Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: westsiderippa on February 13, 2010, 04:26:49 PM
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well since i have the new yz coming, should have it on thursday, any good recomendations for proper break. been a while since i had to put break in on a new 2t. im thinking a couple short heat cycles with full cool down in between and shifting through all the gears then change oil. also have a zipty magnetic plug to put in. what are your guy's traditions?
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My break-in (the one that Robert Reynard uses/recomends) Is three heat cycles with a complete cool down between (make sure it is not lean but don't tune it until your done with your final break in). Ride it for a moto 20 min or less then change the oil. There is no need to change the oil before it is ridden, it is a 2t the motor oil is changede every time it fires :D.
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so 3 heats then a 20 min moto. how long should a heat cycle last and how do you do it?
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I just leave it on the stand, let it get hot enough where you don't want to touch the cylinder, it should not take but a few min. He also warns to not let it idle, as this causes flooding and fauling of plugs in a 2-stroke. I just barely bump the throttle though because it is hard on a engine to rap it out before it is warmed up and expecially before the rings are seated.
This is kind of off subject but.
If I had the time and $ I would use a fluid heater like they do in sprint cars/indy cars/ect... to heat the engine before starting it, you would still have to run it and put it through the heat cycles for break in but it would avoid the cold cylinder starts. I would think that the factories would be using these on there race teams but I have not seen it.
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Can someone please explain to me what heat cycling is supposed to do, because i believe there's no need for it whatsoever.
I am firmly of the opinion that your number 1 concern is ring seal and bedding the rings ASAP, sitting on the stand for too long or extended periods of low throttle light load during break in are going to cause glazing and blow by. What i've always done with no problems is start her up and bring to operating temp with light blips on the throttle then get on and ride and get some light load on straight away, short shift up a hill or drag the brake a little. I only go to around 3/4 revs in the first 5 mins then quick check for fluid leaks or obvious problems and over the next 5 mins or couple laps i work up to maximum revs.
I believe the main thing is get some load on it early without high revs.
If all i've replaced is the piston and rings then i virtually don't run it in at all, just get on and ride.
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I do three heat cycles but I don't believe in leaving it on the stand.Once it's warmed up as you normally would without excess idling and while blipping the throttle and choke off asap-go ride for a bout 10 min or so.Don't lug,heavy load or wot but a good varying rpm about 1/4 to 3/4 throttle.Then let it cool completely then go ride again.As for not changing the oil before hand,you don't have to but definitely ck it,they've been known to be dry before.I always change the oil after the first cycle to get rid of any manufacturing metal bits etc then again after the final one.Break in questions are sort of like oil questions with regards to opinions.Still,the best way way to break it in is to send it to me and let me do it for you 8) ;D
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Send me the 09 and I will send you a fully broken in 08. 8)
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haha, nice try brotha. i think i got it covered. got a guy coming in an hr to pick up my 450. i hope he doesnt flake......i go pick up the yz on thursday.
plan is...
pick up bike thursday morning, come home perform break in.
friday, no tracks are open around here so i will head to a buddies private small track to continue with set-up, suspension clickers, sag etc..
saturday will be all day race practice at argyl in dixon
sunday is race day at argyl.
called some of my sponsors today and confused the hell out of them. they were like what? but you ride a honda dont you? they were actually all really stoked. i think its because now i will be getting a lot of attention just being mid-front pack on the dinger. witch is great for them. i cant wait for the qualifiers.
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Good luck with the new bike!!
Please send photos when you get it in your garage... and of course some riding/racing photos as well!
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thanks, i will get pics up im sure by friday. cant wait.
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Interesting, no ones keen to explain the need for heat cycling. or what it's supposed to even do.
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Here's my take on heat cycling.
All the components in the engine are of different shape and materials, so they expand at different rates so clearances and fits start to differ. It's when the engine is hot when the relationship of these clearances is important, so allowing them to adjust to running together during this period is important.
I go with the several not too loaded give it some revs heat cycles personally. At work with our big engines with cylinders you can hide in we do several heat cycles also. Interestingly we also set the cylinder lubrication higher during break in.
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Here's my take on heat cycling.
All the components in the engine are of different shape and materials, so they expand at different rates so clearances and fits start to differ. It's when the engine is hot when the relationship of these clearances is important, so allowing them to adjust to running together during this period is important.
I go with the several not too loaded give it some revs heat cycles personally. At work with our big engines with cylinders you can hide in we do several heat cycles also. Interestingly we also set the cylinder lubrication higher during break in.
But those changes in clearance happen every time you start and stop your motor, can't see why the first times any different.
The clearances are all factored in when the pistons manufactured and i don't believe the heat from the first time the motor runs is going to cause any permanent change that hasn't already happened during the forging or casting process.
What you've explained is the need to bring your motor to operating temp before you thrash it, you need to do this everytime not just during run in.
I still don't understand the need for the cycling process during break in. Bedding your rings should be the primary concern. I've seen motors that have been broken in too easy and they 've had bad blowby straight away.
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Run it like you stole it, nikasil bores don't have much of a cross hatch to them and you need to fully seat the rings as soon as possible. Somewhere on the net I once found a guys dyno results where he concluded you need to run the piss out of them initially. That doesn't mean you should run it for a lengthy first ride, just a hard first ride to build up pressure and force those rings against the cylinder walls.
