventually sold it to buy a K******i - as you did in those days! I am not recommending this method, but it worked then! Andy

Nothing wrong with that Andy. White metal big end and mainshaft shells were scraped to give a good fit back in the day.

Jim

[thornebt]

Thanks for the advice everyone. The crankshaft is out of the engine so there's no danger of bits being dropped in the crankcase. Obviously I don't want to disassemble the crankshaft just to ream the bush. You never know, I might be lucky and the gudgeon pin could be a nice fit without any reaming of the small end bush.

Cheers. Bruce.

[56G80S]

Just to add, I've done this twice only on the G80S.

Both times I've borrowed an adjustable reamer. The last time was the best as it was an older piece of German kit. The bottome half was in the framed and as mentioned in previous post I packed the crankcase moth with clean rags. I had also made up a couple of soft wooden blocks to hold the conrod steady and avoid rock.

All good. But I did remember my Dad's advice, it's easy to remove / cut away but much more difficult to put material back. Patience and frequent re-introduction of of the "mating" parts is the key.

Best

Johnny B

[Braaap]

i would take this job to a reputable engine reconditioning shop... and have them hone it to size.
Then it will be straight.
Having said that... the little end in my G3L is a scraped fit. And has run fine at 70 mph all day, for a few years.
I would think very very carefully before putting a hand ream in there.

[56G80S]

Stuart is clearly a more than competent engineer and sure his advice is worth having.

Last time I went to a previously reputable engineering shop they ignored my advice about how to do a job I'd done successfully before (fitting valve guides in the G80S) treated it like a car head, flogged them out cold, tried to fit the inlet guide in the exhaust while cold and removed and tried to refit by driving up out of the head.

Cost me a packet to have it put right by T&L Engineering who made up an oversize exhaust guide to make up the slack created.

Make sure whoever does work for you understands vintage kit. These aren't swiss watches though.

Johnny B