Fabricate your own PU engine mounts - feasible ?

[carioca1232001]

I was contemplating fabricating motor-mounts for my twin-diesel installation (as well as body-mounts for my aging Willys CJ-6 ;) ).

Proposal:

1. First, turn a piece of PU (polyurethane) rod (90 Shores stiffness)into a cylindrical (or barrell-shaped)bushing of the appropriate dimensions.

2. Drill undersized holes at either end of the bushing for holding 304/316 SS threaded-rod (1/2" 0r 5/8" dia).

3. Swob aforementioned holes with the appropriate glue (?)

4. Screw-down the threaded rods into the undersize holes and let the glue dry completely.

The use of threaded-rods at either end - instead of just one threaded-rod traversing the PU bushing, as evidenced in some vehicle-body-to-chassis mounts - is to isolate the engine/body side of the bushing from the rail side, via the PU material.

Feasible or just nonsense ?

Does such a glue exist ?

The mount could even be pre-loaded by holding a washer down (with a nut) at either (or both) end(s)

Thanks

[Gary E]

Have you ever seen the canoe built by 2 fellows on description alone? It's siting on horses and one end is poing up, the other pointing down... THat is what happens trying to understand a word description of a assembled motor mount.

I am sure you can make about anything and have it work well. First thing I would do is try to find one that is close to what you want and copy that design to suitable dimensions. If you cant find a real one to hold and measure, use a catalog description and picture to help you to draw up what you want.

If you have a local machine shop to help you, they probably know what materials to use, where to get them and how to make it work.

[sdowney717]

Threaded rods sitting in drilled holes. I keep thinking what happens if the boat is being tossed about by the waves under power and those bushings let go. Thru bolting with some kind of large washers on the ends to keep it all together under stress is what you want. What happens when the boat rolls and the forces want to rip the engine from its mounts?

How about this

Take a flat rectangluar 1/4 inch steel plate. Weld a mounting stud to the exact center of the plate or drill it and run the mounting bolt thru and weld it attaching to the plate.
Cut your polyurethane block to match the plate, make it 1 inch thick.
Create a boat mounting steel plate 3 inchs longer then the upper plate, drill mounting holes to attach plate to boat and drill 2 holes to secure plate to plate running thru the polyurethane block.
This will not fall apart. You can even run a rubber bushing onto the bolts that hold the plates together to minimize noise or vibration to keep bolt from touching plate.

[carioca1232001]

I have seen the auto-body-to-chassis mounts as well as the boat-engine-to-rail mounts.

The former are no more than a blob of PU with a hole traversing from top end to bottom end. A through-bolt and a lock-nut at one end secures the body-to-chassis via the PU mount.

One type of boat-engine mount (Globe Eng)I have come across is made of two concentric cylinders of PU material, the inner being softer, the outer harder. A bolt is threaded into the inner PU material. The concentric cylinder arrangement sits on a slab of PU, the ends of which are bolted to the supporting rails.

I imagine that this type of mount is cast (Pu resin + hardener) in the factory. Quite a messy thing to do at home. :rolleyes:

Does anyone know of a glue that will bond SS threaded-rod screwed into an undersized hole in a PU bushing ?

[sdowney717]

You dont want the plates moving around sliding past each other. A mount needs to keep the engine in place. If the engine moves it can stress the transmission bearings shaft etc...
If you got real inspired you could weld a rim onto the sides of the plates which would keep them from aligned.

[JimConlin]

Go to McMaster-Carr (http://www.mcmaster.com) and search for mounts.

I'll be very surprised if you can't make a standard component do the job.

[carioca1232001]

Thanks for the McMaster-Carr tip. Twelve mounts (twin-engines, plus gear-boxes) will cost upwards of US$ 700.

Also thanks to sdowney for the suggestion.

Now take a look at the Globe engine mount. The threaded-rod was probably cast with the rest of the PU resins in a mould:

Globe Rubber Works (http://www.globerubberworks.com/nav.php?products_motor_mounts)

Does LOCTITE make a glue that will bond PU and SS threaded-rod ?

[Canoeyawl]

Mc Master lists them as "ISOLATORS,VIBRATION"

[kc8pql]

However you do it keep in mind that the engine mounts on a boat not only dampen vibration likre they do in a car, but also transfer thrust from the prop to the boat.

