Engine knock/rattle (not rod knock), low RPMs, low top speed, 1994 Johnson Oceanrunner 175

[boatiemcboatface]

Engine knock/rattle (not rod knock), low RPMs, low top speed, 1994 Johnson Oceanrunner 175

Hey folks. Picked up the boat last year, and it has been running pretty good aside from the following:

At cruise it is pretty much fine, gets up to plane 25 MPH it is nice and steady. That is around 3,000 RPM. Trying to go over that I can start to hear ticking/knock from the engine (not lower unit), and it tops out at about 35 MPH and 4200 RPM, at which point the rattling/knock is significant enough that I back off back to 25 MPH to avoid damage.

It is not the fuel, ran through several gas tanks to make sure the winterization stuff is gone, only run 93 that's fresh. It sounds exactly like engine knock on a car engine (I tune cars so I'm quite familiar with it).

I doubt it's low compression, that would just have low power and no knock. Sounds almost like fuel starvation? Anyone have had a similar thing happen?

Thanks!

 

[racerone]

Well it would rev to 5500 in neutral on 3 of 6 cylinders.---It be a meaningless test.----Are you pushing the key in while cranking it over for a cold start ?----Explain the 50/50 mix.----What does that mean ?

 

[boatiemcboatface]

Well it would rev to 5500 in neutral on 3 of 6 cylinders.---It be a meaningless test.----Are you pushing the key in while cranking it over for a cold start ?----Explain the 50/50 mix.----What does that mean ?

Key pushed in to crank and it does fire up fine now that the leak has been fixed. The 50:1 mix, not 50/50 (brain fart).

 

[Faztbullet]

These motors are bad about internal water leaks due to leaking glue lines from factory castin All these blocksg process. I will not rebuild one unless I pressure test it first and it not just the 91 model its all of them and #1 is usually the cylinder that fails.PROBLEM:
Internal water cavity leaking
into #1 cylinder.
Engine:
1991 & up carbureted
150/175 HP 60 degree V-6 Evinrude
and Johnson outboards (
6V-6 Eagle)
Description:
Approximately 25% ofthe 6V-6 blocks we test will show a leakinto the #1 cylinder from the center watercavity underneath the regulator/rectifier. In certain cases, a leaking engine may develop a knock
at around 3500 rpms. The sparkplug may also show signs of water, and the cylinder head’s combustion chamber, piston dome,
and/or exhaust port may show signs of being steam cleanedby water. It is important to note
that some engines in the early stages of
leaking may not show the mentioned
symptoms and can only be detected by
pressure testing
the block.
Cause:
The leak develops from a thin section
in the block.Due to engine vibration,
varying pressures, expanding and
contracting, the aluminum cracks
over time and causes water to leak
from behind the sleeve.
Repair & Results:
MarFab can provide
its dealers with a remanufactured block
or powerhead, or can repair the leaking
block by welding and re-sleeving.MarFab
has been repairing 6V-6
leaker blocks since early
2002. Blocks are pressure tested after all work is
performed to ensure proper repair has been
made.
Limited Warranty:
MarFab warranties its 6V-
6 powerheads, blocks, and repairs for 1 year
from date of purchase and/or repairs against
water leaking into #1 cyl from area discussed
above.MarFab’s warranty is limited to repair or
replacement of block only. Other warranties
may apply to a MarFab remanufactured
powerhead. (See Mar-Fab powerhead
warranty sheet)
TB0209