Engine Rebuild Cont'd Cont'd

 

Well it turned into a bit of an ordeal. Ran into trouble when installing the new left side crank bearing, the outer race was spinning in the bearing housing, not good. So I bought another engine case on ebay, only to find it had the same issue, what are the chances. I’m certain its not the wrong sized bearing – the old OEM bearing was also spinning in the housing. The housing had just been worn out and widened over time. So anyway, rather than continue tracking down more engine cases I decided to try this old mechanics trick of punching small divots into the housing with a center punch. Seems to be a good bit of debate about the efficacy of this on various forums – some swear by it, others say its not a proper fix. Well I don’t feel like paying a machine shop more than this engine is worth to have the housing bored out and shimming the bearing for a proper fit, I went with the bodge. I also installed it with some Loctite 620, we’ll see if it holds up, I’ve got a good feeling about it.

So I got both crank bearings + new seals + new crankshaft installed, closed up the case, thought I was home free, then noticed the crank seemed a little stiff – still easy to turn by hand just not as easy as before. I was afraid the bearings weren’t seated correctly so opened it back up to investigate. I think it may just be that the new (non OEM) seals, especially the right side seal, are a little too tight around the crankshaft and not allowing it spin effortlessly like I am accustomed to seeing. Of course, I’ve only had experience with 2k+ mile engines at this point, with 40 year old original seals, so perhaps a little stiffness with brand new seals is to be expected. I ordered OEM seals anyway to see if this makes a difference. Perhaps the stiffness relaxes overtime as the seals are broken in. On a side note I invested in a case splitter and crank puller tool, which is what I shouldve done before I started this rebuild. I don’t ever want to have to strike a case or crank with a mallet again if I can avoid it.

In other news I’ve repainted all the little black parts (satin black + satin clear) and am really pleased with the results. The front wheel is kind of rough so I may look into repainting that too. Continuing to clean/touch up the frame but I don’t want to repaint that, I want to keep the patina and imperfections there, it’s a survivor. After wrapping the engine up I need to repaint the forks and replace fork fluid. Then we can begin the reassembly process.

Engine Rebuild cont'd

 

Gaskets are removed and cases cleaned up. Touched up little scratches and chips in the paint. Also attempted to fill a few little knicks in the gasket mating surface with JB Weld high heat epoxy. The left side crank seal mating surface had a tiny scratch along with some little holes caused by the corrosion and rust that afflicted the crankshaft. I filled these with JB and sanded them flush. I intend to put a little ultra grey around the crank seal as well, hopefully it will hold.

From here I will replace all the seals, install the new crank bearings and crankshaft, then reassemble the transmission and close her back up.

First engine rebuild + #2 project plans

 

Finally got around to dropping the engine on my #2 project bike. The crank and left side bearings were badly rusted and have to be replaced. This engine only has 2k miles on it so I'm not too concerned about replacing every bearing in there, will replace all the seals though. I've been held up by the hardest most baked on gasket I've ever come across. Gasket removing chemicals and plastic scrapers hardly made a dent, razor blades gave me quite a few knicks though. I came across this video where this guy makes a scraper out of a piece of aluminum flat bar, boy did this save my life:

I happened to have a piece of flat bar left over from constructing those headlight mount bars on my #1. Took me 5 minutes to make a little scraper, and it works like a charm, almost no risk of knicking the aluminum case unless you really dig into it. 

I've got a new crank, crank bearings, and engine seals on order.

I've been thinking about project priorities lately, thinking of focusing on #2 and putting #3 on the backburner for now. #2 is a complete bike but it is dirty and rusty, I'd like to completely disassemble it, clean/derust/repaint the components, and rebuild it. I want to keep the original frame paint. Its not in great shape, a lot of knicks and scratches and rust, but it was never my intention to make #2 beautiful, its a survivor, those flaws show its story - likely wrecked in NYC then left to rust in a SC yard. I just want to get rid of the rust and grime and maybe clear coat it for protection. If the engine rebuild is successful it could very well be the best runner I have. 

MB5 #1 - Daily Runner

 

I don't have names for my bikes so I just refer to them by number in the order I acquired them. This is #1, my daily bike. I bought it in great condition April 2023, not knowing anything about MB5s or motorcycles. I thought scooters looked goofy but was daunted by "real" motorcycles and all the red tape involved in owning one, so I snagged this thing when I saw it pop up on marketplace. At that point I was unaware MB5s are notorious for tank issues, but I soon found out. I spent a lot of time trying to repair that tank, including sealing it with Caswell liner, which was unsuccessful. The tank pictured is from the #3 bike I just acquired (see previous post). Regardless of the tank trials it was still worth every penny I paid for it and has brought me endless joy. I bought it just as something to play around on, but it soon became my main source of transportation. #1 isn't perfect but she runs great and has character.

Its all stock except for the turn signal mounts - I took inspiration from the European MB5s and fabricated 3" aluminum bars to mount the turn signals to the lower triple tree. Not only do I think this looks better (stock looks kinda like bug eys), but it is more practical. In the event the bike is dropped, the weight falls completely onto the turn signal, which if the turn signals are mounted to the headlight bracket in stock fashion means the bracket gets bent. So now the whole bracket must be removed, which requires removing everything mounted to the bracket (turn signals, headlight, cluster, wiring), then it must be hammered back into shape, then repainted. It is common to see these brackets bent up and the turn signals all crooked because bikes inevitably get dropped. I dropped it once (slipped out from underneath me on my gravel driveway going <5 mph) and after repairing that bracket I vowed never to have to go through that again, its way too much work for such a minor and common accident. If the bike drops now and the aluminum bar gets bent, all I have to do is bend the bar back into shape or cut a new one.

82 MB5 Project #3

Acquired Dec. 2023  in Brevard, NC. completely disassembled for $270. I thought the price was too good to be true and I spent most of the 2 hr drive from Athens wondering if I was about to be dismembered in this stranger's basement, but he turned out to be one of the nicest guys I've ever met. The tank was worth the price alone, in good condition (for an MB5), had 2 small holes at the seam that were repaired successfully via soldering. Derusted and cleaned thoroughly inside. This tank has since been swapped onto my daily #1 bike since it is currently the best tank I have.

Since I now have 3 red MB5s, and the frame could use repainting, my plan is to repaint this bike in black. This bike has good bones but there is a lot missing, it was likely someone's parts bike. It is missing lights, cluster, seat, and a laundry list of other small components, all readily available. Someone cut the silencer out of the exhaust it came with, I have since acquired another OEM pipe in excellent condition for $85 from another very nice man in Flowery Branch, GA (you meet the nicest people on an MB5). I estimate it would cost another $500+ to make this bike complete.

The bike appears to have been hit by something hard at some point, putting it out of commission. The swingarm, center stand and brake pedal are bent. I acquired a new swingarm for $50, the center stand and brake pedal will need to be replaced too. The frame and wheels do not appear to be bent or damaged at all.

Thats my cat

The engine looks to be in great shape, crank is squeaky clean and moves effortlessly. I have already rebuilt the top end and the carb. Either someone put a healthy amount of engine oil into the crankcase to protect from rusting (thank you), or the right side crank seal is shot, remains to be seen. I’ve cleaned and touched up the engine paint, except for the left crankcase cover, it looks pretty sharp if I might say so myself.

Currently I am focused on cleaning up/derusting/repainting the smaller parts in the bins. I must wait for warmer weather to paint the frame, this project will be a slow burn but I believe I can build a clean black MB5 out of this pile of junk.

As for Project #2, it is running but will require an engine rebuild due to a horrendously rusted crankshaft. Stay tuned.