CMS Bolts - with washers?
Turbo Mini Forums

About to start the rebuild of my engine and just wondered wether the centre main strap bolts should be fitted with washers or not?

I've seen pics with them done both ways. My gut feeling says without but the hole in the CMS is very sloppy around the bolt so maybe a washer would give a better surface area to clamp with?

Thoughts from the more experienced......

I don't use washers myself, reason that they might crush and then release clamping on the main cap.

As Tom says - please do not use washers on anything like mins caps or cylinder heat nuts unless they are proper hardened pieces. The washers you get as std are made of toffee and will yield under the torque application - after a period of time, most likely when they've been heat cycled. Then you are left wit ha bolt with no "stretch" in it and it will come loose. Just make sure the chamfer on the top of the hole is large enough so it doesn't interefere on the radius on the underside of the head on the bolt - otherwise the stress concentration will cause the head to fatigue off. In honesty this is more of a problem on rod bolts.

John

If Carling made Mini engines
it would probably be like this one!

hardened washers for me every time,

carl

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I'm with carl on this. I'd prefer proper washers. They will only improve calmping issues as the bolt head won't have as much friction when torqued up.

When working out axial loads from torques you have to consider the surface friction between the underside of the head and whatever it's contacting. If a washer is present and the diameter is different to diameter of that under the bolt head then you have to pay attention to if the washer rotates against the part or the washer holds against the part and the head of the bolt rotates relative to the washer.

Depending on which pair of surfaces were ortating relative to each other the frictional loss could be higher or lower.

In all honesty though they would have to be quite different diameters to make a real difference in the real world.


I must admit that I prefer to use hardened washers to no washers at all on the mains.

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