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JW381
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JW381 4/1/2014 2:29pm
4/1/2014 2:29pm
Lowlander wrote:
Warm it up on the stand until top of Radiator is warm to touch. Then let it cool down. Check your coolant level at this point...
Warm it up on the stand until top of Radiator is warm to touch. Then let it cool down. Check your coolant level at this point and it might need to be topped up a little as the system completely fills up. 1 heat cycle done.

Warm it up again until the top of the rads are warm to touch. Then go ride the bike. Whats most important for a good seal on the rings is not RPM's, its constant LOAD.

So short shifting through the gears for 5-10 mins is enough to create a good ring seal. The fresh piston/Rings is now run in. Go back and let the bike cool down. Double check your coolant level.You have now done 2 efficient heat cycles minimising the chances of over heating the bike due to a coolant leak etc.

Now time to set the jetting up as compression and performance is a little better than your old piston/rings. Once jetting base settings are done its time to go play. Ride as hard as you like.


Now on a brand new bike this is not the way it should be done as your running in a lot more components than just a piston/rings in the engine. That should be a good few hours increasing load and rpm's throughout the day. Always checking fluid levels and changing oil every hour. Again you should be focusing on keeping load on the engine to ensure the cylinder does not glaze up and to ensure the gearbox and clutch components are worn in evenly and all debris have been flushed with a couple of oil changes on the first day.


As for the comments on breaking in with the initial warm up. Nonsense. You need load to ensure an even seal on the bore or you do get blow by past the rings. Any decent dyno guy for example will run the bike on the dyno for a good 3-5 minutes under load short shifting up through the gears and coasting back down. Why? As it beds the rings in correctly ensuring the best bore to ring seal possible and ensures the best longevity for performance as well as overall peak performance.
JM485 wrote:
This^ is good advise.
Thinkin about doing a top-end in the nearish future, this is good stuff. Kind of a happy medium between the guys like me that baby them at first, and the guys that say to ring their tits off pretty much right away.
Radical
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Radical 4/1/2014 3:36pm
4/1/2014 3:36pm
My bikes and cars have always been faster than they should. My stock YZ80 was about as fast as my friends highly mod'ed one.
The reason I believe is how I break them in.

First of all, I don't buy the assemble dry advice. Having metal on metal even for a few RPMs is bad. I won't even turn the engine over by hand dry, ever. Just the thought makes me cringe a little.

I coat everything with oil. Not a tremendous amount, but everything is wet: cylinder, piston, rings, and of course the piston pin, etc...

First ride should be fairly long. Let the engine reach full operating temperature and stay there on the first ride; at least 15-20 minutes.
Why not short rides? Warming up the piston partially, then letting it cool, means that the heat was not evenly distributed. The entire top end needs to reach full operating temperature, and stay that way for a while. That way everything reshapes, seats, etc.. at full operating temperature, then cools down. In my opinion, after the initial ride, and even before you let it cool, it's ready to race.

Load is the most important of all.
Don't let it sit and idle on the stand or ride a steady RPM. Your engine needs load right away. Blip the throttle on the stand until you can turn the choke off, then ride it fairly easy to the track entrance, then go for it.
No idling. Don't let the engine run at all without at least a light load.

For the first few laps (2-3), while the engine is still warming up, don't ring the crap out of it, but also DON'T BABY IT! RIDE IT!
First Lap: Accelerate medium-hard but smooth, and ring it out to about 80-85% of max RPMs (not 50 or 60%), but don't leave it there. Accelerate medium hard, Just visit that rpm, then shift. The engine is still a bit tight. The RPM you're shooting for is right where the engine starts to resist the higher RPM. You can feel it.
Second through 10th Lap: Accelerate harder, take the RPM's higher, and hold it there longer each lap. What you're after is to push the point where the engine resists slightly higher with each lap. It'll loosen up pretty quickly.

Within 5-6 laps, you should be pretty much riding it as hard as you want. Just continue to listen to the engine. If it feels tight, don't push past that RPM.

At this point it's ready to race!

The last time I did a top end on my 2005 YZ125, I raced it after about 4 laps of break-in.

