Main bearing moved in the casing - HELP!

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Trevor-3_1/2
Posts: 10
Joined: 23 May 2020 09:47
Location: Devon UK

Main bearing moved in the casing - HELP!

Post by Trevor-3_1/2 »

Hi all my 350 1976 Strada is stripped again & looking for a solution to the roller main bearing on the timing side moving.
I had stripped the engine to replace the bearing on the mainshaft, behind the clutch as it had play & oil was leaking into the clutch. When separated the timing side main ball bearing came out of the case on the crank. It was a tight fit on the sleeve & the sleeve was not a sliding fit on the crank. I managed to pull the bearing from the crank using heat/pullers etc. The sleeve remained in place tight on the the crank.. All bearings, seals, sludge traps & big end shells replaced.
I used a SKF NU206ECJ/C3 Steel Cage Single Row Cylindrical Roller Bearing 30x62x16mm on the crank timing side to allow for the axial expansion. I used Loctite 603 & it was a good fit, even with it frozen I had to press it in using a threaded tool.
Some running in miles & then after 1000 miles in total the outer race moved in the case towards the crank & the rollers weren’t supporting the inner race properly. Hence movement on the crank & oil leaking. I could see the cam belt flex as I moved the end of the crank!
Caught it just in time - Phew! Any advice on preventing the bearing moving received gladly, that would be solutions please.
My theory is that the original ball bearing/sleeve arrangement wasn't able to allow for axial expansion & has worn the housing in the casing for the bearing. The new one was tight, but perhaps not tight enough???
Can the case be metal sprayed or welded; then machined to fit the new bearing. I am open to ideas & information will be received gladly.
Look forward to hearing from you Trevor
Please note this is not a plain bearing engine that has been converted, it had the ball race main bearing as standard.
harrymuffin
Posts: 292
Joined: 07 Apr 2014 16:06
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Re: Main bearing moved in the casing - HELP!

Post by harrymuffin »

When you 'pressed' the outer race into the crankcase did you warm the crank case up first? If the 'other half' isn't looking it is usaual to stick it in the oven for hallf an hour at about 150c which is enough for the bearing to drop in.If you press bearings in a cold crankcase you can lose the interference fit by distorting the aluminium housing. If the outer bearing is now sloppy it was usual in the old days when money was not as easy to come by, as now, to 'wipe' the outer bearing with solder, electrical preferably but you could use low temperature tinmans solder, wiping bit, is to wipe off excess lumpy bits because of no practice and just increase the fit warming up the bearing so the solder will then melt won't alter th heat treatment of the bearing, they are design to run at normal temperatures of 150deg. There is always the codgers method and use one of the cyanacylate adhesives for raised temperature.You could as you have asked to have the housing built up and remachined, try a tool makers, I have just had a broken off drill spark eroded out of a hole in an alumnium casting. I do however know of someone who has a pair of 350 crankcases who I have persuaded not to turn them into a 507 engine, they have just been vapour blasted and ready to go.
By the way, even if you still have the plain baearings installed, you should still heat up the crankcases to fit so the housing does not get distorted. You shouldn't have the oil feed on this crank, but just check and plug if you have.
Just reading through you desporation, it is a long time since I played with a roller timing side engine and from recollection you should find a roller bearing that replaces the ball bearing, the plain bearing cranks have to be turned down to use the roller set up. You shouldn't have to fit a sleeve to the crank. The ideal bearing is the one with the roller/inner with roolers fitted to the crank and the outer fitted in the crankcase.
EVguru
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Re: Main bearing moved in the casing - HELP!

Post by EVguru »

The fact that the original ball race had shifted in the case is likely to have reduced the interference fit. Having to press the new bearing in would have made it worse.

I generally don't bother with chilling bearings. If the bearing started off at room temperature (approx. 20C) and you put it in the freezer (approx. -20C) then the 40C change in temperature would have resulted in the bearing being a little over 0.001" smaller. The same temperature change would make the housing 0.002" larger, with a 100C change (+20 to +120C) the housing would be about 0.005" larger and the bearings will just drop in. I heat the cases with a decently powerful hot air gun.

The usual proper fix is to bore and sleeve the housing. This can be done in Aluminium or Bronze, although some Japanese cases (usually 2 strokes) came factory fitted with cast Iron sleeves. Some loctite grades would appear to be up to the job, but I've seen reports of them failing, probably due to the thermal cycling.

Another set of cases is probably the most cost effective fix.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
Trevor-3_1/2
Posts: 10
Joined: 23 May 2020 09:47
Location: Devon UK

Re: Main bearing moved in the casing - HELP!

Post by Trevor-3_1/2 »

Harry, Paul thank you for your input.
I shall probably try the replacement cases as suggested.

If I remember correctly Paul I heated the case with the hot air gun & chilled the bearing, but it still had to be pressed in. Perhaps the casing was not round after the ball bearing had moved (it looked good condition)???

I used Loctite 603 on the bearing as this is supposed to be tolerant to oil contamination on the surfaces & I cleaned everything thoroughly. What do you think to the idea that as the bearing was frozen it was taking moisture from the air(freezing it to the metal) & this prevented the Loctite from adhering properly. I wiped it before applying the Loctite but there would be a slight delay. Could help others potentially avoid this mistake!
Trevor
mbmm350s
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Location: Berkshire UK

Re: Main bearing moved in the casing - HELP!

Post by mbmm350s »

Hi Trevor
My theory is that the original ball bearing/sleeve arrangement wasn't able to allow for axial expansion & has worn the housing in the casing for the bearing
The arrangement with the sleeve was/is supposed to allow for axial expansion.
However there is enough evidence that this doesn't always work as intended.
The fundamental problem is that there is a compounding of tolerances: the crank, the sleeve, the inner race, the bearing itself, the outer race and the crankcase bore.
A common finding is the sleeve gets loose on the crank.
However your situation appears to be that although the bearing inner race was perhaps too tight
on the sleeve the sleeve was able to resist being rotated
A theory could be that a previous installation did not use the C3 clearance bearing.
The question is what is too tight?

There is evidence that with the roller bearing modification the outer races creep out of the cases.

An alternative to replacement cases is to replace the crank with a later one and use the plain bush, this needs the upgrade the oil feed gear
as per the factory modification in 1977 ish.
The plain bush in its housing is held in the casing by three screws and I believe it to be the same engine case bore,
someone more knowledgeable will be able to say for sure. But i think you can drill the holes in the earlier cases to secure the bush housing.


Mark
Trevor-3_1/2
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Joined: 23 May 2020 09:47
Location: Devon UK

Re: Main bearing moved in the casing - HELP!

Post by Trevor-3_1/2 »

Hi Harry
As for your bearing recommendation that the rollers are on the inner 'race' could you explain your thinking as I used the opposite type with the rollers in the outer 'race' .
Most interesting
Trevor
Trevor-3_1/2
Posts: 10
Joined: 23 May 2020 09:47
Location: Devon UK

Re: Main bearing moved in the casing - HELP!

Post by Trevor-3_1/2 »

Hi Harry
I have tried to send PM about crank casees
Trevor
simonnorthroad
Posts: 388
Joined: 16 May 2017 10:57
Location: Bath, UK

Re: Main bearing moved in the casing - HELP!

Post by simonnorthroad »

I've PMed you about this Trevor
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