New cylinder eating rings!
 

So I got a new Italkit cylinder kit for my Hyosung Sense 2T. Installed it, tried to start the scooter, and it ran poorly for a little while then made a loud click from the engine and stopped.

Took it all apart, found a broken top ring. Replaced the ring, put it all together again, started, ran ok, took it for a test ride and it ran around fine for a while. Then I left the back roads and tried to get it up to around 50km/h; again loud click, sputter, dead, compression gone. Probably another broken ring! >:

I didn't see anything wrong with the inside of the cylinder when I took it apart. Could the porting be done wrong or something? I didn't have any trouble installing the cylinder, and everything went together fine with no parts out of place. WTF is wrong with this thing!?

Each time you install rings you must 'ream' the cylinder (hone) walls, even if you are using a brand new cylinder (jug).

Also have you verified your low-end is okay (crank, rod and crankbearings) as excessive play in the bearings can cause a crankshaft to wobble, thus killing the rings (among other stuff).

Lastly is your oil-feed working correctly as oil-starvation is the #1 cause of 2t engine problems.

Hmm, had no idea a new cylinder needed to be honed. What is the procedure for that?

The bearings seemed ok when I had everything apart, no noticeable play.

Oil feed was working fine with the old cylinder, and I never took apart any of the oil feed system, so it should still be working fine.

Thanks for the tips!

some were on one of the ports got a sharp edge. need to chamfer the ports.

So just a light touch with a stone on the dremel around the upper edges of the ports? Can they be chamfered too much?

I wouldn't do that.

Go get one of these and do it right. :tup:

http://farmallparts.com/products/photos/2_235531.jpg

Proper ring-end gap.

Lol, yea, I won't be honing the cylinder with a dremel! That was about chamfering the ports.

Thanks, will give that a look too.

All the ports you need to take a file to and kind of round the sharp edges if not the ring catch on them and cause damage

When I was a kid I had a james motorcycle that had a very worn villiars engine in it. At the bottom of the stroke you could wiggle the piston sideways about an 1/8th of an inch. I used to replace rings with some for a briggs engine every 2 or 3 weeks.

At the top of the stroke there will be a ridge that has to be removed if it is there. Then as mentioned a ring can catch on a port. Also the ring gap has to be right. Put the ring in the cyl, use the piston to get it square and then put a feeler gauge in the gap. measure at the top of cyl and at the bottom where it would be if it was in the piston. Your manufacturer will have the numbers to go by, If the gap is too large the cyl would need either replacing or boring. If it is too tight you may have the wrong size rings. They can be filed if it is only a few thousands. And there are better instructions on the internet for doing this.

i dont know were you live...but if by any chance you are in pa or nj bring the jug to my shop and i will ball hone it and port it...sorry thats the best way i could help ya out......thanks...buford.

Thanks all, this all sounds like way more work than I was anticipating.

I thought the process was:

1. Buy new cylinder, piston, rings, etc. from scooter shop.

2. Install cylinder parts, decarbon old head, make sure gasket surfaces are in good shape.

3. Put everything back together.

4. Break in engine.


Howcome nobody ever mentions doing this honing/porting stuff when talking about BBK installs?

Anyway, I will probably just sell it, not too fond of the scooter from the start anyway. I just bought it because it was cheap, and figured it would be easy to work on like other scooters I have owned, but due to the design of the welded in underseat storage compartment, it is a PITA to work on the engine.

Going to start looking for something with better aftermarket parts support, like a Zuma, or maybe another chinese scoot. Finding parts for this Morini motored Hyosung is not fun!

Thanks for the offer Buford, but I'm on the West coast in Canada.

People don't mention honing on a bbk install because it's new. It's when you replace the rings on a used cylinder you have to hone it. New cylinder and new rings means honing shouldn't be necessary if they're quality units.