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Motor Noise

49shepherd

New member
Hey Folks I have 49 Hercules straight 6 with a Scripps drive. Motor starts and runs great! The boat is new to me. Up on plane at 2500 to 3000rpms it starts to make an ignition ping or motor knock/Rattle?
It has 20hrs on Engine from a rebuild, crank rods etc in 2009,
I have set the timing back and it helped but still comes after 5 mins of running under load. Cooling is great.

Thanks.
 
Ayuh,.... Probably a fuel delivery issue, as a lean condition also causes detonation, which can destroy yer motor in few short minutes,.....

Everything from the tank to the carb is Suspect,......
 
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Hey Folks I have 49 Hercules straight 6 with a Scripps drive. Engine starts and runs great! The boat is new to me. Up on plane at 2500 to 3000 RPM it starts to make an ignition ping or Engine knock/Rattle?

A pinging is likely caused by pre-ignition.
A knock (if not from pistons or connecting rods) is likely from Detonation.

It has 20hrs on Engine from a rebuild, crank rods etc in 2009,

I have set the timing back and it helped but still comes after 5 mins of running under load.
Setting the BASE advance is ONLY one portion of ignition advance.
More importantly will be the progressive and total advance.
You will want to find the OEM ignition advance curve graph for this engine, and then check your ignition system to see if it's delivering the correct curve.
If it is not, you will need to make the corrections.


Cooling is great.
Detonation may be caused by several things:

.... excessive cylinder temperatures
.... poor fuel quality (not high enough re; the octane rating)
.... lean fuel/air mixture
.... excessive ignition advance per engine RPM

Detonation can become self propagating.
Once it occurs, cylinder temps climb.
As temps climb, so does the potential for Detonation.

Do whatever is needed to correct this before serious engine damage occurs.


Thanks.
 
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