Posts
498
Joined
12/2/2016
Location
SE
Fantasy
2195th
Edited Date/Time
9/20/2019 9:12pm
I normally race a 16 rmz 450, but on Saturday the rod seized to the crank. I got out of it lucky, with no crash and no other evident damage.
Problem is I have a team race on both sat/sun this weekend. I decided that I didn't have time to fix the RMZ, so I started getting a RM125 that I bought last year ready.
I have never ridden the 125 since I bought it and I spent the last 3 days getting it race ready. I took it for a test ride tonight, it lasted 8mins at a sand track.
I melted the front of the piston, damaging the cylinder.
I stupidly never check how the bike was jetted. Fuel was mixed at 32:1
With only 2 days before the race, I was wondering if you guys think I could clean up the cylinder with some sand paper and just put a new piston in? Ultimately I will get a new cylinder and piston,
Do you guys think this damage it too bad to get away with just the piston and a clean up of the damage?
Problem is I have a team race on both sat/sun this weekend. I decided that I didn't have time to fix the RMZ, so I started getting a RM125 that I bought last year ready.
I have never ridden the 125 since I bought it and I spent the last 3 days getting it race ready. I took it for a test ride tonight, it lasted 8mins at a sand track.
I melted the front of the piston, damaging the cylinder. I stupidly never check how the bike was jetted. Fuel was mixed at 32:1
With only 2 days before the race, I was wondering if you guys think I could clean up the cylinder with some sand paper and just put a new piston in? Ultimately I will get a new cylinder and piston,
Do you guys think this damage it too bad to get away with just the piston and a clean up of the damage?
Either that, or you wasted the cylinder because of the jetting (if it's actually off.) Either way, I'd say you need to find a new cylinder or get that one replated before you reassemble the engine.
It will clean all of the embedded aluminum left from the piston that is stuck into the bore. Looks pretty hammered ,though.
Obviously I want to make sure I don't ruin the new piston/cylinder. I have checked the jetting,
#400 main
42.5 pilot
6CHY17-65
3rd clip from the top
Air screw one turn out
These settings don't seem that far off #370 is the standard main jet, and the pilot is standard. Clip is in the middle, I don't see how this could be the problem.
I fitted a pro circuit pipe and shorty muffler. Can any experts tell me if I'm wrong? It's been 17 years since my last 125.
The Shop
Scratching my head a bit as to why this happened. I looked at the piston through the exhaust port before I rode the bike and it looked fine.
Yes, it was mixed at 32:1
I'm starting to feel more and more like your cylinder was already ruined when you got the bike.
Take a short test ride after you get it all back together and then check the spark plug. You should have a nice tan plug. (In your case, it will probably even be black, which is safe but not as fast.)
I will get a new cylinder and piston, then I will do a leak down test, just hoping the crank seals are good. Maybe there is an air leak at the reed block?
At some stage the chain has come off and smashed the crank case. The previous owner has put some sort of metal putty to repair it. As this is part of the gear box I don't think it would have any effect on the engine.
I thort i got a bargain, as it looked like a very clean 07 rm125, no play in the foot pegs or kick starter, the rims are still shiny and Excel print is still fresh on them. I only paid $1150 for the bike. I rode 3 laps on it at the time I bought it, it felt strong so I didn't hesitate, but now I'm going to be into the bike for more than its resale value
O'well, maybe another rm125 build on vitalmx in the making
Using castrol power 1 oil.
I would have liked to run motul 800, but my local shop didn't have any.
I ran 32:1, but once I get it back together I think I will run 40:1
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