Volvo Penta MD3 Motor Mounts Need Advise

[Foreverunstopable]

Hello everyone. I am finishing up my preparations for heading out to live aboard. My last serious issue is relating to the motor mounts. Take a looks at the mounts themselves. There is a stud that appears to be welded to the engine bed with a round rubber bushing with a hole in the center. The mounts as you can see are badly worn and in the rear provide no dampening. I have been to every marine store/surplus/boat yard and no one seems to recognize them. I need a solution sooner than later. I have read that there are two mounting types, "Hard" or "Flexible" These mounts appear to be hard. I would attribute the badly worn cutlass bearing that I replaced on the last haul out after my purchase of Hannah to the vibration caused under power as the engine vibrates transmitting that through the prop shaft and log to the bearing. Any and all advise would be greatly appreciated. I have thought about making my own from urethane bushings or auto body mounts and as a last resort using a hockey puck shaved to be in trans prop flange tolerance with a hole drilled in the middle in the mean time to finding a solution. Thanks in advance!

I know they are dirty, I'm cleaning out the engine bay next, just replaced the transmission and sealed the valve cover oil leaks.

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[Mike Holibar]

Hi, over the years I have been involved in quite a few engine installations both on behalf of the Perkins/lombardini dealer here in New Zealand, as well as repowering several of my own boats. Your photos appear to show basic industrial rubber mounts which you might source through a bearing or transmission specialist. They would not be my choice for the installation but it appears the real problem is the lack of space between the engine bearers and the mouning brackets which would prohibit the use of the usual resilient mounts. The centerline of the gearbox output, which must of course be in the same plane as that of the propeller shaft, determines the height of the engine in relation to the bearers. By the look of the photo, ther is nothing you could do with the bearers so the remaining options would be:
1) Insert spacer plates between the bearers and mounting brackets of a thickness that will ensure the prop shaft and gear box flange are properly aligned and bolt the whole thing down solid. This couldn't be any worse than the current set up with the worn mounts, and will be better for the stern gear.
2) modify the mounting brackets to create the space needed for resilient mounts. It should be noted that the best arrangement is to have the horizontal centre of the mount at the same height as the engine crank shaft. The gearbox output must be aligned with the propeller shaft and a flexible coupling must be used between the gear box flange and prop shaft half coupling.
3) If it is possible to move the engine forward a cardan shaft or CV type coupling could be employed to enable you to change the angle of the engine, thereby creating space for resilient mounts. A thrust bearing would be required on the prop shaft with this set up. This arrangement delivers the best result as regards reduction of vibration and noise transmitted from the engine.
4) Try industrial sources for similar mounts to those you have.

Apart from replacing like with like, each of the options is quite a big job. Depending on the overall condition of the engine, and the state of the finances, it might be an idea to consider replacing the engine with a more modern one. The newer engines are generally more compact for the same power output and would allow you a lot more room to move. Hope this is of some help, Kind regards, Mike Holibar.

 

[kloudie1]

Mike is right on.. Look at these guys for an idea of what is available to design with. http://www.polyflex.com.au/

 

[Mike Holibar]

That is a good suggestion from Claude. Polyflex are the most popular mounts over here and their technical advice has always been very good. In NZ we have the "category one" rules for vessels heading off shore. One rule relates to securing the engine so that it stays in place in the event of a capsize even if the engine mounts have failed. The usual method is to put a wire strop over the engine and shackle it to the bearers. however, the Polyflex mounts have a failsafe design that will hold the engine even if the rubber part is gone, so they meet the cat 1 requirement for securing the engine. Polyflex also do flexible couplings for the prop shaft.
Kind regards, Mike Holibar

 

[Foreverunstopable]

Thanks for all of the input! After looking at all the options and then my wallet I decided to make a temporary solution for 4.99 and about 2 hours time. I will replace the mounts with a proper setup when I can afford it. Here is what I did in the meantime.

I went to my local hardware store and purchased the 3 hardest rubber mallets I could find. Got my calipers out, feeler gauges, hacksaw, 24mm deep socket with 3ft extension, breaker bar and my smallest jack. I unbolted the transmission from the prop shaft. Then lifted up the engine and removed the old mounts. Then measured lowered the engine until I could not fit my smallest feeler gauge between any part of the shaft mount and trans flange. I then measured the distance between the motor mount and base of the stud. Then I took that measurement and added 3mm and transposed that onto a rubber mallet cutting it with a hacksaw to make a "puck." Then I drilled the puck with a wood butterfly bit the diameter of the stud. I re measured all sides of the puck and if it was off sanded it to the correct diameter. Then pushed the puck onto the stud and repeated the process for the others. After lowering the engine back down it was sitting about 2mm high. Using the break bar I could tighten the stud bolts to take up the exact distance I needed. The end result was no gap at all between the trans flange and prop shaft. I ran the engine for 30 min and re tested the gap to find no gap. The next day I motored off to my new slip 15 nautical miles at 2500 rpms with little to no vibration thought the boat where as before it was quite noticeable. At the slip I re tested to find no gap again.

For the meantime. a $5.00 solution to my problem will do until I can get proper mounts. I figure the boat has had this setup for the last 36 years and even if I have to change mounts each season the time spent making mounts is well worth the expense.

Any thoughts?

 

[Foreverunstopable]

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[Mike Holibar]

A good economical fix by the sound of it. Just a couple of points to keep an eye on. Firstly your checke between the coupling flanges confirmed that the faces were paralell which is good, but would not tell you if the propeller shaft and gear box output shaft are aligned on the same axis. If they are not then there will be some load on the stern tube which may give problems later. A simple check would be to make sure the shaft turns freely by hand with the gear box in neutral. Second thing is, depending on the number of cylinders, your engine will be trying to move in certain ways against the mounts. 2 cyls tend to jump up and down while 3 cyls want to do the twist. For every action there is an equal and opposite reaction so while a downward motion will be softened by the rubber, the upward will hammer against the nut and stud. I have seen studs break in these circumstances so it would be a good idea to include the studs in your daily engine inspection. Cheers, Mike