Howdy

About to change the engine mounts, and thinking through the job ahead.
Apart from the obvious....how to lift the donk....thinking car jack under motor somewhere...please advise if other. Not sure if car jack off hull is the greatest idea, will place pad to spread load.

More importantly, understand shaft alignment is critical, so with my set up I'm a little confused:

Setup

Bukh 24 and gearbox with output shaft connected to 2 x Uni's then V drive
V drive on pivots across the beam of boat
Output from V drive, ridged coupling to shaft/drip less gland

I can easily understand Prop Shaft to V drive, however how do you align motor via 2 x uni's to V drive? Will the uni's just self align, or am I missing something completely?

1 uni , its basic to align, however uni back to back with a uni, is it the way to uncomplicate shaft alignment ?? Or is there a way to align with all the wobble of uni's?



cheers
Cab

how do you align motor via 2 x uni's to V drive? Will the uni's just self align, or am I missing something completely?

The good news is that by having universal joints and not a direct coupling you have more leeway in the case of alignment.
I would get a dial micrometer with a magnetic mount and check what the alignment is now.
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If she is running smoothly now and you have a measurement of the alignment you have something to work back to.
For example the amount of runout that you have now is the acceptable limit.
Those uni joints should be checked or replaced if you are going to the trouble to disconnect everything.

.how to lift the donk....thinking car jack under motor somewhere...please advise

This will depend on how high you have to lift to clear the mounting bolts.
Wooden wedges driven in can be placed strategically.
Are you thinking of a wind up jack with a small foot or a small hydraulic unit?

My main advice is to strip as much as you can off the engine (water pump, starter motor. exhaust system etc).
This will make the engine lighter and give you better access to those bastard places behind the engine.

The second is to chop any access of the top of the mounting bolts.
I have seen bolts that are 30 mm longer than they need to be and that means you have to lift the engine that much higher.
A grinder with a cutoff blade will make short work of that.

Go slowly.
Put all parts in buckets of separate cardboard boxes and move them away from your working area,
Have lots of rags and keep you working area clean.
Have really good lighting.
And may I suggest some Van Morrison in the background.
gary

Most of what garymalmgren said


The double unis take care of the engine to v drive alignment. Its always good to try to keep the universals as straight as possible because wide angles of drive will cause a fluctuation of velocity . The fluctuation of velocity can set up vibration.
Being such a short piece between your engine and v drive and the fact that the rpm is relatively low, small alignment angles (well within the limits of the universals) are most likely a non issue.
If you jack under the engine be sure you don't dent the sump in. Some sump pans are thin and a dent in the wrong place could be catastrophic. Try to jack on a solid part of the engine and if you do have to jack on the sump, put something under the sump to spread the point load.
I can lift my motor from the boom. I have a strategically placed port in the cabin roof above the engine solely for lifting from the boom. Be aware though that using the boom as a crane may require some careful setup.

When it comes to alignment and the use of a dial indicator, most small boats don't have enough room or clearence around the coupling to swing a dial indicator to indicate measurements from a coupling so they are often useless for this operation. Quite often there is also to much movement in shaft bearings and rubber engine mounts for the fine measurements of a dial indicator to make sense.
Although the dial indicator is pretty useful and simple to set up to centralize the shaft in a stern tube and to indicate if a shaft is bent.

This picture shows set up for coupling alignment
note how the indicator needs to swing around the coupling

Select to expand quote

Cabron said..
I can easily understand Prop Shaft to V drive, however how do you align motor via 2 x uni's to V drive? Will the uni's just self align, or am I missing something completely?

Yep, prop shaft to V drive is the critical one, that's why there are two uni's - very rarely will everything align exactly.
The main thing is that the gearbox output shaft is at the correct height to keep the uni's & V drive on the same alignment. The angle of the motor, height of the front of the engine, is not as critical but try to keep the angle of the uni's as little as possible.
Like Gary said, well worth replacing the uni's while everything is apart.

An interesting point about universal joints is that if they are aligned with no angle the internal needle bearings aren't forced to rotate and distribute the lubrication thus causing premature failure

Select to expand quote

Lazzz said..

Cabron said..
I can easily understand Prop Shaft to V drive, however how do you align motor via 2 x uni's to V drive? Will the uni's just self align, or am I missing something completely?

