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New bike - some help please
Re: New bike - some help please
The valves were identical both sides: intake spot-on at .004", and both exhaust valves at between .001" and zero, instead of .008". Presumably, at 63K miles, this is due to the beginning of some exhaust valve seat recession--but could be exacerbated by infrequent or ham-handed work by the PO (or his son, who rode the bike for a short while).
The lack of a proper gap may explain the imperfect running I experienced coming back from Wisconsin. So, I'm eager to finish going through the carbs and see if she runs just right, as I expect.
The plugs, as you can see, show she was running a bit lean--which shouldn't be the case at 6,000 ft, but makes some sense with what was likely incomplete sealing of the exhaust valves once the engine heated up.
Anyway, when I get the leak-down test done, I'll post the results. Hope she's fine!
- srankin
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Re: New bike - some help please
If you have the start of valve seat recession. you will see it when you pull the heads if you do, or do a leak down test or, if you adjust the valves and they go out of adjustment before about 15,000 miles, or won't stay adjusted for 15,000 miles.
The 84 bikes were set to run pretty lean. St.
Re: New bike - some help please
Thank you for this.srankin wrote: ↑Wed Nov 06, 2024 6:24 amOne thing to know about this bike is that when it starts to idle poorly or run rough, the FIRST thing to do is adjust the valves, not mess with the carbs. A lot of guys get that backward and spend a lot of time rebuilding and messing with carbs only to find out the valves were out of adjustment.
If you have the start of valve seat recession. you will see it when you pull the heads if you do, or do a leak down test or, if you adjust the valves and they go out of adjustment before about 15,000 miles, or won't stay adjusted for 15,000 miles.
The 84 bikes were set to run pretty lean. St.
I can't do the leak down test as it's snowing pretty heavily, and the wife doesn't want her car to get wet...

Good to hear that, indeed, the excessively tight exhaust valve clearances may have been responsible for the imperfect running and idling. The manifolds were dried out, so I've got new ones to install, too: they could've been leaking a touch of air, I suppose.
Good to know, too, that the plugs don't look excessively lean. They aren't blistered but awfully clean: I had expected at least a little tan pigment...
You know, the thing's got 63K miles and has been sitting for over a decade, so I don't think it would hurt to replace the needle jets and needles, and jet and adjustment screw o-rings--very simple to do. I may hold off on soaking the carbs and R&Ring the throttle shafts to replace that o-ring until I start the engine and see if air is leaking past the shafts--though getting a butterfly installed properly is no big deal (I designed a blow-through, intercooled supercharger setup for Spridgets and Moggys, and am competent in rebuilding and modifying carbs). https://www.creativespridgets.com/supercharger
Also, I had set the new floats using a slightly different technique than Snowbum describes, on the PO's advice. I inverted the carbs and adjusted the floats so their flat surface was level with the carb body--where the float gasket sits. The gas in the bowls ended up being about where Snowbum says it should be.
Question: I found the VIN on the lower R/H frame member aft of the cylinder, but can't figure out which of the numbers embossed just below and ahead of the L/H cylinder is the engine number (see 1st and 2nd photos, top and bottom of same machined surface). I note that the number in the valley beneath the starter is different... (3rd photo)
- schrader7032
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Re: New bike - some help please
https://bmwmotorcycletech.info/IDnumbrs.htm
I use RealOEM to find out production date - https://www.realoem.com/bmw/select.do
As for the transmission pictures, the one that starts with "83" indicates the transmission was built in 1983 and the next two digits indicate the week of the build, as in the 40th. Not really sure what the EBM number is supposed to represent. The third number is likely an internal production number used by BMW...typically those don't really pertain to dating.
Here is Snowbum's other page on transmissions:
https://bmwmotorcycletech.info/transmission.htm
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.
Re: New bike - some help please
Oh, cool, thanks.schrader7032 wrote: ↑Wed Nov 06, 2024 5:35 pmHave you found a VIN starting with "WB"? This would be the bike's VIN number. The last 7 digits are typically what one uses to find out when the bike was built. Snowbum has a page on ID numbers:
https://bmwmotorcycletech.info/IDnumbrs.htm
I use RealOEM to find out production date - https://www.realoem.com/bmw/select.do
As for the transmission pictures, the one that starts with "83" indicates the transmission was built in 1983 and the next two digits indicate the week of the build, as in the 40th. Not really sure what the EBM number is supposed to represent. The third number is likely an internal production number used by BMW...typically those don't really pertain to dating.
