Rebuilt Bravo Mercruiser 7.4L Break-In

[Juttmk]

Picked up a 23' Mariah late last summers to only have the engine fail after just 6 trips to the lake. I went ahead and had the engine rebuilt by a very reputable machine shop that mainly deals with race engines. The crank completely destructed. The engine is now back in the boat. The distributor is set to TDC, and the engine has been primed.
Can the first 20 min 2000 rpm be performed on the trailer in neutral? I was then planning on setting the timing at idle to 8 degrees.
What is the next step to ensure the rings seat properly? Do I just run the engine in twenty minute intervals at different RPM ranges. I've read the break in manuals online, but want to ensure it's done properly. Any help would be greatly appreciated!
Thanks in advance

 

[alldodge]

Howdy and congrats on the new motor.

How about telling us some more about the motor. Does it have a roller or flat tappet cam? What year?

The guy who built the motor for you should be your first choice in what needs to be done. If he is any good at all, he will tell you and should have told you how to break it in

 

[Juttmk]

The engine received the following new components:
Crank/Bearings
Flat tappet cam
Piston, connecting rods, rings. The distributor was removed and the engine was primed. Engine oil is Brad Penn
The engine is tdc and should fire up.
I know the cam needs to be broke prior to running the boat. Does 20 minutes in neutral at 2K surffice? Once the engine cools down, I need to set the timing to 8 degrees at idle. He suggested then running the boat at different rpm ranges not to exceed 3500 rpm's in 20 minute intervals to seat the rings. Like I said before, he builds tons of engines that are primarily used in dirt track race cars. He once in awhile dabbles with marine engines. When you look it up the information varies from site to site.

 

[Juttmk]

1994 7.4L 310hp

 

[alldodge]

Since Crane is one of the major cam manufactures, I would go to their recommendation. Should start quickly without much cranking, need to go straight up to 3000 rpm and vary between 1500 to 3000 for 20-30 minutes. No need to have it under load, and is best to not be under load (in neutral).

Brad Penn is a great break in oil, and while not break in type

http://www.cranecams.com/uploads/breakin/548e.pdf

 

[Juttmk]

Thanks for the information!

 

[Scott Danforth]

The first 20 minutes is to break in the flat tappet cam. I generally do 10 minutes at 2000, then go up to 2500, then back down to 2000 with the last 10 minutes between 2000 and 2500.

After that, change oil, go boating and vary RPM.

 

[FuelishBehavior]

To reiterate Alldodge, being that I build engines and you have a flat tappet cam, have the engine timing set as close as possible before cranking including fuel in the carburetor bowls. I personally use an old distributor with the guts out of it and a 1/2" drive drill and get the oil pressures up before even cranking. There are tricks to get the timing just about right on 8, 10 or 12 degrees initial timing as well as using a syringe to fill the carburetor up through the fuel bowl vents. Take the engine up to 2500+ RPM's immediately to get the pressure up. Due to regulations, oil companies do not put near the required zinc in the oils so personally I use a reputable break in oil like Joe Gibbs Racing uses or one can use a zinc additive. It's cheap insurance to spend a little on a good break in oil or zinc additive instead of flattening a cam lobe. Whether you're at 2000 or 3000 rpms is not necessarily as important as it is to keeping the oil pressure up while the lifters get used to their new lobe buddy for life.