1976 BMW R90/6 "Jimmy Neutron Wanna Be"

[Hurco550]

I also had to rename the bike. I have the check list to sheet by the shop door, and had names like "roadster" etc on the list. My reverse cones were on it (which my girlfriend doesn't like the shape of, as it reminds her of a lava lamp or something out of Jimmy Neurton. Not sure of exactly how the conversation went, but at some point she used the term "Jimmy Neutron Wanna Be Bike" came out of her mouth, and we both go a good laugh about it. Hence forth, that's the name.

 

[ridesolo]

No kids or grand kids around, I had to look up Jimmy Neutron. Pretty good. I've heard of Pea Shooter mufflers, I guess those reverse cones should be called Lava Lamps.

 

[Hurco550]

If any of yall are trying to find some good product to remove paint, powder coating, carbon from pistons, gaskets from cases (and probably the ozone from our atmosphere) I really recommend this LocTite SF790. Its a bit hard to find, but it is about the only legit paint stripper that I can find at this point. This whole job was about 15 minutes, including scrubbing with soapy water.

@ridesolo stopped by on Saturday to lay eyes on the project, as well as loan me his spring compressor which came in handy. I would not have liked to try to disassemble these without one, plus he made a very handy little board fixture to aid in using it. (thanks again cory) Basically the WP shocks I bought in Chicago seem that they'll be too long, and may have to wait until after I build a custom subframe in order to work, and the other set of WP shocks I have need a full rebuild. I basically pulled the konis apart in order to do a deep clean and inspection. The action of the shocks still felt great with good compression and rebound dampening, and will get me by until I get the time to rebuild the shorter set of WP shocks. The weather is getting warm enough (and this is supposed to be my daily) that I'm pairing down projects to what can be done later vs what NEEDS done now.

While he was there, we also mulled over rear fender options and tail light mounting. I think I like what I ended up with. This simple bracket mounts between the leftover end of a front fender and mounts to the OG rear fender local on the subframe, AND mounts the bates style tail light all in one unit.

 

[Maritime]

Nice

 

[ridesolo]

I guess you could try and come up w/ something to use instead of that spring compressor, but for the price why bother? Definitely worth the (very low) price even if you don't use it often. Lookin' good man!

 

[Hurco550]

A little careful taping, cutting, drilling, filing and sanding and I got the front fender done. It is shorter than I really want it to be. Eventually I may take @irk miller advice and fiberglass the factory bottom of another front in to make it about 3" longer on the back.

Until I get it made the way Id like, a honda elsinore flap will do the job to keep things a bit cleaner.

I got the body work sanded and prepped and laid down a few coats of ss appliance epoxy. They are sitting in the attic closet to cure for a bit, but thought its not the paint job I want for the final bike, it gets everything "Matching" with a fairly tough and decent looking paint job. I found that heating the can of spray paint before use in a container of hot water helps this stuff lay much better.

I also made up a few spacers to get the plugs the proper length from the dual plug head setup. Not sure the history of these heads, but I know the plugs wouldve likely smacked the pistons without them.

 

[ridesolo]

Looking good.

When one of those is set up for dual plus like that do they fire simultaneously or is there a slight delay between them to try for a more complete burn?

 

[Hurco550]

Looking good.

When one of those is set up for dual plus like that do they fire simultaneously or is there a slight delay between them to try for a more complete burn?

They fire at the same time, but at the top and bottom of the chamber, vs just the top. Though it seems like it would be instantaneous, the flame truly does travel across in a front. The theory is that lighting it at opposite ends will create two fronts that meet in the middle, causing a faster complete burn of the fuel. Because of this you also run 4° more advance on the timing. 28 deg vs 32 if I remember correctly, but I'll have to look back at notes.

 

[ridesolo]

Makes sense. Even a slight delay on one of the sparks would have the second one trying to ignite a less volatile mixture.

 

[ex119x]

Since you are running plug spacers, you could adjust the thickness to also use them to index the plugs so the gap is pointing to the center of the chamber.

 

[Hurco550]

Since you are running plug spacers, you could adjust the thickness to also use them to index the plugs so the gap is pointing to the center of the chamber.

Thought about that, but if its good for he first set of plugs, I'm guessing it wont be for he next set. To my knowledge plugs are not indexed to have the electrode to the same position every time, or are they?

 

[ex119x]

Thought about that, but if its good for he first set of plugs, I'm guessing it wont be for he next set. To my knowledge plugs are not indexed to have the electrode to the same position every time, or are they?

To the best of my knowledge they are not indexed. Teazer may know about this since I only saw it at the racetrack with the 2 stroke guys fiddling with their box of copper washer spark plug shims. But they were also checking humidity, altitude density, temperature, barometric pressure and sacrificing chickens to get their jetting and timing exactly to the point that if you looked at it wrong it would seize up solid. I ran 4 stroke singles and put a new plug in it every year whether it needed it or not.

