Is my engine fubar???

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enzo3856

enzo3856

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I got a new to me 5t last summer, but never had much time to run it until now...
I had it mixed a little rich, proper fuel (not my first 5th scale).
I ran it for maybe 30 mins and it is was going smoothly, and then all of a sudden on a high speed pass the motor quits...
I cannot pull the pull start cord at all... once it engages the piston feels stuck. I removed the plug in case it was a hydro lock and still no joy.
plug.webp
PXL_20240615_183852122.webp

PXL_20240615_183735110.webp

Any ideas? recommendations?
Any chance it can be saved??? pretty much on a budget right now, and in Canada, so I am hoping I am not SOL on this...
 
Sounds like a lean seizure to me. You can lean seize an engine on 16:1 mix if tuned lean. Any mix ratio actually. It will probably need a new top end. If you remove the pipe you can look in the exhaust port for piston damage.
 
spents said:
before you start buying parts fella, please check that its not just the coil thats dropped and locked against the flywheel,
its a very common thing to happen and may just need the air gap resetting and tightening up again (y),
Click to expand...
Thanks for this tip... I did not know this was a thing.
I will get the truck up on my bench tomorrow evening and take a look.
 
So we have some heat seizure...
cylinder.webp
piston1.webp
piston2.webp

So piston and cylinder are toast... there is metal scoring and both sides by the circlips you can see signs of heat damage I assume...

Is there a top end kit which will fit this dynamite?
I thought I read somewhere that there are no parts for this motor? not even the clutch bell fits another motor?

My initial thought, worst case, was to get a Zen 29cc longblock...

I also checked the carb... LSN was 1.25 out, HSN was about 1.25
Wondering if the fuel was bad maybe? It was fuel mixed by my buddy last fall... not sure what oil or mix ratio he had... should have known better!

Was hoping for a new pipe this year, but looks like my $$ is going to fix this motor instead...
 
Are there any grooves or deep scratches in the cylinder bore? It might still be usable with a trick on the aluminum transferred on to the bore.
 
enzo3856 said:
So we have some heat seizure...
View attachment 93836
View attachment 93837
View attachment 93838

So piston and cylinder are toast... there is metal scoring and both sides by the circlips you can see signs of heat damage I assume...

Is there a top end kit which will fit this dynamite?
I thought I read somewhere that there are no parts for this motor? not even the clutch bell fits another motor?

My initial thought, worst case, was to get a Zen 29cc longblock...

I also checked the carb... LSN was 1.25 out, HSN was about 1.25
Wondering if the fuel was bad maybe? It was fuel mixed by my buddy last fall... not sure what oil or mix ratio he had... should have known better!

Was hoping for a new pipe this year, but looks like my $$ is going to fix this motor instead...
Click to expand...
Bummer bud. I wish I could help you on your questions about a replacement cylinder and piston but someone will be able to soon I'm sure. As to your needle settings, that varies depending on your outside temp, humidity, oil, fuel ect. I tune by ear and have no idea where my needles are at once tuned. As far as turns out goes.
 
TODD said:
Are there any grooves or deep scratches in the cylinder bore? It might still be usable with a trick on the aluminum transferred on to the bore.
Click to expand...
The pic doesn't show very well, but the cyclinder is scratched up badly...

how do you mean: "usable with a trick on the aluminum transferred on to the bore"
 
enzo3856 said:
The pic doesn't show very well, but the cyclinder is scratched up badly...

how do you mean: "usable with a trick on the aluminum transferred on to the bore"
Click to expand...
Often the piston material melts to the chrome bore. It can be removed with acid which often renders the cylinder usable because there are no scores in the cylinder. Its just the aluminum smeared on the walls. Its worth a try to see if its salvageable. These vids are without acid

Using acid...

 
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You had a transfer of material to the cylinder, most likely it will have taken some of the coating off the cylinder so I wouldn't bother. I've tried it so that's why I mention it, also you overheated the cylinder if it seized. As far as exactly what engine this is it is a l Cy F290, I believe a zen top end will fit but a zen piston will not. Steve at ddm said this engine uses an oddball sized piston, personally I wouldn't be upset as this gives you a reason to throw a zenoah in it now.
 
Rep732 said:
You had a transfer of material to the cylinder, most likely it will have taken some of the coating off the cylinder so I wouldn't bother. I've tried it so that's why I mention it, also you overheated the cylinder if it seized. As far as exactly what engine this is it is a l Cy F290, I believe a zen top end will fit but a zen piston will not. Steve at ddm said this engine uses an oddball sized piston, personally I wouldn't be upset as this gives you a reason to throw a zenoah in it now.
Click to expand...
Thanks for that info and the vids...
I have reached out to DDM for some guidance... will see what info I get... Hoping to keep the cost of damage lower as I do have to pay for shipping to Canada, plus import duties, plus the exchange rate :eek:

I had this sitting for months because i was missing the battery tray lid, then I needed a radio... then I got what i was missing and just was too excited and went out for a rip.. in hindsight I should have refreshed the fuel, double check my needles, etc... Was bummed all Sunday afternoon thinking of what I should have done different.
 
Hi.
What diameter is the piston , there are chinese cylinders and pistons all over the internet in various sizes at modest costs .
If it is 36mm it is a standard bore size for a 29cc engine.
I would check sizes and do a search.
Did a quick search and cylinder is £59 and piston which is 36mm was £11 from Rcmodelz .com in the UK.
I would try a search in Canada or on alli express as that is where people get all the chinese stuff , I bet they are cheaper on there . Seem fairly standard sizes to me.
 
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Quite literally the whole engine is different from a standard Zen or CY small bore aside from the coil, flywheel, clutch plate, fan cover, and insulator.
Piston is different, crank is different, base gasket bolt pattern is different. There's definitely a head out there on AliExpress which fits the dynamite, but I haven't bothered to find it.
The 30°N 29cc head should in theory fit, but I haven't tried. Definitely not worth it considering a whole assembled Fuelie or BWS 29cc is only around $100. Although, I personally would take this a sign it's time for a bigger engine.

Reasons for the lean/heat seize could be bad gaskets/seals, bad carb, bad fuel, or just working it too hard in hot weather.
 
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