tbaysal2000

I had an issue previously with my motor and had the piston changed. I was never sure if the changes were made with Zenoah piston and it's rings so finally I had time to open the thing. I noticed piston center and also the structure to be different. As I'm not an expert, I'm adding photos. Can you tell me the used piston is actually a Zenoah?

I also added photos of the cylinders as they seem to be quite warn, many scratches inside. But maybe it happens with every used cylinder/piston, then I would not bother to do so. If you would suggest me to change the piston/Cylinder, I hope there's a guide how to remove the piston and what I need to do for the first matching of cylinder/piston.

I also added photos of the previous ngk and new one I have. I wonder if one of them is fake?

Update:
OK, I tried many times but can't add photos. Will try again later.

stevo7896

If you click on the "post reply " button on the upper left corner ,the box will open to type your message .Under that box you will see area under that box to add photos. Here is a link to a site that has some great info on our hobby and lots of tech info. http://www.modelgasboats.com/zenoah-teardown/

Ron Olson

My Feedback: (1)

Unless the piston came in a Zenoah box, it could be from someone else. RCMK pistons and many others will fit right in.
A tear-down is easy to do and taking one off the wrist pin isn't difficult. Using one of the bolts, you can screw it into the wrist pin to make it easier to remove. On the MGB site, Scott Schneider shows how to make a simple tool to replace and seat a new retaining clip, I made one out of scrap brass tubing and it does a fantastic job.
My pistons have a little scraping on them around the skirt but nothing that I'm worried about.

If you are still trying to upload pix, don't use the normal reply box but instead, hit the reply button in the upper right corner of for instance this posting and it will take you to an advanced screen where it's easier to post your shots.

tbaysal2000

Ron, I think the upper right reply button worked...

tbaysal2000

So for the photo in the previous post above, the piston on the left is different to one on the right. I wonder why the center has a different shape. It can't be the plug hitting the center or melting due to heat, right. The motor has little hours on it really.

And also see the plugs below. One has green, the other blue printing. The tip is yellowish color on one and it says torch on one, the other NGK.

tbaysal2000

Ron, you mean the clip on the piston right? If you can give me the link on MGB, I'll be very happy.

Ron Olson

My Feedback: (1)

Man, that's ugly in there! I'm thinking that it's got a problem elsewhere that's leading to all of those nasty scratches like a bearing going bad.
The piston could be an RCMK as I've got several that look just like it sitting in my toolbox but made for a rear exhaust engine, not side exhaust.
Take the clip out with needle-nosed pliers but it will have to be replaced.
The article: http://www.modelgasboats.com/piston-c-clip-tool/ . The gist is 2 piece of brass tubing, one slips inside the other. Make the inner one longer than the other by 3/4"-1" or so and the outer one a good 1-1/2" long just to make it easier to grab. The inner one I found a rubber cap to fit on it from a package of carb and tuned piped caps, possibly a Great Planes item that has assorted sizes. Slip the clip inside the outer tubing then slip it into the wrist pin area. It doesn't matter if the clip is sideways in there at this point as once you push the clip in everything will fall into place. Push in or give it a tap with something until you hear or feel the clip seat in the groove. This tool sure beats the hassle of getting the clip in there or trying to chase one around as it flies off to parts unknown.
Note how the clip is sitting in your piston right now as that is the proper way for it to go in there. Yes, there is a right and wrong way for it to be. You want it to look like an "e" when looking at it from the side.

Jackal1983

it doesnt look like the inside of a zenoah cylinder to me either. looks like its got a badly finish liner in there...

wet a wild

i have to agree, that is not a geniuen zenoah, look like a rev unlimited version from gizmo.

tbaysal2000

At least I have spares for original Zenoah. I'll try the boat first with this one again once I'm done with set up and then change to new piston and cylinder. I will need to learn how to properly do the first hours of the motor then. Any link will help.

What do you think about the plugs?

w3bby

Throw the Torch as far as you can into the lake and run the NGK CMR7H.

Ron Olson

My Feedback: (1)

Like Ian said, it's a junk plug.
Break in the engine? I just take them out and run the crap out of them! I don't use any special fuel or oil, just what I plan on running as it should be broken in using less than 2 tanks (or bags) of fuel.

tbaysal2000

I've got another problem. I pushed the piston into cylinder to put back the motor. But it is stuck. Now it neither goes fully up, nor fully down. I thing the piston ring is stuck somewhere. What to do?

Piston arrow facing the exhaust and the ring retainer pin is on the intake side, pin centered in the ring gap.

Ron Olson

My Feedback: (1)

The ring might have shifted just enough to where it isn't going up any farther than the taper in the sleeve. I just rebuilt an RCMK last night and ran into that.

danielplace

Stop everything and be very careful as it could easily be ruined if it is stuck in the bore.

Sounds like the ring has opened into a port. Unbolt the jug and look in the intake and exhaust port and see if the end of the ring has opened into one of them. If you rotated the cylinder to align it as you were putting the piston up in it often the ring alignment pin will ride up under one end of ring while it was rotated and the ring was tranversing the intake port.

You did have the ring alignment pin on the intake side? and the ring gap centered on the ring alignment pin?

tbaysal2000

Looking from the intake port, the ring moved a bit from the center. Pushed it a bit and all sorted.

And I tried running the engine today and no success. The gasket connecting the cylinder was damaged, I used gel gasket to close the gap. Compression was quite ok, at least as good as when it ran. I used irridium ngk for testing.

But I made a stupid thing when putting everything back. Used WD40 at the piston skirt so that the piston moves easier in the cylinder. And also used again WD40 for the crank. Could this be the reason spoiling the mixture?

danielplace

You never want to lubricate the engine anywheres inside with anything other than 2 stroke premix oil. Wd-40 will give you about zero protection at startup.

But no WD-40 would not stop a engine from running unless the crankcase was flooded with it. But then again it wouldn't start if the crankcase was flooded with fuel either.

The Ghost

Looking at the gouges in the cylinder, they look like they go right through the crome lining into the alloy, the engine would be very hard to start, if at all, as all the leakage between the cylinder and the ring. You would be better of putting a new top end on it.
Cheers