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New cylinder heads--do i need to do a break in?

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ptudozer

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It's a 2006 Mercruiser 5.0 mpi
Salt water cooled. 423 hrs
One of the old cylinder heads had a hole in the water jacket.
Just installed two new ones.
New gaskets and bolts
Couple questions:
1. Should I do a compression test before running the motor?
2. If compression test is good, should I do any sort of break-in procedure?

Thank you for any advice or suggestions.
 
I would do a complete (both sides) compression check for a base line and records.

If you did not replace the lifters, push rods or cam, no real break in is needed.

I would suggest that you do a shake down run close to shore/marina for about 3-5 hours varying Rpm/speed and keep max RPM below 4000rpm. Of course if you try to plane off and rpm go above 4000 momentarily that is fine.

If everything is ok at that point, drive it like you stole it.....
 
would second do a compression test nut should be done when engine is warm. Good advice to do a shakedown cruise close to the launch keep an ear out for noise or misfire. then hammer it.

were they new or rebuilt heads?
 
kghost said:
I would do a complete (both sides) compression check for a base line and records.

If you did not replace the lifters, push rods or cam, no real break in is needed.

I would suggest that you do a shake down run close to shore/marina for about 3-5 hours varying Rpm/speed and keep max RPM below 4000rpm. Of course if you try to plane off and rpm go above 4000 momentarily that is fine.

If everything is ok at that point, drive it like you stole it.....
Click to expand...
Thanks for the info. Weather did not cooperate, also found one of the exhaust flappers needs replacing. Did a cold compression, all cylinders around 140-145
Will do a run on the hose once the new flappers arrive, and taker her out for a shakedown hopefully this next weekend.
 
Dieter said:
would second do a compression test nut should be done when engine is warm. Good advice to do a shakedown cruise close to the launch keep an ear out for noise or misfire. then hammer it.

were they new or rebuilt heads?
Click to expand...
New heads.

The original 18 year old head on port engine had a leak from the water jacket into the exhaust port of cylinder #2
In turn that difference in exhaust temp caused the 6 year old manifold to crack.
So adding new manifolds, risers and heads along with a few other bits.
Going to see how these heads perform, and then at the end of the season I will replace the heads on the Starboard engine.
Hopefully that can get me another 12-15 years on these engines
 
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