Shaft / engine alignment

[contessaman]

Trying to get my new engine coarsely aligned enough to drill and tap into engine beds. Fine tune will come after on the adjustment of the mounts.

My propshaft has a cutlass bearing at the prop end, a flexible dripless shaft seal, then a flange to connect to the r&d coupling. I'm aware of the general techniques of aligning the engine. But the problem I have is that I can grab the half coupling on my shaft and move it about an inch in every direction.... So where do I start? I guess I need to find the midpoint?
The boat is currently afloat but I think my cutlass bearing is quite worn. I was thinking getting her ashore and replacing said bearing might be a good start if it lends some more rigidity to the system.

Any tips on finding the midpoint or where to start with aligning such a setup?

Modifying those engine beds was the muckiest job I've ever done the last thing I want to do is to drill into the wrong place and have to re do them! That dust gets everywhere.

Mr rassy decided to put really thick steel plate in the beds so drilling and tapping is gonna be fun (not)

Thanks in advance.

 

[vyv_cox]

The critical part is centring the shaft in the inboard end of the stern tube. Not so critical if the stern tube bore is far bigger than the shaft but mostly it isn't and the two will come together in some circumstances if they are too close somewhere. Make up some small wooden wedges to locate the shaft centrally, then align the engine/gearbox to that. This all assumes that the cutless bearing is in the right place, probably is if in a deadwood, maybe not if in a P-bracket.

 

[contessaman]

The critical part is centring the shaft in the inboard end of the stern tube. Not so critical if the stern tube bore is far bigger than the shaft but mostly it isn't and the two will come together in some circumstances if they are too close somewhere. Make up some small wooden wedges to locate the shaft centrally, then align the engine/gearbox to that. This all assumes that the cutless bearing is in the right place, probably is if in a deadwood, maybe not if in a P-bracket.

Thanks for the quick reply viv. Sounds like I definately need to get her ashore to do this. So I can take the rubber shaft seal off and see the position of the shaft relative to the tube?
Wooden wedges make sense to hold. Outside the rassy 38 is weird the back of the long fin sort of protrudes to support the shaft ( no p bracket ) probably easiest understood by a Google image search on rassy 38 if you can spare a minute for me,thanks buddy

 

[boatmike]

Assume you only have one cutless bearing. In this case vyvs method is fairly easy and should work OK. It might be best if easy to arrange however to remove the inboard seal to ensure that it is not pulling the shaft one way or the other before deciding where the centre is. With the shaft free it should be easier to determine the centre of the shaft line and lightly wedge the shaft in the tunnel as suggested.

 

[cmedsailor]

This is what my mechanic did (boat was not in the water) so I will try to explain it in English! Install a new cutlass bearing at the shaft tube where the shaft exits the boat. This to ensure there's no excess movement there. Now, inside the boat after you remove the flange connecting the shaft to the gear box and the flexible shaft seal, install one more cutlass bearing on the other side of the shaft tube. You will now have two points holding the shaft relatively aligned to start working with the alignment with the engine. Yes, it's a bit time consuming because you will need to remove and assembly again the flange twice in order to remove the cutlass bearing inside but believe me it works. I hope my explanation is clear!

 

[vyv_cox]

This is what my mechanic did (boat was not in the water) so I will try to explain it in English! Install a new cutlass bearing at the shaft tube where the shaft exits the boat. This to ensure there's no excess movement there. Now, inside the boat after you remove the flange connecting the shaft to the gear box and the flexible shaft seal, install one more cutlass bearing on the other side of the shaft tube. You will now have two points holding the shaft relatively aligned to start working with the alignment with the engine. Yes, it's a bit time consuming because you will need to remove and assembly again the flange twice in order to remove the cutlass bearing inside but believe me it works. I hope my explanation is clear!

I'm sure it will work but the method seems to be needlessly time consuming. It is easy to centre the shaft using wooden wedges with a vernier gauge or a bit of spare metal 'feeler gauge' to check measurements. The centring does not need to be super accurate, just sufficient that the shaft does not clash on the stern tube.

 

[oldharry]

When I was replacing the engine in my 24 footer, the yard boatbuilder advised me to make up a wooden jig of the 'footprint' of the engine, with the engine bearers, centre line, and exact centre of the output shaft and its distance aft of the bearers all accurately located on it. A nail or screw located the precise axis of the output shaft on the jig. This was then placed over the engine bearers in the correct position, and the shaft matched up to it. Because of the flexibly mounted inboard bearing there was a good 30mm movement on my shaft also, but using the jig as an initial reference point it was relatively easy to find the working axis of the shaft, and adjust the position of the jig accordingly. If the prop shaft had been out it would have been even easier apparently: holes drilled through battens at each end of the jig exactly on the output shaft centres would have allowed me to pass a rod of the same diameter right through and down the prop tunnel, and allowed exact measurement of the clearances.

