BMW Airhead Oil Pump Issue - The Engine Faces Yet Another Roadblock 

Hello, I am aware of the gap between the outer ring of the oil pump and the engine housing. Unfortunately the original outer ring is still perfectly within the factory specifications, despite being used for 50+ years. The new “OEM” BMW outer oil pump ring, is 0.005” (0.127mm) smaller is diameter! This is straight out of the box. According to the specifications, these parts are scrap or also called (Ausschuss) in German. I am aware that certain upgrades were made over the years to specific components, but running a loose oil pump within an aluminum housing is just calling for issues. I’ve spoken with a few enthusiasts from Europe and they also told me about this issue. They ONLY use “Good-Used” oil pump rotors in their engine nowadays, because they cannot afford to install lousy quality parts…especially when working with customer engines. This issues caught my attention, because for every engine I rebuild, every internal and external measurement is documented in engine rebuild sheet. Without this data, one will never know what quality the engine has been built to. Therefore it’s important to find these small, but BIG issues before the engine goes together. I hope this gives you an insight on what to look out for in case you decide to work on the oil pump area of this engine. Grüsse aus Kanada -Andreas

@@WorkshopRebuild Danke Andreas, hoffe, dass du das richtige Teil findest. Ich meine, dass selbst das neue Teil für ausreichend Öldruck sorgen wird, trotz des geringen Untermaßes. Meine Meinung. Nochmals Danke und viel Erfolg. Tolle Arbeit. Gruß Wolfgang

Yes, please do! One Facebook member had showed me 4 outer rotors that he purchased and he ended up using the old one, as all new ones were not within the factory specifications. This is either the clearance between the rotors and/or the clearance between outer rotors and engine housing. Please keep me updated about your parts. It will also help others😊👍🏽

Yes it would be hard to stretch that rotor😄 Now I just have find a solution in order to continue with the engine assembly. Thank you so much!👍🏽👍🏽👍🏽 Cheers

I'm glad I could share this info with you! The engine drawing you can see hanging on the wall can be found on my website: workshoprebuild.com/ It will be featured in the upcoming engine rebuild video. Cheers

Yes it is, and that's why I'm sharing these videos. I want as many people to know about the issues I run into and how they can be resolved. At the end of the day, the parts with flaws are not free 😅! I hope you have better success with your R90/6 and that you can get it back up and running. Let's just hope I don't run into any other issues lol. Regards Andreas

You’re very welcome! At the moment the supplier is looking into this for me (with immediate effect). The only info I found online about this topic was on this website: www.motorworks.co.uk/oil-pump-outer-rotor-ena53293-2.html Under description it reads: “Please note that BMW have changed tolerance specification on these rotors so the tolerance between the outside diameter and the crankcase is now significantly larger. This is normal.” To me this is not normal! If the clearance between the outer rotor and the engine housing is larger, you can loose vacuum between your inner rotor and outer rotor. There is a reason why the original outer rotor is larger😬 I try and find a solution ASAP to move on with the engine build. Thanks for your concerns. Regards Andreas

@@WorkshopRebuild You just QC 'd it for them. Defective. They should provide you another, in spec.

I did not contact BMW directly, but it would be worth speaking to them about this as it‘s a known issue for many enthusiasts! I‘ve contacted the supplier and they did not know of this issue and I am still „waiting“ for a refund. If I will ever get one…I‘m not sure🥲

This is a possibility, but I wouldn't see why. All other clearances within the engine would still be the same, but not on the oil pump outer rotor. This seems a bit off to me. There are smaller clearances within this engine on the top end (pistons, bore, rocker arms etc.) and thicker oil would still be able to flow past these surfaces without any issues. I'm not sure if the newer bikes (/6 and /7) had different housing dimensions, but I will look into this. It's possible that the outer rotor diameter was changed AND the housing diameter! In this case, the outer rotor would be just fine for those models, but NOT for the /5 models. Just something I thought about the other day. Thanks for sharing your insight. Regards Andreas

The old oil pump rotors show wear on the inside surfaces. In order to create good vacuum between both rotors, you want all inner surfaces to be extremely smooth. All dimensions are critical when it comes to the oil-pump assembly and it’s best to replace them if they are worn. This way it will last another 50+ years. Regards Andreas

Thanks for the reply, makes sense. I saw in your engine assembly build that you installed an oil pump - did you come to a conclusion about the 'new' spec from BMW? @@WorkshopRebuild

Not at all! I found a good “original” used outer rotor for the install, but the new spec does not make any sense to me. You wouldn’t make an adjustment years later, without making changes to the housing diameter. Something I have yet to figure out!

Glad you figured something out to keep moving forward at least. I've just ordered one from Bayer since mine was scored. it's described as 'Improved version with oil pocket for better lubrication when starting the engine'. it will be curious to see what the diameter is. @@WorkshopRebuild

Yes, I'm glad I found a really good outer rotor! I hope the one you will get is not undersized as well. The ones with pockets are the newer versions, but it's hard to believe someone would change the tolerance-spec after 50 years. The old one that was within my R60/5 engine was still PERFECTLY within spec on the outside diameter, but the inner surface was not good enough to reuse. This means the clearance was just fine...anything smaller will cause more problems. Please keep me updated on your findings. Cheers

The oil pump outer rotor specifications are as following: 57.075mm to 57.100mm. If your rotor is within this tolerance, than you have a good outer rotor. On the other hand the engine housing specifications are: 57.200mm to 57.246mm. Anything within this tolerance means your engine housing is to size. Now the new oil pump outer rotor I received is 56.941mm! This is beyond the wear limit for the outer rotor, which means it cannot be used for the engine rebuild. The clearance between the rotor and the engine housing is also NOT within the specifications. Did you measure your original outer rotor or did you purchase a new one from a company? Please let me know as I am having issues with this.

@@WorkshopRebuild Hi,I keep thé original one that I fond on the bike. It seem to be all right. I see an old one in the parts I receveved this the bike but I dont know when this part Washington renew

@@PistonetSavon The outer rotor you you will reuse is most likely within factory specifications, because it is the original one. I'm glad you can reuse your old one. This way you won't have the same issues as me (haha!). I will see what solution I can find finish my engine. Thanks again for sharing this information with me. Regards Andreas

I personally don't want do that, because I am dealing with the supplier to sort out this issue behind the scenes. This won't just help myself, but it will also help everyone else down the line that orders from them. Many people ran into this issue before me and they dealt with it in their own way! I couldn't find any info online and that's exactly why I made this video. Hopefully I can resolve this issue and share an update in the next video. Thank you for your comment. Regards Andreas