22 replies to this topic

[MontpellierVanMan]

Have managed to do something horrible to my 1275 A+ crank.
Changed the primary gear front and rear bushes, had ordered the MS floating front one but received a press-fit version. Once both fitted took elaborate precautions to machine them concentrically and believed the tolerances were OK.
However progressively worsening rattle has led me to strip everything and after 1.500km I find I have a front bush with no bronze left, a crank that has been rendered rough and undersized, and enough slop to drive a coach and horses through. Top hat rear bush is of course worn too but otherwise looks to have done its job and the crank is OK there.
It's a wonder the thing ran at all ............
Question please : is the crank scrap, or can It be remachined and a specific front bush made to cope with the new diameter ? : any addresses in the UK whom I could go to ? : what went wrong ? road use and nothing violent : is lubrification indeed just splash ? I did soak it 24h In engine oil before assembly.
Steep learning curve here.

[pete l]

snap. 

 

http://www.theminifo...e/#entry3388284

 

 

and i'm in france too !!

[MontpellierVanMan]

Hi That Man In Pont St Vincent !

 

Yes, I've just read the thread and am reassured to not be the only one, albeit I seem to have inflicted this on myself ...........

 

I'll be following this exchange closely.

 

http://www.deva.de/e...al/where-to-use

 

They supply the stuff as machinable blanks so at least we can make one-offs.

 

http://www.deva.de/e...tal/basic-forms

[pete l]

I've just copied your link to show moke spider who probably knows it anyway, but just in case.

Any idea who supplied rover with these bushes ?

Pete

Edited by pete l, 23 May 2016 - 08:01 PM.

[Spider]

Do you know where the bush came from?

 

Also, when machining the bush after fitting, what did the swarf look like as it came off the bush?  ie, was it '6's and 9's', long twisted strings or powder?

 

Could you put some photos up of your crank and bushes?

 

In the case of the damaged rank that's currently on my bench, I'm having that ground and will now likely be making my own DEVA bushes, so for this one, it'll be sized to suit, which is how I go about all of them, just this one will be considerably undersized from standard.

Edited by Moke Spider, 23 May 2016 - 08:53 PM.

[MontpellierVanMan]

The front bush was ordered from MS as a DAM8889 floating one, and invoiced as a floating one, but in fact came as a steel-backed split liner with some sort of pink alloy lining.
So it needed pressing in.
Machining it gave curly swarf and nothing like any sintered bearing material would produce.
I am still prepared to entertain the idea that I fitted it too tight, although I did use Graphogen and oil upon assembly.
Upon disassembly the Graphogen seemed to have been useful only as a glue for the swarf generated by the pick-up of the bush on the crank, and after 1500km I was surprised to see so little evidence of engine oil ever finding its way in.
Did you find a suitable blank from DEVA that provides a good starting point for bushes ?

[MRA]

For a Bronze material to pick up on the crank tail it would have to contain aluminium or a lot of tin, which is of interest.  Ideally it should have a reddy orange tinge to the material.

 

What lubricant did you use on the tail under the bushes ?  ie to lubricate the 2 bushes ?

[pete l]

i read:

 

" I did use Graphogen and oil upon assembly."

[MontpellierVanMan]

Yes, 20/50 and Graphogen seemed to be a safe first-rotation mix, but not good enough when the tolerance was too tight.

 

 DSC01132.JPG   48.34K   21 downloads

 

The MiniSpares blurb on the site is misleading regarding the bushes, and made worse by my not reading it correctly - DAM8889 is not in fact the floating type, but it's not clear whether the floating alternative C-AEA3240 is or is not suitable for A+ engines.

 

Be interesting to see whether they bother to re-write the accompanying texts for those two parts.

 

The shells looks worse after 1.500km than the previous lot did after 50.000km .................

 

 DSC01134.JPG   48.94K   17 downloads

 

 DSC01136.JPG   53.71K   8 downloads

 

 

 

[MontpellierVanMan]

This is the MS gibberish for the DAM8889 : my comments in bold :

 

running clearance for this gear-front bush running clearance finished size 1.503" +0.002"-0-0" (which implies an ID of 1.503" to 1.505" ? but the FRONT bush zone on the crank is 1.625" !!)

for race 1 thou more clearance with plus 1 thou tolerance obut never undersize. (implies what ? 1.503" to 1.507" ?)

front bush 1.628" +0.002" -0.0" never undersize as it requires clearance. (this is better, a front-bush size, 1.628 to 1.630 ; presumably because 1.625 plus 3 to 5 thou gives 1.628 to 1.630 ?)

For race allow an extra thou 1.504" +0.001" only. (implies ID upper limit of 1.505" ? two lines above it's 1.507 ? - again these are REAR sizes)

if cranks are worn measure crank and allow 3-5 thou running clearance (on which one - front or back, or both ?) and race use 5-7 thou on front bush and 4-5 thou on rear bush

 

ANYWAY

 

I have grasped the nettle and following the advice from my local machine shop I have done the work on my own lathe .......... sorry about the boring bar, it was the only tipped tool I could get into the right approach.

 

 

 

 

The crank has cleaned up at 41.13 - 41.14 mm, 1.619" - 1.620", so the only question is whether a DAM8889 can be used.

 

 

Attached Files

•  DSC01151.JPG   33.49K   17 downloads
•  DSC01150.JPG   72.07K   20 downloads

Edited by MontpellierVanMan, 02 June 2016 - 07:56 PM.

[pete l]

It's all chinese to me. 

I don't have permission to view your pics !

 

Who polished your crank ? looks amazing

 

Pete

[MontpellierVanMan]

You have to sign in to see the pics, or maybe they weren't fully loaded when you tried ?

 

The finish is 240 emery-cloth, followed by 500 grit, if I was any good on the lathe I wouldn't need them.

[Spider]

Only just now picking back up on this thread.

 

The crank has cleaned up at 41.13 - 41.14 mm, 1.619" - 1.620", so the only question is whether a DAM8889 can be used.

 

DSC01151.JPG

 

 

Yes, they are typically 0.020" under sized.

 

I wouldn't use a floating bush (even if they were suitable for A+), they are much too hard (they have to be due to the nature of them) and if you think this bush made a mess of your crank, the floating bushes would do far worse.

[pete l]

Just found this for info. Might be something interesting in it etc.

 

http://mini-racing.f...ment-des-bagues

[MontpellierVanMan]

I'm inclined to agree with you, Moke, about the floating idea - whilst it's nice to think of sharing the wear across two surfaces I can't help feeling that the original system worked fine (with the right materials) and I don't want my primary gear bore getting shagged by a potentially inappropriate bronze running in it.

Edited by MontpellierVanMan, 27 May 2016 - 11:10 AM.