New Engine after 18,000 miles

[rigpa]

okay, i got a compression tester.  looks like you have to put the spark plug attachment into the spark plug hole before the compression gage hose snaps on.  I haven't actually yet done that--this weekend i will, but i took it out of the package and couldn't get the hose to snap onto the part that goes into the plug hole.  At any rate, I have some questions about new rings.  Do the new rings come at the prescribed end gap measurements?  If they are too big, how do you make them smaller, and vice versa?  thanks.

Linda

[thebatman]

hey rigpa/linda...you may need a dab of lubricant on the end for easier snapping, should snap on pretty easy tho.. the rings come already gapped from the factory..idk about adjusting ring gap,maybe somebody will have an idea there.. a few of the zx ppl have taken the summer off i think..lmao if to big, they need changing.it will allow air to seep into case, losing compression. i took my engine apart to look inside over last weekend, alls well inside my motor, should clean cyl again tho...lmao...hope any of this helps...post back and let us know whats happening....good luck...

[Hoolander2]

If you can get that spark plug hole piece on the hose first, then can always spin the whole thing round and round as you're threading it into hole.  I've had to do that at times.  Just make sure to tighten it well.  8 or 10 kicks should give you the reading then. 

New rings usually are real close on end gap.  If too big it prob means your cylinder walls are worn. In fact that's one way of diagnosing a worn cylinder.  But the new rings might still help.  Don't think there's any way to close up a gap that's too big.   

If too small then the ends of the new ring can be VERY delicately filed with like a jewlers file or fine nail file. Would have to have like a jewlers vise too.  Rings are made of very brittle carbon and will chip easily so must be patient and delicate.  You prob won't have to do this.

When dropping the cylinder back in place, you gotta squeeze the rings one at a time and feed em up into cylinder.  Can do this by hand.  A ring compressor is almost more difficult to use than the hand method on these small engines. 

Main thing is to clean the ring seats in the piston well to clean out old carbon deposits.  Use cheap jewlers screwdrivers from Wal-mart/hardware store, small knife, etc.  Careful not to nick piston outer surface too much.   

[blue]

after 11.000 miles on my agillity I got my motor re bulit it seams to be great and running good.
I would just rebult what you got you should be able to get another 18 out of it. just get new rings
a get it board out a little. and a good tune up and you should be good.

[Hoolander2]

By the way, there're other things to do/watch for in a ring job.  You might need a cylinder base gasket and head gasket.  ZX guys, does she?  And some gasket sealer.  Something to scrape old gasket material off.  A plastic knife for instance?  Some solvent of some kind to remove old sealer.  WD-40 prob work for that. 

Stuff rag into crankcase opening to keep debris from falling in there while working -- very important not to let anything at all drop in there. 

It may be easier to take piston off for the cleaning of the ring seats, though not absolutely necessary.

When you get just the head off, turn engine till piston is way down low, then feel the cylinder wall all around with fingers up and down especially within an inch or so of the top.  If it's worn badly, you can feel a bit of a ridge around the top at the level above where rings never travel.

Then check end gap on new rings by gently squeezing them down into cylinder well down in.  Must try to have the ring sitting perfectly level in the cylinder. Oil the walls first. Then can measure or judge the end gap.  If you've already got old rings off, you can judge their end gap in comparison to the new ones, though if you get that far might as well just put the new ones on.

Take the opportunity to inspect the head for carbon deposits and clean if needs it too. Also check if piston can wiggle on it's wrist pin.  Good time to replace that too if needed.  Not hard.

[rigpa]

wow guys and gals this is great stuff.  thanks.  yeah i was wondering if i need a new cylinder gasket.  i don't know if they are the rubber kind or what?  also, what do you clean off the carbon with, what kind of solvent?

[Hoolander2]

Scraping or wire brushing is main way.  Careful not to scrape or brush over gasket sealing surfaces.

[sidthesloth]

Very good write up Hoolander. With regard to gaskets, the base gasket, at the bottom of the cylinder is paper, if you cut one yourself make sure you use material of the correct thickness. When buying rings you usually get piston, rings, wrist pin, circlips, head gasket for about $30 on ebay. If you are concerned about the bore, you can buy a cylinder hone from an auto parts store. If you like this sort of thing you will find it to be fun and a good way to learn. To top it all off a sense of satisfaction when it all goes right. Good luck and enjoy your scooter. Go the ZX. :-)

[rigpa]

i'm reading the zx 50 service manual for piston ring removal and installation.  it's saying something about an expander.  when installing new rings it says first install the expander in the 2nd ring.  is an expander an installation tool.  if i'm not using one would it just mean to install the 2nd ring in the 2nd ring groove first.  is this the compression ring?  also, if i need to rebore the bore or re hone it, won't i have to get a larger piston.  i mean how do you allow for the larger cylinder?  thanks.

[sidthesloth]

The ring expander is a type of shim that goes in the groove behind the ring. Both rings are compression rings. If you run a hone through the cylinder you won't need a larger piston, if you bore it out you will.

[rigpa]

okay, does the expander just pop in or is it hard to install like the rings.  can i just reuse the old expander?

[sidthesloth]

You should get a new one with the new rings. It is easy to fit.

[thebatman]

yep, and thats how its done.....

[sidthesloth]

G'day rigpa, I have taken a pic of a piston kit I have for my scoot, it is a ZX50 but it has a 50mm cylinder kit, (82cc).
The stock piston is 39mm.
One pic shows the contents of the kit, which is 1 piston, 1 wrist pin, two circlips for the wrist pin, 2 rings and one ring expander.
In the other pic you can see the ring expander is the wavy looking item, this is wrapped around the piston in the lower ring groove, unlike the rings this is very flexible and there is no risk of damaging it. When installing the ring to this groove, make sure the expander ends are butted to the pin in the groove, not overlapped. I reckon there was a head gasket with the kit but I have already used it, hence it is not in the pic. I hope this helps.

[rigpa]

Thanks, that is helpful.  You see the ends of the piston rings and how they are not flat, the one edge seems to jut out.  Why is that?  Especially if you have to grind some off to get the proper gap.  Would you not be grinding that shape away from the rings?