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Engine mounting woes


Gareth E

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I recently refitted my engine after it was overhauled. Just checking it over today I noticed that one of the engine mounting nuts was missing. I'm pretty sure I fitted and tightened all 4 but there you go. The nut is nowhere to be seen so I need to buy a new one. Trying to measure it with a tape my best guess is it's a 15mm thread. Are these a standard thing, or does the thread size vary from engine to engine?

I also checked the tightness of the other nuts. One of them, if I try to tighten it, results in the male part turning as well, so I can't tighten it. Is this cause for concern?

Thanks. 

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34 minutes ago, Gareth E said:

I recently refitted my engine after it was overhauled. Just checking it over today I noticed that one of the engine mounting nuts was missing. I'm pretty sure I fitted and tightened all 4 but there you go. The nut is nowhere to be seen so I need to buy a new one. Trying to measure it with a tape my best guess is it's a 15mm thread. Are these a standard thing, or does the thread size vary from engine to engine?

I also checked the tightness of the other nuts. One of them, if I try to tighten it, results in the male part turning as well, so I can't tighten it. Is this cause for concern?

Thanks. 

I am having difficulty in relating that to modern engine mounts so suspect the rubber mount and steel insert have parted company. It sounds like new mount time to me but they really need changing in pairs, if not the whole set. That is pairs of front or rear mounts.

If the engine is not aligned to the shaft within about 0.05mm (angular and radial) the vibrations can damage mounts and loosen nuts.

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If you are going to stay with the existing mounts, try taking off one of the remaining nuts and taking it to a local supplier to get a replacement for the missing one. 

However, I am with Tony on this, it may well be time to replace the mounts, and do get the alignment spot on, or all your time and money will have been wasted.

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31 minutes ago, Gareth E said:

Sorry I attempted to measure the thread diameter, not the size of the tool needed to tighten it. I don't know the latter, it's more than any of my spanners, so i used an adjustable one.

Not to worry; Tony and Stillearning have posted a way foward for you. A photograph is always useful.

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Thanks for the replies. Managed to find the offending nut in the bilge. I've put it back on and tightened it down. Started the engine ran it in neutral and then in gear. Nothing seems to be moving around more than it should. I think I'll keep my eye on it, check it after each cruise. I noticed that this particular nut tightened straight down onto the engine. The others have a serrated washer between the nut and engine. This one must have got lost when the engine was taken out. Would you recommend to replace this with a nyloc nut, get a serrated washer, spring washer, what's best?

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Thanks. How do I check it's properly aligned? It just lifted off the bolt part of the mountings, then back on, no adjustments were made, I didn't think of checking, and wouldn't have known how to. I tightened the mounting nuts before I fitted the drive coupling, was that the right sequence? 

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23 minutes ago, Gareth E said:

Thanks. How do I check it's properly aligned? It just lifted off the bolt part of the mountings, then back on, no adjustments were made, I didn't think of checking, and wouldn't have known how to. I tightened the mounting nuts before I fitted the drive coupling, was that the right sequence? 

You can disconnect the shaft from the coupling at the gearbox and push it back clear, draw it forwards again and see if it aligns up with on whatever spigots there are on both half couplings or flexible coupling, equally all around and that the bolts pass through with ease. If you have  thrust block on the shaft it might need unbolting from its mount to move the shaft back and forth. Take note of any shims under the thrust block mounting and replace them from which side they were from.

Edited by bizzard
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8 minutes ago, bizzard said:

You can disconnect the shaft from the coupling at the gearbox and push it back clear, draw it forwards again and see if it aligns up with on whatever spigots there are on both half couplings or flexible coupling, equally all around and that the bolts pass through with ease. If you have  thrust block on the shaft it might need unbolting from its mount to move the shaft back and forth.

OK when I installed it, with the engine mountings fastened down tight, the drive coupling was easy to fit (after I nearly broke a finger when the shaft, which seemed stuck, move back very quickly) the holes and bolts lined up easily. Does that cover what you wrote above?  

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5 minutes ago, Gareth E said:

OK when I installed it, with the engine mountings fastened down tight, the drive coupling was easy to fit (after I nearly broke a finger when the shaft, which seemed stuck, move back very quickly) the holes and bolts lined up easily. Does that cover what you wrote above?  

Yes, but that was before the nut came off, wasn't it? If that bottom nut has wound down you would need to do it again. If the shaft suddenly moved back the half coupling spigot may have stuck because it was out of alignment to begin with.  Are the rubber mounts adjustable  with the nuts under the engine mounting legs? If not you'll have to adjust them with shims between rubber mounting units and  the main bearers.

Edited by bizzard
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10 minutes ago, bizzard said:

Yes, but that was before the nut came off, wasn't it? If that bottom nut has wound down you would need to do it again. If the shaft suddenly moved back the half coupling spigot may have stuck because it was out of alignment to begin with.  Are the rubber mounts adjustable  with the nuts under the engine mounting legs? If not you'll have to adjust them with shims between rubber mounting units and  the main bearers.

If they are adjustable rubber mountings they should have a couple of flats on the tops of the studs,''where you screwed that lost nut on''. These are to hold the stud still  with a spanner whilst you tighten that nut.

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27 minutes ago, bizzard said:

If they are adjustable rubber mountings they should have a couple of flats on the tops of the studs,''where you screwed that lost nut on''. These are to hold the stud still  with a spanner whilst you tighten that nut.

I have the flats on mine, wondered what they were for. When I first tightened the nuts the studs didn't move, guess that was just luck?

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