Shaft Alignment

1978, 53' YF, DD 8V71-TI's. Both engines/shafts need alignment. Appears as if the rear motor mounts are hard mounted without any means to adjust them.

I'm guessing the mounts have to be unbolted and the rear of the engine lifted to put shim material under the mount.

Does anyone have experience how to align the shafts with this configuration?

Does your mount look like these? These are shimmed. If you have the rubber jobs, you are SOL ! I just rebuilt and re-aligned my MH20 Allison w/12-71Ns
last year. Let me know if you need the "dissertation". ws

How do you know they need realignment??

Often there IS more weight on the rear than forward engine mounts and as a result the rear mounts may well be low....but you can't assume that...you must remove each shaft flange, port and stbd, from the transmisson flange and check top and bottom, left and right...four points with a feeler gauge....then rotate the shaft 1/2 turn and repeat.....ideally you will measure identical differences among the four measures....the absolute values are immaterial as they depend on how close you manually place the two flanges....differences should be within a ...two or three thousandths should be good....it depends on the flange diameter....whether you raise the back or lower the front mount shims depends on the center alignment of the two flanges...just hope you don't also have to move the engine left or right....lots of older Hatt engine mounts are adjusted via shims...thin metal pieces that are inserted to adjust the mounting height between the engine mount and engine bed stringers....often you can lift the engine ata mount after loosening all four engine mounts and using a long pry bar with wooden pivot point...otherwise an A frame and lifting chains are ideal....

Read this, good info:

http://www.yachtsurvey.com/alignment.htm

Post some pics of your engine mounts and engine beds. Take pics of both front and rear. There are different setups depending on year, model and engines. I'm thinking you probably have the rubber mounts and hopefully the adjustable engine beds. The rubber mounts sag over time but can be fixed if not too far gone. They can be replaced but the cost is outrageous. Post some pics, I'm sure someone will have the answers you need.

Thanks everyone for the replies.

To answer a few of the questions:

REBrueckner
How do you know they need realignment??

>>The reason I think they need to be adjusted is I see the shaft log (both engines) wobbling at speeds from idle on up. I can also feel the misalignment with either engine out of gear.

When I purchased the boat, 2 years ago next month, we had the props tuned (propscan technique) as well as had both cutlass bearings both (P&S) replaced.

Here are a couple of pictures. First one is the starboard engine, aft, port mount. The other is the same engine, starboard aft mount.

If they're WOBBLING there's a decent chance the shaft is BENT.

Alignment should be checked but its odds on you've got a bent shaft if you can see visible runout during operation.

Shafts are not bent. They were checked when we replaced the cutlass bearings.

With the Allison gears and couplings, the shaft end is a tapered unit... maybe the taper isnt seated square... that would cause the wobble. I would pull the couplings and clean and inspect, then go from there.
How do you feel the mis-alignment when in neutral? ws

You may have a bad output bearing on the gears. Very common problem on the old Allison M gears. Split the shaft coupling from the gear to check the allignment. Then check to see if there is play on the output flange of the gear. There should be slight movement fore and aft, but if you can move them up and down or side to side, you have a problem with the gear. Fix that first since the gear has to come out. You'll have to realign once the gears go back in.

To clarify - I feel the vibration with either engine out of gear and the other in gear. In other words, with either the port or starboard engine in forward and the other in neutral, I can feel a vibration.

All: thanks for all of the advice and comments, however, my initial question was and remains: does anyone have experience with how to align the shafts with this configuration?

To remind everyone - this is a 1978, 53' YF with 8-71-TI's. Engines/trannies have never been pulled/replaced - as far as I know.

An answer was provided by Bruce Morrison of Jarrett Bay thanks Bruce) which I will include below. Pretty much what I figured but not good news at all.