The shape of my hull made it possible to wedge a batten under the shaft and tap it in and out to adjust the height of the shaft pretty precisely, but if not it would be easy enough to make a system of wedges to support the shaft accurately in place. Its all worked happily for several years, so I cant have been too far adrift! This gives sufficiently close initial alignment to be within range for final adjustment after the engine is in place. I know two or three people who have done it this way, succesfully. The key is to ensure the jig measurements are set up exactly to start with, and the jig is made solidly enough not to flex in use.

I hope that makes sense, unfortunately i did not think to take pics at the time, but It was all much more straightforward than i expected!

 

[GrahamM376]

I'm sure it will work but the method seems to be needlessly time consuming. It is easy to centre the shaft using wooden wedges with a vernier gauge or a bit of spare metal 'feeler gauge' to check measurements. The centring does not need to be super accurate, just sufficient that the shaft does not clash on the stern tube.

The only thing I would add is that once you have the engine positioned fore/aft, it makes life easier to leave the flexible coupling and prop off so the shaft can slide further forward and do the alignment flange to flange. MK1 eyeball will get it pretty close before moving to feeler gauges with the coupling in.

 

[contessaman]

All good gen thanks guys. Have to take the prop off anyway as I'm going from lh to rh rotation.

Sounds like my plan should be:

1) finish welding brackets so that engine is on sat its four mounts just resting on bearers.
2) get boat ashore. Remove prop. Replace cutlass bearing.
3) remove flexible dripless seal and slide up shaft out of the way. Position propshaft in centre of tube as acurately as I can and chock in place.
4) with prop removed slide shaft up so the coupling on gearbox and shaft come directly together (I.e without r&d coupling).
5) align engine in usual manner with feeler guage between couplings.
6) drill and tap into bearers and bolt down. Tweak alignment.
7) put it all together with the flexi coupling.re launch boat. Run it check for wobbles and vibration.

Does this all sound reasonable? I can get a new prop made up once I can measure the taper of the old one. No problem using scuba to fit the new prop when she's back in the water.

 

[boatmike]

If you are going to replace the cutless bearing anyway the old one would make a good spacer to use as a dummy on the inboard end of the shaft......... If you are doing a final assembly with an R&D coupling do a final check with a feeler gauge on the red bolt head as R&D suggest. I just re-aligned 2 TAMD41A monsters after fitting new gearboxes this way and it gives very accurate results if done properly.

 

[pvb]

All good gen thanks guys. Have to take the prop off anyway as I'm going from lh to rh rotation.

Sounds like my plan should be:

1) finish welding brackets so that engine is on sat its four mounts just resting on bearers.
2) get boat ashore. Remove prop. Replace cutlass bearing.
3) remove flexible dripless seal and slide up shaft out of the way. Position propshaft in centre of tube as acurately as I can and chock in place.
4) with prop removed slide shaft up so the coupling on gearbox and shaft come directly together (I.e without r&d coupling).
5) align engine in usual manner with feeler guage between couplings.
6) drill and tap into bearers and bolt down. Tweak alignment.
7) put it all together with the flexi coupling.re launch boat. Run it check for wobbles and vibration.

Does this all sound reasonable? I can get a new prop made up once I can measure the taper of the old one. No problem using scuba to fit the new prop when she's back in the water.

You should find that your HR38 uses standard Volvo Penta stern gear, with a tube (they call it a "shaft sleeve") going down to the cutless bearing holder (which is screwed on to the end of the tube). Similarly, the prop shaft should be a standard Volvo Penta part, in which case it will have a 1:10 taper.

You need to position the prop shaft appropriately for your new prop (and rope cutter if fitted), then allow the thickness of the R&D coupling in order to ensure that the engine is correctly located.

 

[contessaman]

Thanks for that. Hallberg couldn't tell me too much about my 1982 boat other than to say its a 30mm shaft. They seemed surprised it was still on the original engine and further surprised that I would fit anything other than another Volvo! Ironic really given that an md21 is a Peugeot engine and an md22 is a Perkins prima. Both non Swedish , both car derived engines.

Just waiting for my front mounts to be welded up then I can get her ashore and progress things. It was a lovely sight seeing that old md21 being craned away and scrapped! Good riddance!

Is there a rule of thumb on how much clearance I should leave between the back of the prop and the cutlass bearing? The anode goes on the prop but rather than clamp on the shaft. I was thinking 150% shaft diameter I.e. 45 mm minimum.

 

[pvb]

Is there a rule of thumb on how much clearance I should leave between the back of the prop and the cutlass bearing? The anode goes on the prop but rather than clamp on the shaft. I was thinking 150% shaft diameter I.e. 45 mm minimum.

