Roller main bearing cage broken up

[TonyP]

Hi, I'm sure this is not a new issue and it will have happened to to someone else in the past.
Bike rebuilt by previous owner 3,000 miles ago. So engine all in good condition / not worn. I noticed primary chain noisy / loose recently, but thought oil probably low. Going through routine servicing to sort it,  I checked the engine sump strainer just in case......only to find 6 metal straps with snap marks and semicircle cut out at ends (where the rivets go) each being about 3/4 x 1/8 inch (and quite thin) sitting in the strainer.  Easy to identify the bits when put end to end as a bearing cage.
Question to members:- Is there any way I can split the crank case leaving the gearbox bits and associated crankshaft in situ on the right hand side (off side), Or do I have to completely strip the engine, and release the crankshaft completely in order to fit a new roller bearing on the drive side please?
Many thanks.

[BEESY]

What model of bike do you have?

[Pete C]

I would definitely strip it to make sure there is no other damage, or debris lurking inside.
Also you might find out why a main bearing failed so soon after a rebuild. If it was the result of a poor quality bearing, then what are the others like?

[DAVE BRADY]

Hi,

Splitting the cases without total disassembly is theoretically possible but assuming A10/A65, the cylinders will need to raised to undo the internal nut holding the cases together.  Resealing the cylinder base could be a problem and then the push rods will be out of place so the rocker box will need to come off etc.etc.
As said by Pete C, a strip down is the best option for getting the internals clean and checking any other damage to the timing side bush, crank pinion, oil pump drive would a good idea.
Please feed back on the make of the bearing.  There are lot of un-branded ones out there.

Dave.

[JulianS]

The other difficulty would be holding the crank firmly whilst removing the old bearing and fitting the new one- they are usually quite tight on the shaft. You may need to do it several times whilst adjustsing the end float.

If it was my bike, after finding bits in the sump, I would want to check the whole engine including all the oilways, the PRV, the pump, the sludge trap and the other bearings for damage and further debris.

[TonyP]

Hi and thanks to those replying. This is not the usual bearing failure I believe.

The bike is a C25 - 1967 Early engine (number below 250) but with a later off- side engine casing and an iron oil pump. Thus a single roller bearing on near side and plain on the off side as far as I am aware.
Yes, I am striping the engine complete as several small rivets (but not  all of them) have now arrived on the scene.  My thoughts are that the two half engine cases should be (would originally have been) machined together and align bored as one unit; but as one side has been swapped from a different engine, there is possibly some misalignment off side to near side and which places strain on the bearing through run out  - we will see when all stripped.
Guess I may be looking for an engine shop capable of checking for bearing housing run out and sorting the issue - either that or scrap the casings / ease the bearing housing etc.  Feedback welcome - Newport Pagnell  M1 junction 14 area.
It may of course simply be a duff bearing !
Yes I will identify the make as requested. Watch this space.
Cheers
Tony.

[TonyP]

Once again, Many thanks to members who offered their thoughts.

It turned out I was only partially correct in my initial diagnosis.

The crank cases are actually a matched pair with corresponding numbers on each half stamped at the base of each case underneath about in line with the long bottom bolt which runs from offside to nearside, bolting the engine into the frame.

The Drive side Roller bearing was fine. The clutch basket has a chunk out of it and I seem to have too many clutch plates (5 steel and 6 fibre).  Also one of the clutch spring bolts turned in the housing, requiring the spring cup to be chiselled off.
So, a bit of unexpected work there.

The problem of lost bits in the sump strainer was in fact the ball bearing main bearing on the timing / gearbox side of the engine. The inner race has multiple peppering damage where the surface seems to have broken up. The outer race and balls all OK but it was the cage that had broken into pieces.
Bearing is stamped USSR, thus not O.E. but is of the correct dimensions.
Cheers
Tony.

[LightningAndStarfire]

Wow, seems like a bearing from the Soviet Union in a BSA.

[TonyP]

Hi, Yes, strange but it really is a Russian part in a BSA !
I did learn that, along the way, I could in fact do what I asked in my original question - which was, can the N/S craank case be removed leaving the rest undisturbed.
The answer is yes, after the clutch, alternator etc. are removed. The top end has also to be removed. You an however leave the gearbox side intact, BUT as others have stressed. Why would you when it is only an hour extra to do the job properly!
In my case the whole needed to be stripped down as the failed bearing was in the O/S crank case.
Why did it fail - Possibly because a replacement oil pump had been fitted - An iron pump,  but not seated fully. So low oil pressure all round, but  I suspect main culprit was the roller bearing not up to standard - or a bit of rust or dirt in it. !
Cheers
Tony