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G: Gearbox Burman Drive Sprocket Loose


oexing

Well Known and Active Website User
VOC Member
Sorry, no, I cannot see a way to feed all that torque into the sprocket just by torquing up the nut without having a good condition spline there. Just imagine, the gearbox plus the primary drive multiply all torque produced from the crank to about ten times into the rear chain at the sprocket spline. No way to hope for the effect of torquing the nut. Same with the clutch nut plus its spline. There is only one way to achieve a lasting solution by restoring a PERFECT spline fit with definitely minimal play in it. Imagine, the rear chain pull onto the sprocket tries to dislocate it offcenter and only the spline fit can keep it centered. Any play in there produces wear by rubbing motions at all contact faces.
So really only rescue to the actual Burman question is to get a new quality sprocket , get the gear shaft hard laser welded and machine it to sprocket dimensions as close as ever possible. The gear shaft will be less worn at the rearward face on the spline, so when machining it after welding plan to first clean up these faces and have only the forward faces welded up by laser thick enough to restore the lot to perfect fit into the sprocket.
In case no good new sprockets available, I´d probably get a new soft universal chain sprocket and have the spline wire EDM cut - except you can use a standard broach. Broaching would be less costly but wire EDM is allright, only six slots to cut, so no big deal. Just care for a good finish after wire cutting, roughing and finishing cuts, any rough finish will wear fast and slop returns in the assembly.
Basically laser welding in the internal splines of the sprocket is another way, not so nice to do and best to be avoided . Again, machining will be best by wire EDM as the weld will be necesssarily hard. But I´d rather go for stock chain sprockets, get the spline wire cut, case hardened - and the last step is to machine the gear shaft for perfect fit. You can find carbide milling cutters for 65 HRC material and milling is best done face milling for evenness of faces , all set up in a dividing head. Below photos of laser welded splines and ground , same place for sprocket on B-Rapides.

Vic

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P1050495.JPG
 

Matty

Well Known and Active Website User
VOC Member
All very interesting but I think the basic problem is that many of the spare sprockets in the past were probably manufactured from poor and possibly cheaper material than the originals.
As pointed out the drive sprockets on many modern bikes are only held on with a circlip and are quite sloppy on the splines and seem to be fine though it does not look on the face of it a very good piece of engineering.
I have changed chains and sprockets on many modern bikes and not noticed any significant problems with badly damaged splines.
As I have said in the forum before, I have only once changed the front sprocket on my Comet at around 50,000 miles and am still using the "new one" at 106,000 miles.
I am however now a bit worried and may have to go through the trauma of inspecting mine by removing the primary drive casing etc. though the last time I rebuilt the gearbox around 6,000 mile ago it seemed OK and I did the nut up VERY tight on the bench with no Loctite.
The nut which holds the clutch on is subject to similar forces and I have in the past had to replace the clutch cage where the splines were reduced to about half the width - though the mainshaft splines looked fine - probably because the shaft was made of superior steel.
I am only an electronics Engineer and not a metallurgist or mechanical engineer so my views are really only subjective without a great deal of real science applied.
I hate to say this, but have heard that some people have welded the sprocket onto the shaft which I should think would have Phil Irving turning in his grave.
 

oexing

Well Known and Active Website User
VOC Member
I just returned to the first page of the thread and discovered that I posted about the same ideas one year ago like in that one above, sorry for repeating me. But I still stand to my propositions. As told by someone else above even extremely torquing up the sprocket nut will not fight any loosening of the assembly, in fact, the nut did NOT loosen but the shims, washers and sprocket material were worn due to rubbing action by micro motions as soon as the splines get minimal play. Some owners here have got very high mileages out of their bikes at no troubles, some had more than once to replace components. I say this is dependend on what perfect fit within the spline joint you had to start from. With perfect fit there will not be much wear for very acceptable mileage, but as soon as some play has developed you can observe progressive wear in due time and securing the nut will be no help at all with the underlying defect.
One can test the material of the sprocket, it is only the hardness that is critical, so try with the edge of a file to get a feel about heat treatment. If too soft you could have the sprocket case hardened once more, best in inert athmosphere or vacuum to keep it clean - but only if the part is in perfect condition, else it is a hopeless case. Then you better get a new spare or if unobtainium or junk production, have one remanufactured from stock sprockets and have the gear shaft lasered and milled to fit. TIG welding will heat up the shaft too much so only laser will do safely. Seems the Burman type is only very narrow spline length , my guess 5/16 or 3/8 ?? Modern bikes got a more substantial dimension possibly, so more durable ?
Anway, not much to add now, you will have to see what is available today.

Vic
 

MartynG

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VOC Member
Thanks for all the info and guidance. I have ordered a replacement PR50-15BA (thou second hand) driving gear from Draganfly and I already have a new sprocket PR50-22A on hand along with a new lock washer.

