30.5 CC CY Motor.....Struggled to rev up. Opened motor up and found......

[RoushSport]

Hello all. Long time lurker, first time poster. I had a bit of an interesting issue with my Baja. Engine would fire up and idle with no issues. Beyond that, well.....you give it full throttle, and the motor would rev up partially...almost like it was hitting a rev limiter at about 2000 rpm (out of a possible 7000 for reference). The car would move, but very slowly. Tweaking the needles on the carb didn't change the performance at all. If you picked the back end of the car up and took the load off the rear end, wouldn't make a difference. So, I thought it's probably an air leak at the carb. Pulled the carb, replaced the plastic grommet with a metal spacer (Rovan RC), new gaskets, sealed it back up. No change in performance. Next I thought perhaps it's something in the trans or in the diff. From what I understand, there are two bolts behind the spur gear that like to back themselves out, press up against the spur gear, and bind up the whole works. When I opened mine up, everything was as it should be. So, then I thought - perhaps the magneto is off and or moved. Removed the covers to get to the magneto only to find everything was as it should be. At this point, I'm like ok....what the heck. For whatever reason, I spun the flywheel, and I hear a "clink clink" coming from the motor. I'm then thinking - connecting rod, bearing, something is broke. Pull the top of the motor off, and find that the piston has a LOT of carbon on it for only having 3 tanks through it. Additionally, it looks as if there is some kind of copper coating on the rotating assembly - er, was. As you'll notice from the pictures - chunks of it are missing, and flaking off. Additionally, there is a lot of play in the connecting rod where it connects to the crank.

I've ordered a new motor (upgraded to a 36 cc Zenoah, as I hear the CY motors aren't the best in terms of reliability). My question though for you guys - what would have caused this? If it's user error, I'll take it on the chin. I'd like to figure it out though as to not repeat this issue with the new motor. Fuel wise I run 25:1 (which seems like a very high oil content...I'm thinking that might have led to the carbon issues). 93 octane gasoline. Motor was never run lean - I always run a bit rich, intentionally. Motor never ran for more than 15 minutes at a time as I usually had other issues (various parts breaking). So the question again is - could this have been bad fuel that caused this? Running too rich? Perhaps I got a motor made on Friday afternoon or Monday morning and the fit and finish just weren't up to par and it was destined to tear itself apart?

Please let me know your thoughts. Thanks for taking the time to read, and offering any feedback.

 

[Rep732]

That's a stuffed crank, I've heard of instances of the "stuffing" material coming loose and it appears yours has done so.

 

[RoushSport]

That's a stuffed crank, I've heard of instances of the "stuffing" material coming loose and it appears yours has done so.

Thank you for your response.

Any idea what would cause that material to come loose? Would that be a result of something I did, or just poor materials within the engine?

Also, correct me if I'm wrong, but, not worth rebuilding it? I ask because I see the kit to rebuild the motor on Rovan RC (60 bucks), but, if I'm only going to end up with a motor that will self destruct again, I'd rather not waste the time / money.

 

[Rep732]

So the stuffing material is a dissimilar metal to the crank so it really isn't able to be welded or brazed so since it appears to be copper it probably is cast around the crank and milled. Eh it's a cy clone engine I wouldn't bother with rebuilding

 

[RoushSport]

So the stuffing material is a dissimilar metal to the crank so it really isn't able to be welded or brazed so since it appears to be copper it probably is cast around the crank and milled. Eh it's a cy clone engine I wouldn't bother with rebuilding

Understood. Thank you very much for the responses and information.

 

[Rep732]

Anytime. Also to add its hard to tell.what the material on yours is but most of the time it's not a metal its like an epoxy or resin

 

[Seandonato73]

Stuffers can be made of Many different materials typically they are light weightand aome aort of plastic, since they are just hogging up case volume. I have a few saws with staffers and they are plastic in a steel carrier, that gets sandwiched between the counter weights and crank bearings. They fly apart every now and then, typically it's the plastic loosing it's bond to the carrier.
I can't honestly say you have yoir apart far enough to say one of them flew apart, not knowing how they were attached to begin with. That missing section could have never been there to start with, and from the pictures the only thing I'm seeing is some excessive carbon build up. No scoring, no bounce marks on the piston or dome from something flying apart. Kinda surprised it wasn't smacking the head from all that carbon, good grief that's a lot of carbon.

 

[Rep732]

I'm not sure If it's oil streaks but I see what looks like some scoring by the transfer port sean.

 

[Seandonato73]

I'm not sure If it's oil streaks but I see what looks like some scoring by the transfer port sean.

Hard to tell with those pictures. I zoomed in on it a few times, and just couldn't tell if it's scoring or not.

