Locked Up

[biglong350]

My dirtbike locked up on me. the basics. its a 97 rm 125. i havent done any major work to it just the basics. i was riding home on the dirt road from my buddys and i was almost home and it died. it locked up. after i got home i let it sit, went back out and it kicked over. hardly no compression. now i know its going to need a top end. but should i dig deeper? do you think there could be a problem in the lower end? i need help!?

 

[TRexRacing]

Pull the top end and check the crankshaft.As old as it is a full rebuild may be the ticket.Ain't gonna be cheap but neither is a new bike.

 

[biglong350]

well i will only be able to see the top of the crank, how can i tell if everything is good down there?

 

[John.Jr]

Go ahead and do a top-end job on it make sure you check the rod for play at the crank, if it okay Iwould say you are fine with a new top-end,thats my 2 cents,good luck

 

[biglong350]

how do i check for rod play at the crank?

 

[biglong350]

and how do i do crank seals? i heard those can lean it out and cause this problem? do i have to split the case to do it? i just want to do the one on the left as i hear its the one that can cause this problem...

 

[rmc_olderthandirt]

The first step is to pull the cylinder off and inspect. Until you get it apart you can't make any reasonable estimates.

If you get it apart and find that the piston has broken into pieces then where those pieces went, getting them out again and what damage they may have caused are all issues best dealt with by splitting the case.

If the piston is basically in one piece then you can do a visual inspection of the rod. When it locks up at high speed the sudden stop can result in a bent rod or damaged bearing. With the crank held still the rod should slide side to side a bit but it shouldn't move up/down any at all.

 

[biglong350]

alright cool, when you say side to side, how much is that meaning? like 1/4 inch etc.. is there any oil down there for the crank to ride in? if so where is the drain and refill for it? how do i know if the rod bearing on the lowerd end is good? i can just feel for it?

 

[John.Jr]

Hey Big the crank should have a SMALL amount of side to side play AND NO up and down play what so ever if so the crank bearings are shot.The drain plug is on the bottom of the engine, put the CORRECT Socket on it so you wont round the nut,refilling the motor on the top right side near the kick starter should be a large twist type of screw( black in color ?) check with service at your local motorcycle shop for correct amount of oil when refill I hope I can help you, John, keep me informed

 

[rmc_olderthandirt]

Hey Big the crank should have a SMALL amount of side to side play AND NO up and down play what so ever if so the crank bearings are shot.

Much more likely the rod (journal) bearing, not the crankshaft main bearings.

The drain plug is on the bottom of the engine,

I am pretty sure a RM 125 is a two stroke, hence there won't be a drain plug for the engine case, it would be for the transmission.

With a two stroke the only oil in the crankcase is carried in with the gas. There will be a light coating of oil but there will not be any "pool" of oil. If you are not careful you can end up dumping some water down in the crankcase as you take the cylinder off. If that happens you will need to get it out before you reassemble.

 

[spark250]

alright cool, when you say side to side, how much is that meaning? like 1/4 inch etc.. is there any oil down there for the crank to ride in? if so where is the drain and refill for it? how do i know if the rod bearing on the lowerd end is good? i can just feel for it?

Dude......

maybe you shouldn't be taking on a job like this. Get a service manual at the LEAST!!!!

Not to be a jerk but if you don't know the basics of a 2 stroke engine maybe you shouldn't be splitting cases