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Old 25-01-2012, 14:03   #46
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Hmmmm. I am taking a two day class this weekend taught by one of the best diesel men in New England. I have a 3GM and want to get this right
For sure. He is rebuilding my engine for me and when I re-install it I want the correct mounts. He did tell me when I dropped the engine, the mounts were wrong. I'll pass along what he tells me on Sat.

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Old 25-01-2012, 14:22   #47
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Re: Engine Alignment

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Originally Posted by Mark Zarley View Post
Sailor man was spot on with the max alowable tolerances. The machined bushing in the shaft log will not work as the shaft log and the strut cannot be perfectly aligned. We are talking in 0.001 here. Any slight misalignment again in 0.001 will create coupling whip. So it follows that the only way to perfectly "center" the prop shaft so it is running "true" prior to alignment is with a dial indicator. Cradling it to hold it in place. Miss this step and you will fight your alignment for eternity.
I disagree. If you were to put a machined bush in the shaft log, and a fiber cutlass bearing into the strut with the shaft installed, your cutlass bearing would settle in pretty close to aligned. (Assuming the strut was installed pointing in the right direction!) Keeping the shaft centered in the log seems to me to be a pretty important affair given the mess my current shaft log looks like. The lower surface of the shaft log was worn by the shaft and a side view of the stuffing box and hose shows just how badly it was off alignment. Now whether that was because the strut was off or what doesn't mean anything to me now as the strut will be rebuilt at the same time so all in all it should be pretty straight when done.
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Old 26-01-2012, 07:30   #48
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Re: Engine Alignment

A nice way of dealing with the past two issues is to use a clearance fit bearing (we do this regularly)

The composite bearing is made as a clearance fit in the bearing carrier (strut/p-bracket/dead wood/through hull/shaft log) in this way you can have a dry run with shaft installed and chocked you should be able to slide the new bearings along the shaft and into the bearing carrier, and spin it by hand. This ensures you are starting with your bearings in alignment. Then leaving shaft chocked you epoxy them in as per Maritex procedure (used by Lloyds vessels).

Now and only now should you look at the front end and engine.
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Old 27-01-2012, 21:48   #49
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Re: Engine Alignment

Umm I can wrap my head around chocking the inboard end, using blocks n such but how would you go about chocking the prop end? All I can think of is an X shaped set of 2x4s on the ground and scissored to raise the shaft. Kinda unsteady.

Got any other suggestions? I'll be needing to do that soon.
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Old 27-01-2012, 22:47   #50
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Re: Engine Alignment

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Umm I can wrap my head around chocking the inboard end, using blocks n such but how would you go about chocking the prop end? All I can think of is an X shaped set of 2x4s on the ground and scissored to raise the shaft. Kinda unsteady.

Got any other suggestions? I'll be needing to do that soon.
drill a hole in a 2x6 the same diameter as your prop shaft. Then rip the 2x6 right thru the middle of the hole you drilled. Take 1/2 of the remaining parts of the 2x6 and use that as a place to secure your shaft. How to secure the piece of 2x6 varies by boat. I would like to make a tab on the hull such that I could mount the 2x6 consistently in the same spot so that I would have a permanent piece to place the shaft in. If I did that I would probably use a piece of aluminum instead of wood.
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Old 28-01-2012, 01:36   #51
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Re: Engine Alignment

I prefer a block of wood with a V cut to support and then slim wedges to adjust or screw jack. It's fiddly but then you know bearings are all lined up.
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Old 29-01-2012, 18:46   #52
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Double checked with Jay from J-Way Enterprises, on a 3GM30F, the mounts are 100 on the front and 75's on the rear. Nothing should be mounted with left and right involved just front and back.

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Old 23-04-2012, 05:02   #53
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Re: Engine Alignment

Having never needed to align a boat's engine before, I knew nothing of the procedure. However, after an engine overhaul, requiring its removal and re-installation, I have had to learn about it.
This forum has been incredibly useful, and I've read and watched other sources of info, too.
Cheechako asked about using a table with necessary info, such as number of turns of engine mount nuts to produce a given result at the coupling. Well, the geometry is fairly heavy weight, but can be done. However, I found Google Sketchup to be very handy. I modeled the engine mounts and output shaft using sketchup, along with dimensions at the coupling faces and the mounts.
Now, by rotating the (virtual) engine in the required plane, I can see the effect at the coupling. I have to work in reverse, in a way, by moving the engine first to see what effect it has at the coupling, but it looks good so far. The software is free and works on all platforms. You don't need the pro version to get very accurate figures (< 0.0005" or half a thou).
I think it will help enormously, although I haven't tested it out in the real world yet. We plan to start the job tomorrow, weather permitting. I'll report back.
I've found tons of essential info in this forum, and I hope that this may add to it.
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Old 23-04-2012, 05:11   #54
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Re: Engine Alignment

Greetings and welcome aboard the CF, Lowestoft Mike.
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Old 23-04-2012, 07:11   #55
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Re: Engine Alignment

The best to you on your project! The first time is the hardest but once one has done it, one should get a good understanding how it works.

Just remember some boats twist in a sea way so hopefully the final alignment is while the boat has set in the water, or even run a time or two.
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Old 23-04-2012, 07:16   #56
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Re: Engine Alignment

Just remember not to sit on the engine or lean against it while using your feeler gauges on the coupling interface. Ask me how I know.
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Old 23-04-2012, 09:49   #57
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Re: Engine Alignment

How do you tell if the shaft is aligned in the shaft log with the boat in the water?

I checked my alignment last year with feeler gauges and all looked good, but now I'm seeing that my LasDrop shaft seal's bellow is slightly misaligned. This is leading to a leak because of the unequal pressure around the graphite friction ring. I now need to align the shaft first and then redo the engine, but cannot figure out how to know the shaft is centered without pulling off the stuffing box... and letting in a lot of water.
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Old 23-04-2012, 10:01   #58
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Re: Engine Alignment

uncouple your shaft, move it to the limits of it's travel in all directions and put it in the middle. No need to see the log.
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Old 23-04-2012, 10:17   #59
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Re: Engine Alignment

Dang logic. How did I not think of this?
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Old 23-04-2012, 10:39   #60
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Re: Engine Alignment

"....Cheechako asked about using a table with necessary info,...." Dont think it was me.....sounds like you got 'er done though....
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