Replace Piston and Rings for the first time

[To-The-Wood]

Hey ,

I'm going to replace the piston and rings in my 06 rm250 this winter. It still runs awsome but I want to do it just so I don't have any problems later on. wanna keep it fresh. This will be the first time I try to tackle this on my own so if anyone has any links or advice to make my life easier it would be much appreciated. I don't have the manual with my bike yet. The dealer is suppost to get me one.

Thanks

Chad

[Sadowski21]

My advice would be take your time and be organized don't have every part thrown all over. I would get you hands on that manual before you start your rebuild it shows step by step procedures and torque specs that will essential to you. Be sure you have all the necessary tools. I would recommend once you removed the cylinder to stuff a new shop rags in the case ( don't jam them in there just lay on top covering the the case ) it will save you if you happen to drop anything while installing piston. Be sure to replace all gaskets, and again take your time and don't rush anything.

[Aurex]

Ever hear the saying, if it ain't broke don't fix it?

My '01 250 is still on the original top and bottom end and still eats 450's for breakfast. If it starts easy, runs good and passes a compression test, why mess with it?

Also, where are you in saskatchewan?

[dirtnsnoryder700]

Ever hear the saying, if it ain't broke don't fix it?

My '01 250 is still on the original top and bottom end and still eats 450's for breakfast. If it starts easy, runs good and passes a compression test, why mess with it?

Also, where are you in saskatchewan?

Thats what I go by. Im almost positive my 94 RMX has the original piston and rings in it. Just did a compression test in the fall and i was at 195. If it starts good, runs good, has good compression and doesnt rattle, why fix it?

[BLACKHAWKNZ]

dirtnsnoryder700

TT Bronze Member

Join Date: Jul 2007

Location: New York

Posts: 117

Quote:

Originally Posted by Aurex

Ever hear the saying, if it ain't broke don't fix it?

My '01 250 is still on the original top and bottom end and still eats 450's for breakfast. If it starts easy, runs good and passes a compression test, why mess with it?

Also, where are you in saskatchewan?

Thats what I go by. Im almost positive my 94 RMX has the original piston and rings in it. Just did a compression test in the fall and i was at 195. If it starts good, runs good, has good compression and doesnt rattle, why fix it?

Because thats when the main bearings are shot, or something along those lines that you dont notice and the thing goes BOOOOOOOOM!!! and then you have a ***** bike that will cost twice as much to fix.

Every year you should do a piston and ring just to check out the barrel, movement in the main bearings and other such things as that.

We are talking about a high performance machine that do crazy rpm and designed shit light. They dont have as much tollerence as something like a good old xr 200!!

[Aurex]

There are 250's running around on the original top and bottom ends from the 80's. These "race bikes" are more reliable than most people think. Also, how often are you really wringing all the power out of a 250 anyway? Its not like a 125 where ever second of every riding day you are reving it to the moon.

[BLACKHAWKNZ]

If I ride a 250 or 125 they both rev out the same... fully open!!

If you dont maintain your bikes they are just a ticking time bomb, even worth if you are running a 4 stroke.........

[BriAnJG054]

If I ride a 250 or 125 they both rev out the same... fully open!!

If you dont maintain your bikes they are just a ticking time bomb, even worth if you are running a 4 stroke.........

agreed! change top end and then buy an hour meter. when you have 50+ hours on a 2 stroke piston you can expect to see blowby past the rings.

[Uncle Alpo]

My take on it is it depends on how hard you run it and how often you run it hard.

I wring the snot out of mine every time I ride, so I change piston & ring at least once a year. More often if I can hear the piston slapping. Every time I change it I measure piston, ring and bore; invariably the ring needs changing. For me it's cheap insurance.

[shrubitup]

have heard the OEM cast pistons tend to shatter when they wear out. hmmmm, shattered metal in your cylinder.... not fun. get a forged Wiseco and then you can forget about it longer if necessary.

[Aurex]

have heard the OEM cast pistons tend to shatter when they wear out. hmmmm, shattered metal in your cylinder.... not fun. get a forged Wiseco and then you can forget about it longer if necessary.

All the more reason to get a big-bore!!!!!!

Plus, if you rebuild every season at say 100$ rings, piston (might as well through a piston in if you're already there), gaskets, or rebuild every nth year for 600$ makes no difference.

All i'm saying is that when the motor is 7 years old, still gets awesome compresion (185-190 psi) why mess with it? When she blows, she blows.

Don't get me wrong, its nice to catch these things before they go. But they usually blow-up for a reason. Poor fuel, clogged jet in the carb, or infiltration of dirt into the cylinder.

I don't want to start an arguement here, so, if you think it's time, rebuild it. If you're satisfied with the things are leave it alone.

[shrubitup]

ya but,

shattered (cast OEM original) piston in the cylinder almost always makes its way into the low end. then, the rod breaks or at least the crank seals go. split the case, whole new rod, big hassle and cost. sure, he'll have to do a bottom end when it dies from old age but why rush the schedule?

[To-The-Wood]

I'm from Foam Lake, You?

[To-The-Wood]

I know the motor was redone just before it was parked for the season. Like you guys said, cheap insurance. My plan when I baught this bike was to do the piston and rings once a season. It will get done. Just looking for some help is all.

[Aurex]

I'm from Foam Lake, You?

Regina....the city that rhymes with fun.

