Engine Break In

What is a good break in regimen for a newly rebuilt engine?

There is a recomend in the owners manual. Which engine?

I just had an engine rebuilt and there seems to be plenty of advice for a car engine but not for marine engines. So I’m pretty much making it up as I go.

I know if its a flat head, K, B M W etc, keep it under 2300 rpm for a while, ALSO and this is a possible difference btween car and boat. Dont sit at one RPM for a long time. Thats the big difference. Also an oil change after a certain amount of hours, since many of our engines dont have oil filters. Thats a difference as well. If its a V8 the big thing is the RPM up and down.

It sounds like I’m on the right track. How many hours of run time?

You should also use a break in oil and change it after about 2 hours running time. When you replace that oil with SAE 30, add some ZDDP zinc additive as the flat head 6’s have solid lifters and ZDDP is necessary to keep the cam lobes from wearing.

Are you running with an oil filter? Then use a detergent oil. If no filter, you should run a non-detergent oil.

This is all great info, just what I’m looking for! How many hours of run time before I can bring the RPM’s up?

Here is an article on WoodyBoater that was just written for this question. A huge thanks to Dave VanNess for the official information Breaking In Your Engine, And Why You Need TO Do it. – Classic Boats | Woody Boater

I have heard from valid sources that using synthetic
oil will have ill affects the transmission

Yes, no synthetic oil in a Chris Craft/Hercules 6 cylinder as the transmission shares the oil from the engine oil pan. Its too slippery for the clutch packs.

     ENGINE break-in

There are many theories when it comes to ENGINE break-in in there probably are variety of processes that will work satisfactory. when trying to determine the break-in procedure, you need to consider the type of ENGINE in the machining processes that were used during the rebuild. Engines are built to very precise standards and require very final machining occurs during break-in. The primary issues in break in the relationship to the piston rings to the piston walls, valve rotation, and contact with the shaft, and the sluffing off of imperfections and new bearings. It is our belief that with flathead vintage engines. The best process is to get the engines started as fast as possible. This is opposed to cranking the engine over repeatedly to build up oil pressure before starting. Getting the engine running quickly and bringing it up to approximately 1500 RPM allows for the piston rings and the grooves are normally honed into the cylinder wall together properly. Running the engine too slowly can cause cylinder wall polishing and make it difficult for the rings to seat causing blow. If this isn’t accomplished early on, it will be impossible to get seating. After machining the valve such as the lifter bores, the camshaft, the valve guides and stems there will be an initial friction, even if the tolerances are correct. The camshaft and lifters you want the lifters to rotate. This will allow the camshaft and the lifter to “ get to know each other“ but again is best accomplished at about 1500 RPM. It’s also important when the engine is configured to run in the test mode to make sure that you achieve operating temperature and not run the engine to cold. You can do this recirculating, some of the exhaust back into the water inlet and monitor the temperature. We like to run the engines at about 180° for 20 minutes before we drop the engine down to idle speed. After that time Final tuning of ENGINE, timing and carburetor adjustment and the cylinder heads are done. We continue to run the engine for 5 to 10 hours after the break and procedure. Change the oil the break-in process will put a small amount of metal into the oil. As I mentioned earlier, there are lots of different views on Break in but this technique seems to work best for us.

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