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Old 29 October 2008, 08:35   #1
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Merc 90 fs. Problem with driveshaft, help please.

Year 2000 Mercury 90 4str.

Plucked up courage and removed the gearbox to check on water pump, seals etc. It's not been off for 5 years so I anticipated problems, but it came away with no trouble. I took it slowly and kept checking the Clymer manual and all looked good until I lowered it clear. Half way up the shaft was a rubber thing that's not shown in the manual - well, not in the bit about removing the gearbox anyway. There's nothing worse, when you're a beginner, than finding something that's not in the instructions. Nothing else fell out of the hole and a glance with a torch showed nothing seemingly amiss. Back in the workshop the rubber jobby looked a bit squint and well worn. I pulled it off and there was a bronze(?) bush inside, firmly stuck to the shaft. This has to come off if I'm going to be able to service the water pump.

Searching through the manual I think I've found the part. It's called a drive shaft bushing. I would think it's a steadying bearing to stop the shaft whipping. The rubber bit has obviously been rotating in its housing up the drive shaft tube. Is it supposed to do that? A bit like an inside out water lubricated cutless bearing on standard prop shafts? Or is it supposed to fit in the drive shaft tube and the shaft rotate in the 'bronze' bearing that's now stuck to the shaft?

So far I've been unable to move the bronze bush. I don't want to hit it too hard in case I damage anything in the gearbox. If it's just siezed then I'm sure some WD40, patience and maybe a bit of heat will free it. If it's supposed to be stuck there, then I'm probably out of my depth and will have to take it to a dealer, which is a struggle. Any help from knowledgeable people here much appreciated.

Looked on RIBS Marine Parts website and it's listed at about 38.00 but not in stock. Anyone know who else I could try? Rather not try shipping from USA, though the stuff's probably dearer here. My nearest Mercury dealer is more than 100 miles away so it's difficult to 'just pop along' and ask. A phone call will likely end in a 'you'll have to bring it in' sort of conversation.

Pics of offending article attached. Thanks for any info. Tony.
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Old 29 October 2008, 10:46   #2
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you could try,

1 warming it up with a blowlamp, tap it off
2 cut it nearly all the way through with a small grinder, tap it off
3 use two hammers, hold one against it and tap the opposite side with the other to stretch it.
4 make a puller to suit.

i would be say it would definetley come off with either option 1 or 3
and probably be re useable if youre careful.
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Old 31 October 2008, 06:55   #3
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Originally Posted by doggypaddle View Post
you could try,

1 warming it up with a blowlamp, tap it off
2 cut it nearly all the way through with a small grinder, tap it off
3 use two hammers, hold one against it and tap the opposite side with the other to stretch it.
4 make a puller to suit.

i would be say it would definately come off with either option 1 or 3
and probably be re useable if youre careful.
Yes, thanks for that. Warming it up should do it. I'm not keen on damaging the bush in case I can't get a replacement and have to try and repair and refit this one.

What I was hoping to learn was whether anyone else had a similar problem and could tell me whether the 'bronze' bush was a siezed bearing, or whether it was designed to be stuck on the shaft. I guess if I can find a replacement it'll become obvious.
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Old 31 October 2008, 13:08   #4
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I would guess its meant to be stuck in the rubber and the rubber stuck in the housing, unless the rubber has a sleeve in it for the bush to run in.
i would say the shaft is meant to be a slight clearence fit in the bush, so it does nothing unless the shaft starts to whip or skip about.
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Old 01 November 2008, 08:49   #5
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I would guess its meant to be stuck in the rubber and the rubber stuck in the housing, unless the rubber has a sleeve in it for the bush to run in.
i would say the shaft is meant to be a slight clearence fit in the bush, so it does nothing unless the shaft starts to whip or skip about.
I think you're probably right. I think the rubber had been stuck to the bush, but of course it was unstuck when the thing seized. What made me wonder if the rubber was supposed to rotate in the housing was that, on the on line Mercury drawings, the rubber bushing was to be fitted using a tube of rubber lubricant.

I was just hoping someone here would have specific knowledge or experience. Seems not. Guess I'll go ahead and get the bush off the shaft anyway. Many thanks for your thoughts and suggestions.

Cheers Tony.
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Old 01 November 2008, 13:05   #6
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I think you're probably right. I think the rubber had been stuck to the bush, but of course it was unstuck when the thing seized. What made me wonder if the rubber was supposed to rotate in the housing was that, on the on line Mercury drawings, the rubber bushing was to be fitted using a tube of rubber lubricant.

I was just hoping someone here would have specific knowledge or experience. Seems not. Guess I'll go ahead and get the bush off the shaft anyway. Many thanks for your thoughts and suggestions.

Cheers Tony.

What would be a far better idea would be to ring the nearest dealer and ask first. You may not get the 'you'll have to bring it in' answer...

It's not something I've seen before on an outboard.
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Old 03 November 2008, 07:43   #7
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What would be a far better idea would be to ring the nearest dealer and ask first. You may not get the 'you'll have to bring it in' answer...

It's not something I've seen before on an outboard.
Thanks Nos, sensible as usual. Interesting that you've not seen such a thing.
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Old 03 November 2008, 07:58   #8
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The bushing has a roll pin installed to hold it in place. It's not supposed to come out without a fight!

It's purpose is as a shaft alignment guide, and needless to say you need a special tool # 91-875215 to re-install a new one!

If I get time I'll scan the manual and post the pics.

Gareth
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Old 03 November 2008, 08:05   #9
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It's lunch time!! so here they are.
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Old 04 November 2008, 11:40   #10
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The bushing has a roll pin installed to hold it in place. It's not supposed to come out without a fight!

It's purpose is as a shaft alignment guide, and needless to say you need a special tool # 91-875215 to re-install a new one!

If I get time I'll scan the manual and post the pics.

Gareth
... On reflection, it's not too bad. Many thanks for the insight and drawings Gareth. The roll pin may explain the rather chavelled rubber on the lower edge of the bush. Didn't notice it (the pin) when I looked up the shaft tube, so I guess it lost the fight with the seized bearing. Pah! That means I'll have to get the cowling off too, to re-fit it.

Had a look at the 'special tool' on the spares catalogue. Reckon I can make one out of oak on my lathe. Should do the trick as a one off.

It seems incredible that there's a bronze bearing in there with no apparent way of lubricating the thing. Presume it needs some waterproof grease in it when the shaft's refitted?

Cheers, Tony
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