That's my $.02.

Have a great day!
Radical
Socket946
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AZ US
Socket946 4/1/2014 4:29pm
4/1/2014 4:29pm
Lowlander wrote:
Warm it up on the stand until top of Radiator is warm to touch. Then let it cool down. Check your coolant level at this point...
Warm it up on the stand until top of Radiator is warm to touch. Then let it cool down. Check your coolant level at this point and it might need to be topped up a little as the system completely fills up. 1 heat cycle done.

Warm it up again until the top of the rads are warm to touch. Then go ride the bike. Whats most important for a good seal on the rings is not RPM's, its constant LOAD.

So short shifting through the gears for 5-10 mins is enough to create a good ring seal. The fresh piston/Rings is now run in. Go back and let the bike cool down. Double check your coolant level.You have now done 2 efficient heat cycles minimising the chances of over heating the bike due to a coolant leak etc.

Now time to set the jetting up as compression and performance is a little better than your old piston/rings. Once jetting base settings are done its time to go play. Ride as hard as you like.


Now on a brand new bike this is not the way it should be done as your running in a lot more components than just a piston/rings in the engine. That should be a good few hours increasing load and rpm's throughout the day. Always checking fluid levels and changing oil every hour. Again you should be focusing on keeping load on the engine to ensure the cylinder does not glaze up and to ensure the gearbox and clutch components are worn in evenly and all debris have been flushed with a couple of oil changes on the first day.


As for the comments on breaking in with the initial warm up. Nonsense. You need load to ensure an even seal on the bore or you do get blow by past the rings. Any decent dyno guy for example will run the bike on the dyno for a good 3-5 minutes under load short shifting up through the gears and coasting back down. Why? As it beds the rings in correctly ensuring the best bore to ring seal possible and ensures the best longevity for performance as well as overall peak performance.
You lost me at "jetting".....

EFI crew checking in...
BAMX
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BAMX 4/1/2014 5:12pm
4/1/2014 5:12pm
Over the years, I have probably done all of the mentioned methods. The only time I have ever had problems is with jetski motors and no break in. I will add that they were Wiseco pistons on full mod skis so they probably would have blown up or the ring locating pin would have fallen out regardless. Other than that, I can't say that I have any evidence that any one method is better than another. Although, putting a motor together metal to metal and revving the shit out of it doesn't seem wise. Also, letting all of the dissimilar metals in the motor come up to temp before going crazy is probably also wise.

As a general method on a 2 stroke, I install the piston wet but no need to go crazy. I usually wet the cylinder then wipe it out with a paper towel. Oil will get caught in the honing even on a plated cylinder. The piston gets a light oil on the skirts and sides before it goes in. Also, I make sure that I put my oil on the wrist pin bearing. I have no idea what oil they have on it in that package but I clean it off with brake cleaner and apply mine. I warm it up when done and maybe cruise through gears at the house. At the track I give it a good warm up then ride for 10 minutes going good but not going full Barcia. Next ride, I warm it up then usually start where I left of and after a few laps, anything goes.

The Shop

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MotoX85
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Centralia, IL US
MotoX85 4/5/2014 9:39am
4/5/2014 9:39am
2 stroke is broke in about 2 seconds after you start it, but no need to ring its neck, take a couple easy laps and you are good.

4 stroke you need to heat cycle the piston, I usually run a gallon of gas through it, about 3 heat cycles and then a 15 minute practice session at mid throttle and then let er rip.

I have never blown a motor due to "my" failure in 30+ years.
CBailey306 4/5/2014 12:15pm
4/5/2014 12:15pm Edited Date/Time 4/5/2014 12:27pm
Lowlander wrote:
Warm it up on the stand until top of Radiator is warm to touch. Then let it cool down. Check your coolant level at this point...
Warm it up on the stand until top of Radiator is warm to touch. Then let it cool down. Check your coolant level at this point and it might need to be topped up a little as the system completely fills up. 1 heat cycle done.

Warm it up again until the top of the rads are warm to touch. Then go ride the bike. Whats most important for a good seal on the rings is not RPM's, its constant LOAD.

