Break in period

[was92v]

Do you guys think there is a difference between a new engine /gearbox and rebuilding an engine that all the other hundreds of parts are already run in?
There are hundreds of friction points in a new engine/gearbox that are lapping in besides the cylinder walls, piston skirts and rings in a new motorcycle engine/gearbox that are not at all a concern when rebuilding a used unit. I worry more about gear tooth faces, dog surface and bearing run in, than the ring to wall seal. With the rings and the cylinder finish used these days, unless something was screwed up when it was built, the ring/wall seal in a done deal almost as soon as you start the engine. After rebuilding an engine, a couple of heat cycles to shape the piston is about it. All the rest is already done.

[Tmall]

Originally Posted by was92v

Do you guys think there is a difference between a new engine /gearbox and rebuilding an engine that all the other hundreds of parts are already run in?
There are hundreds of friction points in a new engine/gearbox that are lapping in besides the cylinder walls, piston skirts and rings in a new motorcycle engine/gearbox that are not at all a concern when rebuilding a used unit. I worry more about gear tooth faces, dog surface and bearing run in, than the ring to wall seal. With the rings and the cylinder finish used these days, unless something was screwed up when it was built, the ring/wall seal in a done deal almost as soon as you start the engine. After rebuilding an engine, a couple of heat cycles to shape the piston is about it. All the rest is already done.

Every thing I've touched is honed and within spec from the factory. If it isn't, it goes back. So, I'm not quite sure what you're getting at.


If it's within spec, it will fit. If it's a faulty component, it's going to break regardless of break in. So, what benefit is there to babying it?




I wish I had my "transmission of power" notes kicking around. I can't seem to think of the manufacturing process used in gear design. Burnishing, lapping, hobbing, whatever the heck it is costs a lot and is far more accurate and is commonly used in engine applications.

Ultimately, the only time I've seen catastrophic engine failure has been because of maintainer error.

Edited to add: Most times spun bearings are caused by lack of lubrication. Crank bearings and cam bearing are made out of babbit for a reason, to allow particle embedding to the bearing and not the major components as well as to allow the bearing to wear instead of the expensive parts. And crucial components such as cams usually have bearings matched to them to precise tolerances. The ones we use, if you ding the cam or bearings, you replace everythign as a set. And to do that, we have to send the block away to have new cam bearings pressed in.
These components cost more initially for a reason, they're made to more precise tolerances using more expensive manufacturing processes.

[RedRider2k2]

Originally Posted by was92v

Do you guys think there is a difference between a new engine /gearbox and rebuilding an engine that all the other hundreds of parts are already run in?
There are hundreds of friction points in a new engine/gearbox that are lapping in besides the cylinder walls, piston skirts and rings in a new motorcycle engine/gearbox that are not at all a concern when rebuilding a used unit.

No, not really. All those friction points you speak of are either replaced with new or measured to make sure they're within Spec. You dont toss on a new set of rings and call it "Rebuilt". I'm talking front to back, top to bottom, EVERYTHING gets stripped down and gone over with a micrometer.

[Sean]

This is what my piston looked like after 2000 miles with a hard breakin:

[Homeslice]

Who knows whether that was due to the break-in, or questionable British quality control

[Sean]

Originally Posted by Homeslice

Who knows whether that was due to the break-in, or questionable British quality control

Yup, those Italian manufacturers all employ British quality control agents.

[Homeslice]

Originally Posted by Sean

Yup, those Italian manufacturers all employ British quality control agents.

So this was the Husky, not your Triumph? My bad.......but the Italians aren't really known for quality either. Also, you said it had a previous owner......What else might he have done to it besides a hard break-in?

[Tmall]

Originally Posted by Sean

This is what my piston looked like after 2000 miles with a hard breakin:

Explain how scoring on the thrust side of the piston would be caused by hard break in?

Likely causes, no cooling to the bottom of the piston, the piston rings had the gap close to each other, or fuel dilution of your oil. Unless that piston is coated, it looks like there is a ton of soot on top. Which leads me to think fuel dilution.

I'm far from an expert. Just falling KISS logic.

Edit: Where's the top ring? Were the rings installed upside down? Or in the wrong position?

[RedRider2k2]

Originally Posted by Tmall

Explain how scoring on the thrust side of the piston would be caused by hard break in?

Yes, please do.

That's either an assembly error, manufacturing error, or the person doing this "Hard break in" didnt know the difference between "Break in" and "Abuse".

[Sean]

Originally Posted by Tmall

Explain how scoring on the thrust side of the piston would be caused by hard break in?

I never said it was a cause -> effect relationship, I'm simply showing my personal experience. The guy who did the rebuild listed a number of factors, but I do know the previous owner put it on a dyno straight out of the box. The new top end has hardly coughed up anything.

Originally Posted by RedRider2k2

That's either an assembly error, manufacturing error, or the person doing this "Hard break in" didnt know the difference between "Break in" and "Abuse".

It's my guess that most people doing a "hard breakin" don't know the difference either, including the guy who had my Husky.