Engine alignment PDF (Thx Steve D!)

[mvweebles]

I did a quick Google search for tolerance when aligning my Perkins 4.236 to a BW Velvet Drive. I found this file from Steve D'Antonio with his usual detailed information so I posted it to Resources for posterity.

Engine alignment instructions

Courtesy of Steve d'Antonio marine consulting.

www.trawlerforum.com

BTW- max tolerance for my BW is 0.003"

Peter

 

[SteveK]

The picture in post #1 appears to have about 1 foot outside the stuffing box.
Looks like 1-1/2 shaft so 6.008 lbs per foot plus weight of flange ~0.75-1lb.
But at what point do you measure from, another 6" into the tube to find the support?

The picture shows uncoupled flanges yet they look lined up. ?? Does that suggest the trans end needs to be raised, etc. if the shaft is drooping?

What is the picture supposed to display?

 

[mvweebles]

The picture in post #1 appears to have about 1 foot outside the stuffing box.
Looks like 1-1/2 shaft so 6.008 lbs per foot plus weight of flange ~0.75-1lb.
But at what point do you measure from, another 6" into the tube to find the support?

The picture shows uncoupled flanges yet they look lined up. ?? Does that suggest the trans end needs to be raised, etc. if the shaft is drooping?

What is the picture supposed to display?

Don't read too much into the picture - it's the very beginning of the alignment process. Took a couple hours of two mechanics. I posted it just for some fluff to add to the post, nothing in particular. It was over 90-degrees and humid. I was happy to watch.

I'll repeat the process in a couple weeks once the boat has been in the water for a while.

Peter

 

[SteveK]

@mvweebles
Peter, the picture is linked to alignment instructions. Maybe it should not be there. I think discussing this would be great to understanding the process.
If we read SteveD literally the shaft unsupported should droop below the trans coupler in the picture.
I know I recently read a more clear description of the shaft weight must be countered before coupling.

 

[mvweebles]

@mvweebles
Peter, the picture is linked to alignment instructions. Maybe it should not be there. I think discussing this would be great to understanding the process.
If we read SteveD literally the shaft unsupported should droop below the trans coupler in the picture.
I know I recently ready a more clear description of the shaft weight must be countered before coupling.

Thanks Steve - I removed the picture as the intent here was awareness of Steve Ds work and guidance, not to cloud the topic.

I will say there are some practical limitations to field re-alignment vs new install. Ideally the engine would be aligned to the strut bore with a laser and shaft removed. Secondarily, weight of shaft (droop) has an effect, though the propeller weight will counteract, especially on a shorter shaft.

Not sure what the right answer is, just pointing out some practical challenges.

Peter

 

[ScottRhodes13]

One note in the instructions didn't seem right to me:

"The geometry takes a little
getting used to, but you’ll grow accustomed to it. If, for
instance, you were to view the couplings from aft facing
forward and a gap existed at the 3:00 o’clock position, then
the front of the engine would have to be moved to port."

Shouldn't the front of the engine be moved to starboard to close a gap at the 3:00 o'clock position?

 

[mvweebles]

One note in the instructions didn't seem right to me:

"The geometry takes a little
getting used to, but you’ll grow accustomed to it. If, for
instance, you were to view the couplings from aft facing
forward and a gap existed at the 3:00 o’clock position, then
the front of the engine would have to be moved to port."

Shouldn't the front of the engine be moved to starboard to close a gap at the 3:00 o'clock position?

I think you're right. But I have to observe that this is one of those projects that looks easy on paper. My little 75hp Perkins weighs something like 950 lbs without the gear and reduction. Closing to a 0.003" gap and keeping alignment is far more difficult on practice.

Some friends on a Nordhavn 55 had troubles with a shaft vibration when they first purchased the boat used. They had three different mechanics diagnose including replacing the shaft. Finally the husband/wife owner team spent a couple days aligning it themselves. Problem solved. Sure would be nice to have a nice large engine room.

Peter

 

[mvweebles]

Speaking of shaft sag, I wasn't happy with the alignment - prop didn't swing as freely as I remember. So the master mechanic returned and uncoupled the shaft/gear coupling and I checked the gap. I don't know what it was exactly but was clearly too much on one side.

The master mechanic saw immediately that the shaft sag hasn't been accounted for. Took him less than hour to resolve. Might be better than it was.

Happy camper here......

Peter

 

[Eagle Pursuit]

I used to worry about couples, shafts and stuffing boxes. Then I bought a boat with an outdrive… Gimme back my good old tranny and shaft!

 

[Steve DAntonio]

One note in the instructions didn't seem right to me:

"The geometry takes a little
getting used to, but you’ll grow accustomed to it. If, for
instance, you were to view the couplings from aft facing
forward and a gap existed at the 3:00 o’clock position, then
the front of the engine would have to be moved to port."

Shouldn't the front of the engine be moved to starboard to close a gap at the 3:00 o'clock position?

Scott, good catch, yes, that is an error, it's now corrected. Engine Alignment | Steve D'Antonio Marine Consulting

 

[mvweebles]

Scott, good catch, yes, that is an error, it's now corrected. Engine Alignment | Steve D'Antonio Marine Consulting

Thanks Steve - I updated the version of the Doc in <RESOURCES> section of TrawlerForum.

As always, thank you for being so generous with your time and knowledge.

Peter

 

[Steve DAntonio]

Always happy to help.