[To-The-Wood]

I've heard Regina has a mint track. I just started riding tracks last year. I'm catching on quick. I love it. I'm going to try a few races this year. I'll try beginner a time or two and probably go with the juniors. We'll see. I just got this two stroke and it's taking some time to get used to it. I was way faster on the track with my 450 but they cost to much to fix.

[Aurex]

You've heard right. It's pretty decent. I only got out once last year. Generally you want to avoid it until it has been groomed after nationals. it gets really rutted up and harder than rock. Actually to be honest, I would rather crash on rocks.

I got ten laps in last year and then cased a double. Result, broken toes, bent bars, broken levers, broken chest protector. I wasn't even going that fast either!

When they do groom it, it's pretty awesome though.

[B_Brad]

11 TIPS FOR REBUILDING A TWO-STROKE TOP END

Before you disassemble your engine, power-wash the engine and the rest of the vehicle. That will reduce the risk of dirt and debris falling into the engine. Once you remove the cylinder, stuff a clean rag down into the crankcases.

The cylinder and head use alignment pins to hold them straight in position from the crankcases on up. The pins make it difficult to remove the cylinder from the cases and the head from the cylinder. Sometimes the steel alignment pins corrode into the aluminum engine components. Try spraying penetrating-oil down the mounting studs before attempting to remove the cylinder and head. Never use a flat-blade screwdriver, chisel, or metal hammer to remove the cylinder. Instead use this technique; buy a lead-shot plastic mallet, swing it at a 45-degree angle upwards against the sides of the cylinder. Alternate from left to right, hitting the sides of the cylinder to separate it from the cases evenly. Clean the steel alignment pins with steel wool and penetrating-oil. Examine the pins closely. If they are deformed in shape, they won't allow the engine parts to bolt together tightly. This can cause a dangerous air leak or a coolant leak. The pins are cheap at about $2/£1 each. Replace them if they're rusty or deformed.

Never re-use old gaskets. Remove them with a razor blade or gasket scraper. Don't use a drill-driven steel wool type pad to remove old gaskets because they can remove aluminium from the cylinder and head. That will cause a gasket to leak.

Always check the ring end gap on a new ring by placing it in the cylinder between the head gasket surface and the exhaust port. The gap should be between .012 to .024 inches.

Always install the circlips with the opening facing straight up or down, that way inertia will hold it tight into the clip groove. Place one clip in the groove before installing the piston on the connecting rod. Its easier to install a clip with the piston in your hand rather than on the rod. There also less chance that you'll drop the circlip in the crankcases.

Always install the rings on the piston with the markings facing up. Coat the rings with pre-mix oil so they can slide in the groove when trying to install the piston in the cylinder.

Always install the piston on the connecting rod with the arrow on the piston crown facing towards the exhaust port.

The traditional way to assemble the top end is to install the piston assembly on the connecting rod, compress the rings, and slide the cylinder over the piston. That can be difficult with larger bore cylinders, or if you're working by yourself. Try this method instead. Install one circlip in the piston, install the piston into the cylinder with the pin hole exposed, install the piston pin through one side of the piston, position the cylinder over the connecting rod and push the piston pin through until it bottoms against the circlip, install the other circlip. It only takes two hands to install the top end using this manor and there is less chance that you,ll damage the rings by twisting the cylinder upon installation.

On cylinders with reed valves and large oval intake ports, take care when installing the piston assembly in the cylinder because the rings are likely to squeeze out of the ring grooves. Use a flat-blade screwdriver to gently push the rings back in the grooves so the piston assembly can pass by the intake port.

For steel head gaskets, place the round side of the "bump" facing up. Don't use liquid gasket sealer, use aerosol spray adhesive types instead. For hybrid fibre/steel ring head gaskets, place the wide side of the steel rings facing down.

When you initially start the engine after a rebuild, manipulate the choke to keep the engine rpm relatively low. Once the engine is warm enough to take it off choke, drive the vehicle around on flat hard ground. Keep it under 2/3 throttle for the first 30 minutes. Two common myths for proper engine break-in are:

Set the engine at a fast idle, stationary on a stand.

Add extra pre-mix oil to the fuel. When the engine is on a stand it doesn't have any air passing through the radiator and it is in danger of running too hot. When you add extra oil to the fuel you are effectively leaning the carb jetting. This can make the engine run hotter and seize.

*this complete article was blatantly stolen from Eric Gorr, gotta love the internet!

[To-The-Wood]

great post. thanks

[NVDESERTPETE]

Hey ,

I'm going to replace the piston and rings in my 06 rm250 this winter. It still runs awsome but I want to do it just so I don't have any problems later on. wanna keep it fresh. This will be the first time I try to tackle this on my own so if anyone has any links or advice to make my life easier it would be much appreciated. I don't have the manual with my bike yet. The dealer is suppost to get me one.

Thanks

Chad

If you follow the manual they want you to change piston and rings every 12 hours! Yeah right! I've got an "05" RMZ450 with 130+ hours on it and just routine maintenance. My "07" RM250 has been out every weekend since I bought it at the new model year and still puts out the ponies. Compression or leak down test (4 strokes) can determine engine condition. If you're worried about cylinder wear have it Borescoped. There's all kinds of cheaper alternatives besides throwing money at a non-existent problem. I tend to agree with some of the other posts...If it aint broken don't fix it.