So short shifting through the gears for 5-10 mins is enough to create a good ring seal. The fresh piston/Rings is now run in. Go back and let the bike cool down. Double check your coolant level.You have now done 2 efficient heat cycles minimising the chances of over heating the bike due to a coolant leak etc.

Now time to set the jetting up as compression and performance is a little better than your old piston/rings. Once jetting base settings are done its time to go play. Ride as hard as you like.


Now on a brand new bike this is not the way it should be done as your running in a lot more components than just a piston/rings in the engine. That should be a good few hours increasing load and rpm's throughout the day. Always checking fluid levels and changing oil every hour. Again you should be focusing on keeping load on the engine to ensure the cylinder does not glaze up and to ensure the gearbox and clutch components are worn in evenly and all debris have been flushed with a couple of oil changes on the first day.


As for the comments on breaking in with the initial warm up. Nonsense. You need load to ensure an even seal on the bore or you do get blow by past the rings. Any decent dyno guy for example will run the bike on the dyno for a good 3-5 minutes under load short shifting up through the gears and coasting back down. Why? As it beds the rings in correctly ensuring the best bore to ring seal possible and ensures the best longevity for performance as well as overall peak performance.
Thanks for all the info everyone. I ended up doing Lowlanders theory. Anyway I can get it to start by compression starting but it won't start by kicking and it won't idle. It will ride ok but it feels hesitant and will bog every once in a while. Is this commen when you do a rebuild?
Edit: Also it was making a random clanking sound as the rpms were going down and it feels REALLY low on compression.
RedDirtDog
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RedDirtDog 4/5/2014 10:14pm
4/5/2014 10:14pm
CBailey306 wrote:
Thanks for all the info everyone. I ended up doing Lowlanders theory. Anyway I can get it to start by compression starting but it won't start...
Thanks for all the info everyone. I ended up doing Lowlanders theory. Anyway I can get it to start by compression starting but it won't start by kicking and it won't idle. It will ride ok but it feels hesitant and will bog every once in a while. Is this commen when you do a rebuild?
Edit: Also it was making a random clanking sound as the rpms were going down and it feels REALLY low on compression.
no thats not common, somethings wrong are u sure you put the piston in the right direction? it happens alot. did you have any of these issues before it blew up? if not I'd take the top end off and inspect things especially if its clanking.
CBailey306 4/5/2014 11:12pm
4/5/2014 11:12pm
RedDirtDog wrote:
no thats not common, somethings wrong are u sure you put the piston in the right direction? it happens alot. did you have any of these...
no thats not common, somethings wrong are u sure you put the piston in the right direction? it happens alot. did you have any of these issues before it blew up? if not I'd take the top end off and inspect things especially if its clanking.
Yeah I didn't think so haha, and I'm positive I put it in the right way. Also no it didn't have the clanking sound before it blew up.
CamP
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CamP 4/6/2014 12:15pm
4/6/2014 12:15pm
Blew up?

You need to pull it back apart.
CBailey306 4/6/2014 12:19pm
4/6/2014 12:19pm
CamP wrote:
Blew up?

