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divimon2000 12-11-2012 01:00 PM

Rotax 650 Engine Rebuild (BMW)
Anyone here do this? (I'm sure, just haven't searched yet) Too bad for you, here is another one. I have rebuilt a bike before, but never had anything to do with an engine. Buddy has (Eric). My rebuild thread is here.

Buddy and I find a BMW F650 GS '07 with 35k on it for a REALLY good price. :clap Been looking forever. Finally. Engine is pretty much toast :(:, but thats what we do- buy other peoples junk (if its cool) and get'er going. We have more time and beer than brains and money.


Oil out the breather tube into the airbox. So much so, the PO attached the end to a bottle of coke and drove it around. After a couple of checkouts by local dealers, Max BMW gives him the bad news of something serious. My guess is they said a new engine or work totaling close close to that. They did a decent diagnosis with compression test and leakdown test.

We started it and checked it out as well and found it may have less power that the other 650's we've rode, had some sort of clanking unlike the cam chain and a lot of oil coming out when starting. It decreased to a mist when driving.

All in all the bike is in supergreat shape and we're psyched. I have a Dakar and a rebuilt 650GS so we're up to a posse if this thing gets running. We figure we have a few thou to spend and still make money on it so its all downhill from here. (uh huh)

Coming home from Maine (Or, Post a pic of your bike in a trailer in front of a train! thread)

In the Adventure Garage

Tune in.

kubiak 12-11-2012 02:31 PM


Kawidad 12-12-2012 09:17 AM



divimon2000 12-12-2012 12:15 PM

OK then, two in the audience so its a go! It was a go anyway, we want another Beemer!

Step one, check the health ourselves- this means a compression test and a super deluxe differential compression test. To do this on these engines we need to dis engage the decompression lever or we'll have some leakage there. Don't worry, I'll video how the decompression lever works. To get to that, the valve cover needs to be off at a minimum so start throwing parts off. Oh yeah, you need to know what the compression is supposed to be in the first place :deal I think its 170 (pretty high).

Once we got down in there, we hooked up my el-cheapo dial with the included correct adapter to fit in this plug hole (Eric's high-end auto rig didn't have it :rofl taped the decompression lever out of the way with electrical tape (it worked and surprised me), rigged the battery back up, and turned it over. We read 130psi then moved on to the differential compression test:

Here we located top dead center, locked the cam with the special (BMW) bolt and cranked in 100 psi then read what the cylinder was holding (30).

michael1968 12-13-2012 01:46 AM


Originally Posted by divimon2000 (Post 20234522)
OK then, two in the audience so its a go!

I'm watching too!

ferals5 12-13-2012 02:04 AM


I'm in...continue :thumb

Ditch 12-13-2012 09:36 AM

:lurk 35k on my '07 Dakar and still running strong. I still have the original waterpump seals in. (all the parts on hand just in case)

mcma111 12-13-2012 10:14 AM

By any chance did Max say the piston and rings are shot thus the blow-by, pressurizing of the lower end?

divimon2000 12-13-2012 02:02 PM


Originally Posted by mcma111 (Post 20241195)
By any chance did Max say the piston and rings are shot thus the blow-by, pressurizing of the lower end?

They didn't say specifically on the paperwork, however they had all the info they needed listed, compression low, leakdown low. Only thing left is to tell the PO he needed a compete overhaul + whatever parts. My guess is they told him directly the bad news (including the unknowns like piston, maybe cylinder). Of note, the previous non BMW dealer charged a lot of money to not diagnose it.

divimon2000 12-13-2012 02:04 PM


Originally Posted by Ditch (Post 20240923)
:lurk 35k on my '07 Dakar and still running strong. I still have the original waterpump seals in. (all the parts on hand just in case)

Wait till you see the results of our findings! You will be proud to own that engine. We're toying right now whether to change a perfectly good water pump or not. I guess we'll look at the shaft and decide.

divimon2000 12-13-2012 02:13 PM

Diff compression Test
This is a cool diagnostic tool. With the pressure of 100 going in, we read 30 psi holding. Now with all the covers off and exhaust open, we could listen to the areas with a garden hose to pinpoint the problem area. Intakes sounded quite, exhaust valves sounded quiet but the crankcase was hissing like a snake. OK now we have a better understanding of what to look at.

Prior to this we read all the FAQ stuff on the F650 site and everything pointed to a counterweight shaft seal. But with Max's info on low compression and our investigation, we're now looking at that plus some ring/piston stuff. The way the Rotax 650 (I think its the 652 engine) oil system works (Dry Sump), the lower end does have some oil in it before scavanged back up to the tank. So any additional pressure will drive it out through the vent to the airbox. It's even weirder than that, I need another post to diagram that.

oldxr 12-14-2012 01:25 AM

In the automotive repair business that test is usually refered to as a cylinder leak down test.An accurate leak down test gauge set like something from Snap-on is a great tool to have.Knowing what you are looking for before dissassembly is much better than guessing.This could have been caused by poor air filter maintenance.If the engine has a chrome cylinder bore there are companies that can rechrome the bore.The bike will more than likely need a top end rebuild-not that hard of a job.

tommyvdv 12-14-2012 04:26 AM


divimon2000 12-14-2012 05:53 AM

Engine removal
I agree with oldxr. But, we may also have an issue with the seal that typically goes as well. Probably will split the case as well.

Based on what Max described in the paperwork, I give them high marks for giving the customer what was a real diagnosis.

And you can see the other non-BMW shop had some wrong diagnosis.

Time to take the engine out. I don't think we looked at a manual at all- instead just removed stuff in the way. The radiator needed to come out. Of course all the stuff that could get bent/broken like throttle body, oil pipes (metal) and disconnected all the plugs. It's pretty intuitive to get it all back together, like plug-and-play. Key is of course to bag and mark the parts that are a group and better yet, order them for installation.

Taking the swingarm/engine mount bolt out, we just slid in another rod in place to avoid taking the whole end off. I think the last mount to come out/off was the top Castle Nut adjusting thing. We didn't have the "tool" but got to the inside of the nut and that was fine. The lower black kickstand bracket swung back as we left the rear bolt in place

We used the motorcycle lift to support it, then slide out to the left.

Eric, chime in if I missed some things.

divimon2000 12-14-2012 11:32 AM

Beautyful bike

The low windshield and long TT front low fender make it look streety.

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