The photo below is of the existing disaster and having rechecked - twice - I can confirm that the securing nut was not thread bound but was firmly secured and tight against he face of the sprocket. Extent of damage to the gear also confirms this. FYI you can just see the end of the spacer PR50-23BA protruding from the seal.

Checking the NEW sprocket, the spline length is 3/8 inch, that is also the clamp thickness so as the ruler shows the nut does not get anywhere near the end of the thread.

So now its a case of strip the box and wait for bits to arrive. When they do I will be VERY carefully checking for fit.

M

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MartynG

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VOC Member
I think I MAY have found a contributing factor.

I have a brand new PR50-17-1BA driving gear lock washer AND a brand new PR50-22A gear box sprocket both from the Spares Co.

The OD of the lock washer is 2.6165" with a thickness of 0.0350 and it appears to be lazer cut.

The ID of the sprocket central depression appears to be 2.6370" but that is at the outside edge of the central depression (see photo). Problem is that depression has round shoulders at it base so the flat face for the washer and nut to clamp against is only 2.4910" in diameter.

What this means is when assembled, before the nut is secured, the face of the washer is well clear of the face of the sprocket and consequently as the nut is tightened against the washer, the washer acts like a spring absorbing a lot or the hoped for clamping force.

I do not know how significant this is - anyone have any thoughts?

My first thought was reducing the OD of the lock washer to 2.5" to eliminate the spring effect.

On reflection a spacer between the face of the sprocket and the lock washer may be a better solution. Has anyone encountered this before? Should there be a spacer there anyway and if yes I wonder what the part number is??

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Matty

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VOC Member
I have just had a look an old driving gear in my stock, of maybe useful bits and the splines on it look virtually perfect though I have not used it because the top gear dogs are a little tapered so I would lose a little of the 3.5 /4.00 mm top dog engagement.
So why are the splines so damaged on the one in the Photo? Is this the result of bad material or incorrect assembly in the past?
Afraid I do not have a new or old sprocket to check the tab washer problem which of course could be fixed by either reducing the diameter of the outer of the tab washer or making a simple spacer to go behind it.
Matty
 

Cyborg

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VOC Member
I would be wondering about the hardness of that shaft. If shafts like these can survive beyond the useful life of the motorcycle, they must be somewhat harder that yours. The lock plate is just slipped over the splines, rotated in the groove and bolted in place. Sprocket is not rigidly fixed on the shaft.
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oexing

Well Known and Active Website User
VOC Member
Rigid fixing the sprocket by torquing that nut will not have ANY consequence to the useful life of the joint, as the power going through this joint is higher by factors than your torquing as confirmed above in no. 35 by Martin , he found a tight nut but the splines were worn even so. So I wonder how owners who had no troubles had assembled their gear components, good fit I guess but another factor possibly a good lubrication onto matimg faces like good chain grease or even better MoS2 paste ??? The modern Japanese designs rely on decent hardened components and a wider spline for spreading loads to acceptable conditions. So yes, doing up that nut will defintely NOT help, just conceal a flaw for a moment. Material is typically case hardened steel - universally accepted standard since decades so I would not think this to be a topic anywhere. Testing with a file would help though.

Vic
 

Cyborg

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VOC Member
Not sure about the width of the splines on the Burman sprocket, but I measured a 750 Honda sprocket and the contact area of the splines is slightly less than 12 mm in width.
 

oexing

Well Known and Active Website User
VOC Member
Now you could add up all side contact faces of the slots to find a total for Honda and Burman or Vincent that has to bear all loads from chain pull. The Japanese splines look a lot deeper than the very flat type of the Burman - or Vincent as well. I suspect to see very high specific loads in kg per square millimeter or in imperial units if you like, in that old design, that takes all the wear and will be difficult for lubricants to prevent fretting. Still I think all you can do is to care for a perfect fit in the spline plus EP grease or MoS2 paste when assembling. Any extra high torque on the nut is wishful thinking. That is why there are designs with push fit and circlip , no nut and thread as not helpful at all.

Vic
 

vibrac

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VOC Member
Having looked at the tab washer and the face of a sprocket today I can see the interference with the curve of the sprocket recess however the washer is of a thickness that I can compress it to the sprocket face with my thumb so a little tweek on the tabs or just tightening the nut overcomes the interference. I do think that the nut needs a spacer sometimes as it can run out of thread and finally it does look like the gear with the splines is unobtanium
 

MartynG

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VOC Member
Vic and others,

I have been able to locate a second hand Driving Gear (the one with the splines) and am now waiting on the postal service to deliver it - fingers crossed that they don't loose it AND that its in serviceable condition . But it was only 10% of the Spares Co new old stock listed price. Then again the Spares Co have nil stock.

Considering the apparent unobtanium status of any further replacements I'm considering investigation of having the old damaged splines reclaimed as Vic suggested. Now to find a shop who can do the lazer welding then another to recut the splines and lastly - a heat treater.

Today its strip the box completely to see if / what else needs attention.

