View Full Version : Repower - Motor Mounts

G & T
09-20-2003, 06:46 PM
WE are going from a Perkins 4.108 to a Yanmar 4JH3, 56 HP diesel eng. The Yanmar motor mounts are too high for our application. Any recomendations on alternate mounts or is it feasable to hard mount the eng? Also any suggestions for flexible shaft couplings? The eng. stringers are wood covered with glass. The boat is a Tyanna 37, a very heavy boat.

On Vacation
09-21-2003, 06:54 AM
Yes, you can hard mount the engine. I would do it with aluminum caps on the stringers, placing a loop at the mounting brackets, to allow for throughbolting it. Keep in mind the lower you go with the engine, the more problems you will have in servicing the engine.

Many times we remake mounts that bolts to the engine, as most will not do the job in many cases. If you have enough romm above the area on the engine to make a looped type, you can use the vibration dampers mounts, that come with the engine.

In hard mounting, you can use shims for alignment, under the brackets, drilled with holes in them, or cut out u-types slits in the pieces for sliding them in for refinement for the alignment.

If you are talking about the flex coupling that goes between the shaft couplings, Babbitt makes one that has been used in many of the high performance boats with success. Many will distort with heat from the engine room, in warmer climates.

[ 09-21-2003, 07:59 AM: Message edited by: Oyster ]

09-22-2003, 06:27 PM
Try Polyflex at www.polyflex.com.au (http://www.polyflex.com.au) - they have a range of low profile mounts and flex couplings with DNV approval.


[ 09-22-2003, 07:30 PM: Message edited by: Lion ]

09-22-2003, 06:49 PM
Hard-mounting is a fine, long-standing method of engine installation, but brings with it some problems. Vibration and sound are transmitted to the hull more efficiently with hard-mounting, so the engine will be noisier. Alignment is more critical as well.

My preference would be to find a way to soft mount the engine, either by fabrication of new motor mounts or by modifying the engine beds. I presume that your problem is that the Yanmar mounts need to seat farther down in the bilge. Building the beds up to the required mount height is easy. I have spec'd American VULCAN (Winter Haven, Florida) flexible shaft couplings in several projects and have heard no complaints about them. Keep in mind that you get what you pay for in couplings - saving a few bucks will make you pay later.

G & T
10-04-2003, 08:58 AM
Has anyone had experience with the Bullflex shaft coupling by Vetus? They claim it eliminates vibration & allows for up to 2 degrees of mis-alinment.

10-04-2003, 09:34 AM
I have no first-hand experience with that product, but have had good success with other Vetus products.

With all flex couplings, do not presume that you can accept a misalignment up to the variance that the coupling allows. If your engine is soft mounted (feet & shaft) it will dance about quite a bit due to vibration, torque, dynamic motion of the boat, etc. The flexible coupling has to be free to absorb this motion. If the coupling can take a two degree misalignment and your installation is one-and-a-half degrees out of line, then the coupling can only absorb one-half of a degree of movement in the direction of the misalignment before it tears itself apart. IMHO, this is why flexible couplings get a bad rep for failing - not because they are a bad product, but because they are not used correctly.

Use a flexible coupling to isolate vibration from the hull, not as a cure for a poor engine/shaft alignment. Correct alignment during an engine installation is just as important with a flex coupling as it is without one.

G & T
10-07-2003, 07:18 PM
Thanks for all the helpful info.I think I'll go with Bushings flexible mounts & the Bullflex coupling.

Dayton Eckerson
10-08-2003, 03:53 PM
G & T:
I did the same conversion you are doing 2 years ago: Perkins 4.108 to the Yanmar 4JH3 in a Tayana 37. Yes, we also found that the standard Yanmar mounts were too large for the Tayana engine bed; we used smaller after-market mounts. They are not as flexible as the Yanmar mounts, but they have proven to be fine. I don't recall the make, but I can look for you over the weekend when I'm at the boat. For the flexible shaft coupling, we installed the PYI coupling which has workded fine also. I'd be glad to provide any other help you need regarding prop selection, transmission, exhaust system, etc. You can also contact a few others who have made this conversion through the Tayana listserve @ sailnet.com. Good luck!!! The conversion ain't easy, but it's worth it....

G & T
10-08-2003, 07:03 PM
I appeciate your offer. I'm going to use motor mounts by Bushings Inc. They are a lower profile as well as being shorter. One of the reasons I'm considering the Bullflex shaft coupling is to add some length to the shaft. The Yanmar is shorter than the old Perkins,I'm hoping to avoid replacing the shaft. Can't shift the engine further aft due to the curveature of the hull. I am using aluminum angle thru bolted to the engine beds to support the engine. To complicate matters we want to replace the alternator with a high output unit & also add a belt driven pump for a water maker. I'm leaning toward a 100 amp Balmar which can be driven by a single 1/2 inch belt. It should bolt up where the original sits. The water maker pump will have to be driven by a PTO on the front crank pulley. If you have any suggestions I would appreciate it. Thanks

Dayton Eckerson
10-09-2003, 10:45 AM
Which transmission are you using with the Yanmar? We had put our order in for the one recommended by our local dealer, but the factory "upgraded" the tranmission to the next larger size, apparently because of some problems they have been having with the torque limiter on the smaller transmissions. We were happy to recieve the larger transmission at no extra charge until we learned that the larger transmission increased the width of the entire engine by almost 2 inches!!! This necessitated grinding an inch out of each stringer --- NOT FUN.
Regarding the alternator, we wanted to avoid the hassles of doing a retrofit, so we ordered the upgraded 115 Amp alternator to be installed at the factory. It is internally regulated. This winter I'll be figuring out how to disable that regulator in favor of an external "smart regulator". In retrospect, I probably should have gone with Balmar and the larger belt, as you are doing. The 115 amp alternator puts a lot of strain on the standard size belt.

G & T
10-09-2003, 08:12 PM
I think it is a KMP3, 2.61:1 ratio. What did you get? I don't forsee any clearance problems. Distance between engine beds is approx 24". Did you have to use a longer propeller shaft? You can go up to 100 amps on a single 1/2" belt, that's why I choose the Balmar 100 amp alt. The 115 amp Yanmar alt is too big for a single belt. What do you have for battery banks?

Dayton Eckerson
10-14-2003, 01:16 PM
The KM3 transmission is what we ordered; the KM4 is what was delivered. You should have no trouble fitting in the KM3, though you might check into the torque limiter problem I referred to earlier. My dealer said the problems were occurring with repowering heavy cruising boats, like Tayanas. I've since heard of another Tayana that used the KM3 with no problems. Regarding the prop shaft, we did have to order a new one because the Yanmar transmission is much shorter than the Borg Warner transmission we replaced. Also, I think the taper on the shaft was "nonstandard", so we were likely going to replace the shaft in any event.
The 115 amp Hitachi alternator that came factory-installed operates off the standard belt. It has held up OK so far, but until I install a smart regulator, it is probably not being put through its paces. (BTW, be sure to snug up the bolts to the alternator real well, and use some loctite to keep them there. One of my bolts backed out recently while under way, shredding the belt. I've heard of others who have had similar problems.)