Possbly ovearheated my 50cc, what next

ryang · Post by **ryang** » Sun May 24, 2015 9:43 am

Hey guys, i was driving my buddy 50 today, it's stock but derestricted so i was going about 37mph and it was 85 degrees outside. The scooter just died, the engine didn't act like when you hit the kill switch, but just died. After it cooled down a bit i started it and it died again after a minute bogging down. Its full of gas and put in a quart of oil just in case, but after i let the scooter cool down all the way, it would not start, and it sounded different revving, almost like there was not as good of compression and also seemed like it was having a little bit of a harder time starting.

I am assuming the engine overheated and now the cylinder expanded so its having a hard time going up and down, or less likely, overheated and the valve spacing is out of spec.

If it is the first, how could i find out it is indeed that, and would a 70cc upgrade kit be a solution for me?

Thank you for any input!

luckyscroller788 · Post by **luckyscroller788** » Sun May 24, 2015 4:52 pm

It quit, full of gas, and you put in a quart of oil ( what kind of oil, and where did you put it?)and after it cooled it would not start,but sounded different revving??? So did it not start, or did it start, and sounded different revving, Im confused???? If your driving and normal idling, 85 isnt that hot of a temp i would think, but I wouldnt let the thing sit and idle for a long time for no reason when its warm out.

WisKid · Post by **WisKid** » Sun May 24, 2015 7:53 pm

If it ran out of oil or if the oil delivery system failed that would do it, but outside temp doesn't really make a huge difference.

Cold air cools the cylinder better but leans out the mixture, warm wet air doesn't cool as well but the mixture is more rich and cools in that manner.

People ride scooters in regions with 110 degree daytime temps all day.

If you think you ruined the top end you just have to pull it and find out.

I also don't understand the last part of the question.

It wont start but it sounds funny when its revving?

KrispyKreme · Post by **KrispyKreme** » Sun May 24, 2015 9:07 pm

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Stitch · Post by **Stitch** » Mon May 25, 2015 6:31 pm

Aren't all the buddy 50's a 2t?

ryang · Post by **ryang** » Tue May 26, 2015 11:06 am

Sorry for the confusion guys. My buddy has a low oil warning lamp but it was not illuminated, i put a quart in the tank for the oil injection system. The scooter would not start, but the engine was turning over, but it sounded different when it was turning over vs all other times, almost as if there was low compression.

I had issues with the muffler a few months ago where it was clogged, and a muffler shop fixed it, but they said there was a catalytic converter type piece inside that fell out. Could this have caused more of a free flowing exhaust and the scooter was running lean which lead to the failure? I would like to find out what caused this issue so if i do need to replace the top end or anyting else it does not happen again. Thank you for the input!

Also by 2t you mean 2 stroke? yes they are, mine is as well, does it change anything, do the 2 strokes still require valve adjustment?? I'm new to 2 stroke engines, always owned and worked on 4

Elder Scoot · Post by **Elder Scoot** » Tue May 26, 2015 1:44 pm

Sounds like you seized the piston. That used to happen from time to time on my 2T dirt bikes.

BTW - 2T bikes don't have valves - they have ports.

ryang · Post by **ryang** » Fri May 29, 2015 12:49 am

Okay I ordered the 70cc upgrade, any input on what jets i should be running, especially if my exhaust is indeed more free flowing than stock?

JohnKiniston · Post by **JohnKiniston** » Fri May 29, 2015 2:07 am

ryang wrote:Okay I ordered the 70cc upgrade, any input on what jets i should be running, especially if my exhaust is indeed more free flowing than stock?

Wait, You bought a new cylinder before diagnosing the problem?

I think you are jumping the gun a bit if you haven't taken your bike apart and found why it failed. Just assuming it's the cylinder is a good way to spend money needlessly if that's not the problem.

ryang · Post by **ryang** » Sat May 30, 2015 11:12 pm

Well i live in hawaii and delivery is 3-4 weeks, but i need my scooter as soon as possible, and i cant look at it until this next weekend so i took the chance. With the battery being brand new and fully charged, and the starter is having a much harder time turning the engine over I can only assume its seizing up, that and the fact that when it was hot it turned over just fine but once it cooled down its turning over really hard and not starting. It seemed logical to me..

