Breaking in a rebuilt engine

[ThomW]

Hey all.

This past winter I had to have some serious work done to my 2001 Mercury 200hp. It needed to have a piston sleeve bored out, new piston, block honed, new head gaskets, and new rings installed on all other pistons. My question is what exactly should I do for breaking in the new piston and rings this spring? Is it similar to a new motor, where I run it at idle for a few hours, then vary rpm's slightly for a few more hours...and avoid full throttle for at least the first 10 hours?? Any tips, advice or big no no's would be greatly appreciated. Thanks!

 

[Doh]

Yes, as if it is a New Motor. Also, I would add a quart of 2 stroke oil to the tank.

 

[Scott Danforth]

follow break-in procedure per the manual

 

[444]

Run it at idle for hours!? I would warm it up for a few minutes at the dock then put a load on it right away to help break in the rings. Varying the rpms, not staying long at the same rpm. WOT but not for extended periods, avoid idle. 50:1 ratio + your oil injection.

 

[ThomW]

I don't have the manual for this motor...:blue:

If I shouldn't idle it, why does this break in sheet say otherwise? I guess that is why I'm confused on what I should do. This sheet I was provided with confused me more than helped me.

Also, the oil injector is removed an plugged, I am good just running 50:1 like normal, or go a bit richer?

 

[444]

Everyone has their own opinions on this but to me, idle is to be avoided beyond initial warm-up. You can read up online about the way rings seat. I would run double oil during initial break-in so 25:1. One thing to note, if you've deleted your oil injection, you might want to think about jetting a hair richer as the oil mixed in displaces gasoline as it passes through the carb jets.

 

[ThomW]

Thanks 444! So from what i understand, the break in period is to allow the rings to seat with the piston sleeve properly. You need to vary the RPM's so they will heat up enough to properly seat, while also giving them breaks to cool down and not become too hot? So you suggest letting motor warm up, then go out cruising, varying RPM's? Get it up on plane, then drop throttle down to 3000 or so--enough to stay on plane--cruise a few minutes, then raise or drop RPM's again. Keep doing this, and avoid WOT for more than a few moments at a time for the first 10 hours of use, right? Sorry for all these questions, I just know that proper break in is essential to motor longevity, and I don't wanna be tearing this block down again anytime soon! Thanks again!

 

[444]

Yes, that's basically what I would do. I would vary the rpm by around 500 to 1000 every 30 seconds or so. This is my personal opinion so take it with a grain of salt. Think of this, what do they do with race engines? They don't build them and slowly break them in for 10 hours. They go on the dyno, warm them up then run the snot out of them to seat the rings. Do you have a water temp gauge on yours? Might not be a bad idea to be able to keep an eye on temp in case it heats up during break-in.