Break in on a 260 EFI motor.

**Carter Powell** · 09-01-2025, 09:33 AM

Ideas on a new rebuild on a 260 Merc EFI. Thanks, Carter

**tlwjkw** · 09-01-2025, 12:29 PM

pretty much up ta you.... some are gonna say 180 days at varing rpm!?!?!?!.. some are gonna say 10 hours at varying rpm, double oil etc... some will have very different ideas of how ta do it.. ever watch some of tha roundy round (before most acquired dyno's) boys do it???.. don't take long.. i, myself have done it many different ways.. shortest time i remember was 'bout 10 minutes and can "proudly say", i've never exploded and/or stuck a piston in a new build in tha 34 (quit in 2010) years of dealin' with tha V6 merc/mariner...

**Greg G** · 09-01-2025, 09:56 PM

Totally depends on who did the full rebuild

**skialot2** · 09-02-2025, 08:16 AM

When I built my 200 I crused around for around an hour varying RPM. Then a couple short bursts wide open. Then let it rip. Motor runs great. Break em in how your gonna use them. How many racers do you know that break in their race motors? They usually run on the stand a few minutes then go race.

**aj06bolt12r** · 09-02-2025, 09:43 AM

So many different strategies.. On my last motor I followed the Carson Marine method posted on their website.. Worked great for me..

In my mind the main thing is get it to full operating temp trolling around at like 12-15oo RPM before you plane off and don't let it idle much beyond that. Use a bigger prop and cruise around at 3-4k RPM and wind it up a little higher with 3/4 throttle bursts. Get off plane and plane back out a bunch to load the rings. Avoid extended WOT operation for a couple tanks of gas.

**LakeFever** · 09-02-2025, 11:04 AM

The big issue with break in imo is seating the rings and getting the piston scuff complete. It’s rare to build a motor and have zero meaningful piston contact. The first few times this happens generates a lot of isolated heat. This makes the piston swell and can cause friction problems leading to failure. The rings need to be loaded to set properly or the motor might not make the proper amount of power. Sometimes you get lucky and the fit and piston alloy is all just perfect and you can just run the dickens out of it from jump. My feelings are because you can’t see any of this to verify it’s wise to run at least a full tank of fuel through it mixed at twice the oil it needs just for safety. There’s always the potential for slight dirt contamination during assembly so running it easy make it a lot less prone to marrying that grit into your motor allowing it to simply leave via exhaust. Varying throttle helps seat the rings. A few wot romps from low speeds to medium speeds helps seat the rings. That’s about all I did and do on any other motors I’ve built. If you build enough motors you eventually produce failures no matter what you try. Redoing a fresh motor once sucks for sure. The third time in a row? That can really test your patience.