Mercruiser 3.0 knock

[Oldpos]

Ok, i recently bought a pontoon with a mercruiser 3.0 I/O that had blown the head gasket 3 times. I am a jet mechanic by trade so i know how to turn a wrench but not so experienced on boat or car motors, so i took the engine apart and had it bored, decked, the head rebuilt, installed all new pistons, cam, timing gears, bearings, ect. rods were checked by machine shop, block tanked. When changing the drive water pump impeller i found the water tube melted and the teeth on the impeller broke off, so i assume that is why the last guy kept blowing heads. this is a 2001 parti kraft 24 ft pontoon with the merc 3.0 and alpha one gen 2 drive.

So i get the motor back in the boat and take it to the lake, starts and idles great, purs like a kitten. idle it around the ramp area for a little while and then head out to open water running varied rpms up to 4000, runs great and i am real happy at this point so i push it a little more up to about 4600 rpm to play with the trim and see where it planes out at and then crap started.

keep in mind the oil pressure always stayed about 40-45 psi while above idle and engine temp stayed at or below 160, neither fluctuated even during my problems.brand new gauges checked both prior to running engine.

It started by loosing power, i throttled back to about 2000 rpm then back up to 3000 and its started sounding like it was bogging out. so i pull off to the side at idle and it dies on me and will not fire again. i pop the hatch to the engine and the bilge toon has oil in it, the back of the motor was soaked.it appears it all came out of the rocker cover breather elbow. Yes it was properly service prior and when i broke down i did add two quarts to bring it back to full. i could not get it started again until i rotated the distributor about 3/4" of an inch to the right (advancing the timing) then it fired right up but it has a deep engine knocking sound. now.i cannot remember if the knocking started when it bogged down or after i moved the distributor, i limped it back to the dock at idle and oil press and water temp were good, never changed more than 5 psi for oil and 10 degrees for engine temp. i took the valve cover off and checked the rockers and push rods and all were good. the knock increased in frequency with the throttle but did not get louder.it is definetly not a ping or ting or click, or tick, It is a metal to metal clank or knock. I have read a bunch of other threads on this forum and another site about engine noise with this engine, from timing ping, to fuel pump eccentric arm, to rocker arm adjustment.

this all happened yesterday and i had to go back to work tonight, so i have not had time to look at it too close. With the details above i am looking for suggestions before i rip the engine out ....again.

I assume i threw a rod bearing, but have a few questions

1. why did it only spit heavy oil at WOT? it did not vent oil from the breather until i went over 4000 rpm and even after the engine started knocking it did not vent any oil the rest of the time, none

2. why did it loose timing? i only adjusted it 3/4" and it idled perfect again ( other than knock), i know it didn't move by itself because i painted alignment marks when i timed it before we tried it on the water.

3. is there anything you can think of before i pull the motor?

 

[alldodge]

The first 10 hours on a new motor is critical. The motor should not be taken to WOT until after the first 10 and rpms should be varied during this time.

What is the motor serial number?
If serial number is unknown what is the year?


Was bearing clearances checked during reassembly with plastic gauge?
What was timing set at?

 

[Scott06]

You shouldn’t loose that much oil though blow by. Would think something in machine and or assembly was wrong leading to the blow by. Even if the rings weren’t seated yet you should loose two quarts that quickly unless oil control rings were wrong or installed wrong. Timing may have moved if distributor bolt wasn’t tight, did you verify the timing?

Is a slight possibility that something in the U joints gimbal bearing or drive is causing the knocking but this would be a odd coincidence. Since you have to pull the drive might be worth jamming a hose in bellhousing water port after you pull the drive and running it to see if knock is still present, but still doesn’t explain the huge oil loss..

yes if the water tube is melted this is a sign of a big overhead and why the guy kept blowing head gaskets. Someone ran it hot for a while. Was the head and block warped when you rebuilt it

 

[Rick Stephens]

In my yute I had a motor I just rebuilt do that. It lost a wrist pin retainer. The pin cut the most beautiful slot in the cylinder wall you ever saw. Broke me of assuming any of the parts are non-critical, even the 10¢ ones.

 

[Oldpos]

The first 10 hours on a new motor is critical. The motor should not be taken to WOT until after the first 10 and rpms should be varied during this time.

What is the motor serial number?
If serial number is unknown what is the year?


Was bearing clearances checked during reassembly with plastic gauge?
What was timing set at?

the serial starts with 0M it’s a 2001, timing was set at 2 degrees, I did not plastic gauge it.

 

[alldodge]

the serial starts with 0M it’s a 2001, timing was set at 2 degrees, I did not plastic gauge it.

