B+ engine tear down

[relic]

Hi everyone.
I thought it best to start a new thread rather than add on to my previous "Too many questions". In that one you answered my questions regarding my spare engine parts and possibilities and I thank you for that.

This time the engine in question is the one that was in the frame of my project bike and appears to the original. The only modification that I found is the addition of a reed valve intake. The carb is the stock 20mm.
And the cylinder hasn't been modified at all for the reed conversion. Not even the size of the intake port. As you can see this reed intake was a four bolt with a couple of extras drilled in between.

Would the simple addition of a reed valve intake make much difference in the performance without doing any of the other mods?

The good news- I found why the kicker wasn't working but I have good parts in with my spares to replace the bad.
- The piston and cylinder are standard bore
- The crank, con rod are in good condition
- The crankcases are in good condition
The bad news - One of the circlip tangs is missing and I suspect that is what scored the piston and cylinder somewhat. I'll clean up the cylinder and measure it to see if I need to go to the first oversize. Regardless I'll buy a new piston and rings either standard or first over.

From what I see here I can build up a stock B+ engine, (maybe 1st over) using what I have and what's in my spare parts stash with the only items needed to purchase being the piston kit, bearings and seals.

Then I can see if the performance suits my intended use. And I can build up a reed valve top end using what I have in the spares either finding a .060" oversize piston or maybe doing the port work my self on the one of the other spare cylinders that are closer to standard bore. (refer to my other post for pic's of what I'm talking about here)
And fitting the reed valve modded top end at a later time wouldn't be a big deal.

Looks like I have a plan!

Relic

[Zyx]

You ask if a reed conversion would make a difference, all other things equal: yes. No question. So would a larger carb than the 20mm. I raced a Webco 125 conversion on a 24mm Mikuni, and it was modest. Worked fine, no bogging. Mo' Betta than a 20mm.

I used to snip about half of the circlip tang before installing, and still do. Just a precaution. I also orient them vertically, but I suspect they don't stay put, and will rotate no mater where you put them. I just put them oriented up and down as a regular practice.

If running reeds, I would open up the intake and the transfers a bit. I would really be tempted to raise the exhaust slightly too, but that's up to you. There is more power lurking in there. You just have to go looking for it.

I am thinking that if you can't get this bike to run 55+, someone left a pair of socks in the air filter.

[relic]

You ask if a reed conversion would make a difference, all other things equal: yes. No question. So would a larger carb than the 20mm. I raced a Webco 125 conversion on a 24mm Mikuni, and it was modest. Worked fine, no bogging. Mo' Betta than a 20mm.

I used to snip about half of the circlip tang before installing, and still do. Just a precaution. I also orient them vertically, but I suspect they don't stay put, and will rotate no mater where you put them. I just put them oriented up and down as a regular practice.

If running reeds, I would open up the intake and the transfers a bit. I would really be tempted to raise the exhaust slightly too, but that's up to you. There is more power lurking in there. You just have to go looking for it.

I am thinking that if you can't get this bike to run 55+, someone left a pair of socks in the air filter.

Do you think this reed conversion with NO cylinder mods whatsoever did anything for performance? I'm just curious.

I maybe barking up the wrong tree with my missing tang diagnosis but the one side is all there and the other side is all missing. And I found what appears to be some smashed up tang in the slit in the side of the con rod at the big end. It couldn't fit all the way into the bearing, got stuck in the opening so no damage to the bearing. And it sticks to a magnet so that is what brought me the broken tang idea. Again, just curious.

Good advice about orientation and cutting some off,thanks.


Relic

[Bullfrog]

The photos show NO porting thru the ceiling of the intake passage and NO holes in the intake side of the piston . . . so what you had was simply the substitution of the reed valve assembly in the place of the stock intake manifold. This assuredly reduced peak horsepower . . . and most likely reduced performance at virtually all engine speeds except perhaps from idle to a couple of thousand RPM. At those very low engine speeds, the improved control of carburetion (by reducing/eliminating pulsating backward flow throw the carb) may have actually improved performance.

The "finger ports" which pierce the ceiling of the intake passage and the holes in the piston are required to achieve the expected benefit of adding a reed valve.

Ed

[relic]

The photos show NO porting thru the ceiling of the intake passage and NO holes in the intake side of the piston . . . so what you had was simply the substitution of the reed valve assembly in the place of the stock intake manifold. This assuredly reduced peak horsepower . . . and most likely reduced performance at virtually all engine speeds except perhaps from idle to a couple of thousand RPM. At those very low engine speeds, the improved control of carburetion (by reducing/eliminating pulsating backward flow throw the carb) may have actually improved performance.

The "finger ports" which pierce the ceiling of the intake passage and the holes in the piston are required to achieve the expected benefit of adding a reed valve.

Ed

Thanks Ed, that is what I was thinking. Some previous owner thought they were making improvements but really were not. No telling the history behind old bikes and what the thinking was at the time but I couldn't see this working at all.
I will move on from here.

Ken

[Zyx]

By " no other mods" I took you to mean changes to porting. Wasn't looking at the piston. Porting can be improved to make better use of the reeds, but isn't necessary.

Strictly Hodaka offers an improved version of the kick roller cage, which is machined from heavy steel, rather than stamped from sheet stock. There are two versions, you need the one for earlier bikes such as your B+.

Heavy duty cage for 90's and 100's

image.jpg (9.04 KiB) Viewed 1936 times

The kick shaft has taken a beating but may still serve. You will have to inspect the working surface of each ramp on the shaft. If deeply worn, might be better to replace it.