camchain drive sprocket (at crank) -- do they wear out?

I have had one damaged, by a careless crank specialist a few years back, fortunately could be dressed, damage would be obvious as to how it was caused in that case.

Rob
 
Where would you put a window? When the chains's in place the only way you can see the sprocket at all is from directly above, with the head and barrels off. I guess you could use a fibre-optic snake probe with a transducer on the end of it so you could hook it up to a video display. Might look a bit out of place on our Dark Ages beasts, though  :D.

Ken
 
Quite a few folk, me included, managed to put a window in their crankcases, too easily...  :'(
 
beauchemin said:
Does the camchain drive sprocket (on the crank) ever wear out?  Mine has some grooves on some of the teeth.
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So what?

Gonna last longer than all of us together! :D

piet
 
mcnicol said:
Where would you put a window? When the chains's in place the only way you can see the sprocket at all is from directly above, with the head and barrels off. I guess you could use a fibre-optic snake probe with a transducer on the end of it so you could hook it up to a video display. Might look a bit out of place on our Dark Ages beasts, though  :D.

Ken
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Ken Sorry, was being facetious. When conrods snap they put windows in the crankcase. Here's one done with a gear wheel also.

Rob
 

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beauchemin said:
Rob, nice collection of photos!  What happened to blow the hole above the transmisson?
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broken 4th gear cog, punches the gear through the top engine case
seen a few like that though not many, generally very hard ridden bikes or track bikes
am currently machining 5 x billet 4th gears from EN36, should be finished in a couple of weeks, gears going in to get their teeth ground next week and then to the hardners for a touch up
to be used in a couple of track engines we are building

 
Robjota said:
Ken Sorry, was being facetious. When conrods snap they put windows in the crankcase. Here's one done with a gear wheel also.

Rob
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Rob,

Do you happen to know the mileage of that offending gear?  Was the gearbox checked prior to the failure mishap?

I find a lot of extremely worn 4th gear bushes and tend to think the failures are not due to weaknesses within the gear itself but the gear teeth no longer meshing correctly due to excessive wear in the bush, allowing the teeth to "ride" up on the layshaft gear and eventually blocking each other.

Cheers,
piet
 
tend to agree with you Piet that majority of 4th gear failures are caused by worn bushes but is too late now anyway, first version of our billet 4th gear blank is done
will slap 5 blanks out in next few days and then they go to get geared
lot of stuffing around getting 100% face contact from the dogs to the cutout, complex programming and around 4 x 2mm cutters, broke a few on the test piece

credit due to Robjota for the idea in the 1st place to make billet 4th gears

 
sfcpiet said:
Rob,

Do you happen to know the mileage of that offending gear?  Was the gearbox checked prior to the failure mishap?

I find a lot of extremely worn 4th gear bushes and tend to think the failures are not due to weaknesses within the gear itself but the gear teeth no longer meshing correctly due to excessive wear in the bush, allowing the teeth to "ride" up on the layshaft gear and eventually blocking each other.

Cheers,
piet
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Hi Piet, sorry I dont know the mileage of the gears  but I do agree with your theories in principle.

I had  2 gears break within 2 years of each other and also  2 mainshafts. The second time I would have been very concious of excessive bush wear and have a feeling I commented on the forum around then, however both happened on the track and I do use 4th a lot.  Studying the gear itself does show up weaknesses in the design, the dog slots aligning with the teeth, leaves not a lot of metal at random spacings. I haven't explained that very well but have a couple of photos ?

 

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Nothing wrong with making stronger gears, would just like to understand the whens and whys.  Must be a definite reason, it seems only the 4th. mainshaft gear is affected.

piet
 
Hi Piet, I'm Probably stating the obvious but I know if the output shaft bushings are worn (or the mainshaft snaps at the cross drilling) this also causes the problem you described, of 4th gear being pushed out of mesh under load. My understanding is 4th gear driven is the weakest gear and is at the most flexed part of the mainshaft.

One of my broken gears yielded a broken mainshaft which may have been running broken for a while.

Rob
 
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