| Author | Message | ||
     Reepicheep |
(Sorry for the off topic question, that's why I put it on the quick board)... On another forum (KDX forum), there was some good discussion about how a user should not have reused old circlips for his piston. He ignored the advice, and it took about 30 minutes for his engine to seize up. I was in the "don't reuse circlips camp"... not because I think it *can't* work, but because it's just not worth the risk for $5 worth of parts. And because those circlips seem: (a) pretty tuned to a specific piston... so I would want my piston seller to be providing my circlips as well. (b) really minimal... not much steel there, and they have a really important job, and their temper (or whatever you call the ability to stay "springy") not to mention their vulnerability to being stretched or squished (You have exceeded youngs modulus. You will never be the same.). Anyway, don't reuse circlips seems obvious enough. But what about reusing rings? Remember, this is a two stroke, not a four stroke, so to check top end condition I can (literally) remove one motor mount, four jug bolts, a spark plug wire, and two radiator hoses, and I can lift the jug / head off together as a unit. A 20 minute job. I can then inspect the head, the bore, the piston, the rings, and look for crank play. I have (and would like to again) be able to do this for a used bike I have bought just to "know" that the new piston the previous owner claimed to put in was put in and put in right. All is well and good, I don't have to remove circlips for that. But somebody else over there is claiming that the rings can't be reused either... even if they never came off the piston. I'm calling BS, but am open for people that know what they are talking about for a second opinion. Seems to me rings are designed to float and expand and contract. I don't see why pulling the piston out of the jug would somehow magically ruin them. You just have to re-align them on the pin before you put it back together. Thoughts or experience anyone? | ||
| Fast1075 |
If they are in good condition and the end gap is within spec...reuse 'em...otherwise replace 'em....there are most likely only two rings (and in some cases only one ring) in the set...can't be very expensive...be sure to check for cylinder wear and if you replace the rings, light hone if the cylinder liner is iron...also check the ports for sharp edges that may need to be deburred... | ||
| Nik |
On my old two smokes I did inspections and decoking like you're talking about and never changed the rings, unless as a result of said inspection I had to do a hone or full rebuild. | ||
| Sifo |
Not sure why you want to do the tear down in the first place. Remember, this is a two stroke, not a four stroke, so to check top end condition I can (literally) remove one motor mount, four jug bolts, a spark plug wire, and two radiator hoses, and I can lift the jug / head off together as a unit. A 20 minute job. I can then inspect the head, the bore, the piston, the rings, and look for crank play. If you have good compression you have just checked the head, bore, piston, and rings in an indirect way. Any reason to be suspect of the crank play? I say if it aint broke, don't fix it! If you really feel the need to "fix" it you can probably get away with reusing the old rings. I just don't see the need. | ||
| Reepicheep |
I only tear down on an "unknown" bike that has been bought used. My neighbor guilted me into doing it when I bought a 95 KDX-200... I wasn't going to.. . it had good compression, but was otherwise a pretty ugly looking bike. I pulled the top, and sure enough the piston had a big old crack up the skirt, and the jug was scored pretty badly. So now I'm paranoid... especially when less then an hour of tear down, check, clean and reassemble can let me know absolutely and positively what everything looks like. I just got a used KX-60 for my kids. The seller claims "brand new piston, not even broken in yet". But he also said "looks new", and looking at the bike, you can tell the man was an optimist  | ||
| Fast1075 |
Over the years I have seen a LOT of bikes that came in the shop where the guy had just bought it used....invariably the story went "it was just rebuilt and just needs a good tuneup"...(Somebody has the engine rebuilt and doesn't "tune" it???) In more cases than I can count...the engine was trashed...utterly trashed... It is far better to question and check it out...especially if all you will need is a base gasket and "maybe" a head gasket to confirm the condition...oh yeah...make sure the air filter is in place and in good shape....more motors are ruined by ingestion of silicates than any other reason...very hard on the piston/cylinder and crank/rod bearings in a 2 smoke....I built a lot of cranks from CR-250's that died from a single Sunday at the track with an air filter problem than you can believe... | ||
| Mnrider |
On most 2 strokes you can take the exhaust off and see the piston,most damage is on the exhaust side of the piston. | ||
| Reepicheep |
Thanks! Got a new dirt bike for the kid, and have to figure out when to work on it so the kid doesn't wander into the garage and bust me....  | ||
| Oldog |
Reepi, there is a camp that says when the rings are initialy installed and run in, they match the bore precisely, If you disturb them then they dont, My experience in the past with small "thumpers" 2 & 4 stroke so long as the bore, piston and rings are OK its just fine. the will I guess just run back in, I just had the top end off of the X1 and honed and re-ringed the rear jug it has good comp and runs fine, I did it Just incase there were issues with oil control rings, on a toy bike run it, I like you do not re-use wrist pin clips. I buy them by the dozen cause I manage to drop em Have fun... | ||
| Fast1075 |
On a 2 smoke, the rings are pinned in place so there is no worry about ring location. | ||
| Aesquire |
Unless wear or damage call for replacement, and you are not honing the cylinder, sure, reuse. Fresh hone, fresh rings, IMHO. Give everything a chance to break in together. We took my buddies RD400 apart in his kitchen one winter, he said it was a bit weak, his last run. Looking in the exhaust port, looked good. Pop the jugs off, and he's looking at the pistons, muttering about carbon build up while I checked out the jugs. "Dude, this side's trashed" I tell him, then look at the pistons in his hands. "Aren't there supposed to be 2 ring grooves on both of those?" The whole top of one piston down to the first ring groove was gone. The head on that side looked like someone tossed a hand full of dimes into a running engine. I'm amazed to this day it was ridable. When his wife got home, I had to leave......quickly! |
