Engine mount bolts

[Lon nan Gruagach]

So... provided the OP tightens his M8s, you reckon there will be enough friction to stop his engine getting shoved into the middle of the saloon by the mighty thrust of a 30 horse motor then?


...I certainly do!

For sure, and even cope nicely with the rattle during start and stop which make the forces due to thrust pale into insignificance.

Also, the engine ending up in the salon, while unfortuneate, is not the reason to nail the engine down, just a few mm skew will have a good chance of knackering the prop shaft or coupling.

 

[chrishelen]

For sure, and even cope nicely with the rattle during start and stop which make the forces due to thrust pale into insignificance.

Also, the engine ending up in the salon, while unfortuneate, is not the reason to nail the engine down, just a few mm skew will have a good chance of knackering the prop shaft or coupling.

Oooops, just put a new prop shaft and cutlass bearing in.....must make sure them mighty m8s are still tight.

 

[Avocet]

For sure, and even cope nicely with the rattle during start and stop which make the forces due to thrust pale into insignificance.

Also, the engine ending up in the salon, while unfortuneate, is not the reason to nail the engine down, just a few mm skew will have a good chance of knackering the prop shaft or coupling.

"rattle" on start and stop? Surely just hopping about a bit on the rubber, you mean, or something different? Again, however weak or strong the M8s are, it's a pretty safe bet that the tension induced due to tightening them is going to be a lot more than anything the rubber can transmit to them before it tears, surely?

Yes, "engine in saloon" comment was tongue-in-cheek. In reality, prop shaft probably wouldn't be that long.... However, if the bolts are done up it really isn't going to move at all. As you showed in your brake disc calculation, the friction dwarfs every other force at work. Yes the bolts are in tension when tightened, but then. that's true pf pretty much any threaded fastener, so it becomes an argument in semantics as much as anything else.

 

[chrishelen]

"rattle" on start and stop? Surely just hopping about a bit on the rubber, you mean, or something different? Again, however weak or strong the M8s are, it's a pretty safe bet that the tension induced due to tightening them is going to be a lot more than anything the rubber can transmit to them before it tears, surely?

Yes, "engine in saloon" comment was tongue-in-cheek. In reality, prop shaft probably wouldn't be that long.... However, if the bolts are done up it really isn't going to move at all. As you showed in your brake disc calculation, the friction dwarfs every other force at work. Yes the bolts are in tension when tightened, but then. that's true pf pretty much any threaded fastener, so it becomes an argument in semantics as much as anything else.

I ran the boat for around 7 hours yesterday, still some very minor vibration at low revs, but at 2200 revs the boat is as smooth as silk. Bad weather today, so I will play around with the mounts, and maybe put packing under the rear one's, the engine is half way up the thread.

The m8 s seem to be fine, all tight and no movement.

 

[pandos]

Car: Ford focus
weight: 1,300 kg
Wheel nuts:108 * 5 * 12mm
wheel nut torque: 95 ft lbs

bolt clamping force = 41kN
per bolt break torque = 900Nm
all wheel brake torque = 18,000Nm

if that can be applied to the road, braking force = 75000N = 7.5 tonnes

seems like Ford design wheel studs to be tension only[/QUOTE

on same car, wheel bearing and drum brake etc held on only by m6/m7 bolts !!!!

 

[GrahamHR]

The load on engine mounts is taken by the mounts themselves - that is what they are for. Very little load on the bolts that hold them to the beds. They are only there to stop the the mounts from moving and this is achieved by the clamping pressure of the bolts, particularly if locknuts are used, onto the beds. As suggested rust is a bigger problem than galvanic action and I would use stainless rather than mild steel. The corrosion problem is usually the threads which are potentially in a damper environment that the heads, making them difficult to undo when the time comes for replacement.

My last boat had stainless nuts and bolts attaching a pair of hefty extruded aluminium L brackets to the stringers. No problem. The engine mountings were cast iron with steel bolt/ studs/ nuts; a nightmare with corrosion when the engine alignment needed to be adjusted. Once cleaned and covered with colloidal nickel, they were never a problem again.