CMB 28.5 Evo Help

[RaceMechaniX]

Steven, Hopefully you are aware of this piece of information: The large CMB gas motors are quite sensitive to thrust on the crank. Not sure if all the CMB gas motors are small end guided, but the 35Rs was and I destroyed a number of cranks and P&S's using a collet. When I switched to a square drive the problem went away.

 

[Steven Kinney]

Thank you. Yes I am aware I am still running a double square drive cable so it essentially is a floating system.

 

[rhomodel]

and did it sound good?

 

[David Bryant]

what I see in your picture is the primary coil is moved out to the max: I would turn it back to the middle position. Though I have no CMB Alpha I am the Dutch dealer of BZM, but also run SG and these have similar ignition systems. As a rule of thumb I advice my customers (but that is what I also run myself) 1.5 mm before TDC. 1.3 I think is too late

thanks for your information. So, by rotating the primary coil back towards "middle" position places timing closer to optimum setting?

 

[Steven Kinney]

We will find out today. Going to go fire it up if everything sounds good going to head to the pond.

 

[Steven Kinney]

View attachment IMG_0805.mov

 

[Steven Kinney]

Anyone have a base needle settings? How many turns out?

 

[Steven Kinney]

So here is what I learned yesterday.
I had a water issues. The way I had my water running it came on the side port on the engine and out the top of the head. Well the water won’t flow out that way unless you are running at fast speeds and even then it’s not much. I swapped them around water problem solved. Now my needle setting where way off to lean. I richened up both needles but didn’t really get to a good setting. That’s why I was asking for base needle setting.

 

[David Bryant]

Anyone have a base needle settings? How many turns out?

actually, I posed this question to Dave Marles (Prestwich Model Boats, UK), this is what he replied (quote):
"The following is from my friend ...Tillotson i don't do with turns out, I use vernier to measure next to them. Low needle open 11.2mm and high needle 16.45mm. You can see under the needle springs aluminium spacers and an o ring to stop needles coming undone."

 

[Steven Kinney]

Thanks for the info!

 

[Steven Kinney]

Has anyone ever had an issue circulating water through the engine if the inlet is the side port and exit is the one at the top of the head?
I can’t get any water to circulate through the lower portion of the engine.
I tried a couple different rudders. One was a speed master dual pickup the other was one I made that has bigger inlets and exits.
No difference between the two.

 

[David Bryant]

Has anyone ever had an issue circulating water through the engine if the inlet is the side port and exit is the one at the top of the head?
I can’t get any water to circulate through the lower portion of the engine.
I tried a couple different rudders. One was a speed master dual pickup the other was one I made that has bigger inlets and exits.
No difference between the two.

I'll have to check my CMB 27 alpha engine when I get a chance. It has, both, the rear crankcase & head cooling ports

 

[rhomodel]

That should be the normal routing: low in high out. Are you sure you have not mirrored or rotated the gaskets, or the head button? Most engines have the inlet just under the exhaust port before cooling the rest of the cilinder.

 

[Steven Kinney]

Everything is exactly how I received it.
I have the water inlet at the front at the top of the head and it exits out the side port. That’s the only way it will feed water. If I try to have the inlet go through the side it won’t flow water. I am guessing it just can’t push the water up through the head and out.

 

[David Swisher]

That give the motor any internal damage from broken elecrode,electrode, times will go thru motor and really hurt something,bearings,liner,piston damage,had to be lean or faulty plug,timing should have no impact except the way motor runs,check timing with degree wheel,very easy to do on CMB,removable head button

 

[Steven Kinney]

View attachment 297171View attachment 297171

 

[Steven Kinney]

It left a little spec on the top of the piston and a small scar on the liner. It still runs fin. Figured at some point I will end up changing it out any way once get everything figured out.

 

[David Swisher]

Motor needs new liner,if you want full power and scratches are very bad and allow blow by,I have been working with motors my last 18years,I replace cylinder and piston and ring if damaged on a Zenoah,on nitro motors replace liner and piston,bearings anyetching will cause failure,lost a K&B.21 and a CMB.45 from trying to go cheap,just FYI

 

[rhomodel]

It left a little spec on the top of the piston and a small scar on the liner. It still runs fin. Figured at some point I will end up changing it out any way once get everything figured out.

Sorry not sure I understand your post: you say it still runs fine, but then there's a heap of issues you're reporting with the engine after you indicated it run hot and so hot it burned the electrode of the sparkplug: does it run fine and all is ok, or is there an issue and you need advice / help?
May be seperate out what issues there are:
-Possible ignition timing: it run hot: what's the status of that issue and at how mm before TDC does it fire. You say you set it to 1.3: I think you should set it back to basic being 1.5 mm just to eliminate all other possible issues
-No water flowing causing the engine to get hot? This one I really do not understand as the routing of any water cooling system should be low in, high out: this is to prevent any airbubbles or pockets to create causing overheating. If you can't get it to run like that you need to check teh internals as ther eis no one way valve build in.
-Carb needle setting? Is that ok now: you indicated it to richen it up a 1/4: 1/4 is peanuts and would not help any severe lean setting
I wish I could be of more help here, but I'm really lost trying to identify the issue as you jump from one issue to the other.

 

[Steven Kinney]

I apologize for not responding to this sooner I did not get a notice that you had responded.

I have had time to double check and run the engine. The engine runs good.
The only problem I seem to be having is the engine doesn’t seem to circulate water very well. To remedy this I have swapped water lines around and it seems to have helped but still doesn’t seem right.

The water enters at the top of the head and exit out the side of the block. This is the only way I can get water to move thru the engine.

As far as timing and needle settings everything is correct.

For some reason it did burn the electrode off the spark plug the first time I ran the boat assuming because the engine got hot from lack of water running though it.
The spec of electrode that came off did make a small mark on the sleeve.

I realize this this will hurt the performance of the engine but I don’t want to put an new piston and sleeve in the engine tell the water issue is 100 percent fixed.