theoldplucker
Well-Known Member
Renewing allen bolts on Bukh 20 flywheel. Would you use loctite or drill holes in bolt heads and lock with siezing wire ?
Flywheel bolts
- Thread starter theoldplucker
- Start date
VicS
Well-Known Member
The manual I am looking at says Loctite
vyv_cox
Well-Known Member
Those bolts are high strength ones, which means high hardness. Drilling them will be something of a challenge. VicS is correct, the manual says loctite but I did mine before I owned a manual and I didn't use anything, just tightened them up hard.
30boat
N/A
You probably know this but use the ones supplied by Bukh.If the flywheel comes loose you don't want to be anywhere near.A friend of mine was very lucky when his finally broke free at idling.He'd been hearing strange noises from the engine bay for a while but put it down to the engine being an old lump.The flywheel was contained by the engine box but there are some scary stories around.This is what happens if regular bolts are used.This engine is now a mooring...
theoldplucker
Well-Known Member
I have have obtained high tensile bolts, but not from Bukh. How many out there with bolts other than Bukh ?
colhel
Well-Known Member
When we do flywheels at work it's not just the strength of the bolt we look at but also the fit. This may only be relevant to race cars, but the flywheel is reamed and the bolts are ground to fit. Don't know if this OTT for a sailing boat engine, but thought I'd mention it.
Poignard
Well-Known Member
I use Loctite, as BUKH recommend. That is perfectly reliable as long as the bolts and holes are clean, and torqued up to the recommended value. I clean out the holes with a tap followed by pipe cleaners and a solvent (eg acetone).
I have only had the flywheel off twice in 15 years so the cost of new Unbrako bolts has been insignificant and I just added them to an order I was putting in to BUKH anyway.
The picture shown by 30boat just confirms my belief that it's worth taking care to do the job properly. The thought of the very heavy flywheel spinning off and trying to punch its way through the side of the boat is something I can do without.
I have only had the flywheel off twice in 15 years so the cost of new Unbrako bolts has been insignificant and I just added them to an order I was putting in to BUKH anyway.
The picture shown by 30boat just confirms my belief that it's worth taking care to do the job properly. The thought of the very heavy flywheel spinning off and trying to punch its way through the side of the boat is something I can do without.
sarabande
Well-Known Member
Can you explain a bit more please ? Is this to make sure the underside of the bolt head is fully in contact with the flywheel ? What happens to the washers ?
TIA
Norman_E
Well-Known Member
If Loctite is recommended, find out which grade Bukh recommend , as some allow the bolt to be undone again, others make it very difficult.
Poignard
Well-Known Member
The un-threaded part of the bolt is a very close fit in the hole , so that it acts as a dowel as well as being a fastener. The BUKH flywheel bolts serve the same purpose because there is no key or taper on the crankshaft. But because the engine runs at very low speeds compared with a racing car engine (and is not accelerated/decelerated as rapidly) the fit does not have to be as precise.
oldharry
Well-Known Member
Agree with what is already said, you MUST use the special hardened bolts supplied by BUKH, ordinary ones wont do. I found out the hard way, and that engine too is a mooring lump. The 'specials' are indistinguishable in appearance from ordinary ones. Even if you could drill the heads for wiring, ordinary HT is not strong enough.
John Cutlers mechanic at Thornham told me of one he was bench testing that lost the flywheel at full throttle. It punched through a brick wall and went on to do quite a lot of damage in the yard outside. So theres no question that it will 'try ' to punch through a boat hull. at speed it WILL.
Mine went at tickover speed, and thankfully there was some good solid timber where it went, but even so it diid a lot of damage to both the boat and engine.
John Cutlers mechanic at Thornham told me of one he was bench testing that lost the flywheel at full throttle. It punched through a brick wall and went on to do quite a lot of damage in the yard outside. So theres no question that it will 'try ' to punch through a boat hull. at speed it WILL.
Mine went at tickover speed, and thankfully there was some good solid timber where it went, but even so it diid a lot of damage to both the boat and engine.
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fuss
Well-Known Member
If the original bolts were allen bolts then they were probably just standard allen bolts.
Allen bolts have a sheer strength that is much higher than normal bolts, even grade 8 bolts.
Standard engineering rules apply regarding fit... no elongated holes in the flywheel. No washers but loctited.
If you want to get fancy then you could dowl it with 2 dowls.
If dowled, I would expect this to handle at least 180 hp and 9000rpm.
Allen bolts have a sheer strength that is much higher than normal bolts, even grade 8 bolts.
Standard engineering rules apply regarding fit... no elongated holes in the flywheel. No washers but loctited.
If you want to get fancy then you could dowl it with 2 dowls.
If dowled, I would expect this to handle at least 180 hp and 9000rpm.
30boat
N/A
There's not a lot of room there for dowels.IMO the design is bad.The crank should have a flange where the flywheel would bolt to.As is the area is far too small.
tinkicker0
Well-Known Member
Loctite 275 if you please.
Westerly Jetstream
Active Member
Use only manufacturers bolts on a flywheel and locktight them. A Flywheel detaching even at only 2500 RPM is a very serious affair.