Honda Benly - Splitting the Cases & Transmission

[Smithers]

The nice engine that I'm rebuilding is the one that came in the blue frame of the good motorcycle. The bike was retired because it needed a rebuild and it was leaking oil through a crack that someone had attempted to fix with epoxy in the past.

Now that the cylinder has been bored and the .75 pistons are ready I had to focus on the crack on the bottom of the engine case. An earlier crash had pushed the footpegs so hard as to deform the aluminum case that it was bolted to. The previous owner had tried to cover the whole crack with a big glob of epoxy. He definitely tried hard to fix it this was since the epoxy was pushed in pretty good. The problem with this was that the crack usually never stops in aluminum so it cracked even more because of the stressful location. This needed a permanent fix. My options were:

• To try and have the crack welded
• OR split the cases on the spare engine and use the lower half on the good engine

I took it to a engine block welding pro who removed some material with a special chisel and showed me how far back around the crack actually continued. The only way to salvage the case would be for him to force the crack and remove the area that was damaged. Then he would weld in a new piece of material, drill and tap the thread that needed to be added and then just do a lot of finish work. Basically I would be using my spare engine for the bottom case. All the hassle for that piece just wasn't worth his time if I have a spare... and thank goodness I do!!

Here is my nice clean Honda 150 engine that I had to take all apart and change lower cases on.



Here is a close up of the crack on the bottom after it was chiseled down to show the extent of the damage.

[Smithers]

Before you begin this operation make sure you have a set of seals on hand for all the shafts and also some gasket sealer compound such as Permatex Black or Gaska-Cinch

You DO NOT want to try and begin this process unless you are sure that you have at least half of a day to complete. If you have to stop for a few days and return at a later date you will forget a lot of things and it will take you a lot longer to finish assembling. Make sure you already have a set of seals ready or you are wasting your time! Trust me on this one.

Basically to begin you just take the magneto off of the left side and then the electric starter and starting chain/ sprocket. Then you need to take off the ring that encloses all of those and make sure to save all of the screws and note their locations. The seam between the lower and upper cases can be seen in the picture right in the middle running horizontally. Once the large ring (which is surrounding the front crank and the cam chain tensioner) is removed then there is nothing left to hold the halves together.



Going over to the other side you can to remove the clutch disks and the disc on the smaller front crank gear simply slides off. The clutch basket will not be able to release just yet.



There are two 10mm nuts that need to be removed from the oil pump that is located near the front. The pump is run by a piston that is moved via reciprocating arm that is pushed in an elliptical motion by the rotating shaft that the clutch is mounted to. Got that? So remove the oil pump by taking off the two nuts, breaking it free from it's gasket surface and then removing the piston that will slide out of the assembly. This will free the oil pump and then allow you to remove the clutch basket with ease.

Now the only thing left that will hinder the removal of the lower from the upper crankcase is the pesky spring that is located on the kick starter shaft. You need to release the spring from the shaft. Don't try to get the spring end out of the crankcase... it won't come out and taking the spring off the shaft is much easier. I used two screwdrivers to pry the spring (leveraging off the shaft) and it came off pretty easy. Just leave it alone once the shaft is free and it won't go anywhere.

[Smithers]

What's left to take off so we can take the halves apart? Now it's time to take all of those 10mm and 14mm nuts off of the engine on the top and bottom. You can see all sorts of them in this shot here. There are also a few more 14m and a couple more 10mm's on top so don't forget those before you start prying!



It's not that easy to find a place to pry from. DO NOT use a screwdriver or even a pry bar. Those are too thick and focus their force in such a small area that you will damage the mating surfaces. What you want to do it find yourself a 2inch putty knife that is somewhat rigid (not too flexible so you can hit it with a hammer). Looking at the picture you can see where I placed the knife. Since I want the take off the bottom half and swap it out for the spare I'll be flipping over the engine on some wood blocks to continue.



It only took me 2 small blows to pop them apart and work my way around. If you are trying harder than that, you missed something. Closely check around the edges for a 10mm you might have missed on the bottom.



Here is the top case of the Honda Benly engine all cleaned up and waiting for the transplant. I decided to take a close look and see if there was anything that needed attention while I was this far into the engine. I did notice on the spare engine case that there was some rubbing of one of the gear assemblies on the side as you can see below:



Skip down another post and I'll talk about what I did about this situation on the new engine since there was a very small amount of this same occurance as well.

[Smithers]

My main goal and purpose for this thread was to swap the bottom engine cases since my main one had the bad crack in it. The spare engine was left outside for a couple decades so there was some corrosion building up and the oil residue was really really bad for some reason. Once I took apart the cases on the Benly 150 I realized that I had a lot of cleaning up to do inside and out.



I grabbed my favorite degreaser and went to town for about an hour. I then swapped out the corroded steel oil tray inside for the newer one that wasn't corroded. I was pretty happy to see that the shifting rod was part of the bottom case so I was happy to bring over the better looking one. I should have replaced the shifter seal at this time so if you are doing the same process I recommend it. I was able to do this later and the seal came out with some poking at it.

I'll be going over all of the changing of seals in another thread. Everything cleaned up really well (after a couple hours of miserable scraping and swabbing out nesty residue with old rags. It will all be worth it and the bike won't leak one drop of oil for another 50 years!

[Smithers]

As you saw above: Here is where the gear was brushing the side of the case in the good engine and absolutely leaning against the edge in the parts engine. I looked at how close the gears were and how much of a tolerance I had to "adjust" the gear spacing.

I simply tapped the brass end holder for that particular gear set and it was able to move it away from the side without pushing the other end out the other side. Problem solved without any foreseen interference to the gear shifting patterns.



I read in a webpage that the Honda Benly 150 did not sell with the "noisy" transmission being one of the factors. These lines were taken from the World Honda Webpage.

On top of that again, the Benly also got a bad reputation for noisy gears and tappets. The sales office fell into an awful state with disaster in every direction."

[Smithers]

Here we have a shot of the transmission exposed:



That's about it for splitting the cases. Here is one more picture of the dirty one I had to clean for hours in order to replace the clean one that was cracked.

[weestrom05]

Your comment on putting it back together the same day hits a bad memory. Back when these were new I bought a S65 honda in a basket. The engine and tranny were completely apart, and in the box. We never got it to shift right when we got it back together. i am real happy that i only gave 25 .00 for it. Curt

[Smithers]

Oh man ain't that the truth. Leaving a transmission or a set of carbs apart for more than a day is a REAL exercise for the brain when putting it back together! If something like a car or a motorcycle is sold in pieces it better be something super special or it isn't worth a darn thing!!