I have had my 540s on the dyno two times (once without the heads flowed and once after Jim V. did them). I have put about 2 hours on the engines since getting them back. How should I be breaking them in? Not holding them at a constant speed, what about WOT? Since they have been on the dyno, does this make any difference? Looking for some suggestions. Thanks.

Typically people say your motors should be ran 10 hours to break them in avoiding prolonged idling,lugging and wot operation but in reality when you dyno them they are usually ran on dyno for 1/2 hour before making pulls to seat the rings and look for leaks. After a full dyno session or if its a long one 1/2 way thru you should change the oil and filter. The filter should be cut open and inspected for metal before installing motor in boat to catch any possible problems.My last motor I ran on dyno for 25 minutes and it had ar least 20 pulls dialing in fuel injection with alot of run time in between. I changed oil and filter 1/2 way thru and again before installing it in the boat.I did a leak down test before installing in the boat for future reference and it was less than 5% so rings were fully seated. I still ran motor gently for first 4-5 hours,changed just the filter after 2 hrs,changed oil and filter after 5 hours,checked constantly for leaks, vibrations and anything loose then started running it hard after that. I used zero gap rings with ring seating compound so rings seated right away. With hyd roller cams you really don't have to worry much about cam break-in after a dyno session,mainly you want to be sure your not getting blowby and rings are seated ,valves are adjusted correctly,timing is correct and your efi or carb is giving a "safe" fuel mixture before pounding on it,Smitty

Nothing really to 'break in' with modern plasma moly rings and roller cams. Some will say that bearings + journals do need a little time to wear together (microscopic high + low spots) and shouldn't be held long at WOT for the first few hours.

Everyone agrees vary engine rpm (don't hold at same rpm for long) for a little time.

Smitty had smart suggestion - check inside filter a few times. 1st, right after first oil/filter change from 'break in run' on dyno, and then the oil filter change after the dyno session is done. If we are even more thorough, a check would be good a little later on.

Personally - I beat the crap out of it on the dyno, right after the break in run and everything is 'a go.' Once back in boat, I take it easy for a few hours only because of possible rigging issues / human installation mistakes - lines, fuel system, electrical, etc,etc,etc. A shakedown run as you will. If installed in a car it's no mercy. Guages are looked at more than anything else for a while - especially fuel psi, oil psi, and fluid temps.

For my new / rebuilt engines (new blocks, crank, pistons, rings) I was told to vary rpms and no WOT for first 15-20 hours. These ran on stands for 30 min to 1 hour before installing. Watched for leaks for first several hours. Also closely watched oil pressure & temp and water pressure. Oil changed at 15 hours with filter cut open (all good). Engines currently have 50 hours with oil changes every 15-20 hours. Just sent the last oil change samples to Blackstone for analysis. Both engine reports came back with good results. My next new engines I'll do the exact same thing. Pretty sure it's not the only way, but it worked for me.

Thats definately a conservative approach,for some of us high performance guys 20 hours could be 1/2 to most of a season ,Smitty

I chose the converservative approach after spending 4 years working with crooked engine builders that kept me off the water.

Finally found one that that I could trust, so when he said take it easy for a little while and you should have years of trouble free boating, I said no problem.

It's taken me 2 1/2 years to get 50 hours on the engines. At this rate, my 400 hour rebuild will happen in 2024 (assuming gas is still available at the time).

Thanks for all your responses. I might have 20 hours by the end of the season. It looks like the key is varying the speed and possibly, not running at WOT for a time.

-Minimize idling after it's warmed up. No cold WOT's.

-Work your way up to getting on plane easy since the drives are in break-in too.

-Vary cruise RPM.

-A good WOT for 10 minutes will encourage the rings to set.

-Allow a good cool down after each run.

-Check oil frequently during the first 20 hrs.

-Change oil to 15W-50 or 20W-50 Synthetic after 20 hrs.

-Start looking for a buyer to trade up at 25 hours.