Stitch · Post by **Stitch** » Sun May 31, 2015 3:24 am

Did you put the battery on a charger?

ryang · Post by **ryang** » Sun May 31, 2015 8:31 am

yeah got it to full, tried a battery from my other scooter that i know is good for sure.

Stitch · Post by **Stitch** » Sun May 31, 2015 10:21 am

And you checked the spark plug?

ryang · Post by **ryang** » Wed Jul 01, 2015 4:23 am

Hey guys, I FINALLY got the scooter into my apartment and got to work on it.. and now I really don't know whats wrong with it. I thought engine seizing, so i took the plug off, looked rusted, took the head off and the piston moves freely.. So i put the head back on, brand new battery and rev it up and its revving great, but then I hear what sound like metal grinding towards the middle of the engine, down at the bottom of where the piston connects, and the revving slows down. I stop, wait ten seconds, and it rev's fine again, not starting yet because i drained the gas out and had to put it back in, but I'm confused now. I took the CVT cover off, belt looks ok, there is red dust on the inside bu everything looks like its fine. Don't have an impact wrench to look further. I'm stumped, any ideas on why my scooter was acting the way it did as mentioned on the above post. I know its not fuel loss because when the engine died, it was very very quick, and it ran again for 10-30 seconds depending on how long i let the scooter cool down.

babblefish · Post by **babblefish** » Wed Jul 01, 2015 5:10 am

If your scoot ran out of oil and you didn't know it until it died, then there is a possibilty that the noise you're hearing and the poor running is due to the connecting rod bearing being toast. That bearing relies on the oil that gets mixed with the fuel to keep it lubricated.The only way to check it is to pull the head and barrel then check the rod for movement and side to side play.

ryang · Post by **ryang** » Wed Jul 01, 2015 5:14 am

I'm starting to think this is the issue, when the scooter died the oil lamp was not lit, but i put oil in anyways and started it and it died again. When i pulled the plastics off i noticed the oil sensor was disconnected for some reason, so I have no clue how much oil was in the scooter when it died. Anyways i'm pulling the thing apart tonight, ill check then, thank you

ryang · Post by **ryang** » Wed Jul 01, 2015 8:16 am

Okay got i apart, the rod moves left and right a little, the cylinder moves left and right even more. Here are a few pictures, I don't know if any of it helps. Also in one of the pictures, I noticed that behind where the rollers are one piece of metal looks to be coming apart.. any input on that as well?

babblefish · Post by **babblefish** » Wed Jul 01, 2015 9:04 am

The connecting rod should not rock side to side on the big end side at all, but it's ok if it slides back and forth a millimeter or so. It should also pivot smoothly and easily on it's big end bearing with no up and down movement or rocking. You should not be able to twist it on the big end bearing either. You will have to replace the crankshaft if there is too much big end play.

It's hard to tell precisely from your picture, but it looks to me like your piston is scored and burned (not good) and the rings don't look in very good condition either. The bore in the cylinder should be smooth with just a trace of honing hash marks; no up and down score marks.

The picture of your head/sparkplug tells me you're running rich.

The last picture is of your rear pulley/contra spring/clutch. It looks perfectly normal. The contra (or torque) spring is sitting in a metal cup to keep it from tearing up the pulley and moving around. There are no rollers in there. The rollers are in your variator (bolted to crankshaft) which is what drives the rear pulley via the belt.

I'd say your engine is a good candidate for a 70cc big bore. Pairing a nice tuned pipe with the big bore would be good. Since it looks like you're already running rich, I'd leave the jetting alone until you make some high speed passes and check the plug (it should be a tan color). It would also be beneficial to change the contra spring to a yellow (1500 rpm) spring since a tuned pipe will move your torque curve up in the rpm range. The yellow spring is stiffer which will hold the transmission in a "lower gear" longer to help your take-off performance. Lighter variator rollers might be of help too. You can also play around with the three small springs in the clutch. These determine at what rpm the clutch will start to engage; stiffer springs means engagement at higher rpm's. Blue is the softest, then yellow, and red is the stiffest. Most of the time, increasing the power of a 2-stroke engine moves it's peak torque higher in it's rpm range so letting the engine rev higher before the clutch engages will help performance.

