Zenoah oddities

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Dreadnought

Well-Known Member
Messages
50
Hi all,
Got a bit of an engine conundrum, no compression all I know is the following:

The measurements are

Stroke = 27.5mm
Bore = 34mm
Therefore, cc ~ 24cc

Numbers on the cylinder/ head are 2070

Ring isn't stuck
Bore looks good

I'm thinking mismatched top and bottom ends, thoughts pls
 
Cylinder/head # comes up as Zenoah but its a 32mm bore, I think that's the G230 but it has 28mm stroke. Any stampings on the crankcase? worn rings? with the ring itself installed in the cylinder , what is the end gap? with a ring at the bottom of the bore, max 1mm gap..
 
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Jimmyb said:
Cylinder/head # comes up as Zenoah but its a 32mm bore, I think that's the G230 but it has 28mm stroke. Any stampings on the crankcase? worn rings? with the ring itself installed in the cylinder , what is the end gap? with a ring at the bottom of the bore, max 1mm gap..
Click to expand...

Cheers gap is bigger than 1mm nearer 3mm, we'll assume that's potentially the issue.

I'll get some photos ?
Some images, I hope they help20200923_165443.jpg20200923_165449.jpg20200923_165502.jpg20200923_165510.jpg20200923_165526.jpg20200923_165708.jpg
 
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Is it me or do i see big problem at the dome of the head? Looks like really bad detonation to me thats were your compression went and that piston looks like poop too. That should be smooth not like it got forged out of a block of aluminum with a ball pean hammer
 
Rep732 said:
Is it me or do i see big problem at the dome of the head? Looks like really bad detonation to me thats were your compression went and that piston looks like poop too. That should be smooth not like it got forged out of a block of aluminum with a ball pean hammer
Click to expand...

Ok, but almost 0 compression, had detonation marks on motorcycle 2 stroke engines (which I've rebuilt more than I care to think about) and they still run and have compression. This engine even with the base gasket removed is almost 0 compression.

I've also shown that the top end Zenoah and the base is CY, would that be the issue?
 
Rep732 said:
Is it me or do i see big problem at the dome of the head? Looks like really bad detonation to me thats were your compression went and that piston looks like poop too. That should be smooth not like it got forged out of a block of aluminum with a ball pean hammer
Click to expand...

Something sure has gone through that cylinder, looks like it was gone over with a center punch, the piston looks like some I have seen on new clone finish, not the best, even with some of their scooter engine kits.. Maybe Zenoah uses the 2070 casting for both the 23 & 26 CC just different bore, I did a quick search and the 2070 came up as the for G230 cylinder..

Could the cylinder be badly worn, what is the clearance of piston to cylinder?, ring gap is very worn if 3mm, make sure to measure at the small tabs running on the cylinder wall.
 
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Jimmyb said:
Something sure has gone through that cylinder, looks like it was gone over with a center punch, the piston looks like some I have seen on new clone finish, not the best, even with some of their scooter engine kits.. Maybe Zenoah uses the 2070 casting for both the 23 & 26 CC just different bore, I did a quick search and the 2070 came up as the for G230 cylinder..

To measure the ring gap place them at the bottom of the bore, just clearing the side transfer ports, square them up by pushing in with the with the top of the piston..
Click to expand...

Hi, I get 2.8mm ring gap which seems massive but (as you can tell) I don't know much about these motors.

I think the issue is detonation as the ports and bore seem good not like something has passed through.

The top of the piston looked OK to me as its what most 2 stroke motorcycle pistons look like before they are polished and the squish sorted.

Cheers
 
I had a cy engine that lost compression and I just put a new ring in and it was good to go. I'd say if you created a bigger space between the dome and the piston that could contribute to no compression along with a bad ring
 
Was this a running motor for you?, the CY motors are a clone of the Zenoah so putting a Zenoah Cylinder on the similar size clone CY block should be good, many parts interchange.
If you have 2 stroke motorcycle engine experience same goes for these so no worries. Might sound stupid ,maybe install the ring on the piston, put a good coating of the thickest grease you have on it, assemble it ,install plug and see if this gives some compression. Bore gauge would be best to give cylinder/piston clearance maybe cylinder is badly worn.
New 34mm Zenoah ring measures 1.50mm wide and installed in new cylinder .279mm end gap
 
Rep732 said:
I had a cy engine that lost compression and I just put a new ring in and it was good to go. I'd say if you created a bigger space between the dome and the piston that could contribute to no compression along with a bad ring
Click to expand...

Cheers its where I'm going to (not only cos its cheap). Ring gap seems large but I cant find any data on what it should be. And deleting the base gasket should perhaps raise the compression a little.
 
Jimmyb said:
Was this a running motor for you?, the CY motors are a clone of the Zenoah so putting a Zenoah Cylinder on the similar size clone CY block should be good, many parts interchange.
If you have 2 stroke motorcycle engine experience same goes for these so no worries. Might sound stupid ,maybe install the ring on the piston, put a good coating of the thickest grease you have on it, assemble it ,install plug and see if this gives some compression. Bore gauge would be best to give cylinder/piston clearance maybe cylinder is badly worn.
New 34mm Zenoah ring measures 1.50mm wide and installed in new cylinder .279mm end gap
Click to expand...

Never had the engine running, but it has spark, and was completel, so I'm guessing that it was. It came fitted to a car and didn't look too messed with so I'm guessing it gave up.

The gap you quote is significantly lower than I have, therefore, I'm guessing worn ring.

The easiest step seems to be to order a new ring and piston set and go from there.

Thanks
 
mark35 said:
I think you may have a 26cc piston fitted in a 29cc cylinder which is 36mm bore?
Click to expand...

Thats an interesting thought, but I don't have a 1mm gap either side of the piston (just checked)

I'm thinking are there different length con rods with the same stroke?
 
Here I got an idea, take it down to short block. Walk over to the trash and drop it. Zen short blocks are cheap enough, amd you will know where you stand with it. That cylinder ate something. doesn't matter if you can see it in the ports or not. My guess from the shape would be the location pin in the piston. Either way, I'd just replace it or get a new top end and bearings and seals and start over. I think you've been had by the previous owner. If it's a recent purchase I'd found the guy to make it right, or at least give you some money back to cover a top end kit.
 
Seandonato73 said:
Here I got an idea, take it down to short block. Walk over to the trash and drop it. Zen short blocks are cheap enough, amd you will know where you stand with it. That cylinder ate something. doesn't matter if you can see it in the ports or not. My guess from the shape would be the location pin in the piston. Either way, I'd just replace it or get a new top end and bearings and seals and start over. I think you've been had by the previous owner. If it's a recent purchase I'd found the guy to make it right, or at least give you some money back to cover a top end kit.
Click to expand...
Couldn't say it better
 
Not to sound like a peepee but you can't overlook the damage and say thats not contributing to the lack of compression. These engines are small and more sensitive than larger engines. Also in a 1 piston engine thats kind of a big deal since you don't have any other cylinders taking up the slack of the dead cylinder. Like @Seandonato73 said throw it out and start over theres clear physical problems here the ring gap is too big and the engine swallowed something..this is just the way it goes getting something 2nd hand with the person being deceitful.
 
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