57 replies to this topic

[pete l]

Hi all

 

Here's some photos of what I found over the weekend.

 

 WP_20160517_07_40_21_Pro.jpg   50.65K   117 downloads

 

 WP_20160517_07_39_40_Pro.jpg   26.6K   98 downloads

 

 WP_20160517_07_40_01_Pro.jpg   32.39K   105 downloads

 

 

Anyone know what happened ? I bought it like that.

 

Pete.

 

MPI 1997

[timmy850]

I'd guess that the tolerance between the primary gear and the crank wasn't set up correctly. 

 

If you are lucky the crank will polish up ok, and the new primary gear bushes are supplied a little on the large side so you might be able to make do. 

[pete l]

I've sent some photos to AC DODD, waiting to hear from him.

[Gr4h4m]

I've got one of those....was it the correct gear there are two types mixing the wrong ones up can cause this...

[pete l]

It's a 29 toothed one, how do I tell if it's the right one ? It's a 1997 moi, lhd in France.

[Dusky]

The amount of teeth shouldnt matter.

[pete l]

I've got one of those....was it the correct gear there are two types mixing the wrong ones up can cause this...

 

And how much would you want for it ?

[pete l]

Adrian Dodd got back to me and it looks like it is going to cost a bomb to fix, the engine needs a rebore because of rust on the cylinders, probably a crank regrind, new pistons, rings, bearing shells and this primary gear fixing.

 

He recommended a new short block from minispares would be cheaper.

 

I have been well screwed over on this one. Very sad I am :-(

 

Pete.

[Spider]

I'm just now looking at another that has done more or less the same damage.

 

It would seem some bright spark has come up with an idea of using what (at this stage) appears to be Silicon Bronze for the Rear (Top Hat) Bush in the Primary Gear. These are what are now being supplied by many of the spares sellers now.

 

The factory bushes for the Rear ones were Deva, which is a powdered / sintered material, it is oily by nature and to the touch and will also hold oil. The Silicon Bronze on the other hand is dry and won't accept oil, for this application, totally the wrong material.

 

The Original Front Bushes (the one closest to the Engine) were, another soft bearing bronze, which are steel backed.

 

It also appears the Floating Type Bushes are also Silicon Bronze - beware.

 

I'll put some pics up later.

[pete l]

I didn't know it was that complicated. My best bet would be a used original one if my crank is serviceable that is.

[Spider]

I didn't know it was that complicated. My best bet would be a used original one if my crank is serviceable that is.

 

I've now seen 3 (4 including yours) go this same way from the same bushes and a number of the floating bushes too.

 

I'll most likely be making my own bushes now as I can't find anyone who sells the original types.

[Spider]

Some photos

 

The bush still in situ

 

 

 

Bush removed (turned out)

 

 

 

and this is what it did to the crank It now has to be ground and likely custom bushes fitted);

 

 

 

This is a NEW bush, note the extrusion markings;-

 

 

 

Just my thoughts and some investigation work so far.

 

The material is WAY too hard, and while it can be used in some situations for a bushing material, it is commonly used for fasteners in a marine environment as an alternative to stainless. It also has a fairly high rate of thermal expansion (ie, on the sizes and temps we are dealing with, it can grow 0.004 to 0.005").

 

It appears that while these materials are around a similar cost, or maybe a little cheaper then the DEVA material, being considerably harder allows the bushes to be pressed in at room temperature, this is not possible with the DEVA material as it will simply crumble away to powder. The correct factory advise relating to the original DEVA bushes is to chill them in Dry Ice, this shrinks them (according to factory info) by 0.003 to 0.005" for fitting. Curiously, I've never found this info an any UK publication, but it was in our Aust Factory Manuals.

 

According to DEVA, the finish is best done as a machining operation (ie, lathe or reamer), where as while the Silicon bronze bushes can be turned, they would benefit from honing, which for a non-ferous material, is a highly specialised process (and not one most automotive machine shops could do correctly).

 

The Bronze material sooner or later will, not maybe, but will pick up on the shaft of the crank, as the bronze is so hard to start with, and this is the beginnings of the failure process seen in this thread, though on another I saw, it also ruined the primary gear. The DEVA material, being basically compressed powder cannot pick up.

 

As I mentioned before, the Bronze is basically a sealed material (hence why it's so favoured in a marine environment) and cannot accept oil. Grease would appear to be a better lubricant here, however, the speeds involved will cook the grease in short time. If Oil is used, as soon as it runs off, there is no lubrication (and then the bush picks up on the shaft and it's game over). The Bronze to the touch always feels dry.

 

The very early Minis had a White Metal Bush Primary Gear, however, they also had an Oil Feed to them, which lead to a slipping clutch. The factory spent some considerable time and funds finding a dry running alternative - DEVA.

 

The DEVA material is already pre-loaded with Graphite and will accept Oil. This material to the touch always seems to have a slipriness about it.

 

OK, Mr. Primary Gear Bush maker(s), can we now get proper bushes again for our Primary Gears?

 

Disclaimer: No, I don't have any association with DEVA.

[pete l]

This is worrying, so if I get mine rebushed, what will happen ? the same thing ? after how long ?

 

The new ones that are available, are they fitted with DEVA bushes ?

[Gr4h4m]

The issue I was talking about was putting a 1275 primary on a 998 engine. I did this by mistake and it smashed the top hat it like your pic, maybe this was the same as you.

[Spider]

This is worrying, so if I get mine rebushed, what will happen ? the same thing ? after how long ?

 

The new ones that are available, are they fitted with DEVA bushes ?

 

All the new ones I've looked at over the past couple of days are not DEVA.

 

I did have a few DEVA ones that I've been using over the past few years and only bought some new (current) bushes about 6 weeks ago, that's one I photographed ^. I don't know how long these Bronze ones have been about for.

 

I have a current enquiry with DEVA as we speak to get the correct grade of the material (There are a large number of grades and types).

Edited by Moke Spider, 23 May 2016 - 08:27 AM.