I see what looks to be black sludge on your piston too. That usually means a lot of metal wear, particularly aluminum. Or, it could just be excess carbon build-up from running rich. If you are going to rebuild your engine, I would highly recommend that you disassemble the entire engine to give it a good cleaning to make sure there are no metal particles hiding in dark crevices only to get washed out later while you're riding destroying the engine again. There is no need to disassemble the gear reduction part of the transmission (the part the rear wheel is attached to).

Good luck.

k1dude · Post by **k1dude** » Wed Jul 01, 2015 4:32 pm

It's hard to see, but the top ring looks like a chunk is missing. Or do 50 rings have pointed ends vs flat ends? Did you check your compression before pulling the engine apart?

Also, to 50 owners, is it normal to have what looks to be corrosion/burn marks on the stud bolts?

babblefish · Post by **babblefish** » Wed Jul 01, 2015 9:14 pm

k1dude wrote:It's hard to see, but the top ring looks like a chunk is missing. Or do 50 rings have pointed ends vs flat ends? Did you check your compression before pulling the engine apart?

Also, to 50 owners, is it normal to have what looks to be corrosion/burn marks on the stud bolts?

The each ring end has opposite "steps" which over lap when compressed into the cylinder to help the ring seal better.

The studs are tarnished because unlike on 4T engines, the part of the stud that goes through the cylinder barrel in most 2T engines is exposed to the outside elements between each cooling fin. In other words, the holes in the cylinder barrel for the studs are drilled through each individual fin from the base to the head surface. On 4T engines, these stud holes are completely enclosed because those stud holes are also used as oil return paths to the sump for the oil that lubricates the cam and rockers.

ryang · Post by **ryang** » Wed Jul 01, 2015 10:32 pm

Babblefish, thank you!! Your post was very informative, especially on the CVT part as I have never worked on one before. I've done work on car engines but the crank / rod setup on these scooters is new to me as well. I moved the rod around and it feels like its just sliding back and forth, about a mm as you stated, i can't twist it, and it seems to move smoothly . I'm back to not being sure as to what exactly happened to my scooter when it died. I'm still convinced it ran out of oil, but if the bearing does not seem damaged, what else could it be. Taking the whole crank assembly looks to be a huge pain, and I'm working on it inside my apartment with no air tools so I'm trying to avoid it at all cost.

I hate these issues that are not so obvious, I don't want to put everything back together with the 70cc bore only to find out I didn't fix the initial issue.

babblefish · Post by **babblefish** » Thu Jul 02, 2015 12:07 am

You're very welcome, glad I could be of some help.

By your description, it sounds like your crankshaft might be ok, but I would still be a bit concerned about contaminated sludge being in the connecting rod and crankshaft bearings, hence the need to disassemble the engine for a full clean. While you may get away with just replacing the piston and barrel without doing anything else, personally, I'd feel better if the crankcase could be cleaned out. The good news is there's nothing else in the part of the crankcase where the crankshaft lives. You'll have to decide for yourself about whether it's worth your time and energy to pull the engine to take it apart and put it back together.

The main issue with your engine may just be abnormal piston/ring wear due to lack of oil. It would have been nice to get a compression test before you took the head and barrel off. The noise you heard may have been piston slap due to too much clearance between the piston and cylinder wall.

Almost forgot, check the small end play of the connecting rod too. The piston should pivot freely, but not rock.

To minimize cost, you could just replace the piston/barrel with a 70cc BB kit and leave everything else alone, other than carburetor tuning. You would still see a performance increase from the 40% increase in engine displacement.

