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Post by tedp on May 12, 2014 14:36:11 GMT
An unpleasant surpriseLast week I was phoned by the engineering firm that maintains my Volvo MD2020 engine, telling me they had found a broken engine mounting bracket. They were inspecting the circulation pump which is partly mounted on the bracket and found this:  www.009dutch.nl/jeanneau/img_7703.jpgI was in luck as they had an identical bracket on a defective engine. So they replaced the bracket and lined out the engine against the prop shaft, finding no trouble to speak of. Is this a known problem? Any idea what may have caused this? Here is a close-up of the breakage, showing a crystalline surface with a few polished spots where the parts have rubbed together. They look like having been considerably out of line when they touched.  www.009dutch.nl/jeanneau/img_7706.jpgFinally, here is proof of identity:  www.009dutch.nl/jeanneau/img_7710.jpgFunnily the Volvo seal had not been damaged, but it may explain the extra wear on the strut bearing under the stern.
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Post by Trevor on May 13, 2014 23:06:24 GMT
Hello tedp,
Well done to the service firm for finding it. Even better for having a spare. I think this would surely be pretty unusual. The bracket looks very solid but you can see where it has been fractured for a while where the rust has developed.
Great photos by the way.
Regards,
Trevor
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Post by tedp on May 14, 2014 12:09:03 GMT
Thanks, Trevor. I showed it to someone else with an engineering background, and he thought the weld of the diagonal stiffening rib may have been to blame. The fracture may have started there - you can see the extent of the weld in the material in the photo, on the left. It goes deep into the material and there looks like being a hairline crack along it. Vibration probably did the rest.  |
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Post by ianqv on May 18, 2014 17:51:29 GMT
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Post by tedp on May 18, 2014 19:40:48 GMT
Thanks, Ian - I have a replacement. It came off a written-off engine the engineering firm had in store.
This weekend I ran the engine several hours due to lack of wind. Despite having been re-aligned, it vibrates below 1200RPM and above 2200. In between it is very smooth. My main concern is the low end vibration as the prop shaft rattles around visibly in the Volvo seal. This happens when idling without the prop being engaged, and after engaging the prop up to about 1200rpm. I'm going to phone the engineering firm tomorrow to see what they come up with.
I fear this kind of vibration will ruin any motor mount that has a tiny crack in it. Or damage the seal.
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Post by tedp on Jun 5, 2014 18:18:53 GMT
I did a few tests of the engine with the boat secured to the jetty, running it in gear from about 800rpm up to over 2700. I found that up to 1200rpm it vibrates on its mountings, with the prop shaft vibrating in the Volvo seal. Over 1200 it is rock steady, although over about 2200 there is vibration coming in. The engineering firm says that the low rpm shaking is due to the small flywheel size on the MD2020. They say it isn't harmful to either the mountings or the shaft seal. The vibration in the 2000-3000rpm range must come from the two blade propeller. They had observed vibration on different boats using the same power unit, such as a Bénéteau they had been working on. The saildrive version doesn't seem to have this kind of vibration (apart from the gear noise mentioned elsewhere). The prop noise may or may not be reduced by replacing the strut bearing bush. The engineers say they have seen vibration becoming worse after fitting a new bearing bush. I can motor at 5.5 knots in relative silence, which is enough for me. It may not be ideal, but I'll live with this. As long as the engine doesn't jump out of the boat of its own free will, that is!  |
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Post by patryk221 on Jun 9, 2014 11:59:55 GMT
I've also got the md2020 same thing vibration is driving me nuts, similar to your on the other hand I have been talking to someone last week about it, the boats are so light and made of thin fiberglass mouldings that you would feel it vibrating more then on older generation boats (that's what I been told) ib checked my mounts and aligned the engine, I think it's a common fault of either the thin layered boat design or the engine itself....
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