Topper cylinder

[FL54]

Hello,
New member here.
Although I don’t own a Hummer, I do own a Topper And was hoping to tap the brain trust here to help with some information.
I bought this Topper this spring and have struggled with it ever since. I know that it sat for at least 10 years and maybe even 10 years before that owner acquired it.
It only had about 40 lbs. of compression and couldn’t go over 30 MPH. I pulled the head and cylinder to find that one of the ring pins had broken as well as about 1/8” of the end of the ring. The broken ring
end must have caught on the ports of the cylinder and enlarged them. For some reason, I can only upload picture of one damaged port. I had the cylinder bored out to +30 and got a 30 over piston.
My question is this cylinder usable and if so, what would be the effect of the enlarged ports?
Thanks in advance for information.
Barry

[FL54]

E73466E2-D8EE-4F1C-8C17-373C3067E914.jpeg (102.94 KiB) Viewed 77948 times

This is the other damaged port.

[Mutt]

that is the bottom of the intake port correct? You could finish porting it to these specs (use the 165 specs on the chart) It would breathe better than a stock motor. If you dont have the tools, I can do the work for ya

intake port.jpg (47.33 KiB) Viewed 77941 times

[Mutt]

Oops. just saw the second picture. Not much you can do with that.

[pumpguy]

While I have no experience with a Topper, I did own and raced a number of Hummers and 165"s back in the day, Same for Maicos and bikes with Villiers engines. All were similar design 2 strokes.

IMO, so long as you chamfer the edges of the ports so a ring can't hang up, and the piston ring pegs locate the ring ends away from the ports, you should be okay.

There were several similar design 2 strokes that just had grooves in the cylinder wall for the transfer passages. No lower port edges at all. British AMC, and I've also been told this was a way to add extra transfer ports on Bultacos.

[pumpguy]

Isn't a Topper a reed valve engine?

[FL54]

Oops. just saw the second picture. Not much you can do with that.

Thanks Mutt. How much would that damage affect performance?

[pumpguy]

I one time had a Hummer cylinder where too much was bored from the bottom of the intake port, resulting in the induction being way too early and way too much duration.

I had that lower edge built up with Nickel arc and then had the cylinder re-bored.

Another time I got a light alloy conversion top end kit from England that was designed for a 175 BSA Bantam for use on a 165. A big disappointment. The piston had way too much clearance and the iron cylinder liner had a crack near the exhaust port. Had the cracks welded with Nickel rod and then rebored.

In both instances for me, these repairs were totally successful. Of course YMMV.

[250_Sprint]

When you had it bored, did the shop notify you about the disfigured ports? I would think they should have…
IAC - you have a fresh bore and the oversized piston and rings. If you are assembling, I would move forward and assemble the engine. See if the compression is where it should be and if so, continue the build. I would continue to search for a replacement cylinder. You may find a 30 over, you may find a 20 over, but while you are searching, you could be enjoying the ride…
You may have to adjust the carburetor and/or other adjustments.
If a shop is assembling, it is not cost effective.

IMO - I would rather get some pleasure out of 95% than waiting who knows how long for 100% correct, if that day ever comes.
My .02

[FL54]

When you had it bored, did the shop notify you about the disfigured ports? I would think they should have…
IAC - you have a fresh bore and the oversized piston and rings. If you are assembling, I would move forward and assemble the engine. See if the compression is where it should be and if so, continue the build. I would continue to search for a replacement cylinder. You may find a 30 over, you may find a 20 over, but while you are searching, you could be enjoying the ride…
You may have to adjust the carburetor and/or other adjustments.
If a shop is assembling, it is not cost effective.

IMO - I would rather get some pleasure out of 95% than waiting who knows how long for 100% correct, if that day ever comes.
My .02

Thanks Sprint. The shop did notify me but they described the ports as being “nicked up.” It wasn’t after I told them to go ahead and bore it out that I saw the extent of the damage when I picked it up. Not being familiar with 2 strokes I had no reference point. As previously stated, the bike did run but couldn’t get over 30 and it took a while to get to that speed. That was with the broken ring and low compression. What affect would the enlarged ports have on performance in your opinion? I have several Big Twins and I’m familiar with wrenching on them but that’s apples and oranges. I am trying to locate another cylinder but unsuccessful so far.
Thanks for your response.