Bukh dv 24 flywheel bolt fail
- Thread starter europe172
- Start date
Plum
Well-known member
Are they the original/original spec screws? They look like stainess? What are the markings on the heads? Agree with Vyv that they were all loose prior to the point of failure so I beleive they were not tightened correctly and maybe the wrong grade of screw.
Www.solocoastalsailing.co.uk
Last edited:
Boater Sam
Well-known member
All loose I would think. Unless they are old reused machine screws or cheap replacements and not the proper Unbrako ones. They are supposed to be one time screws.
Some folk have trouble torquing Allen screws because they don't have the correct key/socket.
It has sheared the locating dowel too, been rattling around a good while.
Some folk have trouble torquing Allen screws because they don't have the correct key/socket.
It has sheared the locating dowel too, been rattling around a good while.
europe172
Active member
Attachments
Poignard
Well-known member
They have been loose for a while, judging by the appearance of the tapped holes.
LittleSister
Well-known member
Unsettling?
I'm surprised, and pleased, that you are here asking advice on why it happened, rather than reporting the major damage and injury that such a flywheel coming might easily have caused.
That was my understanding, too - that new proper Unbrako screws are specified for each time the flywheel is refitted.
europe172
Active member
When I said unsettling I was using understatement , I am still investigating and in contact with the engine supplier who is assisting, they also want to make sure it is not a bad batch of bolts
Bilgediver
Well-known member
I was once aboard a yacht with one of these engines witnessing a test. Something did not seem right with the flywheel so I signalled to the owner to stop the engine Jast as he responded the flywheel separated from the crankshaft and came to rest cradled on the bearers. Examination showed that the crankshaft was slightly damaged and the wrong bolts had been used. The small dimensions of the flywheel to crankshaft connection requires that everything is correct and perfect. The correct bolts must be used as I fervor bolts can not be torqued to the requir3d setting. Also check the nose of the crankshaft is undamaged so ensuring the flywheel is running true.
vyv_cox
Well-known member
Fatigue fractures are quite difficult to diagnose in high strength steels but I feel confident I can see multiple initiation sites and two zones in most of them. I will check on the PC later but I am fairly certain of fatigue.
jwilson
Well-known member
Given the weight of the Bukh flywheels you're lucky the flywheel stayed inside the hull.
penfold
Well-known member
I concur, they were loose as is demonstrated by the damage to the threaded holes; possibly they weren't torqued correctly or possibly no thread lock applied, allowing the vibration to slacken them
neil_s
Well-known member
I have recently removed the flywheel from my DV20 and the correct Unbrako bolts have a black finish - not bright as in your photo.
PabloPicasso
Well-known member
I'm learning lots from this thread about fywheel attachment/detachment 
.
I'd be inclined to listen to vyv cox above. He is often on here talking sense about stuff like this.
If I remember rightly he has a very informative website with a lot of really useful techinical info
If we're lucky he might come back with a link.
. I'd be inclined to listen to vyv cox above. He is often on here talking sense about stuff like this.
If I remember rightly he has a very informative website with a lot of really useful techinical info
If we're lucky he might come back with a link.
penfold
Well-known member
Is this a new(new or at least new to you) engine from a company reselling lifeboat engines? Or had the flywheel been off for some maintenance?
Moonbeam
Active member
I'll save Vyv the trouble... here is the link to his very useful website Cox EngineeringI'm learning lots from this thread about fywheel attachment/detachment
I'd be inclined to listen to vyv cox above. He is often on here talking sense about stuff like this.
If I remember rightly he has a very informative website with a lot of really useful techinical info
If we're lucky he might come back with a link.
AntarcticPilot
Well-known member
His book, "Metals in boats" ( https://www.amazon.co.uk/Metals-Boats-Vyv-Cox/dp/1785002627/ref=asc_df_1785002627) is an excellent resource, too.
europe172
Active member
Yes, engine had run for about 1.5 hours about 20 mins idle and the rest at 3/4 throttle . I had not touched the flywheel since I had the engine.
The supplier is testing bolts urgently. The supplier uses these bolts for many engines each year and does not have this happen, as evidenced by their reputation. One possible explanation is that the flywheel was not properly seated during bolt installation ( the bolts are replaced as a routine item ) and shortly after running the flywheel seated causing the bolts to be loose
penfold
Well-known member
If it's a company in Dorchester then my old man has one of their engines in his boat, fitted about 6 years ago and no problems after ~200hrs. With such a short run time the bolts are either of insufficient strength or were not refitted correctly, it's impossible to refit the flywheel incorrectly because of the location dowel.
Transcur
Member
I had the same happen to me with a BUKH 10 I was testing having rebuilt the water pump. big bang and six bolts sheared and the flywheel dropped to the floor and then took off a cross the floor. Bit of a flintstone moment. I have since heard it happen to another Bukh 10. I believed it was the high tensile bolts loosened causing them to fatigue. I have a spare new set of socket screws here if needed,