I own an ’08 Amberjack 290. I am...

[drsteves]

I own an ’08 Amberjack 290. I am the third owner. She has twin 5.0 liter Mercruiser engines mated to Bravo 3 outdrives. According to the ECM, the starboard engine has around 500 hours on it. I had a complete loss of compression in cylinder 2 in that engine. There was a tuliped valve over cylinder 2. The head over cylinder 2 had been redone. Compression is now on spec in cylinders 2, 4, 6, and 8. There is a miss again. Cylinder 1 now has no compression. (Cylinders 3, 5, and 7 have normal compression pressures.) The intake valve in cylinder 1 is also tuliped. Is there a known cooling system, fuel system, or mechanical cause that might explain both front cylinders going south? I’m stumped!!

[wingless]

The timing chain is critically important to ensure that the valve does not contact the piston. Has that been verified for acceptable condition and for proper alignment?

Has the engine RPM exceeded the limit?

Have the valve springs been tested for acceptable force?

Assumption of a stock cam, correct?

Assumption that the exhaust is not past end-of-life from corrosion, correct?

[drsteves]

First step is that the head is going to the shop. Then we will continue our assessment. Your ideas are definitely great ones. Thanks for your response.

[gtstang462002]

If the cylinder head was off and went to the machine shop, they should have recommended replacing all the valves and reseating them properly. The head should have been pressure tested before reassembly. As the individual doing the work on the motor it would have had new exhaust manifold installed during reassembly as a preventative maintenance measure.

If, as winglass is possibly suggesting, someone "upgraded the cam" they likely upgraded the valve springs to match the cam likely not taking into account the fact that the stock valves could not take the extra seat pressure. Hence the tulip effect.

[PiscesPearl]

Extreme pressure from steam? Water getting in?

[gtstang462002]

If the valve springs were upgraded to match a cam change. It increases the seat pressure on the valves. The stronger springs are intended to close the valves faster on a high duration cam at high RPMs. Stock valves typically cannot handle this. If the entire motor is still stock, this is a mute conversion.

[drsteves]

Thanks for all of the input.