4.3L V6 Mercruiser w/Thunderbolt V

Nuthammer

Cadet
Joined
May 21, 2016
Messages
11
Ok..I am about to lose it. changed exhaust back to original configuration (check), changed plugs (check), then had to chase an alarm from a bad gear lube reservoir (check) everything checks out and good. Did the hose test everything sounded and looked normal. Decided to get out of work early to get my dose of Vitamin D out on the bay. At first, I heard nothing at idle and anything up to about 1200 -1500 RPMs driving through a no wake zone. Afterwards, applied power, the little girl seemed really sluggish and started hearing some knocking with any rpm over 1500 decided to power down and limp back to the dock. I only hear the knocking when she is under load and not on the water hose. I am thinking that it might be the rod bearings that might need to be tightened or replaced. follow the attached link for your enjoyment.

https://www.youtube.com/watch?v=1fQ4MMbn7Jo

I put this in the wrong thread, so I am reporting here.

Going to go check what the last reply was... it is strange that this just happened, but so is like!
 

Scott06

Vice Admiral
Joined
Apr 20, 2014
Messages
5,543
Hard to tell as we can't hear where the noise is comming from but it really doesn't sound like a rod knock. Have you used a mechanics stethoscope to try and determine where on engine this is coming from? I would look at the following :
Accessories and engine water pump, is starter gear completely pulling back, engine coupler and driveshaft ujoints, gimbal bearing ( especially if worse under load)
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Do the standard checks. Compression, timing, etc. 1st impressions is a hung open valve, but need more data. Also change spark plugs. Another trick I use, using plastic HRC fuse pliers, pull each plug lead to see which cylinder it's coming from. (use normal pliers at your own peril! :eek:)
 

Nuthammer

Cadet
Joined
May 21, 2016
Messages
11
I will check all of that. But now the boat wont turn over. One dumb way to spend a Saturday!!...grrr
 

Nuthammer

Cadet
Joined
May 21, 2016
Messages
11
Ok, this is what I have so far. Cylinders' 2, 4 and 6 have compression. However, I have nothing on 1,3 and 6. I will keep testing, but so far the easiest of all problems is a bad head gasket. I believe the timing was going too. So I will be working on that.
 

NHGuy

Captain
Joined
May 21, 2009
Messages
3,631
But you also need to figure out why so you don't get a recurrence. As you remove the exhaust check the gasket between the riser and manifold for any tracks where water could have gotten to the exhaust. Also check the riser and the manifold for rust or leaks of water into the exhaust.
Reason I am thinking that is there's a possibility that water in the combustion chambers caused a spike in compression which blew the gasket.
 

Nuthammer

Cadet
Joined
May 21, 2016
Messages
11
First and foremost, I would like to think everyone for there help!
Here are what the issues was and the fixes.
As stated earlier, there was no compression on the port side of the engine.
New head gasket
New cylinder head (Was warped really bad) got to it just in time the engine block was good, I think I lucked out!
Had a bend pushrod on cylinder number 3, same cylinder where the valves were somewhat stuck.
New cap and rotor (since why not)
Had to rest the timing and took her into the mech shop to reset the ignition module.
Gear lube bottle was replaced too just so I don't have to worry about the alarm coming on.
So far there is no knocking noise of any sort and she runs sound at 6000 RPMs (didn't stay there just wanted to see what she does)

Again I would like to thank everyone for their help, it was much needed. And I am most got away clean from taking to a shop! Maybe next time I will be lucky!
 
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