How do you ream a bushing?

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clanger9
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How do you ream a bushing?

Post by clanger9 »

Yes, that's possibly a dumb question, but you'll have to excuse me. I'm from a generation where bearings usually "just fit" and I've never had to ream a bushing before. ;)

According to the manual, I need to ream the layshaft bush in a Lightweight gearbox .6260" to .6255". That figures - I tried my new bush on the layshaft and the hole is indeed too small...

I have an adjustable H6 hand reamer here (19/32" - 21/32"). Will that do the job?

Do I fit the bushing in the casing first (with epoxy resin to make sure it doesn't come loose), then ream it?
Presumably, its just a case of going slow & steady using plenty of cutting oil?
How do I make sure I ream the bushing straight?

I can't imagine the clearance is super-critical, given the very oval shape of all three old layshaft bushes I have here.
Hopefully it'll be straightforward, but any advice to help me avoid wrecking the new bush would be appreciated...
1989 Moto Morini Dart 350
1993 Ducati 750SS
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Ozmadman
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Re: How do you ream a bushing?

Post by Ozmadman »

Firstly, make sure you have the correct bush (see the picture, you should have the one with the thicker flange)) If you got the bush from club spares it is likely the incorrect type (there is a long thread by me on here somewhere but if you fit that shallow bush then the top gear on the layshaft will wreck the casing!!! Any problems then Andrew engineering have the correct size one. I have done a few of these and never had to ream any of them. Having said that Andrew Engineering do list an undersize one for some strange reason so you may have that. If should be a tight fit but I still use a bit of Loctite to be sure as they do come loose sometimes. As for reaming, it will only be a fraction and it is not hyper critical either so I would just use a bit of fine wet and dry on a piece of dowel to hone it to the correct size and clean it thoroughly before fitting or of course get the standard one from Andrews
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Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
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clanger9
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Re: How do you ream a bushing?

Post by clanger9 »

Thanks, Paul. I got mine from Andrew Engineering and it is the correct type. Club spares no longer stock this part.
The bush feels a little tight on the layshaft (and I don't want it to seize up) so I think it needs a light ream - or even a hone as you suggest.
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Mick D
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Re: How do you ream a bushing?

Post by Mick D »

Hi

Without wishing to sound patronising, it doesn't sound like you have the facilities to do this, it's probably a task for a local engineering firm.
The bush should, ideally, be fitted in the case as should whatever secures the other end of the shaft. The cases are then assembled and the bush is line reamed to ensure concentricity to the other bearing / bush. This will involve a reamer that can accommodate an adaptor to centre the end in the bearing / bush not being reamed.
Failing this the case with bush installed could set up on a lathe / mill and the bush reamed perpendicular to the joint.

Personally I'd shy away from reaming by hand.

Regards Mick
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Ozmadman
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Re: How do you ream a bushing?

Post by Ozmadman »

Yes, technically what you say and the procedure is correct but this is a basic 1960's box which is very agricultural and spending loads of cash to "do it properly" is just a waste of money when all it needs is freeing up a bit by the sounds of it. If you see the state these get into (generally due to people not keeping the oil level topped right up) and the amount of ovality in the bore and they still run then a bit of wet and dry in my book works wonders. Obviously the choice is up to clanger9
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
Mick D
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Re: How do you ream a bushing?

Post by Mick D »

Hi

Yes I agree, boxes have been abused in the past and will exhibit the signs, but Clanger9 has a new bush, not yet installed, for the sake of an hours work at an engineering facility he can have a gearbox close to as I believe it would have left AMC.

As you say the choice is his

Regards Mick
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clanger9
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Re: How do you ream a bushing?

Post by clanger9 »

Point taken Mick. A proper line bore from a machine shop would be the "correct" way to do it, but looking at the way the 'box is designed, it's not a critical part. It just needs easing a little. I'd have a completely different view about, say, the timing side crank bush.

As Paul says, yer average Lightweight is running around perfectly happy with a seriously oval layshaft bush. It's not a major issue; I'm only planning to replace the bush because the one in my box is also likely to be worn and I need to strip it down to fix a serious oil leak. I might as well renew the bush while I'm on...

As for how it left AMC: I wasn't around in 1966 (and I apologise if I offend any former AMC employees), but I'd be surprised if at that time there was any careful reaming going on on the Lightweight production line. Charming bikes they may be, but "precision engineering marvel" they ain't. :)
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Andy51
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Re: How do you ream a bushing?

Post by Andy51 »

Hi Clanger, you have 2 critical dimensions here - the bore of the bush and its outer diameter. The bush inner diameter will close up to an extent dependant on the the interference fit, as it is pressed in. I find the best way of fitting bushes is to get the inner diameter right - you have the reamer to achieve this, although I would bore it in a lathe, as reamers can 'smear' the metal. It is easier to get the bore right before inserting the bush as reaming it in situ can be tricky. The outer diameter is then turned to be a push fit in its housing, and it is secured in place with retaining compound ( e.g. Loctite or 3M) - the bore will then not close in on insertion. Hope this helps, Andy
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clanger9
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Re: How do you ream a bushing?

Post by clanger9 »

Thanks Andy, that's helpful. I figured I could ream it either before or after I fit it, just wasn't sure what was the right way to go. What you say makes a lot of sense.
I think I will be OK with the hand reamer, I just need to be very, very patient and only take the tiniest amount of material away to avoid smearing the bearing surface. I'll report back on the rebuild...
1989 Moto Morini Dart 350
1993 Ducati 750SS
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Ozmadman
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Re: How do you ream a bushing?

Post by Ozmadman »

clanger9 wrote:Point taken Mick. A proper line bore from a machine shop would be the "correct" way to do it, but looking at the way the 'box is designed, it's not a critical part. It just needs easing a little. I'd have a completely different view about, say, the timing side crank bush.
So did I in fact I got my timing bush reamed at a motorcycle engineer local to me at a cost of £72.00 (most of that cost was the time spent setting it all up)
As Paul says, yer average Lightweight is running around perfectly happy with a seriously oval layshaft bush. It's not a major issue; I'm only planning to replace the bush because the one in my box is also likely to be worn and I need to strip it down to fix a serious oil leak. I might as well renew the bush while I'm on...

As for how it left AMC: I wasn't around in 1966 (and I apologise if I offend any former AMC employees), but I'd be surprised if at that time there was any careful reaming going on on the Lightweight production line. Charming bikes they may be, but "precision engineering marvel" they ain't. :)
I was around in 1966 albeit it 13 years old!!! life all round was more basic and less precise than today!!
Last edited by Ozmadman on Sat May 06, 2017 1:29 am, edited 2 times in total.
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
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