You need to pull it back apart.
Well it seized that's why I rebuilt it.
smoothies862
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smoothies862 4/6/2014 6:56pm
4/6/2014 6:56pm
ever see a bike roll off a line in japan? there is a little asian lady that could holeshot alessi. she rips every bike thru the gears. i think moto mans theory is right. someone posted a top builder in ama superbike said "break it in like a chain saw". they do seem to run forever,wide open at that. new or rebuilt i go thru the gears after warmed up. loading and unloading nothing insane but riding it for 15 minutes. check for leaks,bolts,etc. change oil and filter. then let the dogs eat.
DTHA70
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DTHA70 4/9/2014 7:45am
4/9/2014 7:45am
i build two strokes wet and four strokes dry, heat cycle both gently once riding around just to get them hot enough to barely trickle some water out of the over flow, let it cool all the way off. second ride consists of high load riding(high gear, high throttle position, low RPM) and lots of engine braking(pulls the rings into the cylinder under vacuum), again, 10-15 minutes of this and let it cool down, then youre good to go! i have literally almost zero blow-by even right before i do top ends on my RM and my CRF, use the absolute best oils you can afford, although i have seen high molybdenum oils create ring seal issues on break-in if the motor is not loaded and engine braked enough.
Skerby
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Skerby 4/9/2014 8:44am
4/9/2014 8:44am
Scratch the shit out of it when Im trying to get the wrist clips in.
HenryA
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HenryA 4/9/2014 10:26am
4/9/2014 10:26am
Start her up, check the coolant. Take her for a normal ride. No need to over do things here. It's just a piston not a complete rebuild.
CBailey306 4/17/2014 11:42am
4/17/2014 11:42am Edited Date/Time 4/17/2014 11:43am
Ok so I bought a new oem A piston and installed it, did the break in cycle, and STILL it's very low on compression and still making a rattle at low rpm. Won't idle and it won't kick over, it has to be compression started. I think it could be the crank seal and/or bearing is bad. Does that sound like it could be the problem?
inthebadboycorner 4/17/2014 2:39pm
4/17/2014 2:39pm
smoothies862 wrote:
ever see a bike roll off a line in japan? there is a little asian lady that could holeshot alessi. she rips every bike thru the...
ever see a bike roll off a line in japan? there is a little asian lady that could holeshot alessi. she rips every bike thru the gears. i think moto mans theory is right. someone posted a top builder in ama superbike said "break it in like a chain saw". they do seem to run forever,wide open at that. new or rebuilt i go thru the gears after warmed up. loading and unloading nothing insane but riding it for 15 minutes. check for leaks,bolts,etc. change oil and filter. then let the dogs eat.
Yes, that's exactly how they used to test run each car engine here in AUS Holden/ GM engine plant.

Start it and within 5 seconds, then revved the bejesus out of it for another 15 seconds. DONE!
CBailey306 4/21/2014 2:38pm
4/21/2014 2:38pm
CBailey306 wrote:
Ok so I bought a new oem A piston and installed it, did the break in cycle, and STILL it's very low on compression and still...
Ok so I bought a new oem A piston and installed it, did the break in cycle, and STILL it's very low on compression and still making a rattle at low rpm. Won't idle and it won't kick over, it has to be compression started. I think it could be the crank seal and/or bearing is bad. Does that sound like it could be the problem?
anyone?
project racer 4/21/2014 6:40pm
4/21/2014 6:40pm Edited Date/Time 4/21/2014 6:41pm
Quit throwing parts at it. Take the cylinder off, and inspect it for any obvious scores, gouges. Next take the piston ,and using outside micrometer, measure the piston. Then ,using a dial bore gauge, measure the cylinder bore.

Perform some simple basic math to determine piston to bore clearance. At the very least, slide a long .002-.003 feeler gauge between the piston / bore to give an idea of where the clearance is at. If you can get an .003 in, it's too loose. A .002 should be fairly snug.

On the last Honda two stroke I had, I used the "C" piston in a fairly well used cylinder. The C being ever so slightly larger to accommodate for cylinder wear.

If it's not pumping at least 140 PSI on a compression test, things are loose. The rattle is probably from excessive piston to bore clearance.

Pit Row

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CBailey306 4/21/2014 10:47pm
4/21/2014 10:47pm
project racer wrote:
Quit throwing parts at it. Take the cylinder off, and inspect it for any obvious scores, gouges. Next take the piston ,and using outside micrometer, measure...
Quit throwing parts at it. Take the cylinder off, and inspect it for any obvious scores, gouges. Next take the piston ,and using outside micrometer, measure the piston. Then ,using a dial bore gauge, measure the cylinder bore.

Perform some simple basic math to determine piston to bore clearance. At the very least, slide a long .002-.003 feeler gauge between the piston / bore to give an idea of where the clearance is at. If you can get an .003 in, it's too loose. A .002 should be fairly snug.

On the last Honda two stroke I had, I used the "C" piston in a fairly well used cylinder. The C being ever so slightly larger to accommodate for cylinder wear.

