Acetal for engine mount shims .

[IanCC]

Seems like a good idea to me, no rust and all that. But are they a bit slippy, or will torqued down engine mount bolts take care of that? I have visions of the engine vibrating itself out of alignment.
Thanks for thoughts.

 

[Daverw]

I would be concerned that they would very slowly crush and the mounts loosen

 

[IanCC]

I would be concerned that they would very slowly crush and the mounts loosen

Why?

 

[Daverw]

Most plastics compress over time, I’ve be aligning electric motors for years and only use SS or brass sheet for shims, why use anything else? Especially when your mounting something that try’s to bounce around

 

[IanCC]

Why? Because it doesn't corrode, is easy to work and not too expensive.
If it's cut to fit the whole of the underside of an engine mount it would suprise me if it compressed. I need 20mm thick so buying and cutting stainless, not cheap. Appreciate your thoughts btw.

 

[vyv_cox]

Acetal is a thermoplastic, which means it will deform under heat/load. Its creep strength is stated to be good but it cannot compete with a metal.
Stainless steel would be difficult to DIY in this thickness but aluminium would be a satisfactory substitute.

 

[IanCC]

Acetal is a thermoplastic, which means it will deform under heat/load. Its creep strength is stated to be good but it cannot compete with a metal.
Stainless steel would be difficult to DIY in this thickness but aluminium would be a satisfactory substitute.

Thanks for input. Google tells me acetal good for continuous operating temp of 115C. And very stiff and good dimensional stability. Also unaffected by repeated heating and cooling. My alternator is limited to 100C. Also oceonflex cables will melt before then i think.

 

[penfold]

Bad idea unless you're using it temporarily to get the right packing thickness to then get a packer made from steel. It's not dimensionally stable enough.

 

[Poignard]

If rust is the only objection to using mild steel shims, I wouldn't worry. The engine mounts are mild steel, and there's plenty of other steel components on an engine that can rust, yet you presumably don't worry about them.

You could always use brass shim if you wished, or even stainless steel.

But in post #5 you say you need a shim 20mm thick! That's not a shim, that's a spacer.

Something wrong if you need to take up that distance.

 

[Daverw]

Agree 20mm stainless plate not cheap and small off cuts not readily found but 10mm easy to get as common used for webs etc, and just double up.
acetal yeas has very good dimensional stability but will still compress, even a fraction of mm will loosen fasteners

 

[IanCC]

Bad idea unless you're using it temporarily to get the right packing thickness to then get a packer made from steel. It's not dimensionally stable enough.

Thanks for reply. Do you have some figures for that? And/or what are you basing your opinion on. Most sources i find say it is particularly dimensionally stable.
Weaknesses seem to be chlorine and mineral acid.
Polyoxymethylene - Wikipedia

 

[IanCC]

If rust is the only objection to using mild steel shims, I wouldn't worry. The engine mounts are mild steel, and there's plenty of other steel components on an engine that can rust, yet you presumably don't worry about them.

You could always use brass shim if you wished, or even stainless steel.

But in post #5 you say you need a shim 20mm thick! That's not a shim, that's a spacer.

Something wrong if you need to take up that distance.

Good points, thank you. My mounts are Aluminium. Not much rust. So they are spacers nit shims. It is what it is if i want the shaft down the centre of the tube and the height in the r&d miunt to be within tolerance.

 

[IanCC]

Agree 20mm stainless plate not cheap and small off cuts not readily found but 10mm easy to get as common used for webs etc, and just double up.
acetal yeas has very good dimensional stability but will still compress, even a fraction of mm will loosen fasteners

I have tried to find stainless offcuts locally but no joy. It has 10mm mild steel packers at present but needs 20mm, so was hoping to bin the current ones.

 

[Poignard]

What you could do is have a length of studding and two nuts:

 

[Daverw]

I would use spacers rather than extended studs, most av mount manufactures have max thread spec which can be quite short.

 

[IanCC]

What you could do is have a length of studding and two nuts:

View attachment 147149View attachment 147150

No no no. That's what i am getting rid of. Packer goes under all that. Between that and engine bed. So less than 10mm of stud under supporting nut. But thanks for thinking about it, genuinely.

 

[Poignard]

I would use spacers rather than extended studs, most av mount manufactures have max thread spec which can be quite short.

I would raise the engine mounts by the required amount but the OP knows what he wants.

 

[Poignard]

No no no. That's what i am getting rid of. Packer goes under all that. Between that and engine bed. So less than 10mm of stud under supporting nut. But thanks for thinking about it, genuinely.

Understood now.

 

[Daverw]

A couple of months ago got 800x75x10mm 316l bar from waste bin at a fabrication company that makes conveyors, paid £10

 

[IanCC]

A couple of months ago got 800x75x10mm 316l bar from waste bin at a fabrication company that makes conveyors, paid £10

Would have been perfect. Hey ho.