Forged piston break in

[MikeT]

I am putting in a new top end (forged piston) in my YZ125 and will be racing the bike the following weekend. After getting everything installed, I plan on letting the bike warm up and lightly revving it on the stand. Then I'm going to let it get cold and do it again two more times. Each time I will let it run for about 10 minutes.

Does this sound like enough so that I can race it the following weekend? Is 30 minutes of ideling with revving it a little enough?

 

[marcusgunby]

A engine can easily overheat in 10 minutes as they have no fan like a car-check to make sure it doesnt get too hot.

 

then do a practice session at less than full throttle-allow to cool and then it should be ok.

 

[MikeT]

So, possibly keeping a fan on it, or using a shorter time to keep it from getting too hot, three times plus an easy half (maybe a little more) throttle practice session then a cool down should do it?

 

[whyzee]

Mike, ya need to put a little more stress on the motor during the 2nd and 3rd heat cycles. Take her out to a field and run it to about 1/2 throttle for the second heat run of about 10 minutes, 3/4 throttle bursts for the 3rd. Don't want to use the track for break-in time.

 

[MikeT]

Originally posted by Whyzee
Don't want to use the track for break-in time.

Is that because you'll be there?

JK! I know a guy who will probably let me ride a little on his lot in order to break it in a little if need be. I will also drill those holes in the piston like you said to do the last time we talked about top ends.

 

[whyzee]

Originally posted by MikeT
.... I will also drill those holes in the piston like you said to do the last time we talked about top ends.

Did you not get a wiseco pro-lite?

 

[MikeT]

I'm getting a Wiseco, don't know if it's a pro-lite or a pro-tru. I just called the dealer and ordered a Wiseco. Ithink he said it's part number 647. I think that IS a Pro-Lite.. Why, do they come pre drilled?

 

[whyzee]

mine did.
do you still have the link to my old 133 pics?

 

[MikeT]

Don't have the link, but I'll have the piston tomorrow or Saturday.

 

[bclapham]

My procedure:

fire it up, run it till warm.

go have some beer

fire it up, run it till warm.

more beer.

fire it up, run it till warm.

more beer, fall unconcious and sleep.

drive to the track, warm it up and go thrash it. :flame:

the prolite in my bike really took some thrash and the bike was jetted to the point of detonation and back, and then there was also the loose needle clip incident. it came out the bike looking and measuring like new! :yeehaw:

 

[MikeT]

Originally posted by Whyzee
Take her out to a field and run it to about 1/2 throttle for the second heat run of about 10 minutes, 3/4 throttle bursts for the 3rd.

That's exactly what I did. I used a scotchbrite type pad and rubbed it a little it still has the original cross hatch pattern in it. The piston coming out looked really good with only some minor scuffs on it which I ecpected. No carbon buildup, just a little spooge from my conservative (slightly rich) jetting. I broke it in pretty easy like Dave has said and that seemed to work well. The bike starts on the first kick and we will see how it does at the track on Saturday. I can probably go one leaner on the main to make it a little more crisp, but I think it's fine for now.

 

[vznx1w]

you guys that are breaking in your top-ends on the stand are seriously risking glazing your cylinders and poor ring sealing. realize that when you put a load on the motor cylinder combustion pressure goes up. the ring to cylinder wall pressure is directly effected by combustion pressure, because the cylinder gases enter the ring land and push the ring outward towards the cylinder.

Bottom line: low engine load = low ring load = insufficient pressure to "seat" rings before the oil glaze makes the wall too smooth to "cut" the rings.

 

[MikeT]

And your recommendations are?

 

[bclapham]

i dont really break my piston in. all i am doing is a 3 quick heat cycles, warming the engine up, not running it for extended periods of time. three warm ups and cool downs follwed by a warm up and then ride.

i could challenge your arument by saying, why not just start it and ride on a cold engine?????? you would have to be a muppet to do that, and i would bet that if you tried this on a new wiseco the resulst would not be good!;)

 

[vznx1w]

For proper breakin procedures, I'll refer to Eric Gorr's recommendations for a starting reference point.

E.G. Top-End Tips #10)
"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; 1) Set the engine at a fast idle, stationary on a stand. 2) 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."

For this (and other) Eric's topend tips go to:
http://ericgorr.com/techarticles/twotopweb.html#10%20TIPS

Note: I usually follow Eric procedure. However, if you want to be extra careful you can follow the Yamaha owners manual which recommends a combination of Gorr's tips and the "heat-cycling" concerns:
1. First start; run the engine on flat ground (no hard pulling, i.e; sand/loam/uphills) below 1/2 throttle for 20 minutes. Let cool
2. 2nd start; run the engine on flat ground below 3/4 throttle for 20 minutes. Let cool
3. 3rd start; run the engine up to full throttle for 15 minutes. Let cool


Go racin'

 

[MikeT]

Well, what I actually did was start my bike up and I kept it in neutral and let it run revving it to 1/4 throttle for about 5 minutes. All the while I had my hand on the cylinder to monitor the tempreture of everything. When it started to get really warm, not even close to hot where you couldn't touch it, I shut it down.

My second heat cycle, I had it on a field and rode it around in circles for about 10 minutes up to 1/2 throttle.

My third heat cycle, I rode it around for about 12 minutes amd brought it mostly up to 3/4 throttle and one or two full throttle hits (for only about 2 seconds) at the very end.

I ran regular mix, 32:1 Maxima SuperM with 93 octane. I think I did the break in about as perfect as I could.

 

[vznx1w]

sounds good Mike! Enjoy