GAS Engine's, Basic Info

[David Bryant]

Being completely new to RC GASSER boat's and engines, I am curious- do all the popular GAS engines employ piston rings? Or are there non-ringed types as well? (like ABC construction?)

 

[Rod Fonda]

Being completely new to RC GASSER boat's and engines, I am curious- do all the popular GAS engines employ piston rings? Or are there non-ringed types as well? (like ABC construction?)

David
I think most are using 1 ring,,I read somewhere about the first CMB gasser that was abc and I think they had thermal/seizing probs and went back to a ring,,but I'm no gasser expert,lol,,cheers

 

[Daniel's Racing]

All have rings Most running just a single ring.

 

[Hydro Junkie]

Rod, you are correct on the CMB, it has a single piston ring shown on the IPB. It's listed as part 11 but also shown as part of assembly 9(piston and ring)

 

[Rod Fonda]

Rod, you are correct on the CMB, it has a single piston ring shown on the IPB. It's listed as part 11 but also shown as part of assembly 9(piston and ring)

Cheers Mark,,I think it was a Lohring Miller article on testing the CMB when it first came out,that I found on the net somewhere,,I suppose only 1 ring cuts down on friction in racing 2 strokes,and be thin enough to prevent ring flutter

 

[Hydro Junkie]

To be honest, when you mentioned the CMB, you got me curious as I have the 27cc gas engine at home(unfortunately, I'm presently at work ). I figured it would be an easy one to look up so......

 

[Rod Fonda]

To be honest, when you mentioned the CMB, you got me curious as I have the 27cc gas engine at home(unfortunately, I'm presently at work ). I figured it would be an easy one to look up so......

Oh nice,,that would look good just sitting on your shelf at home or wherever,,lol,,its a nice looking unit, and with a zimmerman disc intake

 

[Hydro Junkie]

Trust me, this one is going to get put to work. It's going to be in a 1987 Miss Madison gas scale that I'm presently building. Just a matter of getting time to work on it ☹

 

[David Bryant]

Thanks. I have the latest CMB 27.0cc Alpha-EVO2 engine. Going into a "Kraken 52" (50in) mono.

 

[rhomodel]

The CMB that had seizure issues was a 35 cc engine without ring, not an 27 engine. (around 12 years ago)
The PUM230 ( 2 port engine) used 2 piston rings

 

[LohringMiller]

We were one of the early users of the ringless CMB 35. We never could get it to run without seizing. We even seized one of the ringed pistons. The sleeve was out of round above the exhaust port. I don't know of any large ABC or AAC gas engines. Gasoline burns a lot hotter and there are thermal expansion issues.

An early modification to the old two ring Zenoahs was to remove the lower ring.

Lohring Miller

 

[Rod Fonda]

We were one of the early users of the ringless CMB 35. We never could get it to run without seizing. We even seized one of the ringed pistons. The sleeve was out of round above the exhaust port. I don't know of any large ABC or AAC gas engines. Gasoline burns a lot hotter and there are thermal expansion issues.

An early modification to the old two ring Zenoahs was to remove the lower ring.

Lohring Miller

Great article you wrote on that test Lohring,,on Modelgasboats.,,you really pushed the limits on that poor little engine ,till the crank flexed and flogged out the wrist pin holes at 23-25,000 and around 11hp,,quite impressive,,was the spark timing static/constant or did it have some sort of advancing system?

 

[John Beardslee]

We were one of the early users of the ringless CMB 35. We never could get it to run without seizing. We even seized one of the ringed pistons. The sleeve was out of round above the exhaust port. I don't know of any large ABC or AAC gas engines. Gasoline burns a lot hotter and there are thermal expansion issues.

An early modification to the old two ring Zenoahs was to remove the lower ring.

Lohring Miller

Lohring,
In the early 70’s I believe Yamaha did some development work on a lapped piston engine for motor cycles. I don’t remember the size or details but if it had been successful I’m sure it would have made it to market and been around for awhile. For some reason I think it was a hard anodized aluminum cylinder and aluminum piston but can’t be sure. It’s along time ago.
Thanks John

 

[David Bryant]

I don't know of any large ABC or AAC gas engines. Gasoline burns a lot hotter and there are thermal expansion issues.

thanks Lohring

 

[LohringMiller]

Thanks. That was one of our more organized test series. We ran a Quickdraw electronic ignition system on the CMB. We tested it on Zenoahs as well. It had fixed timing that we set the same as the magneto timing. It's main advantage was compactness and light weight.

Lohring Miller

 

[David Bryant]

Thanks. That was one of our more organized test series. We ran a Quickdraw electronic ignition system on the CMB. We tested it on Zenoahs as well. It had fixed timing that we set the same as the magneto timing. It's main advantage was compactness and light weight

you're saying the Zenoah had fixed timing?

Have you guys had the opportunity to run any of the CMB 27.0cc Alpha EVO engines?

 

[dr gary turner]

Thanks. I have the latest CMB 27.0cc Alpha-EVO2 engine. Going into a "Kraken 52" (50in) mono.

I am interested in how the motor ran

 

[justaddwata]

Have a pair of CMB35s that did a few short runs with no rings without issue. I know the instructions were pretty explicit about what size water fitting to use etc and remember hearing of a few seizures at the time. CMB sent through new ringed pistons to retrofit it. Have only bench run since.

 

[David Bryant]

I am interested in how the motor ran

I will post once I run it

 

[David Bryant]

Have a pair of CMB35s that did a few short runs with no rings without issue. I know the instructions were pretty explicit about what size water fitting to use etc and remember hearing of a few seizures at the time. CMB sent through new ringed pistons to retrofit it. Have only bench run since.

interesting. They are ringed pistons without the ring's installed? Or regular pistons with no groove for a ring?