Yep, prop shaft to V drive is the critical one, that's why there are two uni's - very rarely will everything align exactly.
The main thing is that the gearbox output shaft is at the correct height to keep the uni's & V drive on the same alignment. The angle of the motor, height of the front of the engine, is not as critical but try to keep the angle of the uni's as little as possible.
Like Gary said, well worth replacing the uni's while everything is apart.

Keeping the angles of the input and the output the same or you could say keeping the output shaft of the gearbox parallel with the input shaft of the v drive is the key,,, even if they are at slightly different heights,,, allowing the engine to be higher at the front may cause a difference in these angles which will put a cyclic fluctuation of velocity into the input of the v drive.
Better to have a slight difference in height between the engine and v drive than to have different angles of input and output.
Best to have all in line

Yep, have to agree on the input and output shafts being on a parallel plane. There's more than meets the eye with universal joints

Thanks all for the replies, the V drive pivots, and can't be fixed, so aligns (best it can ...no adjustment) with prop shaft, Just the nature of double uni's will have a slight wobble/vibration and can't think of a way to stop that, note the uni to v drive is on a spline gear and floats, so the weight of the uni pulls down slightly, and along the spline....only talking around 1mm movement in spline/uni. Not a job i'm looking forward to, however found a mount collapsed, and the others while ok, have seen better days, while no noise, or different vibration, I cant just leave it

Ok, picked up the mounts today, went down to plan the job out, thought to take one mount out to check that the centre's are the same on mounts, all good.
Now the originals had S/S M6 holding to mild steel brackets to GRP, and the main bolt to mount is a M12? steel fine pitch thread, new mounts are normal pitch thread, so question is:
a) Replace with S/S bolts
b) Search to find decent mild steel, gal or zinc bolts-rust?
c) High tensile bolts? Is it required?

Searched across on other forums and the jury is out, seems like each had their reason.
Now the small S/S bolts into mild steel had zero sign of galvanic reaction, but isolated by mount rubber to engine.
The mild steel varieties are actually harder for me to find, Mr S/S is on the way to boat, Bunnings have a poor range of bolts. Don't feel like driving to blackwoods etc
Some said Galvanic reaction only happens when wet, and if these get wet I've got bigger problems than worrying about that...
Now, is high tensile really needed? Mount is holding the weight, it's purely compression load for the bolt?
Anyone have S/S and can report? Can use duralac however don't really want to source plastic washers to really isolate.

Whats others thoughts on galvanic reaction if they are mostly dry... maybe a hose out of engine bay once a year???

Select to expand quote

Cabron said..
...... note the uni to v drive is on a spline gear and floats, so the weight of the uni pulls down slightly, and along the spline....only talking around 1mm movement in spline/uni.

There should be a grease nipple on the spline somewhere - make sure it has plenty of grease!!

This diagram is probably more accurate - the rear of the engine will only really sit properly on one spot. Hard to explain but when you have it apart it will make sense.

Now the originals had S/S M6 holding to mild steel brackets to GRP, and the main bolt to mount is a M12? steel fine pitch thread, new mounts are normal pitch thread, so question is:
a) Replace with S/S bolts
b) Search to find decent mild steel, gal or zinc bolts-rust?
c) High tensile bolts? Is it required?

a) yes if they are easy to get hold of.
b) mild steel yes. Don't bother with gal or zinc.
C) yes if old bolts were high tensile.

Basically, l would go with the way it was before.
You can't use the same bolts because of the pitch so you will need new bolts.
If old bolts are mild steel , that is the easiest way to go.
Usually fine pitch bolts are high tensile (but not always) so my guess is the old ones were. A go with a hack saw will tell you pretty quickly.

How rusted were the old bolts. Usually, they get a good dose of diesel or oil during daily use and that keeps them fairly rust free.

So to round up.
You can use stainless or high tensile and if the old ones were mild steel, you can use that too.

gary

Well they are finally out, and 3 of 4 back in.
1 easy, 1 straight forward in horrible spot, 1 nasty in average spot( photo where I tore it apart to get a grip) 1... worst spot, someone burred the bolt previously, and not 1 of the 3 bolts would come out, removed exhaust system, with a hacksaw blade(hacksaw wouldn't fit) cut the side off the bell, cut underneath, cut all rubber, removed mount to hull, finally got a grip on the nut for stud and got the bugger out.. so all in all successful, though the mount bolts to bracket are actually UNF 5/16 x 3/4, and now need 2 to put it together....
now gotta find 2 x UNF bolts while most places closed... double bugger.... who's got a couple in the shed in Sydney town??