 

[Victor Miller]

I was debating on posting a thread up here, but eh why not. About a month and a half ago I was on the way home from fishing when this 1976 Beemer caught my eye. It was sitting back off the road in a guys driveway with a barely noticeable for sale sign on the back saddlebag. (Perhaps that on top of the fact that the guy never advertised it is the reason he said he had a hard time selling it). The guy who had it was an older gentleman that had been riding airheads since the early 60's, and this was one of 4 he had in his stable, including one really well done /5 with a Volkswagen air cooled lump in it.

Anyways picked this one up for a reasonable price, with around 82k miles on the ticker and trimmed in full 70's touring garb. Lufmeister fairing, complete with vetter cyclesound radio (with cassette) wixom hard bags, crash bars with highway pegs, and a luggage rack hanging way out back, with all the glass painted and striped to match.

I had been wanting a vintage airhead for a while. My good riding buddy Al used to put alot of miles on along side me on his r75 and I wanted one ever since.

As i brought it home.

Sent from my SM-G920V using Tapatalk

do you share your experience with me?

 

[ex119x]

do you share your experience with me?

Fishing for easy content to steal?

 

[Hurco550]

To the best of my knowledge they are not indexed. Teazer may know about this since I only saw it at the racetrack with the 2 stroke guys fiddling with their box of copper washer spark plug shims. But they were also checking humidity, altitude density, temperature, barometric pressure and sacrificing chickens to get their jetting and timing exactly to the point that if you looked at it wrong it would seize up solid. I ran 4 stroke singles and put a new plug in it every year whether it needed it or not.

I spent a good bit of my youth messing with old 2t snowmobiles with my father, some of which were a bit higher performance than others. It was a fun time, but in alot of ways, I don't miss some of those finicky sides of 2 strokes these days. Though this bike is finicky in its own way. Finding lots of mod podge parts that I'm trying to i.d. and make work, all with an ever dwindling budget ha.

 

[Rider52]

We indexed the plugs on our race bikes. I'm not convinced it makes that much of an improvement.

 

[Victor Miller]

Fishing for easy content to steal?

sorry i dont have this type of intent

 

[teazer]

Are the plugs 3/4" reach or 1/2"? If they are 3/4" plugs, it might be a good idea to machine the seat so that a 1/2" plug is a perfect fit. Not sure who let the secret of sacrificing chickens out of the bag, but with a 2 stroke you gotz to do wot you gotz to do.

I have indexed plugs before and I am sure that it helps, but to be honest I can't tell the difference except when I have high dome pistons that need a fire notch (trench in the crown to clear the plug) or the oversize valves I fitted come too close to the center electrode.

And on twin plug motors it is normal to back off ignition timing. 4 degrees is a good place to start.

 

[Hurco550]

The plugs I have in it are 3/4" reach, but 1/2" would be too short. I don't know the full history on the heads. I bought them from a massive bmw auction, and this was the only description.

https://www.auctionohio.com/auctions/10825/lot/147292-r90s-cylinder-heads-dual-plugged-74-75

One side needed a .220" thick shim while the other needed a .080" shim. I don't know who did the work, but that's obviously a bit on the shady side imho. I'll run them as is, as they have fresh guides, valves and springs, but the motor will still be pretty mild. Stock pistons with fresh rings, mikuni vm36 carbs. Opened up exhaust, electronic ignition and dual plugs. There's been some intake port work done too, but I'm not sure to what level or shape. All that to say it's not going to be a "built to the edge performance machine", but hopefully a slightly peppier than stock daily.

 

[Hurco550]

Lots of piddling away still happening. I am not as good at documenting the build on the forum as I used to be.

One of the rocker arm needle bearing cages had a chunk missing from the retainer lip.

Over my years of airhead ownership, I've read multiple horror stories of them dropping a needle which makes its way down a pushrod tube and goes on to destroy the motor. I opted to press out the old and press in a new set. For all the specialty tools that I've made for this bike, I phoned it in and used some sockets and a vice for the job.

At that point, I finally go the top end re assembled with fresh rings and a fresh hone.. I ended up with a mod podge of rocker arm stuff, spanning from late /5 suff, early /6 stuff and a bit of late /6 stuff. At some point, If I run into issues, Ill replace the rockers and perches with new equipment, but for now, it will likely work just fine.

Im not sure if I covered this in an earlier post, but I also replaced the starter with an updated unit. 2/3 the physical size and weight of the OG OEM unit.

Ran up against a road block with the head swap. The heads are for an r90s vs the bike, which is an R90/6. The r90s used delorto carbs and took a different thread pitch intake tube. I bought a set of repop r90s intake tubes and turned them down to use with my mikuni vm36's.

After a substantial amount of cutting, sanding, trimming and fitting, I finally got the carbs mounted in a way that I am happy with. I ran these for a little bit, but I obviously did not have my detail goggles on when mounting the first time. This job is much more tidy.