Tim,
I have installed many of this type of mounts and shims. I will appoligize in advance. You are correct that you will need to raise the engine several times to insert flat pieces of aluminum shim stock. This will be time consuming at first. Once you get the concept of which way each mount needs to go (up or dowm) in order to align the engine things will speed up. You mist first loosen the coupling bolts and insert a feeler gauge around the gap between the gear and shaft couplings and record the readings. For instance top being 12 o'clock, bottom 6 o'clock, left 9 o'clock and right 3 o'clock. If bottom is open more you will have to add additional shims under both mounts to raise the rear of the engine. If the gap is wider on one side, simply slide th engine in the opposite direction to close the gap. You will want to make several shims of various thickness before you start. I will assure you you that the rear of the engine/gear has settled over the years and will now need to be raised. You may find that if the engine needs to be raised, you can remove some of the thinner shims, replace with a thicker shim and recycle those thinner shims elsewhere. Keep in mind that the rule of thumb for alignment is .001 of tolerence for each inch of coupling face. You most likely have a 8" coupling face and you could stop at .008 on the feeler gauge. I always liked to get it to half the allowance (.004) and know you had gotten it as close as possible. I will not be back in the office this week but will be checking email each day....................Bruce A. Morrison

If you can see and feel vibration with either engine in gear, you have confirmed a problem.
Ok sounds like you have confirmed misalignment as the problem since your props are good. sounds like your shafts are also not the problem.....when you use feeler gauges and turn the shaft 1/2 turn for another measurement, that will be your confirmation. Jarret omitted that step and it's crucial to confirm your shaft is true!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Subsequent adjustments do not require 1/2 rotation confirmation...

My post #3 and your post # 12 explain the process....you need a fine touch with the feeler gauges and an understanding of how flange misalignment translates into necessary movement of the engine...you also need some form of power lifting to lift the HEAVY engine and transmission...crowbar, chain hoist or maybe hydraulic lift if you can borrow one...USE CAUTION WHEN LIFTING SINCE IT IS EASY TO UNINTENTIONALLY MOVE THE ENGINE SIDE TO SIDE....

I forget if I posted ALREADY: but,YES, usually the aft mounts sink LOW...I agree with the post #12 as rear mounts carry most of the weight... that means: the shaft flange is higher than the transmission flange and also the bottom of the flange is more widely separated than the top as measured by feeler gauge...hence lifting the back of the engine corrects both misalignments.

Some tricks: have a pencil and pad a record every measure in sequence....after a 1/2 rotation of the shaft and eight measures you don't want to guess wrong before lifting the engine,placing shims, and lowering again...use a sketch if necessary to show results.....After three or four possible sequences, a record can help you tell if you are getting closer!!!!!

When rotating the shaft do not lean DOWN on it...try to rotate without pressing up of down or side to side....never step on a disconnected shaft!!!!

Weight is likely 3500 lbs...figure 2500 aft to be safe...use appropriate lifting gear...

Sounds like your engines might be 1/2" low at the rear...
When I have done engines in the past I have used thin pieces of stainless or aluminum sheet....maybe 1/32" or 1/16"...whatever it was, I cut it with tin snips ahead of time....Home Cheapo has aluminum sheets maybe 2x 3 ft which is PLENTY...cut to the size you need to place under your mounts....likely you could also have one or two thick pieces made for each side ...say a pair of 1/4" thick blocks for each aft engine mount...4 in total..

Figure two days work...deciding how to lift, getting it aboard, setting that up, loosening engine mounts, disassembly of transmissiion flanges, measuring, placing shims, retightening mounts....rear seal??


Comments
Your mounts shown some corrosion...has the water been eliminated? I place a plastic container under my raw water pumps and glued in a clear vinyl hose to a can in the bilge...any water in the can and I know I have a raw water pump seal leak...but not dribbles on my transmission and mounts.

A product like RUST ARRESTOR (Home Cheapo) will chemically change the rust to an oxygen proof seal stopping further corrosion.....can then be painted....

Also, someone posted about rear transmission seal being wobbly?? never heard of that without a spray of transmission oil at the aft of the transmission...look around for it...it appears as a line either side of the transmission just ahead of the flange we have been discussing...

Spot on with regards to how to do it - it is absolutely KEY that you check the misalignment with a half-rotation BEFORE shimming, or you may think you "fixed it" only to find out that the problem isn't what you think it is!

If the shaft is true and the coupler properly installed (not cocked) a 1/2 rotation will NOT change where the gap is larger.

Its not a "difficult" job but it IS a pain in the butt and requires care due to the mass of what you're lifting while this is in process.

Thanks again to everyone for their observations, comments and suggestions.

This is the setup I used for the 12s. Just dont use the bottom of the boat to jack against! The next ones show the shim arraingement on the front mounts. I added about 1/8" on the front and about 5/16" on the rears, PLUS pushed the tail end over almost 3/8". This caused an imminent rear bearing / seal failure BTW... ws