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Primary Gear Front Bush (998 A+, Dam8887)


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#1 Mr Dave

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Posted 11 February 2019 - 09:27 PM

Ok, so I royally [email protected]#&ed up and dragged my primary gear bush across an unseen burr on the C-clip groove, so it is now scrap. What’s more, it’s an A+ 998 (29 tooth) which as far as I can work out needs part DAM8887, which seems to be obselete everywhere

Motherforking shirtballs

Anyway, since there has been a bit of debate on the floating bushes and I have the time/inclination/tools/support available I thought I might make a direct replacement from DEVA or Oilite. I’ve found some good info (courtesy of Mr Calver) on clearances for the running surface to the crank, but I haven’t found anything on the recommended fit into the primary gear.

Does anyone know what the specification for the interference fit was, or can advise on what they use?

Thanks as always

#2 Moke Spider

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Posted 12 February 2019 - 12:05 AM

I'll watch on with interest here, but also caution on the selection of the material.

 

Deva is the only suitable material I've been able to find and I've been look & asking for quite a while now. I did look at Oilite and that's little different to the bushes currently available (which are simply, too hard). Oilite has very limited surface speeds and doesn't like to be run dry.

 

The amount of interference needed is largely dependent upon the material used, so I wouldn't suggest working of figures for Deva. Most decent material spec sheets will have a guide.



#3 rww

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Posted 12 February 2019 - 12:31 AM

Ok, so I royally [email protected]#&ed up and dragged my primary gear bush across an unseen burr on the C-clip groove, so it is now scrap. What’s more, it’s an A+ 998 (29 tooth) which as far as I can work out needs part DAM8887, which seems to be obselete everywhere

Motherforking shirtballs

Anyway, since there has been a bit of debate on the floating bushes and I have the time/inclination/tools/support available I thought I might make a direct replacement from DEVA or Oilite. I’ve found some good info (courtesy of Mr Calver) on clearances for the running surface to the crank, but I haven’t found anything on the recommended fit into the primary gear.

Does anyone know what the specification for the interference fit was, or can advise on what they use?

Thanks as always

 

  If you post a picture of the damage to the bush there are several here who will give you a second opinion as to whether the gear really is scrap.



#4 Mr Dave

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Posted 12 February 2019 - 12:36 AM

Thanks for your thoughts Moke. From the stuff I’ve read so far Oilite seems like a reasonable alternative, as long as you don’t “smear” the running surface in the align boring and do the appropriate heated pre-oiling, plus Deva doesn’t seem quite as readily available, but experience usually trumps theory!

I may have jumped the gun a bit as doing a solid Oilite bush will probably mean boring out the gear (most Oilite bushes I have seen are minimum 1/8 inch thick). There are some standard bimetallic split bushes that I have seen that would physically fit (1 1/2 inch ID, 1 21/32 inch OD), but most are PTFE coated which I don’t think would survive the boring

I’m probably just in denial about having to suck it up and get a new gear... *sigh*

#5 Mr Dave

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Posted 12 February 2019 - 12:42 AM

If you post a picture of the damage to the bush there are several here who will give you a second opinion as to whether the gear really is scrap.


Unfortunately I’ve already (destructively) removed it as I thought I’d bought a replacement, but it was the wrong one (DAM8889 *facepalm*)

It was definitely fubar though, down to the steel backing

Edited by Mr Dave, 12 February 2019 - 12:43 AM.





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