Problems with MiniSpares top hat bushes?

[Miniminor63]

Is this a problem with bushes from all suppliers? I see minispares mention the silicon material...

[Spider]

Is this a problem with bushes from all suppliers? I see minispares mention the silicon material...

As best as I can determine, Yes.

The issue is with ALL Bronze based bushes. It seems some are selling Silicon Bronze and others Manganese Bronze, neither of which are suitable for dry running.

I've had some correspondence back from our bearing designers on a suitable bush material.

They have said that the bronze based materials should not be used for this application, the surface speeds (RPMs) are way too high for dry running. Some Bronze Bush materials can withstand dry running up to (what works out to be) 410 RPM on a continuous basis ramping up to a max of (what works out to be) an absolute upper limit of 2940 RPM for very short times and allowing for a cooling period between. They did say that increasing the clearances will reduce the likelyhood of siezure, however it does not remove the high wear rate that our crankshafts would see as they only have a hardness of 240 - 300 HB. If that were increased to around 800 HB or higher, then this would be less of an issue (off hand, I think that's getting in to Nitrided territory), but doesn't remove it.

For the most part, this confirms my own findings and what we are all seeing.

While they didn't spend time on it, they did say that if pressure fed with Oil, it would be highly likely satisfactory.

They did suggest a couple of materials, however, curiously, they suggested Deva as being the only suitable option.

I've also had some correspondence back from Deva. Due to the high ranging applications and grades of the material as well as their (usual) short lead times for manufacture, they don't hold it in stock. I've order a small number of bushes for my own use, but they do have about an 8 - 10 week lead time.

Since my posting here on this issue, I have pulled down another engine, which was fitted with a Deva type bush, it did have a LOT of miles on it.

The bushes in the primary gear had about 0.025 - 0.030" wear in them, I didn't bother measuring them as I could see they were well worn.

While the bushes were well worn, the crank was as I expected - perfect. A light clean and it's ready to go again.

The one that I posted up on the page earlier with the scored tail we had to grind 0.008" off it to clean it up.

[Aussie Bill B]

I have recently bought a new 1275 type primary gear from Minispares. I was intending to use it to replace a slightly worn 'original' gear in my rebuild. What bearing material does the new gear use? Could it damage the crank tail?
Bill

[Spider]

Good question.

If it's shiny in appearance, then likely to be bronze, if it's quite dull then likely Deva.

The last new primary gear I bought, the bushes were well out of spec, right out of the Rover box!