How to break in a new piston?

[400eXr1d3rZ]

Tommorow my bike is getting torn apart, cylinder bored, and piston hotcam and gasket kit are going it. How do I break the piston in? In the box with the hotcam it says "upon first start-up, DO NOT let the engine idle, keep at 3000 rpm's or better"

[400eXr1d3rZ]

Anybody?

[F-16Guy]

Follow the break-in instructions for the cam; the piston and rings will be fine. As long as you don't see any oil leaks or hear any horrendous noises from the engine, keep the RPM's up and a light load on the engine. I would try to be somewhere that you can take it for an easy ride when you get it fired up. Just cruise around, varying the RPM's by shifting up and down through the gears (but I wouldn't go past 4th). That, in my opinion, will not only break in the cam, but will seat the rings properly without overheating anything. Some will tell you to go balls-out like you would normally ride it, but when it's fresh, the engine creates a lot more heat than normal, so I think you'll end up with looser clearances after break-in when everything comes back down to normal operating temps. Make sure your carb is jetted a little fat BEFORE you fire it up for the first time; you can always lean it out for performance later. You're looking for a cool running engine during break-in, and most of the cooling for the piston comes from the charge of fuel and air during the intake stroke.

[400eXr1d3rZ]

How long does a break-in usually take?

[F-16Guy]

I usually ride progressively harder through about 3-4 tanks. Step it up a notch for each tank until you are doing some pretty hard riding on tank 4. At that point, you can start leaning the jetting out.

[400eXr1d3rZ]

So after each tank of gas, ride a little harder?

[F-16Guy]

Yup.

[GPracer2500]

I'll give you may take.

You've got three things to consider. You can find operating paramaters that will satisfy the requirements of all three:


1) The cam Follow Hotcams recommendation for the cam (i.e. don't let the revs drop too low).

2) The piston Your JE piston is forged and for that reason it would be wise to subject it to several heat cycles. Basically, you want to get the engine up to full operating temperature and then let it cool down completely. You don't have to let it idle up to temp or anything--riding it is just fine. (note: only forged pistons benefit from heat cycling. A stock cast or hypereutectic piston doesn't need any heat cycles. Also, "heat cycling" is NOT necessarily the same thing as "heat treating" so just because a piston manufacture says their pistons are heat treated does not mean you can forgo heat cycling.)

3) The piston rings The rings need cylinder pressure to seat against the cylinder walls. Occasional bursts of WOT acceleration will provide those high pressures (high load = high cyl pressure). But avoid reving it too high in the very beginning. Using engine braking is iimportant too.

After everything is all assembled and ready to go, start the bike up and blip the throttle to keep the revs up until there's some heat in the engine. Then go ride it. You want to be constantly alternating between accelerating on the throttle and decelerating off the throttle (slowing with engine braking). Maybe try and stay between 3000 and about 6500 rpm. Occasionally using WOT in a tall gear is ok (good even) as that will get you the high cylinder pressures the rings want for making a good seal. After maybe 5 to 15 minutes, stop, change the oil, and let the engine cool down completely.

Repeat that 2 or 3 more times (but no need to change the oil each time--just after that first session). Each time you can use more and more WOT and increasing revs. Keep an eye on engine heat. As the rings break in they'll generate more friction than usual and you don't want some isolated spot to get too hot.

After three or so of those cycles you're done--break in is over and you can ride it as you normally would. Just remember: accelerate then engine brake, keep the revs above Hotcam's recomendation, don't let the engine get too hot, change the oil after the first session, and let the engine cool down completely between sessions. After a couple hours of ride time change the oil again and then resume your normal oil change interval.

That's what I would do. $0.02

[krt400ex]

Originally posted by GPracer2500
I'll give you may take.

You've got three things to consider. You can find operating paramaters that will satisfy the requirements of all three:


1) The cam Follow Hotcams recommendation for the cam (i.e. don't let the revs drop too low).

2) The piston Your JE piston is forged and for that reason it would be wise to subject it to several heat cycles. Basically, you want to get the engine up to full operating temperature and then let it cool down completely. You don't have to let it idle up to temp or anything--riding it is just fine. (note: only forged pistons benefit from heat cycling. A stock cast or hypereutectic piston doesn't need any heat cycles. Also, "heat cycling" is NOT necessarily the same thing as "heat treating" so just because a piston manufacture says their pistons are heat treated does not mean you can forgo heat cycling.)

3) The piston rings The rings need cylinder pressure to seat against the cylinder walls. Occasional bursts of WOT acceleration will provide those high pressures (high load = high cyl pressure). But avoid reving it too high in the very beginning. Using engine braking is iimportant too.

After everything is all assembled and ready to go, start the bike up and blip the throttle to keep the revs up until there's some heat in the engine. Then go ride it. You want to be constantly alternating between accelerating on the throttle and decelerating off the throttle (slowing with engine braking). Maybe try and stay between 3000 and about 6500 rpm. Occasionally using WOT in a tall gear is ok (good even) as that will get you the high cylinder pressures the rings want for making a good seal. After maybe 5 to 15 minutes, stop, change the oil, and let the engine cool down completely.

Repeat that 2 or 3 more times (but no need to change the oil each time--just after that first session). Each time you can use more and more WOT and increasing revs. Keep an eye on engine heat. As the rings break in they'll generate more friction than usual and you don't want some isolated spot to get too hot.

After three or so of those cycles you're done--break in is over and you can ride it as you normally would. Just remember: accelerate then engine brake, keep the revs above Hotcam's recomendation, don't let the engine get too hot, change the oil after the first session, and let the engine cool down completely between sessions. After a couple hours of ride time change the oil again and then resume your normal oil change interval.

That's what I would do. $0.02


next time i break in an engine, i will try that. it sounds pretty logical