Just to throw it out there, you don't really need air tools to do engine work. While I do have air impact drivers, I don't use them anymore since I bought an electric impact driver unless it's for something really heavy duty. Also, I understand the inconvenience of trying to do mechanical work in an apartment and while I live in a house, I did the majority of my Blur's engine build on my living room floor. The only reason I got away with doing that was because there's no one here to tell me no, lol. Anyway, just goes to show you anything is possible.

In hind sight though, it was probably a really bad idea on my part. Carrying the mostly built engine up and down the stairs to the garage threw out my back for two weeks...

After reading through your post again, I'm of the opinion that your engine may have ran lean and may have been starved of oil on top of that. De-restricting the exhaust will usually cause a lean condition as the engine can now move more air. A 2T engine produces more power and revs faster the leaner you run it. Right up to the point where it no longer gets enough lubrication from the fuel/oil mixture to keep it alive. It will run really good up until it overheats and seizes. When it cools down, the piston shrinks back down releasing itself from the cylinder wall. In a worst case scenario, the piston welds itself to the barrel. Either case, rapid piston/ring/cylinder wear will occur. That's why 2T tuning is always a compromise between power and engine life. But, I'm a bit confused as to why your sparkplug looks so dark...unless it just a sign of losing compression and not being able to efficiently burn the air/fuel mixture thereby causing carbon deposits. Hmm, just guessing...

A final bit or rambling...there's a good chance of another speed restriction in your engine; the variator. There might be a spacer installed between the two pulley plates to limit how close they can come together. The closer the two plates can come together via the rollers moving out due to centrifugal force, the further up the pulleys the drive belt can go thereby increasing wheel speed. A spacer between the pulley plates will limit how close they can come together. It's like moving the chain on the crank of a bicycle from the small chain ring to the larger one. Hope that made sense.

jrsjr · Post by **jrsjr** » Thu Jul 02, 2015 12:11 am

Babblefish, I see now what the OP was asking about this part I've circled in the photo below. Is that normal? That does not look cast, that looks ragged like a piece that snapped. Is that just an illusion caused by the lighting in the photo or something?

babblefish · Post by **babblefish** » Thu Jul 02, 2015 12:15 am

jrsjr wrote:Babblefish, I see now what the OP was asking about this part I've circled in the photo below. Is that normal? That does not look cast, that looks ragged like a piece that snapped. Is that just an illusion caused by the lighting in the photo or something?

Hmm, I see what you mean, though it doesn't look like a piece of a piston ring to me, more like a bit of aluminum...from the piston, maybe? Another reason for complete engine disassembly.

babblefish · Post by **babblefish** » Thu Jul 02, 2015 12:26 am

Wait! I just looked at the picture of your piston again. It looks like there's a big chunk of the piston skirt missing from the intake side! It's suppose to look like the piston in the attached picture.

I'd say there's no choice now but to disassemble the engine to clean out all the chunks of metal. That also explains the noise and black sludge; it is aluminum sludge. I would also say that the crankshaft should be replaced too because the main bearings and connecting rod bearings are probably toast. And while you're at it, replace the crankshaft oil seals too because they may have been damaged.

The good news is that stock replacement crankshafts aren't all that expensive. For about 3 times the cost, a stroker crank can be used for more displacement and torque.

While it may seem complicated, 2T engines are actually quite simple. There just isn't very much going on inside one of these things. Really, the only things inside the engine case is the crankshaft, oil pump, electric starter gears, and stator. The service manual can be found here: topic17349.html thanks to that Ericalm guy...whoever he is...

Too bad we're so far apart as I would be more than happy to give you a hand on the engine rebuild.

Oops, just checked for crankshafts on eBay. While they are cheap and plentiful for 4T 50cc engines, they're pretty rare for 2T engines, at least on eBay. Found an OEM PGO crank for $75, but it's out of Germany and they won't ship to the US. This one looks like it would work for only $65 shipped: http://www.ebay.com/itm/New-2-Stroke-Cr ... c5&vxp=mtr
Scooterlounge has them for $127.