[Ric_Bergstrom]

https://secure1.nexternal.com/shared/StoreFront/default.asp?CS=ireland&BusType=BtoC&Count1=761425197&Count2=678565621&Ca tegoryID=3&Target=products%2Easp

Should do the trick. I use them in my race car and they hold up to a BMW motor being slung around at speed!!!

Ric

PS the BMW E30 race car is for sale cheap too!

[sdowney717]

Have you read this about mounts. Apparently he says the donut style mounts cant take the weight of a marine diesel.
http://marinesurvey.com/yacht/alignment.htm

[Cuyahoga Chuck]

The design of motor mounts for cars took a quantum leap in the '70's when a lot of gas-mizer 4 cylinders were built. Because a 4 cylinder can only be balanced to the first harmonic the only way to smoothness was to come up with some super motor mounts.
They were able to determine what planes most vibrations were in and design mounts that that were most effective in those planes. It worked for fours and also vee sixes.
Designing motor mounts for big torquey diesels has got to be much more difficult than doing the same for puney 4-bangers.
What you want to do will probably work but I wouldn't put any money on their ability to keep your back teeth from rattling.
Charlie

[Stiletto]

I have been on an old launch with a big diesel and solid mountings. On a heavily built vessel this arrangement can be quite smooth if properly set up.

[carioca1232001]

I am off to work on the boat now (6:30 am)but will give the new posts - and leads - some careful consideration when I get back this evening.

Many thanks !

[carioca1232001]

Thanks sdowney for David Pascoe´s semi-tutorial on engine mounts, shaft line-up etc.

Standard auto motor-mounts may not be such a good idea, even though they may stand up pretty well to being slammed around in a high-powered BMW. ;)

To be quite honest, I refurbished the marine-engine mounts bought in the US in ´99 - the threaded steel stud had corroded rendering the threads useless for engine alignment. These mounts comprise a cast-aluminium housing, the central portion of which carries the threaded stud (5/8") and rubber blob.

I took them apart and this is what I found:

1. A blob of rubber press-fitted into the central cast-aluminium cone , with the 5/8" threaded steel stud vulcanised together with the rubber. A steel washer is fitted at the lower end of the steel stud to resist the lot being pulled out through the cone.

2. The rubber blob does no reach all the way down the height of the cone - stops 3/4 of the way. A rubber washer fits in the cone in the 1/4 lower space.

What I did was:

1.Press-fitted an over-sized PU cone into the cast-aluminium housing, to occupy 3/4 of the cone height.

2. The above assembly was put on a lathe and an undersized hole (1/2") drilled through the PU cone; a 5/8" SS threaded stud, with a 7/8" SS washer welded to the stud bottom, was press fitted into the undersized hole.

3. The above steel washer had two 1/4" holes drilled diametrically opposite to each other, and two short pieces of SS rod were driven into the PU, to inhibit the 5/8" SS threaded stud from turning.

4. A PU washer was now press-fitted into the bottom of the cone to take up the 1/4 remaining space.

5. A SS washer, with 2" overall dia. and a 5/8" hole, was prepared and two pieces of 1/8" thick by 1/2" wide SS flat-bar were welded (radially) at diametrically opposite ends.

6. The above washer was fitted over the 5/8" central stud, and the SS flat-bar pieces oriented in the fore-aft direction while making contact with the PU surface below.

7. A low-height 5/8" SS nut was now threaded down the 5/8" SS stud to just make contact with the above washer; note that the washer is making limited contact with the upper surface of the press-fitted PU and sitting some 1/8" over it, due to the SS flat-bars welded at opposite ends;

8. The low-height nut was now turned an extra turn or so, to pre-load the PU material, with the washer pressing down on the same through the SS pieces (fore-aft direction).

It was observed that the ensuing assembly displayed considerable stiffness to movement in the fore-aft direction, but was relatively free in the port-starboard, as well as up-down axis.

So these refurbished PU engine-mounts were fitted on the twin-diesels when it was noted that the 5/8" stud did not turn when turning on the nut to raise and lower the engine (thanks to the 1/4" SS pins of item 3 !)

The engines also seem to be well-sprung in the up-down and port-starboard axis, but movement is stiffer in the fore-aft direction (thanks to items 5, 6, 7 and 8).

But as the real test of the pudding is in the eating - wait to hear from me when I take her out for sea trials ! :rolleyes:

However, please inform if anyone knows of a magic glue that will bond a SS stud to PU in the above application - may need it for the Willys CJ-6 refurbishment currently underway, to include body-mounts ;)