2nd Head Gasket In one Season

[MJTurner42]

I have a 2002 Bayliner Capri 18 Foot Bow Rider with 3.0 Merc Cruiser.

In July I took the boat in because the head gasket was blown between the third and fourth cylinder. They re-machined the head, had the machine shop inspect the block, rebuilt the head, and replaced the gasket. After that the boat was good to go. After maybe 20 hours of use the boat has now blown a second head gasket. This time on the second cylinder and out to the side. Also one of the valves is mushroomed.

The shop is being extremely hesitant in owning up to this being their issue. One of the issues they are trying to say is the prop might have caused this. Its a 14x19 prop which should be fine for this boat.

I really need to show them that this is their issue. How can I do this? A boat just doesn't blow two head gaskets in a season.

Thanks for the help!

 

[achris]

What rev did you get at full throttle?

Chris........

 

[Bt Doctur]

What timing setting did you use?
Also one of the valves is mushroomed.
Number 4 exaust ?

 

[MJTurner42]

3900 rpm right before the gasket blew.

The shop set the timing so I do not know

 

[Bt Doctur]

over advanced timing is the major cause of blown headgaskets

 

[Lou C]

Ok before you go after them there are a few questions you need to ask yourself:
1) you say the prop should be right but was the actual wide open throttle rpm? Should be at least 4500 rpm. If this was too low that alone could cause the repeat problem.
2) what was the timing set to? Too much timing advance can cause elevated cyl head temps
3) what do your plugs look like? If they are white or very light grey your fuel mix is too lean, they should be a medium grey or medium brown. Lean fuel mix can burn valves and blow head gaskets
4) if the engine pinged did you address it? Some engines need premium fuel despite what the manufacturer says.

Now the things the shop is responsible for:
making sure the surfaces are flat to less than .003”, the sealing surfaces are perfectly clean and all bolt holes cleaned out. If the head bolts were really rusted they should have been replaced to get accurate torque readings. And of course following factory torque procedures.

As can you can see these problems have multiple causes; as owners we have to make sure the engine is maintained in such a way to prevent repeat problems in addition to the shop doing the right thing.

 

[MJTurner42]

Plugs were grey to black when I checked the compression.

I have ave been running 87 in the boat. Not sure what you mean by pinged?

timing was done by the shop

From my research online the boat should have a 14x21 prop on there. A 14x19 prop would cause the motor to do less work and allow it to get to higher RPMs if I understand pitch correctly.

 

[Lou C]

But did you ever test what your max wide open throttle rpm was?
yes if you go to a lower pitch prop the rpm should be higher but it still should be above a minimum of 4500.
you fuel mix is a bit on the rich side. Did the engine ever knock or ping while accelerating on plane?

 

[MJTurner42]

It never pinged or knocked when on plane during the 20 hours between the last head gasket job and this one.

Unfortunatley I didn’t pay attention to WOT until the day that the gasket blew. The 3900 RPM was on the day they gasket blew so it may have been decreasing because of the blown head gasket.

 

[Scott Danforth]

On an 18' boat, a 19p may be too much. I ran a 19p for cruising and a 15p for watersports on my 16' 3.0 powered boat.

Over-loading (lugging) the motor is not good. Hence the reason we are asking what your WOT RPM was/is

If the base timing was too far advanced, the motor will ping (pre-detonate) and blow the head gasket

 

[achris]

3900 rpm right before the gasket blew....

That engines needs to be spinning at between 4400 and 4800 at WOT. Overloading (prop too big) is the one of the most common causes of popped head gaskets.

Also, the other common misconception with too big a prop, is that it only affects the engine at WOT. Wrong! It harms the engine right from idle. It's like trying to take off in third gear, and changing up to a gear or 2 too high. Engines generally don't like that, but boat engines get very huffy about it, as the load is high and constant, at the best of times.

Chris.....

 

[bman440440]

just my 2c but I would bet that the timing is off... same thing happened to my buddys 3.0... make sure it is set to the proper degree in base timing mode and the proper one for the serial number of the engine... he popped his 2 times before he had it set to 2 ATDC... I could not believe that 3 degrees would be the difference... and he now has over 900 hours on it with no problems.

Timing (At Idle rpm)1 1° BTDC2 / 1° ATDC3 / 2° ATDC4
1Timing must be set using a special procedure as outlined in this section. Timing cannot be properly set using
the conventional method.
2Serial number break: 0L096999 and below
3Serial number break: 0L097000 - 0L0340999
4Serial number break: 0L341000 and above.

 

[MJTurner42]

Since I may have had the wrong prop on the boat where is a reliable place to check what the proper prop is for this boat?

 

[Scott Danforth]

Since I may have had the wrong prop on the boat where is a reliable place to check what the proper prop is for this boat?

What was your WOT RPM?

What was your gps speed?

 

[achris]

Since I may have had the wrong prop on the boat where is a reliable place to check what the proper prop is for this boat?

That's done by taking the boat out, normally loaded and run it at full throttle, with an ACCURATE tacho connected. Your dash tacho is NOT accurate enough. (I've seen then more than 500 rpm out) . If the revs are higher than recommended, use a higher pitch prop. If the revs are too low, decrease the prop pitch.

All the 'look up' charts can do is give you a starting point. Actually getting the 'right' prop is done by this trial and error method... And the 'right' prop may vary according to your requirements. Some people are looking for Bugatti-like acceleration, others are looking for holding power in turns, others are looking for out-and-out top speed. My preference is for a prop that takes the engine right to (or just slightly over) the very top of the recommended range, and with a good 'weed-shedding' ability... Top speed, not so much (for me)....

Chris.......