SHMBO tells me I need to cut down on the use of the Comet, that covering around 10,000 miles on it each year is just too much for the old thing. Changed her tune when I agreed and said that maybe I should have a second one to 'spread the load'

Martyn
 

MartynG

Well Known and Active Website User
VOC Member
Finally, Thinking of the impact loads on the driving gear splines seems to me that the ESA is just not doing its job in absorbing transmission shocks and there seems little that can be done about that.

M
 

greg brillus

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VOC Member
I'm guessing the gearbox spline was worn all along, just not so noticeable with a new sprocket slid over the shaft. Movement in the spline will hammer away at any sprocket combination. My machinist has repaired the spline on the input shafts welded up and re machined........It is not cheap as it is time consuming........Probably around the $300 dollar mark in our money, maybe a touch more.......
 

brian gains

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VOC Member
for the record I replaced the output gear during my recent Burman Box Debacle, see tagged on end of Melt Down thread, I thought the dogs appeared worn and may have been contributing to my problems.
I bought a second hand item from Draganfly a s used but serviceable, they did have NOS items at multiples of the price I paid. The dogs I had seen on output gears of the comparable though different ratio Ariel box seemed far beefier leading me to think my dogs were worn. Once I received the replacement, the dogs were not appreciably different in profile to the item being replaced. Having given consideration to the latter if the dogs were appreciably worn would the profile have not been biased as wear would have been just on one side; it wasn't which leads me to think that for whatever reason. meshing, revs that is the way the dogs were designed. As for the damaged splines and sprocket fitment issue. I would suggest that the sprocket nut was not tightened down initially then consequently run, hammering the splines to death.
 
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Cyborg

Well Known and Active Website User
VOC Member
Now you could add up all side contact faces of the slots to find a total for Honda and Burman or Vincent that has to bear all loads from chain pull. The Japanese splines look a lot deeper than the very flat type of the Burman - or Vincent as well. I suspect to see very high specific loads in kg per square millimeter or in imperial units if you like, in that old design, that takes all the wear and will be difficult for lubricants to prevent fretting. Still I think all you can do is to care for a perfect fit in the spline plus EP grease or MoS2 paste when assembling. Any extra high torque on the nut is wishful thinking. That is why there are designs with push fit and circlip , no nut and thread as not helpful at all.

Vic
Good point and yes the Japanese are likely deeper. Again, I don't have a Burman sprocket to compare, but just a quick comparison to a Norton shows the Japanese splines .5mm deeper. In this case the splines (on the Norton) are just over 7mm wider, but some of the extra width is due to the shoulder that the output seal runs on which the Burman sprocket doesn't have. (Japanese shaft is about 6.75mm smaller in diameter). Not that any of this matters in the grand scheme of things...just find it interesting.
The splines in Martyn's photo look odd to me. Probably just the photo, but the groove shown by the top arrow doesn't appear to be in the spline indicated by the lower arrow. In any event, when welding up the splines that groove or whatever it is ( perhaps from a washer fretting away) looks like it should be filled in to maximize the load bearing area, making sure the threads don't go any deeper than necessary.
Martyn, if your new sprocket has good splines, but worn teeth, you could always do as Robert does and graft new teeth on it. He is our resident orthodontist.
Burman.jpg
 
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MartynG

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Good point and yes the Japanese are likely deeper. Again, I don't have a Burman sprocket to compare, but just a quick comparison to a Norton shows the Japanese splines .5mm deeper. In this case the splines (on the Norton) are just over 7mm wider, but some of the extra width is due to the shoulder that the output seal runs on which the Burman sprocket doesn't have. (Japanese shaft is about 6.75mm smaller in diameter). Not that any of this matters in the grand scheme of things...just find it interesting.
The splines in Martyn's photo look odd to me. Probably just the photo, but the groove shown by the top arrow doesn't appear to be in the spline indicated by the lower arrow. In any event, when welding up the splines that groove or whatever it is ( perhaps from a washer fretting away) looks like it should be filled in to maximize the load bearing area, making sure the threads don't go any deeper than necessary.
Martyn, if your new sprocket has good splines, but worn teeth, you could always do as Robert does and graft new teeth on it. He is our resident orthodontist.
View attachment 30337
The 'groove' erosion is in every groove! Good fortune has it that replacement sprockets (the dogs in the old one are buggered as well) are available from the Spares Co at a reasonable cost.
 

MartynG

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Loctite 660 is touted as the go to solution to ensure a 'perfect' fit on splines. Has anyone tried using it? What was the result? I am also wondering about subsequent disassembly issues if it is used.

Thinking of using it as part of the rebuild.
 

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Vincent Brake

Well Known and Active Website User
VOC Member
Or use n style such a thing as wedge keys. I learned one had double set at 120 deg over the axle and flange.
Very very good fixing

Well 6 here yes.

In fact not a bad idea.

Make them from Toolox 44 steel
45 hrc, super stuff
 

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