94lt1

Member
May 11, 2006
6
0
Okay I did a search and I have learned alot about bikes on here. This is my first bike and I am pretty green on it actually it is my second bike but the first one (81 yz250) needs a piston and rings before it can be ridden. My 88 RM125 was "supposedly" rebuilt about 8-10 hours of riding ago but I am not able to get it running after quiting on my brother the other day while riding. It just chugged and quit and wouldn't start again. I did a comrpession test and I got 105 Psi and 140 psi after putting oil in the cylinder. shouldn't it spike higher than that with the oil in it? I also get a weird sorta of backfire but not a typical back fire after about 5 kicks and it sounds like a fluid "psst" sound not a regualr backfire sound. I am getting spark and I am getting fuel so I am to assume it is a compression problem. I am just wondering why after only 10 hours it might have a compression issue after a professional shop rebuild? Does it sound like I need new rings already? I was running 32:1 so I don't know why it would have worn that quickly and I don't ride hard at all. Do anyone have any specs for this motor or bike at all? (yes I know I need a service manual but I don't have one right at the moment! LOL!) Ran fine before it quit on us. Got it running again once and it went part way down the road before it just quit again and will not start again after many many kicks.

P.S. yes I did do the test properly with the kill switch pressed and the throttle wide open
 

94lt1

Member
May 11, 2006
6
0
Spark Plug is brand new and gapped properly and the filter looks clean. Just wondering why I am getting such low compression numbers when it only has about 10 hours on it?
 

just_a_rider

Member
Jul 25, 2006
394
1
A bike that old I wounder if any one has ever cleaned out the tank? Could be trash in the gas shut off screen. The bike should have great compresion after a rebuild with only ten hours on it. I remember when I rebuilt my 85 125 years ago, there was a noticable difference in the compression just from kicking it, thats pretty low compression. Are you absolutely sure it was rebuilt? I know people that will tell you any thing just to get rid of something.
 

94lt1

Member
May 11, 2006
6
0
Well I can't verify but he did give me the name of the shop that did the work. The funny thing is it would kick once and fire right up until it just quit then I had a horrible time restarting it. I did put some new gas in it and it quit after that making me think it was a piece of dirt in the carb that was preventing it from starting since it did not have a filter on the fuel line. I cleaned the carb again after that and it still won't start. I think I will fiddle with it some more before I tear it apart. Cover all the basics before tearing into it. Just confusing for me since it was running fine right before it quit on us. It was not being ridden hard at all.

Oh and I did have a pretty fouled plug which I did change for a new one and it still won't even try to start. The funny "psst" sound out the exhaust every 3-4 kicks was making me think the timing might be off on it.
 

94lt1

Member
May 11, 2006
6
0
Update! I have taken the piston out and it was definately cold seized (not by me!) I know who did it and I am not impressed but what can I do. My next question is it is a wiseco Pro-lite 568M05500 which is 1.00 over. Do I need to rebore the cylinder? It looks scored but I can't feel them so I think it might be just scratched. Can I just re0hone and replace with the a new version of the same size piston and rings? How oversized can you go with these engines?
 

bad96z71

Member
Feb 25, 2006
93
0
i would just try to hone it as long as they are not deep gouges you will be fine lite scratches wont hurt much more than likely they are just visable
 

QKENUF4U

Member
Nov 13, 2005
236
0
easy way to see if its nikasil or steel sleeve, put a magnet on it. if it hold strong then its steel if it holds very litely then its nikasil.
im not sure if thats a nikasil cylinder but if it is then have a machine/bike shop BALL HONE it and put in new piston/rings. (have them check the bore size and make sure you have no big scratches/gouges etc)
if its a steel sleeve then it can be bored a couple times (usually in .5mm sizes.) just make sure you have the piston/rings to go to the machinist to match up the bore to piston
 

IZ 250

Member
Apr 30, 2006
33
0
That cylinder is a steel sleeve. I know because I have a 88 rm 125.
Mine also cold seized. But she still runs and has awesome compression. When you have it apart clean up the ports because there nasty from the factory with casting marks. If I were u id just bore it to the next size put a new piston and ring in it and run it. Good Luck.
 

TimberPig

Member
Jan 19, 2006
859
1
IZ 250 said:
That cylinder is a steel sleeve. I know because I have a 88 rm 125.
Mine also cold seized. But she still runs and has awesome compression. When you have it apart clean up the ports because there nasty from the factory with casting marks. If I were u id just bore it to the next size put a new piston and ring in it and run it. Good Luck.

Are you sure it hasn't been sleeved? By 1988, I believe they had gone to a boron composite plating similar to Nikasil. Either way, his could have been sleeved as well, which is why he needs to confirm which he is dealing with.
 

94lt1

Member
May 11, 2006
6
0
It defiantely looks like it is a sleeve. I can see the insert color difference in the cylinder. I will check tonight with the magnet to see for sure what it is. I have some discoloration on the marks in the cylinder and some high spots but I am 90% sure it is piston material. It was a wiseco piston 56805500 and the piston has material gouged out of it.
 

94lt1

Member
May 11, 2006
6
0
well to dig up an old thread I got back into my bike since spring is coming and sure enough the cylinder has a steel sleeve but I did notice a crack in between the exhaust ports on the sleeve. Now is there a way to fix that without a resleeving? It was just recently rebuilt before the cold seize and I am hoping I don't have to resleeve it already but the crack doesn't make me feel that good feeling!
 

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