Merc 90 fs. Problem with driveshaft, help please.

alystra · 29 October 2008, 13:35

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.

doggypaddle · 29 October 2008, 15:46

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.

alystra · 31 October 2008, 11:55

Quote:

Originally Posted by doggypaddle

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.

doggypaddle · 31 October 2008, 18:08

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.

alystra · 01 November 2008, 13:49

Quote:

Originally Posted by doggypaddle

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.

Nos4r2 · 01 November 2008, 18:05

Quote:

Originally Posted by alystra

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.

alystra · 03 November 2008, 12:43

Quote:

Originally Posted by Nos4r2

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.

Marinautic · 03 November 2008, 12:58

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

Marinautic · 03 November 2008, 13:05

It's lunch time!! so here they are.

alystra · 04 November 2008, 16:40

Quote:

Originally Posted by Marinautic

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

Nos4r2 · 04 November 2008, 16:58

Hmm... I wonder if you actually need it or if it's a bit of daft overengineering that can be removed to make life easier.

I like the Merc terminology for 'hit with a hammer' til it stops btw. "Install into housing until seated"

alystra · 04 November 2008, 23:47

Quote:

Originally Posted by Nos4r2

Hmm... I wonder if you actually need it or if it's a bit of daft overengineering that can be removed to make life easier.

I like the Merc terminology for 'hit with a hammer' til it stops btw. "Install into housing until seated"

I did wonder that myself, but... In between the power head, this bush and the water pump, the shaft diameter has been reduced substantially. So, thin shaft with a thick lump in the middle probably needs a bearing to stop it whipping. Only an American could say why they've machined half the metal away. The full diameter would have been ok and the weight saving would be negligable, I'd have thought.

I'm going to replace it if I can (if I've got a heavy enough hammer) because I suspect there may indeed have been some movement in the shaft. The gearbox oil showed signs of water ingress and I'm wondering if the oil seals under the water pump are leaking. New ones come with with the overhaul kit.

American engineering never fails to amaze me, fascinating but sometimes pointless (NASA biro, USSR pencil), and then they cock up the good bits by putting a bronze bearing round a stainless shaft and expect it to work in sea water without any lubrication.

The bush is quite brittle, so I suspect it's a sintered bearing, with graphite or something included in it to make it 'self lubricating'. Mmm! I wonder how many others sieze up?

Dirk Diggler · 05 November 2008, 17:17

http://www.snopes.com/business/genius/spacepen.asp

alystra · 06 November 2008, 17:46

Quote:

Originally Posted by Dirk Diggler

http://www.snopes.com/business/genius/spacepen.asp

OK. Not quite pointless then.

alystra · 09 November 2008, 00:02

Bit of heat got the bronze bush off the shaft. Ordered pump kit and new bushing from R.I.B.S Marine Parts online. Forgot an oil filter, rang them, spoke to a very pleasant, courteous and helpful lady who took my order for the filter and added it to the packaging of the original order so no extra p&p. She also explained how to get more detail out of the web site. Bushing not in stock at time of call.

Less than 48 hrs later and the whole order is on my bench - pretty good for this part of the country. Just thought I'd let everyone know what excellent service I've received from them (last year too when all I ordered was an oil filter).