Buggers, I just noticed that the crank main bearings are separate from the crank, so those would have to be purchased also. The main bearings on my Blur engine come preinstalled on the crank.

babblefish · Post by **babblefish** » Thu Jul 02, 2015 2:43 am

At this stage, it might be cheaper to find a crashed Buddy with a good engine where the seller might be willing to part out the scooter. Maybe check with local scooter dealers for leads.

ryang · Post by **ryang** » Thu Jul 02, 2015 5:26 am

Wow thank you, I don't think I've ever gotten so much help on any forum! I don't mind taking apart an engine (I rebuilt my Mitsubishi 3000gt VR4 engine), I live in a 500 sq foot studio with my GF, so space and "other reasons" is why i was trying to avoid going too far. Yeah i just saw the piece too, I agree a full rebuild looks to be in order, unfortunately here on Oahu Buddy scooters are few and far in between. I was very fortunate to find this one for sale and at a good price too, otherwise its months before I see one, much less parts.

I appreciate even the thought of coming by to help.. It is Hawaii, you could call it vacation and I can give you a tour for all the help!

Well I'll probably put the scooter in a corner until I can figure out the part situation.

The reason I mentioned air tools, is that the bolt on the transmission side of the crank looks like it might need a impact wrench to get lose?

Ill keep you guys updated, hopefully with good news soon of the rebuild and the final product

I still love these scooters, especially after owning two chinese made 4 strokes

babblefish · Post by **babblefish** » Thu Jul 02, 2015 7:22 am

ryang wrote:Wow thank you, I don't think I've ever gotten so much help on any forum! I don't mind taking apart an engine (I rebuilt my Mitsubishi 3000gt VR4 engine), I live in a 500 sq foot studio with my GF, so space and "other reasons" is why i was trying to avoid going too far. Yeah i just saw the piece too, I agree a full rebuild looks to be in order, unfortunately here on Oahu Buddy scooters are few and far in between. I was very fortunate to find this one for sale and at a good price too, otherwise its months before I see one, much less parts.

I appreciate even the thought of coming by to help.. It is Hawaii, you could call it vacation and I can give you a tour for all the help!

It's been many, many years since I've been to Hawaii, but I can't think of a better place to ride a scooter. Unfortunately, funds won't allow me the luxury of a vacation.

Well I'll probably put the scooter in a corner until I can figure out the part situation.

I did that with my Blur when I goofed up on the engine rebuild, but I eventually started up again and now it's almost done. Just waiting for an exhaust system. If you're interested, you can read about my adventure here: topic16629.html

The reason I mentioned air tools, is that the bolt on the transmission side of the crank looks like it might need a impact wrench to get lose?

An impact wrench would make the job easier as that nut is on there pretty tight. But, it can be done with a 1/2" drive breaker bar. And of course, if you plan on doing more mechanical work to your car or scooter, an electric impact gun would be a good investment. I've used mine countless times.

Ill keep you guys updated, hopefully with good news soon of the rebuild and the final product I still love these scooters, especially after owning two chinese made 4 strokes

Yes, please do keep us updated.
www.scooterloungeonline.com will have most everything you need, but if you shop carefully, it is possible to buy a lot of parts cheaper from other vendors, although they may not be OEM PGO parts. Just keep in mind that your engine may have some differences when compared to other "generic" 50cc scooter engines. One example would be the engine gaskets, I'd buy OEM gaskets. The eBay seller of the crank I posted has all the important dimensions shown, so measure yours to compare and if they match, you'll save a lot of money. The only negative thing is that the quality may not be the same. Or, take the crankshaft out and spin the bearings. If they feel perfectly smooth with no tight spots and no play, then you may be able to get away with just a thorough clean and reuse it. Oil them well before reinserting them in the engine case though.

You won't need very many parts to rebuild your engine, especially if the crank can be reused. As long as the engine case itself is still good, all you really need is a piston/barrel and a gasket set. That is, of course, all you're going to do is build a near stock engine. If you're gonna hotrod, well then...how fast do you want to go and how deep are your pockets? Heheh. Still, it's only a simple 2-stroke. Much less complicated than a 4-stroke with all their moving parts and clearances to think about.