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It will run ok exactly as you say totalnz but the primary reason for heat cycling is to allow the piston shape to more exactly and gradually conform to the cylinder shape.The differences and gains are small but they exist.This generally gives a longer lasting and more powerful engine as compared to just starting it and riding straight away.Pistons of course,aren't exactly round so the better fit you have,the better off you are.This also helps with ring sealing.The truely anal set the engine at bdc between cycles but I don't bother.
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It will run ok exactly as you say totalnz but the primary reason for heat cycling is to allow the piston shape to more exactly and gradually conform to the cylinder shape.The differences and gains are small but they exist.This generally gives a longer lasting and more powerful engine as compared to just starting it and riding straight away.Pistons of course,aren't exactly round so the better fit you have,the better off you are.This also helps with ring sealing.The truely anal set the engine at bdc between cycles but I don't bother.
I'm no metallurgist but i don't buy that at all. There's no way i believe that the operating temps of your motor are enough to permanently change the shape of your piston, anything like that has already happened in the manufacturing process. Maybe back in the day when manufacturing and machining process's weren't as good.
Also it's not the pistons job to be a tight fit and conform exactly to the barrel, that's the job of the rings.
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Putt around for a while, then sting it!!
Feel that 2 stroke rush :D
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I'm no metallurgist but i don't buy that at all. There's no way i believe that the operating temps of your motor are enough to permanently change the shape of your piston, anything like that has already happened in the manufacturing process. Maybe back in the day when manufacturing and machining process's weren't as good.
Also it's not the pistons job to be a tight fit and conform exactly to the barrel, that's the job of the rings.
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Strange but true.Metal is in a constant state of change in one form or another though the biggie is at break in.As for your engine temps being enough to change the shape of your piston,have you ever seen pistons go egg shaped?I have.How about a warped head-or any other engine part for that matter.Engine temps are more than enough.Have you ever put a case in the freezer then literally dropped a room temperature bearing in it?That's a differential of what, 50' or so?I know thats not a permanent change but it shows how little it takes.How about a cold seizure?Heat changes the structure of aluminum.If you bend a lever and try to bend it back you'll break it but if you heat it and then let it cool completely you can bend it back in to shape.If you then try to bend it more you'll break it-unless you heat it and cool it again.I'm no metallurgist either but I'm told it's the effect hot/cold has on the molecular structure.
As for the seal being the job of the rings,you're right but the better the piston/cyl fit the better seal the rings will have.
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The shape of a piston at room temp will not be the shape of it when hot, that is a given. Manufacturers compensate some with the shape but can't completely.
Nonetheless power comes from compression. Getting the best ring seal is the primary goal of a break in. Still I must confess, I've never been able feel any seat of the pants distinction from a slow easy break in or a fire it up and drop the gate approach. Same with longevity, without keeping a detailed log I don't know that you could determine any particular approach that makes an engine last longer. I'm basing this all on experience with 2-stroke single cylinder bikes. Planes, trains, and automobiles may vary.
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OK guys,I surrender.I'll continue to do it this way as that's what I've found in my 25 years as a mechanic works the best.To each his own however,so whatever works for you,go for it. :)
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Interesting, no ones keen to explain the need for heat cycling. or what it's supposed to even do.
Heat-cycling allows the trapped internal stress in manufactured parts to reach equilibrium. It's only really an issue if you are running a forged piston. When breaking in a new two-stroke with the OEM cast piston, the primary concerns are:
1.Allowing any high spots to wear in without putting the parts under high load, which will cause micro-welding, pitting, and galling.
2.Ring seating. It only takes a minute or two for the rings to seat fully, but it requires fairly high cylinder pressures to do so. It's best on a new bike to give it one heat cycle, and after it cools completely, ride it, using fairly large throttle openings, but avoiding high rpms.
Now if you're rebuilding and using a forged piston, this is the ideal method.
From Moto814
1) Assemble the engine properly and torque all fasteners to specs.
2) Start the engine with the bike on a stand and allow the engine to come up to operating temperature (top of the raidator hot to the touch). Do not allow the engine to run at one RPM at all. Constantly vary the RPM and do not allow the engine to idle. When then engine reaches operating temperature (about 3 to 5 minutes of running time), shut it off.
3) Let the engine cool completely (at LEAST one hour). You want the engine to be dead-stone cold. Longer is better.
4) Start the engine with the bike on a stand and allow the engine to come up to operating temperature (top of the raidator hot to the touch). Do not allow the engine to run at one RPM at all. Constantly vary the RPM and do not allow the engine to idle. When then engine reaches operating temperature (about 3 to 5 minutes of running time), shut it off.
5) Let the engine cool completely (at LEAST one hour). You want the engine to be dead-stone cold. Longer is better.
6) Start the engine with the bike on a stand and allow the engine to come up to operating temperature (top of the raidator hot to the touch). Do not allow the engine to run at one RPM at all. Constantly vary the RPM and do not allow the engine to idle. When then engine reaches operating temperature (about 3 to 5 minutes of running time), take the bike off the stand and put it in gear. Take it for a ride. During this ride you want to keep the engine under a load at all times. Do not coast. Do not let the bike idle. Do not allow the engine to stay at one RPM. Riding on a mild slope is fine for this, as is slightly dragging the rear brake the entire time. Do this for about 15-20 minutes. Then shut the bike off.
7) Let the engine cool completely (at LEAST one hour). You want the engine to be dead-stone cold. Longer is better.
8 ) Re-torque the head and base nuts.
9) Go ride.
The cool-down steps are crucial to this operation. You must let the engine cool completely for the break in process to work properly.
Also, do the warm up procedure I outline here before EVERY ride. Your top ends will last much longer if you do.
-Steve