Polyurothene engine mounts for outboard engines ?

[pdt]

what is the opinion on here for using a better type of rubber for the top engine mounts on OMC triples ? or any other outboard engine
I know some people have gone to the extreme and fitted solid mounts, but this just puts the stresses on other places , I.E the transom etc.
some don't like the idea of the solid metal mounts causing gearbox failures due to stress cracks being caused by complete solid mounts too.

What if you were to use polyurethane bushes like those fitted to customised vehicles and off road extreme vehicles ?
The polybushes come in all different grades of stiffness from soft to almost solid as a rock and will last 10 times that of the omc/brp mounts.
Lots of the big customised inboard engine use the polyurethane due to it being so much better and long lasting.

The size of the bushes that will fit the OMC triple just happens to be a size that is very common all around the world, and very cheap !!!!!
salt water don't destroy the polyurethane they also don't mind the heat or extremes of pressure.

some of the benefits of this type of mount would be the resistance to petroleum fuels and hydrocarbon fuels ,its low compression set, good abrasion resistance
good tensile strength and high rigidity, good ozone and weather restance and even dry heat tolerance to over 100 degree C.
so would this not be an ideal application for high performance outboard engine mounts ?

the price of this type of mount is extremely cheap and easy to replace compared to the normal factory mounts costing over 5 .times the price just to renew the normal mounts and
still being a bit soft.
By using a more rigid mount that will still give a certain amount of flex must be a good thing on outboard engines ?


with say the top mounts on the (1992 0nwards) OMC triple engines, once the rubber is removed from the original mount its a simple case of pressing in the bushes,
these can be pushed in by hand with the half each side type or pressed in by machine for the full bush type, the inserts are stainless tubes so also less chance of rotting.
ive noticed that the bushes in the uk range from around £10 for two , so that's the top mount on an outboard such as the omc triple complete and in
the USA prices for these are from around $10 upwards for the pair depending on your choice of colour and stiffness.

considering these bushes take the strain of rally cross vehicles suspension , I would thought that outboard engine mounting with these would be good.
is there any valid reason not to use such a bush as this type ?
I have looked around and seen these bushes taking so much strain and torture from all sorts of vehicles, even heavy duty trucks are now having these fitted
instead of the usual cheapo rubber from the factory.

I could ofcourse be very wrong and maybe these have been tried and tested to be not good for outboard engines for a very good reason, but I cant see any drawbacks to these
and being as the sizes needed are on the shelf in 90% of motorsports shops and very cheap to buy, to me makes good sense.

anyone else ever tried these and got good or bad results ?

[Roflhat]

I've got these on my tohatsu - http://www.boatmad.com/forum/showthread.php?t=19720
I think they're polypropylene as opposed to polyurethane as they are very hard. I have polyurethane bushings on my car instead of rubber though

[pdt]

That's the same sort of thing I am talking about.
these will last 10 times longer atleast if using the polyurethane, probably yours will be the same, and it lets you use existing original metal mountings so the fit is perfect.

I do know that there is a size that fits the omc top mounts, ive not looked at other engines for sizes just yet.
I spoke to guy who has fitted the poly bushes from a MINI CLASSIC lower suspension arm kit to his omc and the fit was dead right !!!!!
Now these bushes if used from the auto industry are mega cheap, just £10 or $15 us money for the top to be done, now that's cheap and will give better
results than the soft rubber used by the factory.
there is plenty of different hardness types to choose , they go from a bit stronger than normal bushings to almost solid, so this means they could be
for leisure motors to out and out race engines.

those for the tohatsu look very nice, have you got these fitted ? and what results do you find with them ?

[Roflhat]

The standard tohatsu mounts are fairly flimsy hollow alloy ones. The poly ones were more solid with just a hole for the bolt. I'd heard that they increased vibration on the tiller, but I didn't notice, maybe because I have so many bungees on my engine.

The poly stuff that I used on my car (1967 VW Beetle) was much softer, far too soft for outboard mounts anyway. I agree that the prices for outboard mounts are high but the demand for them is much less. But if you find mounts from a car that would fit then I say go for it.

[pdt]

with poly for cars you can get about 10 different specs for stiffness.
from ultra soft to almost rock hard.
I had some on a range rover that were about 250% stiffer than oem and they made the car handle so much better.
different colours are normally different grades, black is normally around the same as original fitment then blue then orange then red then yellow etc.
some company only do 3 grades, soft hard and almost rigid, the mounts used for most outboards are a bit soft to try and give a smoother ride on the boats.
But the rubber is prone to deteriation due to fuel spills and salt etc, its the prices as well be so crazy made mne look at whats available on the market cheaply.
The bottoms of the omc triple don't go so bad and are not so hard to replace, but the top ones are the expensive ones and they are the ones taking the real brunt
of the power.
during the winter ill be taking the powerhead ,so while its off ill put poly bushes in I think.
ive got a spare set of top mounts already im sure so ill see what I can do with those, the rubber on them is shot to bits, so cant do anything wrong ha ha .
plus I cant paint up a steering arm and have it all ready to just fit on straight away.
$10 to $20 for new top mounts seems a good deal to me.
Will probably get solids made up for the lower ones though, unless I can find someone who works with the poly to sort me some out..

Just got to build up the courage to take powerhead off now .

[pdt]

the old mini classic bottom mounts are the exact fit for OMC top mounts, plenty around and very cheap.
can get them in 2 part for each hole or single that need to be put in with a press, both types about same money.

[Roflhat]

Yeh I used the red ones, hardest I could get... The ones on my tohatsu are obviously very solid, the old rubber/alloy ones were fairly knackered so I'm glad i replaced them when I did. It's on a thundercat so a lot of stress on it.
It was a job I hadn't been looking forward to removing the powerhead. Was actually a lot easier than i thought, took about 3 hours from start to finish.

[pdt]

3 hours sounds good to me. im always worried about breaking bolts on the powerhead. ive only ever had one engine that never broke any bolts at all, and to look at that you would of expected it to be completely knackered ha ha
from what I see the omc powerhead should be pretty straight forward.
take off the little under belly panels undo the nuts/bolts plus the little one at the back and just lift off !!!!!
ill already have taken t he gearbox off to make life easier anyway, just hope that's all there is too it, then can have a good clean up around the joint to mid section n as well.

what make of bushes did you buy for the vw ? strange the red ones were soft, maybe the supplier of that make done red as soft and others as hard ???
bet they never need doing again neither.

[Roflhat]

I snapped one of the bolts holding the pan (fortunately not the powerhead). It's a good chance to clean everything up and grease bits you can't normally get to.

http://www.machine7.com/product.php?xProd=652 These are the ones I used for the gearbox. Same material for suspension bushings though. The previous ones had been in for 45 years and they weren't even totally knackered, so hopefully another 20 years out of these ones.