Engine Replacement

[daandeurloo]

Hi Guys,

Few days ago my Kymco Agility 50 engine finally decided "You can go walk".
Well all before ( i think 1.5 month ago ) the crank started to make bearing noise once again after i had it replaced about 500~700km before that.
So i kept it driving untill it lets go and hoped it would hold out atleast till January 7th, but it didn't unfortunately.

How it died:
It started make some weird smell but didn't saw any blue smoke, but the gasket of the Rocker cover was leaking a little bit so i replaced that.

Still the weird smell was still there, and it smelled like it was burning engine oil.
Note: The engine oil seal was also leaking a little bit at the stator side.

Till few days ago, it started to produce blue smoke all the time and seems that piston rings ( especially the oil scraper ring did let go ).
Shortly after that the engine died which sucks as i had to walk home with a full tank of gas. No it doesn't have diesel in it. I smelled in the gas tank and it was gas.
How does that happen with a NCY 52mm cylinder that has about 5000km / 3000 miles on it ?. It was broken in properly and oil changed after 500 km / 300 miles and then about every 2000~2500km.

The crankshaft is a Naraku Heavy Duty 16 Tooth.

I will go and look for a another engine, since the current engine has Helicoil everywhere where you can think off and i don't wanna split the engine all apart once again.

And a used engine is still cheaper then a Crankshaft with a cylinder set.


My Set-up:
52mm 88cc NCY Cylinder ( advertised as 90cc )
NCY Cylinder head
Some Chinese performance camshaft
Stock carb with 86 Main jet
Stock camshaft holder with stock valve tappets. Normally they should be replaced since the valve are shorter on the ncy head then on the stock head, but the stock holder does fit properly and adjusting is no problem.
NCY Exhaust
Naraku Variator with 8,75g rollers.

Also seems that the compression is a little bit lower then it was all before. Or atleast it sounds like it is.
Atleast the rings are busted i think.

It has spark, gas etc.
Main jet was not dirty at all.

It doesn't even wanna run on Brake cleaner which is crazy. If it fires, it does run for about 1 sec and turns off once again. 

I hope it's just the spark plug cable since i saw it sparking a little bit onto the frame, but still it didn't make any differance once i moved it from the frame..

It also seems that the starter motor draws alot of amps since the plug on the starter got really hot.

I've been using a Lithium battery as my main battery because of the 88cc.

www.youtube.com/watch?v=5cVcrLlkpdk


The odometer has 31,200km on it by the way.

I need to get the engine replaced since this is the only way to get myself to something.

How much you guys thnk that a used engine is worth ? Doesn't matter if you say dollar since i can convert it back to Euro's.

The kymco engine code is: KG10SA, so not a 139qmb or 139qma.

The Exhaust mount on the chinese engines are totally different in height and also my variator blocking tool isn't fitting on a chinese engine.


@90gtvert if you read this, yes i'm that guy from youtube that was talking about the Naraku crank on one of you video's.

[90GTVert]

I would think a Naraku crank should last much longer, but if you want a greater chance at longevity it's best to stick with a 47mm bore next time. You'll sacrifice a little power, but it's better than walking when the next bottom end fails. I'd also prefer oil changes every 1000km or so, maybe 1500 with synthetic. I can't tell you how much difference that will actually make, but these little air cooled engines are pretty hard on oil.

[daandeurloo]

Thanks for the reply.
I'm going to install a 47mm bbk on the next engine. Still have that bbk in my garage with the stockhead and that stupid emissions thing which is not installed with the 52mm bbk.

Thinking about to remove the head to take a look at it. Since it also jams up totally sometimes when using the electric starter.
I have had taken apart a chinese 139qmb engine with only 7400km on it few years ago that had a jammed Big end bearing and that was just a 50cc . Metal Shavings everywhere.

Does the Piston pin of the 52mm fit on the 47mm piston ? I'm using the 47mm piston pin on the 52mm piston. Worked just fine for 5000~5500km. Only need to replace the piston pin clips.

Reason why i was using the 72cc piston pin on the 88cc is because i had lost the new piston pin and found it back already since today. It was in the bag of spare OEM parts from Kymco . 
 
I know a webshop where i can buy a crank for really low prive ( about 25 euro ), and a 47mm bbk for €21,95. And then engine gaskets for €5,95. So basically i can rebuild the engine for really cheap.
My 47mm bbk was also a cheap chinese thing, but worked great and almost no burning oil.

Probably also gonna replace the spark plug cable or ignition coil, also 8 euro for that. 

[Clank]

I'm speechless. 52mm with a 86 main jet! That had to be running super lean and super hot. Imo I would say you're fortunate to get 3k out of it.

[daandeurloo]

Some guy on the dutch forum is using a 82 jet for his 47mm and that's fine. No mine was not running lean at all. Spark plug a dark coffee colour, almost to black.
I was using 82 jet for my 49cc and 84 jet for my 72cc.

Air mixture screw to 2,25 turns.

Remember: My crank was already shot when this happened and had a knock in it. Probably rod knock or something like that. It was running fine while driving and nothing noticeable untill this happened.