If it's not pumping at least 140 PSI on a compression test, things are loose. The rattle is probably from excessive piston to bore clearance.
Yeah I don't think it's anywhere near 140.. Like there's almost nothing. Cylinder doesn't have very much time at all on it so I don't think it's worn out. I made sure to get an A piston since it's an A cylinder. There's no scores or gouges and the bore clearance is within spec. Could it possibly be the power valve is stuck open? Also after it sits for a few hours it will have some compression and will sometimes kick over but once it's warmed up all compression goes away.
Tracktor
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Tracktor 4/22/2014 12:12pm
4/22/2014 12:12pm
What's your squish set at? Open power valve should have no affect on compression? ..............
CBailey306 4/23/2014 5:13pm
4/23/2014 5:13pm
Tracktor wrote:
What's your squish set at? Open power valve should have no affect on compression? ..............
whats squish? sorry for any noob questions...
And if the power valve has no effect on compression then i'm totally stumped on what the problem is..
Tracktor
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Tracktor 4/24/2014 10:16am
4/24/2014 10:16am
Tracktor wrote:
What's your squish set at? Open power valve should have no affect on compression? ..............
CBailey306 wrote:
whats squish? sorry for any noob questions...
And if the power valve has no effect on compression then i'm totally stumped on what the problem is..
Simple answer is the distance between the piston & head at TDC. You can measure by bending a piece of solder into an L shape and inserting it into the spark plug whole. Slowly crank over engine & measure with calipers. Not sure what the measurement should be for this engine but shouldn't be too hard to find.......................
DTHA70
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DTHA70 4/24/2014 12:08pm
4/24/2014 12:08pm
Tracktor wrote:
What's your squish set at? Open power valve should have no affect on compression? ..............
CBailey306 wrote:
whats squish? sorry for any noob questions...
And if the power valve has no effect on compression then i'm totally stumped on what the problem is..
squish should be at 0.75mm to 1.1mm depending on what kind of gas you feel like running. i run my 250 at 0.8 with 50/50 c12 and 91 pump
theonlinelegend 4/25/2014 4:00pm
4/25/2014 4:00pm
CBailey306 wrote:
Well it seized that's why I rebuilt it.
I'm no expert, but if you only replaced the piston, rings, cir clips, main bearing and wrist pin on a motor that seized. Unfortunately, that is not enough. Should have posted some pics of the piston you replaced and the cylinder. On a bike that's almost 10 years old. I'm gonna bet that cylinder is out of spec for the piston and it's time to split the cases and do the bottom end. I've just never heard of someones bike seizing and a top end rebuild being the fix.
CBailey306 4/25/2014 11:44pm
4/25/2014 11:44pm
CBailey306 wrote:
Well it seized that's why I rebuilt it.
theonlinelegend wrote:
I'm no expert, but if you only replaced the piston, rings, cir clips, main bearing and wrist pin on a motor that seized. Unfortunately, that is...
I'm no expert, but if you only replaced the piston, rings, cir clips, main bearing and wrist pin on a motor that seized. Unfortunately, that is not enough. Should have posted some pics of the piston you replaced and the cylinder. On a bike that's almost 10 years old. I'm gonna bet that cylinder is out of spec for the piston and it's time to split the cases and do the bottom end. I've just never heard of someones bike seizing and a top end rebuild being the fix.
oh man that sucks. i really didn't want to have to do the bottom end. I have no experience with tearing apart a bottom end and i really dont wanna pay a shop to do it. Cant be that hard can it?
RedDirtDog
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RedDirtDog 4/26/2014 4:57am
4/26/2014 4:57am
its doable with alot of research and taking your time, asking alot of questions along the way. I did a top/bottum rebuild on my 02 125sx myself with no experience. start reading that service manual.

first take the topend back off and inspect the topend. I think sometimes cranks look fine but are off spec(from that 'hit' it takes when it locks up) didn't u say u were 4th gear pinned when it locked up? i bet your crank is toast.

I always replaced the crank when my bikes seized, even though the crank looked fine a couple times, after it takes that hit you never know.

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