Vibration in Lower Unit -- Repair or Replace???

[Craig]

This is a mid summer bummer story. I was out yesterday and noticed a vibration in the boat. I was worried (obviously) as I just re-powered last summer and thought "great my new motor is shot", but after I got to listening and looking around a bit, it seems that it may be something in the lower unit (Volvo 270). The vibration is present at idle (neutral), but when I raise the unit with the electric tilt motor, it stops. I'm pretty sure its not in the engine (water temp and oil pressure seem fine). Does this sound familiar to anyone? I was thinking possibly a worn out bearing or universal in the lower unit may be the culprit. This also got me to considering other lower unit options. How much effort is invloved in switching to a Mercruiser Alpha or Bravo. I've seen previously that some of you have made this switch in the past. (Boat is a 1969 16' with Holman Moody Marine Ford stuff). I kind of hate to go in the "less original" direction that such an alteration would achieve, but I have also thought a lot, over the years, of the benefits of power trim, more prop options, etc. What about Volvo units (270T, 280, 290)?? Would it be easier to switch to them from an old 270? I think I remember someone saying if you wanted to keep left hand rotation prop in a Mercruiser you had to go with a Bravo as opposed to an Alpha. Is that correct?? Well that looks like about 8 or 9 questions. Guess I should quit for now. Thanks to any respondees!

[Craig]

Forgot! One more thing. I had suspected for a while that my prop may be "out of balance." If that is the case, could that have damaged the unit? I think I know the answer to that one. I had noticed (prior to yesterday) a slight vibration at WOT, but elsewhere seemed o.k. That seems to make sense if the imbalance was slight that it would be more noticeable with increased speed.

[AVickers]

You probably have U-joint or intermediate shaft bearing problems -- or both. Did I understand that the vibration occurs in neutral???? It might also be the bearings or gears in the upper housing, but if the oil is good (no water, no metal), it's probably the other items.

U-joints and rear I-shaft bearing are relatively easy to fix... You'll need a good set of long-reach internal snap ring pliers to get the bearing out.

The front I-shaft bearing will require removing either the engine or the transom shield... But, if lubricated, it rarely fails. And you can see and check it with the rear bearning out.

I have to take off right now, but if you need step-by-step instructions, I posted the u-joint deal a while back and it should be in the archive section. The rear bearing is a continuation.

I'll check in later.

[Craig]

Thanks Avickers -- I'll check the archives re: u-joint stuff. I will also let you know if I need more info. Probably will! Thanks, again.
Craig

[AVickers]

An out-of-balance prop will damage your drive -- eventually. It can cause the bearings to wallow out the housing and it can cause the prop-shaft seals to fail which, in turn, would allow water into the drive and/or oil out. How fast is determined by how far out of ballance things are. However, this out-of-balance/vibration would only be noticeable with the drive in gear.

You indicated that your vibration occurs in neutral. None of the stuff that would be damaged by prop problems rotates when the drive is in neutral. The only things engaged when the drive is in neutral are in the transom housing and upper gear housing. Again, I'd suspect u-joints and the rear extension shaft bearing first.

Most people don't know that the extension shaft bearings need to be lubricated periodically. There are two of them (one on each end of the shaft) and they are of a type that has a seal on one side and none on the other. The two unsealed sides face each other in the extension shaft housing and (as near as I can figure) you need to shoot a bit of gear oil into the hole on the top of the housing occasionally so that these bearings will get lubrication...the rear gets a shot when you accellerate and the front gets bathed then you slow down. However, this housing is by no means oil tight so the oil will eventually seep out between the bearing's outer race and the housing, if nowhere else... In the front it drips out of the bell housing into the bilge; in the rear it ends up in the bellows. I can't see any other way for these bearings to get lubrication. When I replace my bearings, I used fully sealed bearings... Thinking here that the sealed bearings would outlast the engine so when I pull it to rebuild, I can change bearings again at the same time -- they only cost about $10 each.

As for installing a different drive on your boat, think twice! I called outdrives.com to get pricing on changing out an Alpha1 with a Bravo1 on my 22. New, they wanted about $7000 for everything required to do the job. Yikes! Rebuilt would cost about a grand less. Used could have been a lot less, but who wants to go through all that to install questionable components?????

Perhaps another way to go would be to install an upgraded drive on your Volvo transom shield -- like a used 280. I'm not sure, but I think it'll just bolt on. From what I've heard, they're good for very high horsepower and Rs and they shift better than any Alpha ever will!