I need to investigate how it all happened by taking off the cylinder and head.
Which i'm going to do today. First have to remove the engine for much easier working on it.

[90GTVert]

The pins for different bores may be too wide or too narrow. Try to use a pin for the intended piston.

[daandeurloo]

Tried a 50cc pin in the 72cc piston and yes it was way to narrow. But will check that with the 90cc versus 72cc to.

Just removed the engine from it's frame which was easy to do so.

There are two ways to do it:

1. Take the back panels off to for disconnecting the stator and pickup coil plugs or just remove the stator and pickup coil from the engine and let it hang on the frame. Much easier tho. Never thought about that previous time.

Just ordered new gasket set for the 47mm cylinder with the pin and circlips. Yes the pin is for a 47mm cylinder. Checked that first.


Small update:

It all looks pretty bad inside.

It has a blown connecting rod bearing and it had metal shavings on the cylinder liner at the outside and the boring is scored aswell the piston.

so Piston, Cylinder and crank is toast.
And the piston pin was pretty tight in the piston itself. It did fit properly ( atleast it did look like it did )

Gonna look for a another engine asap.

And if no engine found, then a new crank will be ordered. Actually a very cheap one since the shop said that the crank is especially made for to run with 47mm cylinders. That crank is for sale at €25,- and in some other webshops even for 60 euro. That price is rediculous isnt it ?









Edit: Took a look at a guy i know which has a chinese scooter with a 139qma engine. He told me it wouldn't start anymore, and i immediatly felt that the valves were way to tight. Actually they didn't have had any clearance left. Did set them back to 0.05mm ( .002 ? ) intake and 0,10mm exhaust ( .004 ? ). And yes it did start again, but not faster then 30km/h. Engine was knocking also and sounded like a bearing to me.

The oil itself was way to black. Did look like a oil that had been in a diesel engine for 10~15,000km atleast.

I asked when he changed the oil and he did that recently.

[daandeurloo]

I'm asking myself: Can a faulty ignition coil and spark plug wire can cause all this trouble for nothing ? I had it running for about 3 ~ 4 seconds again and died again. I had it running without exhaust system as i just had the engine installed back into the frame with the cylinder and head with old head gasket. Did still look good, but i don't preffer to do it this way. Even re-used the base gasket out of my 50cc cylinder. All though it doesn't leak engine oil so far.

Yes the piston and cylinder is scored, but dunno when this happened. It can be happened like 2 months ago and all driving with this without any big issues. It does have enough compression to start.

Used a Lithium battery in this video, so that's why it turns over that fast. It won't with a lead acid because of the compression. It does have a little bit more life in it then before

www.youtube.com/watch?v=nnoMQ-jMZI8

[spaz12]

Your timing could be off

[daandeurloo]

Hahaha no it's not. I checked that on the flywheel and camshaft and it was all good.

It did run yesterday for about a few seconds and it died again. Also the engine got stuck a few times.

There is one thing to mention: The con rod bearing is gone. I also think the two crank bearings.

I didn't wan't to take a risk with the 72cc cylinder as this one is still fine without any scratches.

I could sell that damn thing for 25 euro to someone i know. Looks a fair price to me with all new base, head and cam tensioner gasket and also new piston pin and clips.

[Fox]

If the lower con rod bearing is sloppy it stops the piston from reaching full TDC which in turn lowers compression. You are whipping a dead horse every time you hit the start button.

[daandeurloo]

Anyways i passed my motorcycle driving exam today, so it's not worth fixing anyways since i have GS500 already. I hope it holds atleast 100,000km / 60,000 miles. I heard that the con rod bearings are also not the best on these engines.

[90GTVert]

Congrats on passing the test!

[daandeurloo]

Thanks anyways.

I managed to get my Agility 50 running again with you guess it: Horrible bearing noises. No power at all when opening the throttle for a 52mm cylinder. More looks like a 49cc now.

It starts fine, but it won't idle due to those problems ( con rod and crank bearings gone ).
Installed the stock cdi back yesterday as my agility is sold. Dunno what to do with my Racing CDI right now. Probably ending up selling it or keep it once i have a another agility in a few years or so.

The lead acid battery doesn't have the greatest capacity left ( about 1,8~1,9ah out of 6 ). I can only make a few good start attempts till the battery is drained.

[diynuke]

Jan 2, 2016 6:15:34 GMT -5 daandeurloo said:

Some guy on the dutch forum is using a 82 jet for his 47mm and that's fine. No mine was not running lean at all. Spark plug a dark coffee colour, almost to black.
I was using 82 jet for my 49cc and 84 jet for my 72cc.

Air mixture screw to 2,25 turns.

Remember: My crank was already shot when this happened and had a knock in it. Probably rod knock or something like that. It was running fine while driving and nothing noticeable untill this happened.

I need to investigate how it all happened by taking off the cylinder and head.
Which i'm going to do today. First have to remove the engine for much easier working on it


i am running a jet 90 on mine 72cc with a9 cam and stock air filter and the spark plug seems around right 
92 is too rich then it starts stuttering so 90 seems about right