Engine Alignment

[The Mons]

Hello:

I am attempting to align the engine on my Volvo 2003 with prop shaft and Volvo stern gland.

I have adjusted it so that it appears to be aligned. The engine seems to be well centered with little vibration up to about 1500 rpm. Past 2000 rpm, the engine, shaft, and stern gland begin to visibly vibrate somewhat.

Should I have little or no vibration throughout the rpm range or is some acceptable at higher rpms.

Thanks in advance for the input.

[Pblais]

Should I have little or no vibration throughout the rpm range or is some acceptable at higher rpms.

It is possible with some experience to get the shaft to .003 inches tolerance. Many specs are about .007. At that point you won't hear much of anything. If you can see the error you are not even close to good enough. Getting it really good is worth it. No vibration would be the goal.

[David M]

You will experience more vibration at higher RPM's anyways because of normal propeller vibration.

[Paul L]

You could have old, soft engine mounts. Volvo replaced the rear mounts on the 2003 with a newer design that is stronger. When I couldn't get my 2003 to align properly, I eventually found a hairline crack in the rear mount and had to replace both rear mounts.

Paul L

[Pblais]

You could have old, soft engine mounts.

It's something that can throw the shaft out of alignment too. I'm not sure how long Yanmar say they will last but they don't last all that long.

If you replace one mount you might as well do them all. You still have to do a realignmnet even if you replace just one. They all start fail at about the same rate.

[ribbony]

We have been through this same thing over the last month. We installed a used nanni 30 HP and got 4 extra identical mounts with it when we bought it. First up i got it reasonably aligned to about 5 thou. But then changed one dodgy engine mount that was compresing too much. Then I got the tolerance narrower but engine vibration increased ? It appears that the engine mounts were all of different density, not by design but from time and usage (mounts under heavier parts of the engine break down more). Last week I removed all mounts one at a time and tested them, I then put the 4 best mounts under the engine with the stiffest under the port fwd position where the engine is heavier (heat exchanger, alternator, etc). Now the vibration is much much les even though the tolerance of shaft adjustment is only 9 thou at the moment (ran out of time before going away), so the mounts are an important factor in the drive train and engine vibration problems.

I will have to do the alignment again this week to get a better tolerance.

Another factor is the torquing of engine mounts differentially from when the engine is aligned. The engine should sit on them with neutral sideways tension, if you align the engine to shaft by balancing the sideways tension in the mounts then that static adjustment achieved will be thrown out when the engine is driven forward under drive. This was also a contributor to our initial problem with vibration. A local boat owner who is also a marine mechanic told us to do it this way and we felt it contributed to less vibration.

[senormechanico]

Ribbony,

I followed you until the last paragraph.
Am I supposed to align my Volvo 2020 when it's in gear and with throttle applied ??

Steve B.

[ribbony]

No, you do not need to do it other than engine off, at rest in the boat, preferably in the water, not on the hard stand or slipway. What the goal is here, is to have the alignment to a close tolerance without any sideways stretch of the rubber in the engine mounts.

If you have your engine bolted down to the engine beds via the engine mounts and check you tolerance, noticed it was out in the lateral alignment (vertical adjustments are much easier), and needed to make an adjustment. Then you need to move the motor sideways to get the tolerance to specification. However, all bolts holding the engine to the beds need to be loosened so any adjustment is made by moving the entire engine, left, right etc. If you move just one mount then you will have some sideways pressure on the shockabsorbing material of the other mounts, if you bolt down the motor then that residual tension can cause the engine to assume a slightly different position after the first use or while under load. The engineer who told me of the best approach did it with gear a bit too complex for me to worry about, he used a lifter that sat in the vessel with an arm that came over the engine and had 4 sling to above each of the engine mounts, the rig could be adjusted in any direction so the engine could be positioned laterally for alignment with minimal pressure on the mounts. Then when the lateral position is found the engine is lowered on the beds, fastened and the vertical adjustments done along with any fine tuning of the lateral tolerance (if needed).

Hope that helps, bit hard in this case to use words to describe a manual skill.

[drinky]

Just a little bit of info but I can't find the printed sheets to be exact. Yanmar people told me and printed out a sheet showing that mounts are different hardness and MUST be attached in the right place or vibration will result. Wish I could find the info in my filing system.

[ribbony]

I wish our cushyfloat engine mounts had two stiffer ones for the forward mounts as the engine is much heavier at that end and you can see the flimsy things squash a lot more under the load there.

I priced some Isoflex mounts last week, and we may go down that path if the cushyfloats give upunder the strain. There are differences between mounts and some do a better job than others.

The marine surveyor David Pascoe has some good info on his site somewhere at
Yacht Survey Online: David Pascoe, Marine Surveyor

[harmony80]

This may be an old thread...but when the shoe fits...
Really helpful info.

EvieB

[Cheechako]

I see no mention of how you are doing it , but assume you are disconnecting the shaft from the engine and aligning by checking the gap between and concentricity of the mating flanges right?

[Beausoleil]

We just went through the same thing when our shaft coupling bolts all sheared off. An engineer I had look at it came to the conclusion that the engine (less than 500 hours on it at the time) was mis-aligned when it was installed, and that after 500 hours of vibration, finally sheared off the coupling bolts.

An other contributing factor, I believe, was that the engine came from the factory with engine bracket mounting bolts (which bolt the mount brackets to the engine block) were 5mm shorter than spec'd by the said manufacturer. Back in January, one of the engine mount bracket bolts sheared off. Should have recognized then that the engine was out of alignment. That and the fact that the stuffing box continued to leak even after I re-tightened the packing gland nut...


As I'd never done an alignment myself, I paid the engineer to do it with me as his helper - invaluable OJT!

Now, I'm not one to malign a manufacturer which built the engine, a boatyard which installed the engine, nor a distributor who "certified" the installation, but let's just say I'm not a happy camper right now. I let them all know they're responsible for at least part of the haul-out (had to repair some rudder damage from the prop striking the rudder when the coupling ceased to couple!) and the associated fees...

I know people say "it's a boat - these things are to be expected". But what would you say if your car's U-joint failed with less than 500 hours of drive time, and it was proven that the engine mounting bolts from the factory were not up to spec? Just about any car manufacturer (not in bankruptcy ) would honor their warranty and re-imburse repair expenses...

Sorry - just gotta vent somewhere!

[mikereed100]

[quote=ribbony;274333] The engineer who told me of the best approach did it with gear a bit too complex for me to worry about, he used a lifter that sat in the vessel with an arm that came over the engine and had 4 sling to above each of the engine mounts, the rig could be adjusted in any direction so the engine could be positioned laterally for alignment with minimal pressure on the mounts. Then when the lateral position is found the engine is lowered on the beds, fastened and the vertical adjustments done along with any fine tuning of the lateral tolerance (if needed).
quote]

That sounds extremely slick, but I am curious, how did you do it? I am running up against the same problem and all I can think of is hammering the mounts into position and then ever-so-slightly jacking the engine up one end at a time to relieve tension between the mounts. I imagine though that as soon as I do this I will nudge the engines out of alignment again.

Mike

[harmony80]

We are having similar problems, including with the various folks who did the original work, and with our lack of knowledge about how to do it ourselves, we feel in over our heads. We had one mechanic who said we needed to replace the stringers the engine mounts sit on...but for the life of me we cannot figure out why when we look at it ourselves. We have one more mechanic arriving next week to take another look. If we don't get answers we can understand, we plan to bring in an engine surveyor for consultation.