Question about Suzuki RM 250 Motorcycles
I have an 85 rm 250 my bike stopped running and was leaking coolant from the bottom of the cylinder.
A coolant leak from the bottom of the cylinder indicates a blown base gasket. easy fix if you have a manual and some mechanical knowledge.
If you lost all you coolant, you may have also seized the piston.
you will require a top end gasket set, and most-likely a piston kit (Now is probably a good time to freshen that up anyway.)
If the engine was running good you probably did not get any coolant in your engine which is good.
-here is an idea of what is involved
(label everything and keep it nice and clean)
1) clean your bike good. You do not want dirt in the engine.
2) remove seat, fuel tank, rear subframe, and the pipe. This should give you easy access to everything.
3)drain whats left of your coolant into a bucket, the drain is usually one of the lower bolt holes on your impeller cover . A copper washer might give it away.
4) remove the carb from the boot going into your engine. the carb can stay connected hanging out of the way on its cables.
5) remove the cylinder head
6) remove any exhaust linkage covers if so equipped, and the screw holding the linkage. there may be a hole that will line up with a slot in the arm/clip. Use an appropriately sized drillbit to stop the thing from turning on you. Be careful, these are fragile (on Yamaha's anyway)
7)remove the 4 nuts holding the cylinder on. you should now be able to slide the cylinder off of the piston.
Inspection & cleaning
Inspect the piston for any rough metal, scrapes or gouges. same with the cylinder. if damaged it will need to be replaced. Iron sleeved cylinders can be bored out 1 size and honed, nikasil can be cleaned of minor aluminum deposits with muriatic acid (don't get this on your skin) or will need to be replaced as a unit. Make sure there is no coolant inside the engine case. Crank should turn over smoothly with the bike in neutral.
Clean the old gasket off of the cases where the new base gasket will go. A plastic putty knife does wonders. make sure you get it all off, DO NOT use metal on the sealing surfaces. gasket remover can be used, but don't get any into the engine, and avoid using it where the bottom case halves are joined. Then stuff a rag in the case to keep it clean in the meantime.
Repeat the process for the cylinder, bottom and top if necessary.
Check with your dealer for torque specs.
The piston kit should have instructions. Remove 1 circlip (don't lose it in the engine- (rag is in there right?). Slide the wrist pin out (long socket+ light tapping on it from the opposite side if you don't have a puller). CAUTION: I do not know if the wrist pin bearing is caged or not (check the new one when you get it) if it is not a caged bearing all the little roller pins will fall everywhere if you are not carefull. There is like 25 of them!
Now remove the piston, leaving just the rod. Prep the new piston (gap and install rings...line up gap with ring keeper pin...also, pay attention to orientation...some have an angle on the upper side of the ring. Install one of the circlips, rotate it so the gap does not line up with the hole, gap should be up or down not sideways. Install the wristpin bearing in the rod, slip on piston (usually arrow points to exhaust port...check instructions). now lube up the wristpin bearing and pin, slide pin through, and install the 2nd circlip.
Remove the rag, add a capfull or two of 2stroke into the bottom at this point. use a little break cleaner on a rag to make the gasket surface is clean.Throw down the new gasket. Line up ring in groves, Squeeze with one hand, and slide the cylinder down the piston. Once partway up, rotate the crank so the cylinder lines up with the studs. tighten nuts appropriately. Rotate it slow by the kickstart with the kilswitch held in the off position. Everything should be smooth. With the piston at the bottom throw a few capsfulls of oil in it to lubricate it as you rotate it through slowly. now clean the top, install topend gaskets and the nuts. Reassemble the bike in reverse order, make sure the carb is on tight, and don't forget to ADD COOLANT at proper ratio. Break in mix is gonna be 15:1 or 20:1 somwhere in there, for the first few hours riding anyway. Vary the throttle lots don't be afraid to run it though, just don't hold it WFO for more than a few seconds till everything gets happy. also, Especially when using FORGED pistons. Make sure the first time you start it, only let it idle, don't ride it. Let is get all the way up to temp, then let it cool completely. Do this heat cycle twice.
then continue normal break in.
I don't think I left anything out. Good luck.
Posted on May 20, 2009
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Posted on Jan 02, 2017
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