Anyway, best of luck with your scoot and keep us posted. Feel free to ask any questions.

babblefish · Post by **babblefish** » Mon Jul 06, 2015 6:45 am

Found this on YouTube that explains very well how the variator and rear torque pulley works. He happens to be working on a 50cc engine that he has hopped up so this too might be of interest to you.

<iframe width="560" height="315" src="https://www.youtube.com/embed/d3cQKYT0ojg" frameborder="0" allowfullscreen></iframe>

ryang · Post by **ryang** » Sat Jul 11, 2015 2:41 am

Great informative video! Thank you.

So I took the crank to get checked, looked good, so i replaced the main bearing and piston bearing, put everything back together and it moves smoothly. I put on the 72cc upgraded piston and the rest of the parts from the upgrade kit (Do i need to add oil or anything to the cylinder before starting it for the first time?). Also what jet should I start with for the carb and do i need specific jets for this carburetor or will a generic 50cc jet work?

I can't wait to see if everything works!

babblefish · Post by **babblefish** » Sat Jul 11, 2015 5:38 am

Congratulations!
Yes, you should have put a light coat of dino oil (not synthetic) on the piston, rings, wrist pin, and inside the cylinder barrel before assembling. You should have also coated all of the bearings with oil too. The reason for using dino oil is because synthetic is too good and may prevent or greatly delay ring seating/breaking-in. The piston rings should be installed with their gaps opposite from each other.

I don't have any experience with the Buddy 50 carb, but according to the service manual, the stock main jet is a #75. You'll have to check jet type though because I'm not sure if the 2T and 4T carbs use the same jets. I would try a #80 jet first, then a #85 if needed. You might even get away with the stock jet if you're using the stock exhaust system. Only way to know is to try it and check the spark plug color for leanness or richness.

The majority of 50cc engine parts I see seem to be 4T parts, probably because 2T engines are getting phased out due to environmental reasons.

Here is an eBay vendor selling an assortment of jets, though you'll have to make sure they're the correct ones for your carb: http://www.ebay.com/itm/Main-Jet-Kit-GY ... d0&vxp=mtr

And here is a general search for 50cc engine jets, though again, I'm not sure if some of them are unique for 4T carbs: http://www.ebay.com/sch/i.html?_odkw=gy ... t&_sacat=0

ryang · Post by **ryang** » Tue Jul 14, 2015 6:29 am

She started right up!! Such a great sound to hear after everything

I let her idle for a while, I bought three new plugs, i got the engine warm on one plug, put a new one in, went WOT for 10-15 seconds, and killed the engine and stopped, removed plug.. looks really lean to me :-/ ... should i go with 85 jet first then down to 80? The scooter did vibrate a little more than normal at idle, and was quite a bit louder, i think its just the muffler though, I think that's expected when you go higher displacement?

babblefish · Post by **babblefish** » Tue Jul 14, 2015 6:46 am

1) You really didn't need to change plugs so soon.
2) Your new piston/cylinder isn't broken in yet which means the rings aren't fully sealing yet. Give it 300 miles or so.
3) You shouldn't have rev'd it so high on new rings.

It isn't too clear by your description, but I sure hope you didn't just rev the engine to WOT static (not moving/riding).

Check plug color after you've broken it in. Avoid full throttle for at least the first 100 miles. Basically, follow the owners manual as if you were breaking in a brand new scooter.

ryang · Post by **ryang** » Tue Jul 14, 2015 10:02 pm

Oh i did not know that, I didn't WOT it at a stand still, but i did do one run to check the plug after finding info on how to do it elsewhere.

I am worried about running it for 300 miles if its running lean, should i try to change the jet now, or just baby it for 300 miles until its broken in ?

babblefish · Post by **babblefish** » Wed Jul 15, 2015 5:23 am

I think the manual says to limit the throttle to 1/2 for the first 300 miles. You might want to double check your manual on this.

Modern Buddy

Possbly ovearheated my 50cc, what next

Possbly ovearheated my 50cc, what next

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