Here is Snowbum's other page on transmissions:
https://bmwmotorcycletech.info/transmission.htm
Yes, I did find the VIN, which does indeed start with WB, and matches the title (didn't look in Wisconsin when I bought the bike, as the guy had the original dealer paperwork from his purchase in 1984 that matched his driver's license and address, original mechanic's shop manual in binder, maintenance logs, etc, etc...).
Okay, thank you on the engine info. Of course, I've got a tranny number, too, and then there's the additional badge on the steering neck, pictured here... these bikes have a lot of numbers on them!
The Real OEM tool says the bike was manufactured in October of '83, which makes sense for an '84 RT. Thanks for that!
Re: New bike - some help please
Of course, this could be a replacement tranny that the PO installed and didn't feel obligated to tell me, or it could have been one BMW had on the shelf and used for whatever reason in 1983 when they put the bike together.
I can say that it shifted very reliably during the 1,300-mile ride from Wisconsin, with only one false neutral that I recall, coming out of 1st into 2nd--and which could well have been my fault, as I've got big feet and hadn't gotten used to sneaking my toe under the carb yet...
It looks like there will be no motorcycling in the near future for me...
- schrader7032
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Re: New bike - some help please
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.
Re: New bike - some help please
Yes, the motorcycle's VIN does indicate an October '83 manufacture date for what BMW and the state of Wisconsin call an '84 R100RT, and the engine appears to have been manufactured in '83 as well.schrader7032 wrote: ↑Wed Nov 06, 2024 6:22 pmI didn't see where you showed the "Z" number. But one set of numbers suggests an '83 40th week build. So how can another number show an '81 model??
However, the tranny no. is indeed Z 018538, which appears to fall within what Snowbum says is an '81 production run--and the numbers for '84 trannies, according to him, are very different.
So, unless I'm tired and missing something, there are two possibilities. Either Snowbum's information regarding which numbers go with what year-model transmissions is wrong, or it is right--and in that case, as I said above, the transmission is from an earlier model, either fitted by BMW or the PO, who kept that event from me for some unknown reason.
But ultimately it's of no importance, as it's a five-speed, doesn't leak, and the bike shifts fine.

- srankin
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Re: New bike - some help please
Don't go thinking too much about pulling the transmission apart, if it shifted fine, it will be fine. BMW had few complaints about that era transmissions, and they last a long time before they need any work. Or I should say mine has, 250,000 and never had anything but gear oil changes. St.
Re: New bike - some help please
Okay, good to hear that I'm not over-estimating the possible role of those old, dried-out manifolds--which, I should add, appear to be simply slices of fuel-filler hose, if what Euro MotoElectriks sells is typical. Had I realized that, I would've just bought a 1' length from NAPA and saved the balance in a plastic bag for semi-annual replacement at a fraction of the cost...srankin wrote: ↑Thu Nov 07, 2024 9:02 amIf there is a dried out rubber manifold between the carb and head, with any kind of a vacuum leak, oh it will burn very very lean. So kudos for installing new manifold rubbers.
Don't go thinking too much about pulling the transmission apart, if it shifted fine, it will be fine. BMW had few complaints about that era transmissions, and they last a long time before they need any work. Or I should say mine has, 250,000 and never had anything but gear oil changes. St.
Hmmm... well, since I did replace the diaphragms, floats, needle valves, and remove and clear out the jets and float-bowl holes, perhaps I should just install the new manifolds and see how it runs before futzing with the butterfly shaft o-rings? Then, if it persists on running poorly and/or gets lousy mileage, I could soak the carbs, R&R the needles and needle jets, replace all o-rings, etc.
Fantastic to hear that our very similar transmissions will last so long without attention. I'm a big believer in regular gear oil changes (despite the overly optimistic manufacturer intervals). I think I saw in the manual that 5,000 miles is recommended--but isn't that the same engine oil interval?
Seems to me that one would reduce the engine oil change and valve adjustment interval to below 5,000 and increase the gear oil changes to above that figure. But what do you think?