permisable backlash on timing gears

malmac · Post by **malmac** » Thu Jan 01, 2015 3:09 pm

My son and I have been working on his 1967 R60 - a few problems which need attention. We are trying to source the permissible backlash on the timing gears.

Can anyone tell me what that should be?

Thanks in advance.

Mal

schrader7032 · Post by **schrader7032** » Thu Jan 01, 2015 3:33 pm

The Barrington book mentions BMW specs for newly installed gears of 0.01 to 0.02mm for gear lash. Not being that learned on what this means, hopefully that will make sense on how to measure it. The book goes on to discuss the issue about the engine case stamping of numbers ranging from +10 to -10...this was associated with the center-to-center distances of the two shafts. Apparently, when the original engine was assembled, the selection of gears was trial and error until the proper fit could be found.

malmac · Post by **malmac** » Fri Jan 02, 2015 3:47 am

Kurt

Thank you for that, I have the book but must have skipped over that paragraph.

My son's gears are sitting at about .065mm -

New gear sets are at least available - the problem seems to be with crankcase distortion - ordering the set that would have originally fitted - may not be guaranteed to solve the problem - mmmmmm we will have to chew on this one for a bit.

Thanks for your help.

Mal

schrader7032 · Post by **schrader7032** » Fri Jan 02, 2015 6:35 am

My understanding with the distortion was that the shaft centers got closer over time, thus I would think that the lash or tightness of the gears would get smaller. Any idea with the last was before starting the work? It would be lucky to order or find the right gears to start with...I think the factory had the luxury of many gear sets available and they just kept trying until them found a set that worked.

malmac · Post by **malmac** » Fri Jan 02, 2015 7:22 pm

Kurt

Based on what you say - my son's cases are stamped -2 - so is it fair to assume that means the shaft centres are -2 units closer than zero - therefore to get more clearance one might order -1 set of gears and hope to be close.

His current clearance is like over three times the maximum ideal backlash - does this just add up to extra gear noise and more slop in the engine timing - TDC being a moving target between under load Vs backed off - when the crank would be driving the camshaft from the other side of the gear faces?

I am not an engineer so this is all new territory for me.

Thanks for your point of view - much appreciated.

mal

schrader7032 · Post by **schrader7032** » Fri Jan 02, 2015 9:16 pm

This has been an overall difficult subject for me to understand...I'm not sure I have it all correct. My notes say that the perfect difference between the two shaft centers is 90mm. The different numbers means hundreths of millimeters different from perfect. So a -2 stamp means that the difference is 2 hundreths of a mm less than perfect. The real problem is that the gears were not and cannot be made perfectly. So, you can't pick up a gear that has a -2 on it or maybe a +2 on it and know that will work. The gears were simply chosen from supply until they found a gear set that produced the correct backlash. You would have to have a whole range of gears and use trial and error until you found the right set that would work. It was about gears working together to make the mesh correct. I think it's wishful to think you could order something specific and know that it would work.

malmac · Post by **malmac** » Fri Jan 02, 2015 10:48 pm

Kurt

Yes this is confusing, and this link relates to the ordering of a new gear set - I assume they try and interpret what one needs based on the crankcase numbering.

What do you think?

Mal

http://www.ulismotorradladen.de/uli/web ... ation.aspx

Ian R11 · Post by **Ian R11** » Sat Jan 03, 2015 5:41 am

I have an engine case stamped -8 the old gear set fitted was marked -2. Knowing things alter over the years I took the case to a local company with CMM measuring facility and found the case measured +/-0 confusing things further.
I discussed this with Uli’s and decided the best solution was to send the engine case to them, not too difficult from the UK. They use a dummy crank and cam fitted to the casing enabling different gear sets to be tried and clearances checked. They have the luxury of trying the full range if needed and in this instance found -8 gear set fitted correctly.
I doubt that’s a solution for you living in Oz but does demonstrate the problem you can have with these. I would certainly make contact with them, they are very helpful, have good English and I doubt you will be the first person to ask their advice on this.

malmac · Post by **malmac** » Sat Jan 03, 2015 3:37 pm

Ian

We have actually been in contact with Ulis (a chap called Heinz actually) on a number of matters, though the timing gears have not been explored yet.

They sent out a new crankshaft for the bike and the bearings and seals we need plus some other bits and pieces - as we have been disassembling the engine we have found other items that need to be addressed (such as some damage caused when one of the pins have come out of the breather plate - and found its way to the bottom of the engine) - some damage resulted from that event.

We will discuss the matter with Heinz and see what we come up with. Thank you for sharing your experience.

Mal

bmwmyplace · Post by **bmwmyplace** » Tue Jan 06, 2015 10:04 am

Mal when you come down I will give you my collection of gear sets about 6 sets in all you should find one set to suit. call me Peter

Vintage BMW Motorcycle Owners

permisable backlash on timing gears

permisable backlash on timing gears

The Barrington book mentions

thanks

My understanding with the

Lots available but where to start

This has been an overall

Kurt Yes this is confusing,

I have an engine case stamped

thank you Ian

Mal when you come down I will