I am a bit curious about when people say "no high revs until you break in....about 500-700". What does it really mean to break in?

Also, why not rev it high? Will it damage the engine? I Just need a bit of clarification. Thanks :cheers:

 

The rings need to "seat" to the cylinder walls. All engines have microscopic imperfections in the machining, which will tend to "wear-in" with the first few hours of use. The same also applies to gearsets, particularly the ring and pinion.

For this reason it is best to operate the engine at varying speed and light to moderate loads in order to avoid heavily loading the rings/walls and ring and pinion.

This means it's best to avoid heavily loading the engine - either low manifold vacuum at low revs, which loads up the rings with a lot of radial force because combustion pressure forces the rings against the wall, or WOT and high revs which will do the same thing and generate much more friction and localized heating. Likewise, low manifold vacuum increases torque that the ring and pinion must transmit, and for these reasons I recommend avoiding the use of sixth gear for the first few hundred miles.

Racing engines are often broken in on a dyno with varying speed and load for two hours. The best way to simulate this is to drive at freeway speeds in fifth gear and vary the speed and load - accelerate lightly, then lift, and keep repeating this in a speed range between about 50 and 80 MPH. Gearbox breakin can be facilitated with the shifting required by normal urban traffic. A continuous run-in is best, so take a trip and drive the car at varying speed and load for at least four hours. That should result in about 250 to 300 miles and at that point it's probably broken in, but for insurance, it's best to maintain break-in schedule type driving for another few hundred miles.

Because breakin will generate some very fine particles, I recommend changing the oil filter after the breakin is complete - after a few hundred miles, but the oil can go the normal interval, because the filter will eventually trap all the particles.

Duke


[Modified by SWCDuke, 10:22 AM 7/15/2002]

 

Changed my oil the same time as the filter. Not worth the $$$ saving to change the oil at the same time.

 

The five top reasons for the break-in cycle:

1. The piston ring/cylinder wall face when brand new are somewhat rougher/more abrasive than they will be after just a few hundred miles. High rpm's generate a lot of heat in the rings, which can cause them to loose their spring, as they become annealed. After the initial cut/seating time, the interface is smoother and the heat gain is lower.

2. Cam lobe and follower surfaces also require some time to seat. High rpm operation too soon can gall the cam lobes from high heat and friction loads.

3. Valve springs take a little while to heat-cycle before they are fully capable of handeling higher cycle rates. After 500 or so miles, they are ready to take their designed cycle times and maintain valve seat pressures. Push them too hard too soon and they have been known to break.

4. Should any assembly not be properly assembled, it is best to discover that failure at lower engine speeds, under lighter loads. The last way you want to discover an improperly torquerd rod bolt is at full blat under full load!

5. The entire engine assembly will move around a little as it experiences heat cycles when brand new. This creates slight mis-alignments and takes up small tolerances that can create problems if the engine is heavily loaded. The more then engine is heat cycled, the less this effect will be. A little seasoning will stabilize the numerous masses and alloyed components and create an assembly that begins to operate as a unit.

 

Thank you for the explanation. I now have a better idea of engines.