Numbers on R90S engine housing

tm.chao · Post by **tm.chao** » Sat Feb 10, 2018 9:35 am

Ask for the meaning of these two groups of numbers on R90S engine housing.(Not VIN)

schrader7032 · Post by **schrader7032** » Sat Feb 10, 2018 1:49 pm

I checked my R100/7. I, too, have a number there but no numbers in a box. But from my numbers, 387508, I believe the 38 represents the week of manufacture. I know that my bike was built in September 1977 and the 38th week falls within September. The 7508 doesn't really equate to anything that I can think of...my guess is that it is a sequence number. I calculate there were a little over 5100 /7s made for the 1978 model year. However, there were R100S, R100RS, and R100RT models built for 1978 for which the block should be the same, just the top end and other items would be different.

If that holds true, then your R90S would have been built in the 35th week of that year, possibly either late August or early September. Go to here to determine month/year of build:

www.bmw-z1.com/VIN/VINdecode-e.cgi

schrader7032 · Post by **schrader7032** » Sun Feb 11, 2018 7:47 am

I posed the question to a few Airhead people, one being Tom Cutter. I showed him a picture of my stamping and he says it's not by BMW and that likely it's something associated with a retitle, theft, or totaled bike. He says the size and font are not correct. At some point, I think in the early 1980s, an engine number was added to a milled flat area below the left cylinder. But I can't find any such area on my /7.

I'm second owner on my /7 and have no reason to think that there was something weird going on that the bike was retitled or it had been totaled. The fact that we have two bikes with similar markings makes me think it's along the lines that I offered.

I was rethinking this and wonder if the "7" in my number might be the year of manufacture. It would be interesting to hear from the original poster if the R90S was actually built in 1974.

tm.chao · Post by **tm.chao** » Sun Feb 11, 2018 8:41 am

Thanks Kurt, The R90S was manufactured in Sep. 1974.

schrader7032 · Post by **schrader7032** » Sun Feb 11, 2018 9:21 am

Thanks! That's a nod towards the theory that the third digit might indeed by the year of manufacture.

skychs · Post by **skychs** » Mon Feb 12, 2018 8:18 am

Yesterday when I was cleaning my 75 R90S engine I discovered the same thing. I do not have the numbers in the box but I do have an "R" on the other side in the same area.

So ... 235243 June 1-7th of 1975 is week 23. My ID plate is stamped June 1975. Makes sense. VIN decoder verifies it.

What about the "R" ?

schrader7032 · Post by **schrader7032** » Mon Feb 12, 2018 8:23 am

Interesting! I think we may have a trend here. Not sure about the "R"..."Right"???

Vintage BMW Motorcycle Owners

Numbers on R90S engine housing

Numbers on R90S engine housing

I checked my R100/7. I, too,

I posed the question to a few

It was manufactured in Sep. 1974

Thanks! That's a nod towards

numbers

Interesting! I think we may