45mm sounds a lot, maybe 30mm? The clearance is for 2 reasons; firstly to leave space for water to flow through the cutless bearing, secondly to allow for the shaft to move forwards under max thrust. It shouldn't move more than 5-10mm with regular engine mounts.

 

[SimonD]

Vyv's wedges work OK. However, I had a sleeve made up to do the job. It's a top hat in section so that it rests on the edge of the stern tube. The advantage is that it locates the propshaft centrally in the stern tube but, with a bit of clearance, lets it slide fore and aft. This makes aligning the engine a doddle. Bolt the propshaft flange in place then shove the engine around until the shaft slides easily into the propshaft flange.

 

[Tranona]

Thanks for that. Hallberg couldn't tell me too much about my 1982 boat other than to say its a 30mm shaft. They seemed surprised it was still on the original engine and further surprised that I would fit anything other than another Volvo! Ironic really given that an md21 is a Peugeot engine and an md22 is a Perkins prima. Both non Swedish , both car derived engines.

Just waiting for my front mounts to be welded up then I can get her ashore and progress things. It was a lovely sight seeing that old md21 being craned away and scrapped! Good riddance!

Is there a rule of thumb on how much clearance I should leave between the back of the prop and the cutlass bearing? The anode goes on the prop but rather than clamp on the shaft. I was thinking 150% shaft diameter I.e. 45 mm minimum.

In the lower hp range Volvos have not been Volvos for over 30 years but Perkins. The last volume range was the 200x series which was hardly the class of the field at the time.

Agree with pvb. The normal gap to leave is 15mm, but if you are fitting a rope cutter then follow the installation instructions. Definitely do not leave space for an anode. However you may find a prop anode inadequate and consider fitting a hull anode bonded to the shaft via the gearbox with a bridge over the flexible coupling.

It is worth checking the shaft taper as although metric shafts are normally 1:10, some Volvo supplied ones are finer - 1:20 from memory. Of course you may find you need a new shaft when you get it out in which case it makes sense to have a standard taper.

 

[BabaYaga]

All good gen thanks guys. Have to take the prop off anyway as I'm going from lh to rh rotation.

Sounds like my plan should be:

4) with prop removed slide shaft up so the coupling on gearbox and shaft come directly together (I.e without r&d coupling).
5) align engine in usual manner with feeler guage between couplings.
6) drill and tap into bearers and bolt down. Tweak alignment.

Does this all sound reasonable?

I would recommend considering Old Harry's advice to make a jig. So much easier to find the new positions for the bearers/feet, without having to lift the engine in and out (if I understand your planning correctly).
This photo shows the plywood jig I made for my new engine. The 25mm alu tube represents the shaft line.

 

[Neil_Y]

A couple of points.
Seeing as I just noticed this thread, I would go with Vyvs advice, not that useful for you but if you have a P bracket chock the shaft centered in carriers with wedges and you can also check alignment of the bearing carrier (some P brackets end up being skewed off at an angle) use a bearing that is made as a clearance fit in the carrier and you can slide it in by hand on the shaft and it should turn easily. With a stern tube tricky unless you can chock/support the aft end of the shaft.

Gap from bearing to prop, minimum on a soft mounted engine/shaft we suggest as 12.00mm, this allows 9.00mm for max shaft movement and 3.00mm to allow water to exit bearing at worst case. 32.00mm is the minimum that allows the fitting of a 20.00mm spool for a rope cutter.

 

[contessaman]

The template engine is a valid argument for sure but a bit late now for me. Also, i didnt know how i was going to mount the engine so it was a bit chicken and egg. After removing the old engine, I took the new gearbox and bellhousing and feet to the boat. I wanted to keep bearer modification to a minimum so I made most of the corrections to the bell housing itself. When I got to the stage that with the bell housing resting on the aft two mounts, the gearbox and propshaft could be slid together in alignment, I then fitted the bell housing to the engine and put the engine in the boat. The engine currently sits on the aft two mounts of the bellhousing at the rear and a block of wood under the sump at the bows. I manoeuvred it in to rough alignment then made plywood templates of the front mounts. These are currently being fabricated in 8mm steel plate.

Once I've got the front mounts on, the engine will be sat on all four anti vibration mounts in roughly the right position and its time to start drilling. I have been careful to make sure that there is steel plate in the bits of the bearers that the mounts sit on.

I'm sure there are lots of different ways of doing a new engine install. This method just evolved in my head as I went along.

I'm considering deepening the sump of the engine and extending the oil pickup. I'm at about 9 degrees slant and the recommended max is 15. There's loads of room underneath the engine and on top of the fuel tank so it would make sense...