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Loose Bearings

Graham Smith

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Am busy rebuilding the engine on Joshua’s 1979 Yamaha RD125DX.

Unfortunately, one of the crank bearings is a bit loose in the case.

Am after suggestions for the best type of Loctite to use?
 

CollingsBob

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Graham..I found these..




I also found suggestions for using masking tape or tin foil..
 

John Reynolds

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Graham

If the bearing is really loose you could try Loctite 660; it is suitable for filling gaps of up to 0.5mm. See data sheet
 

Attachments

  • Loctite 660-EN.pdf
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oexing

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No type of Loctite or any other equivalent will keep the bearing put when you try to glue it in a cold alu case. The heat growth at these dimensions is enough to undo the glue as you have to remember the bearing is steel and the case alu - with twice the growth. So really you have to drop the bearing in the heated case with Loctite applied to both items - quick !! I´d go for 100 degrees C of case for this.

Vic
 

Robert Watson

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Maybe you could loctite it and then stake it like we do with Vincent mains. Those are c/sunk screws and then the outer race ground with a dremel to match the c/sink so the screw holds the whole plot in place. Making a jig that slips in the bearing bore before the bearing goes in helps to put the screw in the exact right spot. 20180122_142403_HDR.jpg
 

MartynG

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No type of Loctite or any other equivalent will keep the bearing put when you try to glue it in a cold alu case. The heat growth at these dimensions is enough to undo the glue as you have to remember the bearing is steel and the case alu - with twice the growth. So really you have to drop the bearing in the heated case with Loctite applied to both items - quick !! I´d go for 100 degrees C of case for this.

Vic
Correct Vic -

That Loctite will grip in a fraction of a second - and once it does, it's a bugger to get it to release.

Martyn
 

Pete Appleton

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You could always just fix it properly, with metal. Can we see a picture? How loose do you mean?
 

nkt267

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Back in 1970 I used a ring of shim steel to hold the loose bearings into my 1932 sunbeam crankcases..they're still in place.
 

timetraveller

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Graham, it's probably not what you want to hear but Oexing and Pete probably have the right ideas. If it is intended to keep the bike for a long time then it would pay to do the job right. There are probably enough competent engineers in the club who would be prepared to help you out in view of the remarkable amount of work you put in. Let one of these masters of machining have a look at the job. I expect it would only be a relatively small job to machine out the bearing housing, make an insert and then shrink in a new bearing.
 

oexing

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Vincent,
basically you may be right, I cannot specify exact tempertures for hot glueing bearings in an alu case as no oversize is known. Also you don´t know how fast the Loctite cures while the bearing outer heats up in the hot case. I can definitely say cold fitting a bearing in an alu case is useless, tried it on the gearbox input bearing behind the clutch : After loctiting cold and heating it to operating temperature of around 80 degrees I had NO problem to knock it out with plastic hammer. Did same procedure at 100 degrees dropping in the bearing quick and later at same temperature it was very OK. There is a minor uncertainty about what amount of preload you´d get on the hot glued bearing at what chosen temperature so you better do a test before and feel. If you don´t like the feel of being too tight at working temperature you just heat the case to above 150 degrees and it will definitely be easy to knock out for next try at lower fitting temperature. Certainly it is safer to machine an adapter bush for exact shrink fits but this is often overkill when only a bit of oversize is to fix. Bad alignment of bearings would not be a matter with little wear in bores.
And NO, STAKING is CRAP !! It is a disgrace to any designer of machinery to try get him out of troubles with this bodge. Nor would I ever dare to tap the circumference of the main bearing seats as this will end in disaster for this highly loaded place !
I went for lipped outer roller races - no staking - and no big oversize bushes in the engine because I went all metric for sure , including all crankshaft sizes except for the oil pump worm and timing gear plus the ESA items. So when chosing a modern roller bearing you can get the 30x62x20 or x16 sizes and suitable lips on inner or outer races to your liking and assembling strategies and so no oversize boring in engine case is due , just licking up any wear from 63,5 mm imperial to install a reduction to 62 mm. The modern polyamid glas reinforced caged bearins are way higher load specified than the old all metal type, even when having all over smaller dimensions. The 1 " crank mainshaft can be bushed to 30 mm in no time to get to sizes then. Well, all depends on lots of factors , no easy out for all cases . . . .

Vic

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Robert Watson

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And yet my mains and many others have been THRASHED for 100's of thousands of miles with ZERO issues with the bearing moving. Mind you the OD of the bearings are hard chromed and ground to give a proper fit in the cases.

Perhaps when you have done a couple of hundred thousand km's mostly running two up with luggage, or lapping the IOM or getting a reputation for being just a bit wild you could give us a report on your Vincent!
 

oexing

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So, Robert, you are saying the typical shrink fit of outer races were crap at lots of engines ? You went for chroming the outer races in consequence as a cure . I´d agree with you on that but then all the staking done from day one was no real cure for poor fits obviously , a disgrace anyway, and all sorts of troubles starting from here like heavily ground crank pin nuts from walked outer races plus cracked bores etc. . I see one reason in no available lipped roller bearings in imperial sizes with lips on outer race in those times . At least I could not find any when making my mind up on strategies with my projects. So quite logically I went full metric for various motifs and lots of choices today.

Vic
 

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