How is the engine/gearbox assembly mounted to the tub?

[marcush.]

747h...the point of shank length is an interesting one but it only comes into play when you design the bolt as a stretch bolt ,or at leaast with considerable waisting along the shank length.
I remember coming up with this idea of increasing shank length toward ARP a few years back and they put two very different length shanklength bolts(otherwise equal) into their zwick machine...and both did show exactly the same behaviour....
We concluded that only a tailor made bolt for the application could offer an advantage .
To come back to the original question ,we are aligned that inevitably the two structures will expand in different ways and they will also hava a very different
delta t in use.So we are clear that two of the needed three hardpoints would need to provide compensation in shear plane without compromising bending and torsional rigidity of the assembled structure.In my book bolting the heads to the tub via two bolts each will open a can of worms making it necessary to design scope for compensation somewhere else otherwise you will compromise the joint heavily.

[747heavy]

[xpensive]

Great shot jumbo, the conical seats at the bottom are duly noted.

[Arunas]

Isn't here gearbox end of engine?

[747heavy]

Yeap, I think you are right Arunas,
but maybe it gives us a idea about the general philosophy, of these
mounting methods.

@Marcus,
thanks for the comment.
I would assume, that the studs used are a specific design, and used as a stretch bolt
(slim(er) shank), tailordered to the appclication.
But, to be honest, I don´t know any specifics about them.
But I would be surprised, if there different length compared to the bottom ones are pure coincidence.

[autogyro]

Not much of a surface for the gearbox to sit on, looks more like point contact, unlike the tub.
I like the visible head studs/bolts, is the open gap to allow for expansion?

Riff_raff mentioned the need to prevent surface creep at the facing joint if using wasted bolts, between cylinder head and block. Surely this is allowed for in the head gasket design.

[ringo]

Take a look at these bolt holes, notice they have steel/titanium inserts.

This could be an attempt to have similar coefficient of expansion between bolt and threaded hole.
This could eliminate the concern for dissimilar materials for bolt and threaded bore.

So we are clear that two of the needed three hardpoints would need to provide compensation in shear plane without compromising bending and torsional rigidity of the assembled structure.In my book bolting the heads to the tub via two bolts each will open a can of worms making it necessary to design scope for compensation somewhere else otherwise you will compromise the joint heavily.

Compensation in strength or movement at the shear plane? I'm confused.
If the contact pressure of the joint is strong enough, and tight enough, I suppose there should be no compromise. The engine would just have to take the strain.
No big deal really.

About the engine, something tells me dowell bushings are used with the bolts, i am seeing a recess that is wider than the bolt hole. The bushings would definitely restrict movement.

[Richard]

I suppose there should be no compromise. The engine would just have to take the strain.
No big deal really.

It is a big deal, thermal expansion cannot be constrained.

[xpensive]

I suppose there should be no compromise. The engine would just have to take the strain.
No big deal really.

It is a big deal, thermal expansion cannot be constrained.

Just leave it at that richard, this member is not on the forum to reason, not in in any engineerish fashion anyway.

[marcush.]

I just ask myself if you could spend as much time and effort on designing the engine mount layout if you were responsible for the complete car ...
I find it quite intriguing that someone is prepared to leave the found facts alone and stress the engine mounts on the tub and the threads for ease of life at the drawing board(as the engine for sure will grow and shrink no matter what bolts you will stick to it).

[xpensive]

Well marcush, many innocent passengers have lost their lives through the years when railway builders thought they
could harness thermal xpansion by leaving it to the rails to "take the strain" on a sunny day.

As a tribologist, I could tell you a few stories about smoking bearings when designers had failed to realize that the inner race heats up quicker than the outer. Or what happens with the idea of lining a carbon steel pressure vessel with 316.

[marcush.]

I feel we should all be a lot more modest when analysing problems ,as there is the distinct possibility that we are unable to grasp the full set of implications for the case we are trying to solve.we might be able to find the major issues but still there is a rest of doubt in it ...and you will have to add a factor of safety just to make sure you will be able to sleep at night.

[ringo]

I suppose there should be no compromise. The engine would just have to take the strain.
No big deal really.

It is a big deal, thermal expansion cannot be constrained.

Yes it can.

[ringo]

I think there is a general misunderstanding here of what stress is and what it does.
A part can be stressed by any amount as long as it is bellow the design stress.

If a part has a design stress of 27,000 N/cm^2, and it is stressed at only 12,000 N/cm^2, there's still plenty more stress it can take without failing.

Additional stress doesn't automatically equate to failure.

A perfect example is an exhuast manifold, I am sure most of you know what that is and how it is bolted to the engine. Where is the "compensation" for movement in that?

The answer: There is none!!

The manifold takes the stress completely.It only expands beyond the bolts and in the longitudinal direction. Increase in dimension by thermal expansion can be equated to a strain. Using the modulus of elasticity, a strain can be expressed as a stress.
I can do a sample calculation right here with 3 dissimilar metals bound together.

Trust me, I am not the one who is not being unreasonable here.

[marcush.]

in laymans terms :
I have seen A LOT OF cracked exhaust primaries in my life ,be it cast or welded components.... so in my slim experience in the automotive field this is not quite a good example for your point,as it is for sure one of the main failure modes present in the field for this component interface is warpage and crack ...