 

[Rep732]

Agreed sean, hard to tell.

 

[Seandonato73]

Agreed sean, hard to tell.

I downloaded the poc and blew it up on my phone, it's got some scratches there, but still hard to tell it it's enough to cause poor running based on that picture and the limited information we have on hand.

Op. Better cylinder pictures, and take the crank out. Inspect the bearings and seals.

 

[MonsterAir]

How old is that motor and how much fuel have you put through it? One more question, what oil are you using?

 

[RoushSport]

Oil i'm using is the Castor 927, 25:1 ratio. That was half way through the 3rd tank of gas when it started running poorly. I've had the car almost 2 months. I haven't torn the motor all the way down yet, but I will do that this weekend and will post up pictures. Only other thing I thought was odd was that the spark plug appeared as if it had been struck by the piston....no gap on plug at all when I removed it from the head (perhaps the piston hit it?).

 

[Seandonato73]

Didn't see any hit marks on the piston that were obvious from your picture.

 

[RoushSport]

So, in tearing the motor completely down - the only thing I found is that the "plastic" coating on the crankshaft was in pretty sad shape, and also the connecting rod bearings both in the bottom of the piston head and on the crank had a lot of slop in them. So, I'm wondering if what happened - the coating deteriorated, unbalanced the crank, which led to a loss of compression, which is what stopped the motor from being able to traverse the entire RPM band as it normally would. Mind you, I'm not a mechanic, nor am I a "know it all" by any means. My theory as to what happened could be completely wrong. However, if anyone has any idea as to what caused that coating to fail, I'm all eyes / ears as I don't want it to happen again. Interestingly, the coating feels like plastic. Seems to me you wouldn't use plastic inside of a motor that has potential to get really hot - unless that plastic has a melting point that is higher than the temps the motor would ever potentially see?

Additionally, I have no idea what happened with the spark plug. I can't find any indication of the piston hitting it. I'm wondering if, perhaps, a chunk of the plastic from the crank was slammed into it by the piston while the engine was running, as it wouldn't take much force to bend it.....?

 

[Seandonato73]

Kinda surprised you split the crank. But any way. By loose how loose do you mean? Like lots of up and down movement, or side to side movement? No I don't think the rod is/was your initial issue. I think you had it right the first time around after seeing the new pictures. Stuffers delaminated off the crank, engine cewed them up. You can see the deposits in the combustion chamber where the plastic burned/ melted fast to the dome. Good ole head banger at that point.

More to the point, it's nit normal for the plastic in stuffers to melt or fly apart. It's an anomaly. It happens , but not normally.

 

[RoushSport]

Kinda surprised you split the crank. But any way. By loose how loose do you mean? Like lots of up and down movement, or side to side movement? No I don't think the rod is/was your initial issue. I think you had it right the first time around after seeing the new pictures. Stuffers delaminated off the crank, engine cewed them up. You can see the deposits in the combustion chamber where the plastic burned/ melted fast to the dome. Good ole head banger at that point.

More to the point, it's nit normal for the plastic in stuffers to melt or fly apart. It's an anomaly. It happens , but not normally.

I split the crank because I want to keep the piston and rod....I think it's neat, and going to make a keychain out of it. I'm a dork, I know....sue me. HA!
The play was side to side. I didn't have a tape measure handy unfortunately. I would imagine the rod moving a 1/16th of an inch in either direction (again side to side) would be normal, but in my case....it was much more than that.

I don't presume the plastics flying apart would be under any sort of "the motor shouldn't self destruct" warranty, would it? I mean, if I go back to Rovan, I'd imagine their first argument would be "prove to us that you didn't abuse the motor, didn't tune it to run super rich or super lean, etc"......ergo, prove to us that the failure wasn't the result of something that YOU did...

 

[Seandonato73]

I split the crank because I want to keep the piston and rod....I think it's neat, and going to make a keychain out of it. I'm a dork, I know....sue me. HA!
The play was side to side. I didn't have a tape measure handy unfortunately. I would imagine the rod moving a 1/16th of an inch in either direction (again side to side) would be normal, but in my case....it was much more than that.

I don't presume the plastics flying apart would be under any sort of "the motor shouldn't self destruct" warranty, would it? I mean, if I go back to Rovan, I'd imagine their first argument would be "prove to us that you didn't abuse the motor, didn't tune it to run super rich or super lean, etc"......ergo, prove to us that the failure wasn't the result of something that YOU did...

The crankcase doesn't/ shouldn't get near as hot as the head,and the stuffers shouldn't come apart. Manufacturing defects if it's still under warranty. I'd reach out to rovan. From others that had issues, it seems they will make it "right".