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Engine Break-in

bcrdukes2010-06-18 05:19:31 +0000 #1
Hey folks,

My motor is 90% complete after tearing it apart for a rebuild. I've never broken in an engine before but after doing some reading online, it appears there are two methods to approach this:

1. Take-It-Easy for 800-1200KMs

2. Ride-It-Like-You-Stole-It for 300KMs

The two methods are debatable but I was wondering, for those of you with new bikes or bikes with rebuilt motors, which method did you approach and what has been the outcome so far? Thanks in advance!


huck-jai2010-06-18 05:34:22 +0000 #2
2. Bike ran fine after. Never had problems. Make sure to keep the revs at varying rpm and not keep it at a constant rev. Always accelerating then quickly decelerate with engine braking.

Don't redline the hell out of it. What I did was on the first 300km kept it under 7K RPM. The redline was 10.7K on the bike. I would rev it close to redline occasionally. Then for 700km I would ride it spiritly at varying rpms up to 9K rpm max and again occasionally hit redline. Once I hit 1000km, brought it in for first service. Break in done. Everyone has their own method. Just got a new bike and will be doing the same on this one. More or less, it's the Moto Tune USA method.

Find two people with the same bike of which one did 1 and the other 2, and I'd bet that both bikes ran fine after.

Tonnes of debate on this topic all over the net.
LKim2010-06-18 06:05:31 +0000 #3
I've never broken in a rebuilt motor however, the 1 brand new bike I have broken in, I followed method #1.

I basically did what the salesperson recommended, which is pretty much what the owner's manual said to do.

I can't remember the exact procedure, however it was something like keeping it under 7K rpm and making sure I use all the gears during the break-in period. I think I did that for the first couple tanks of gas, which was around 500-600 Km.
XdtesZombie2010-06-18 05:28:31 +0000 #4
I'm in the same situation and have read about the fast break in procedure and was leaning that direction as at first it was just new block and pistons but now my head is getting a bunch of new valves so I am not really sure what to do.

I figure take it easy for a half dozen heat cycles then do the quick break in and change the oil at 500k.
SnoDragon2010-06-18 07:03:07 +0000 #5
race engines are usually broken in with 3 or 4 heat cycles on the dyno. Idle and just barely going for the first 2 cycles, then gradually building up to redline for the last 2. After that, they should be living the rest of their lives at close to redline.
CG2010-06-18 07:34:58 +0000 #6
Here is what Honda tells us to do for there 2stroke gp bikes, i dont know much about the 4strokes but i wouldn't be surprised if it was similar, the only major difference i would see is on the 2strokes you have to take extra care with the pistons as you dont want them to deform early on and catch in a cylinder port, obviously this is a non issue on 4strokes.

Recondition machine:

After replacing the cylinder and crankshaft, operate the machine for the first 95km (57miles; about one hour) with the first 30mins of no more than half throttle and shifting gears so the engine does not lug.

Below 7,000rpm (About 50km, 30miles: About 30mins)

Below 8,000rpm (About 15km, 9miles: About 10mins)

Below 9,000 rpm (About 15km, 9 miles: About 10mins)

Below 10,000 rpm (About 15km, 9 miles: About 10mins)

Total: About 95km (57miles: About one hour)

When just the pistons, piston rings, gears, etc. are replaced, they must be broken in for the first 50km (30miles: about 30minutes) using no more than half throttle and shifting gears so the engine does not lug:

Below 7000rpm (About 20km, 12miles)

Below 8000rpm (About 10km, 6miles)

Below 9000rpm (About 10km, 6miles)

Total: About 50km (30miles, 30mins)

However keep in mind, the operating rpm range for there 2stroke gp bikes is up to 13,500rpm, so that should give you a idea on the rpm ranges.

I dont follow there guidelines though. When I do just the pistons, I just warm it up and let it cool down about 2 times, then i go out and do 3 laps but using half throttle at the low gears and full throttle (with opening and closing) in 5th and 6th gears to keep it below the recommend rpm range.

When i do a crankshaft and cylinders, I follow the first procedure they say but cut it down in half the time.

On HRC's tech hand out pages, they say this about running in:

The reasons why running in is required

Running in means the work which makes moving parts to move smoothly without resistance. Running in must result in smoothness instead of looseness. Smoothness without looseness means that parts are able to move to intended positions accurately, speedily without any resistance, resulting in, when parts are assembled, the best performance.

Good running in practice will give parts prolonged life, providing constant performance for extended period of time.

For instance, if loads are applied to pistons at a stretch at the initial stage of running in, deformed pistons will result, which will reduce service life of the cylinder as well since already deformed pistons cause severe contacts partially at the extended travel kilometers. Also, the performance will be degraded as well.

Good running in practices will secure constant performance for periodic part replacement periods.
PRSmechanic2010-06-18 06:22:57 +0000 #7
What exactly did you replace in the engine?
XdtesZombie2010-06-18 06:35:34 +0000 #8
On my bike it is a new cylinder,new pistons/rings and some head work being done ,new exhaust valves and seals.

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