engine mountings replace

[Guest]

On certain revs my bukh dv8 seemed to be experiencing a thump which could be felt through the boat. Someone on the boat said it was probably the engine mountings. I purchased said mountings form bukh uk (£265 + vat !) and now intend to fit them. the orig bolts into the boat are corroded. I was going to cut them out and epoxy in new bolts. would this be ok to do it like this or would a big screw into the mounting bearers do.
thanks.

 

[Guest]

Your question is not entirely easy to follow, but I can try an answer.

Firstly, unless the existing mountings are obviously wrecked, I doubt if they are responsible for the knock. If the rubber has been severely softened by fuel or if some of the steel parts have completely corroded away, then possibly, but not otherwise. I replaced very severely corroded mountings on a Bukh 20 two years ago but they were not knocking. Far more likely that the shaft is tapping the stern tube due to poor alignment, this typically happens at certain revs. It may be exacerbated by softened mountings.

Secondly. Your engine is supported by the mountings at angles of heel to 30 degrees, perhaps with severe slamming, plus maybe its own torque reaction if motor sailing in bad conditions. The mountings must be held very securely and, with all due respect to the manufacturers of epoxies, I don't think that this method is anything like good enough. You need to undo the existing bolts and remove them. If they are into steel beds and they shear off you will need to drill out the remains and tap new threads, perhaps a size bigger. Try a good soaking with penetrating oil a day or so before starting. If the beds are wooden it is normal to use coach bolts but these should be at least two inches long. Don't try to botch this job, the consequences will be most severe, from water leaks, stern gland or shaft failure due to poor alignment, up to an engine falling through the hull of the boat.

 

[Guest]

hello
i agree with vyv cox. with regards to the ankering of motor foundations.
if something is knocking. what is it knocking on.look around for marks where the motor could strech itself to hit. or other things that in a seaway could move.
if you change the mountings you have to check the alignment of the coupling. normaly a bad alignment gives vibrations which of course increase with rpm. and could reach a point where the engine hops enough to start bumping against something or other, but the patern of increased vibration is easy followed.

good luck tony grant

 

[Guest]

My DV20 was knocking, but i found that the mountings left little clearance to the bed. As the engine takes the thrust ( I have no seperate thrust bearing) I found that at certain revs the vibration & torque caused the flywheel to contact the engine beds. I shaved the beds and shimmed the mount with no further problems.
Garry