Spun Hub?

O

Orcbait

Member
exMember
Joined
Sep 2, 2006
RO Number
23038
Messages
94
I had a problem with the starboard engine lagging the port side in terms of WOT by about 300 rpm or so. Did all the electrical/fuel tune-up stuff.

So when I hauled the boat to paint it recently, of course I took a close look at the props, and in fact the starboard side had some pretty good nicks.

So I decided to replace them both. Now the boat came with an extra set, which had been re-done by some prop shop (not sure which one, no way to trace) by the prior owner.

Problem now with the 'new' props is this:

When going on plane, the starboard engine revs too high and whines, goes right up to about 5,000 rpm (previously 4,000 with the old prop) in an awful hurry, before I back it off, then it sort of seems to settle in.

Also, port prop just seems to 'bite' more. Starboard doesn't seem to be catching as much of a load, if you know what I mean, until it sort of 'settles in' after first whining up to 5,000 rpms (I've only tried this a couple of times, and obviously don't intend to keep doing it...).

Seems like what a 'spun hub' should feel like, based on other posts, but as I've never had one, thoughts appreciated...

And if it is, is it difficult to change the prop while the boat is in the water? I can back it into my slip stern to, should be able to get at it, but that said the water is about 50 degrees here...

What's the procedure for pulling the prop, and is it different if the boat is in the water?

Thanks a lot.

Orcbait
 
Let us know all the particulars of your engines props and drives and we'llhelp
 
Unclear from this post what type of boat/engines/drives/props you have. Assuming it's an I/O or O/B with one prop per engine or drive... Most props on these have "rubber hubs" and once one of those slips, it usually won't drive at all above an idle speed. MerC came up with a different hub that's got a stepped plastic bushing in it. Pretty much the same there, but sometimes the boat owner can tighten a "spun" one and make it home at a higher speed than with a spun rubber hub. Rubber hubs have to be tested an replaced by a prop shop or at least a machine shop while the plastic hub can be changed by the owner.
If it's most I/O or O/B: remove cotter pin or release locking washer. Place wooden block between top of prop and bottom of cavitation plate. Remove attaching nut and washer. Prop should slide off the shaft splines. Remove front centering washer. Inspect and repair/replace as needed.
You really should get a manual. There's probably a torque spec for putting the nut back. Grease spline, put washers etc back in order, slide prop on, add rest of hardware, nut, torque, install cotter pin, set locking ring, etc as appropriate.
I believe if you're getting bite at near full throttle, problem is not prop hub. Prop itself, cavitation, motor height or angle, ventilation [air forced in from under hull] or the like.
As I said, once a hub slips, it doesn't grab again with any degree of force.
 
as far as replacing a prop in the water, been there, done that. not the worst w/ an I/O. raise the lower unit to trailer position, get a prop wrench and a screw driver and put a heavy string on them, you could drop them. other then that same as on the dry.

good luck
 
thanks - it is a Volvo, 280 or 290 leg, inboard/outboard, on a 305 V-8 Volvo Penta, 1991, prop pitch is I believe 15". It wasn't doing this at all before I changed the props.

I don't think it's a ventilation issue anyways, as the legs are trimmed in as I keep them normally (with the old prop), near zero (neutral) on both.

Orcbait
 
It does sound like a spun hub, but, if you need further convincing, you could try running just the drive that's questionable. If it performs O.K. at idle or slightly above but fails with more rpm, a spun hub would be confirmed.
 
If you use a metal ratchet/socket and they are stainless steel props make sure you disconnect your shorepower and turn your batteries off before you try to change the prop while in the water. This is the voice of experience. The shock was bad enough that I couldn't let go of the ratchet.
 
quote:
Originally posted by Cobalt 25

It does sound like a spun hub, but, if you need further convincing, you could try running just the drive that's questionable. If it performs O.K. at idle or slightly above but fails with more rpm, a spun hub would be confirmed.

Click to expand...
 
so I replaced the starboard prop with a brand new Volvo prop of the same size & pitch and took the boat back out - similar problem with the starboard engine just jumping to a really high WOT (up to 5,000 if I'm not careful) and I have to be really careful with the starboard throttle to keep that engine rpm in line and balanced with the port engine. And it really whines high.

So I thought it was maybe a spun hub but it obviously isn't, given now I've got a brand new prop. And the 'bite' in the water is certainly fine with the new prop anyways.

Am starting to wonder if it's a carb problem, or electrical. I do have a constant stalling problem with that same engine at low speeds, and the throttle is very finicky, with a strange 'tipping point' where you are sort of giving it slowly more and more gas but nothing much happens and then all of a sudden it 'tips in' and immediately plays 'catch up' on the revs and whines high. And if you back it off too much it very easily stalls, always at just the wrong time.

Keep in mind I've done a complete tune up here anyways in terms of plugs, new wires, timing checked & rechecked, gas filters etc.

The carbs are the Rochester 2 barrels, probably haven't been redone in like forever.

Is this a likely culprit, or what would be the next thing you'd check?

Again, the engines are Volvo Pentas, 1991 305 V-8s, Volvo legs, 280 or 290

Orcbait
 
Not sure about volvo but merc has a rubber hub in th engine coupler. If that's the problem, you usually smell the rubber burning in the engine compartment.
 
You must log in or register to reply here.
Back
Top