98 rm250 compression PSI?

cjd294
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cjd294
Edited Date/Time 8/7/2021 11:59am
I looked thru the forum, didn't find anything, maybe I missed it, but anyways..
I'm new to the 2 stroke world so bear with me pls!

Does any1 happen to know what the compression psi should be on this bike? I just bought this bike yesterday. Guy I bought it from had it for 3 yrs, said he rode it only a couple times and doesn't know when it was rebuilt last. It has a bit of a ticking sound at idle, I've read that could be piston slap? Indicating it needs a top end rebuild. I did a compression test, 3 times. Came up with 138psi evertime. Now my question is is the compression in range of what it's supposed to be? Should I do a top end anyways just to be safe?
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kb228
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kb228 7/25/2021 5:09pm
7/25/2021 5:09pm
Not sure for that specific bike but 250s should be in the 180-210 range when freshly built
cjd294
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cjd294 7/25/2021 5:14pm
7/25/2021 5:14pm
kb228 wrote:
Not sure for that specific bike but 250s should be in the 180-210 range when freshly built
So then it is a bit low on compression most likely. Also I've tore it apart a bit and I can put my finger on top of the piston and move it around a couple mm in every direction....
kb228
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kb228 7/25/2021 5:58pm
7/25/2021 5:58pm
kb228 wrote:
Not sure for that specific bike but 250s should be in the 180-210 range when freshly built
cjd294 wrote:
So then it is a bit low on compression most likely. Also I've tore it apart a bit and I can put my finger on top...
So then it is a bit low on compression most likely. Also I've tore it apart a bit and I can put my finger on top of the piston and move it around a couple mm in every direction....
Yep youll need to measure the piston and bore to see if you need to send it off for replating.
cjd294
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cjd294 7/25/2021 6:04pm
7/25/2021 6:04pm
kb228 wrote:
Yep youll need to measure the piston and bore to see if you need to send it off for replating.
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't I? Lol

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walent215
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walent215 7/25/2021 7:05pm
7/25/2021 7:05pm
kb228 wrote:
Yep youll need to measure the piston and bore to see if you need to send it off for replating.
cjd294 wrote:
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't...
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't I? Lol
No
I just rebuilt a 98 and it wasn’t too bad at all
Biggest expense was sending to millineum
sandhills
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sandhills 7/25/2021 8:02pm
7/25/2021 8:02pm
cjd294 wrote:
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't...
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't I? Lol
Do you mean up and down play? Side to side play is normal just in case you weren't aware.
cjd294
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cjd294 7/25/2021 8:17pm
7/25/2021 8:17pm
cjd294 wrote:
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't...
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't I? Lol
sandhills wrote:
Do you mean up and down play? Side to side play is normal just in case you weren't aware.
I mean a little bit of up and down play. Barely noticeable, but there is alot of side to side motion, like in an arc not straight side to side...know what I mean?
sandhills
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sandhills 7/25/2021 8:33pm
7/25/2021 8:33pm Edited Date/Time 7/25/2021 8:39pm
cjd294 wrote:
I mean a little bit of up and down play. Barely noticeable, but there is alot of side to side motion, like in an arc not...
I mean a little bit of up and down play. Barely noticeable, but there is alot of side to side motion, like in an arc not straight side to side...know what I mean?
I know what you mean but I still think that might be normal. I'm not exactly qualified to say I'm only moderately experienced with my yz125. Mine does have side to side play like it rocks back and forth in an arc like you describe and afaik that's normal.

I believe a more definitive test for up and down play is a timing micrometer in the spark plug socket and you look for a hang while hand rotating the stator back and forth. Mine has what I would also describe as barely perceptible up and down play when I'm tugging on the crank that I can't tell if is real or not but no hang or dead spot on the micrometer and it's running fine.
cjd294
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cjd294 7/25/2021 8:46pm
7/25/2021 8:46pm
kb228 wrote:
Yep youll need to measure the piston and bore to see if you need to send it off for replating.
cjd294 wrote:
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't...
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't I? Lol
walent215 wrote:
No
I just rebuilt a 98 and it wasn’t too bad at all
Biggest expense was sending to millineum
Walent215 any chance you would know how much play is acceptable in the connecting rod? Mine has quite a bit of side to side arcing motion in it. Barely perceptible up and down play
LKHill
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LKHill 7/28/2021 6:04am
7/28/2021 6:04am Edited Date/Time 7/28/2021 6:04am
cjd294 wrote:
So then it is a bit low on compression most likely. Also I've tore it apart a bit and I can put my finger on top...
So then it is a bit low on compression most likely. Also I've tore it apart a bit and I can put my finger on top of the piston and move it around a couple mm in every direction....
If it was even a mm you would have broken a skirt by now. Just sayin'.
LKHill
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LKHill 7/28/2021 6:12am
7/28/2021 6:12am Edited Date/Time 7/28/2021 6:13am
cjd294 wrote:
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't...
Cylinder is scored aswell, connecting rod has play in it. Looking like a complete rebuild. Man I just took to the cleaners on this buy didn't I? Lol
Maybe I am not seeing it but that cylinder looks usable. I would measure it just to make sure. TBS it's not perfect but the bike was still running and you don't have aluminum wiped everywhere. The connecting rod is supposed to have play.
kb228
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kb228 7/28/2021 8:50am
7/28/2021 8:50am
There should be zero up and down play. If there is your connecting rod bearing is shot and the crank needs rebuilt. The crank assembly is a press fit which means absolutely zero play. ~1/8” side to side is acceptable.
LKHill
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LKHill 7/28/2021 10:54am
7/28/2021 10:54am
kb228 wrote:
There should be zero up and down play. If there is your connecting rod bearing is shot and the crank needs rebuilt. The crank assembly is...
There should be zero up and down play. If there is your connecting rod bearing is shot and the crank needs rebuilt. The crank assembly is a press fit which means absolutely zero play. ~1/8” side to side is acceptable.
The play could be caused by the small end bearing and piston pin being worn out. That does not require crank work.
cjd294
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cjd294 8/7/2021 11:59am
8/7/2021 11:59am
Thanks for all the replies everyone. Upon further inspection and talking to a bike shop, the cylinder is getting sent out for machining and replating, the crank is getting sent out to be rebuilt aswell. 5-6 weeks before I get it back 😭

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