I've also seen used, rebuildable transom shields out there for what I would think would be reasonable prices... Installing a used 280T, a 290T, or a Duo-Prop T from a wrecked Cobalt or something like it might be a way to go...

[Craig]

Avickers,
Thanks for all the good advice and food for thought. I knew that a new drive was pretty costly. Hadn't looked at prices lately. Didn't think they were quite as high as you said. That probably rules out that possibility for now. It was just a thought. Will probably try to fix (or have fixed) the one I have. However, what you said about an upgrade to a 280, 290, or 280T or 290T sounds interesting. I talked to a guy somewhere recently that had a 270T for around 2 grand. What do you know about them? I thought he said the mounting collar was a little different than the regular 270. I guess I could find out from Volvo what newer drives would fit easily to my 270 mounting collar (if any). Another thought crosses my mind in all of this is that, in changing drives (even sticking with some Volvo model), I could get a different drive ratio. I think mine is the 2.15:1 270 which requires very high pitch props to get any speed. I've got a 290 hp engine (Ford 351) and it is only getting in to the low 50's with my 14x27" aluminum prop!! Used to do 57+- with an older 351 that died a couple of years ago. Oh well, I've got some thinking to do. Thanks again. I'll let you know what I do.
Craig

[AVickers]

I'm sure there are lower prices out there if one shopped around. I made a call just to see what a complete Alpha to Bravo swap would be -- drive, bell housing, gimbals, throttle and shift mechanism, water pump, etc. -- and then decided to run the Alpha until it won't run any more -- or to do a complete swap when engine AND drive are worn out. Maybe to a Rat/Volvo Duoprop (they're now making aftermarket, heavy-duty stuff.)

As for a Volvo to Merc swap on a 30-year-old boat, the costs and difficulty might quickly outweigh the benefit and value of the boat -- especially given that I think your problem is a relatively easy fix. Besides, I actually like the Volvo setups -- except for trim, Merc and OMC didn't have anything close until the Bravos and cone-drive Cobras beginning the late 80s/early 90s. I actually hate my Alpha -- it cuts the engine off when shifting and it whines when underway. Docking in a wind with heavy wave action is a real bitch when you shift from forward to reverse more than twice and the engine dies 'cause it simply doesn't like having the ignition cut out from under it that often when it's trying to idle. (I've also been told by several authorities that my Rat Motor will eventually lunch it -- the only reason it has lasted as long as it has is that the boat doesn't weigh too much.)

I don't know interchangeability on Volvo models. The service books I have don't go into that except to say that service procedures on all drives are "similar." My guess is that a 250 is less heavy-duty than a 270, which is less heavy-duty than a 280 and so on. There also seem to be some year-model distinctions between different models of drives. On the outside, they look very similar except for exhaust ports and the like... I don't know whether a 280 top end would mount on a 270 middle casing and I don't know whether a 270 lower would bolt onto a 280 middle. Although interesting, my boat had a 280 on it and that's what I know best.

I do know that with a 5.7L engine you need a 1.61:1 drive -- as far as I know that's the tallest ratio available. (Some books list this as a 1.68:1, but whatever. I've not seen anything that shows a 1.5:1 or, as with Mercs, a 1.32:1).

In my travels, I have been to more than a couple of "boat junkyards" and have seen some old Volvos with trim rigs. I have looked carefully at the "elephant ear" Volvo 280T transom shield and it is a bit different from a standard variety. But, I think the difference is in the number of bolts and their layout and not in the cutout through the transom. In fact, some of the bolts looked to be in the identical locations, which means you might be able to use the shield itself as a template to drill the extra holes -- or, you'd be able to make a template and use some of the same-hole locations as index marks on your old transom. I did notice that the two bottom bolts are spread wider to accommodate the trim mechanism. These units are fairly ugly, but they were effective.

I also saw a Chrysler outdrive unit (obviously a Volvo) that had a single-ram trim setup on it. It was a very short-stroke ram -- almost like a brake cylinder -- mounted dead center under the yoke. To get full trim travel, all that would be necessary would be about 1.5" of travel -- which is about what this unit had. The only "problem" with this unit is that it had a massive and complex power steering rig mounted on the inside of the transom. I have a feeling that the complexity here would offset the simplicity of the trim very quickly... But maybe you could strip off all the power stuff and go directly to the tiller/fork/yoke setup of the non-power steering setups of old and be done with it.

[This message has been edited by avickers (edited 07-06-2000).]