Manual 26 - Serial number break: 0L341000 and above set 2 ATDC (note A and not B)

EST ignition and set using shunt to place in base timing mode

 

[Oldpos]

You shouldn’t loose that much oil though blow by. Would think something in machine and or assembly was wrong leading to the blow by. Even if the rings weren’t seated yet you should loose two quarts that quickly unless oil control rings were wrong or installed wrong. Timing may have moved if distributor bolt wasn’t tight, did you verify the timing?

this is my real concern, i can deal with a rod knock, simple enough to figure out once the engine is taken apart, but blowing oil at high rpm worries me. the machine shop i took it too is very reputable here in Atlanta area, they tanked the blocj, squared the block, bored it, and tapped all holes. as far as the oil rings i watched many video's and had the manual with me to ensure i was stacking the rings correctly and making sure the ring gaps were separated. everyone screws up so who knows maybe i screwed it up. and as for timing i painted alignment marks on the base of the distributor and block when i timed it, so unless it was internal to the distributor i dont think that was what happened.

Is a slight possibility that something in the U joints gimbal bearing or drive is causing the knocking but this would be a odd coincidence. Since you have to pull the drive might be worth jamming a hose in bellhousing water port after you pull the drive and running it to see if knock is still present, but still doesn’t explain the huge oil loss..

seems possible and very easy to check thanks for the idea

yes if the water tube is melted this is a sign of a big overhead and why the guy kept blowing head gaskets. Someone ran it hot for a while. Was the head and block warped when you rebuilt it

he replace the head twice, my guess after he cooked it the first time he never fixed the water tube or didnt realize he melted it so it cooked it a second time,

thanks for the suggestions

 

[Oldpos]

In my yute I had a motor I just rebuilt do that. It lost a wrist pin retainer. The pin cut the most beautiful slot in the cylinder wall you ever saw. Broke me of assuming any of the parts are non-critical, even the 10¢ ones.

that sucks, and im guessing when i tear this motor apart i am going to find something i did equally disappointing

 

[Oldpos]

Manual 26 - Serial number break: 0L341000 and above set 2 ATDC (note A and not B)

EST ignition and set using shunt to place in base timing mode

trying to figure out your statement, " set 2 ATDC, that means set to 2 deg above top dead center correct? i believe thats what i did. i used a jumper from the little white wire sticking out from the distributor connector.

 

[alldodge]

trying to figure out your statement, " set 2 ATDC, that means set to 2 deg above top dead center correct? i believe thats what i did. i used a jumper from the little white wire sticking out from the distributor connector.

No, 2 degrees After TDC. Most motors are timned Before TDC, yours is After

 

[Alumarine]

Not that this is your problem but did you break the cam in?

 

[Oldpos]

just a thought, a guy is selling a fiberglass boat that is rotted out near me for $500 includes complete motor, drive, tilt system, and trailer. the motor is a 1995 3.0 lx. what is the difference between my 2001 3.0 and a 1995 3.0 lx? i see the linkage is different for the throttle cables , but nothing else that would stop a straight swap over, am i wrong? im thinking i strip the boat for spare parts, sell off the tilt system and trailer, and junk the boat i should come out pretty good money wise.

the guy doesn't speak English very well or at all, so asking questions is tough but he said it runs. im thinking if i check the compression and look at the oil it stands a chance of being good. The main question i have about doing this is that i hear tons about cracked blocks due to freezing. im in georgia and the boat has a south carolina registration sticker, should i worry about cracked block down south? would the compression check and oil inspection reveal a bad block? he said it wont start because of a bad fuel pump, i should be able to rip the one off of mine and put it on his to check it, how would you quick wire this just to hear it run? do i just need the yellow red and purple wire hooked to a battery ?

 

[alldodge]

This imay not what yours looks like, but use for reference. It may not have been the issue which broke the motor, but if timing was not done correctly, then it can cause some issues

If you used base timing mode and set at 2 BTDC then timing was 4 degrees off. If base timming mode was not used then there is no reference where timming was set

 

[Oldpos]

Not that this is your problem but did you break the cam in?

No i did not, i dont think. i spun the motor on the engine stand for 5 minutes to pump up the lifters but dont think that was breaking it in

 

[Oldpos]

This imay not what yours looks like, but use for reference. It may not have been the issue which broke the motor, but if timing was not done correctly, then it can cause some issues

If you used base timing mode and set at 2 BTDC then timing was 4 degrees off. If base timming mode was not used then there is no reference where timming was set

after seeing what your saying yes i agree i was at least 4 degrees off. when the boat stopped and i moved the distributor i was on the water and of course had no timing light, i went by ear. got it to fire on first rotation and it idled smooth enough to limp it back to the dock. when i was running it before i broke down the engine ran so smooth and quiet, no valve chatter, pinging, or run on after shut down. i hear about detonation in the motor due to timing, what does that sound or look like if this did happen? what should i inspect for when i tear it apart if it was detonation? just a blown head gasket?

thanks for all the info !

 

[alldodge]

I'm not saying detonation did it or did not do it, its just a maybe.
Detonation happens real fast and most times you cannot hear it until its to late. If you find a hole burnt in a piston, its detonation, if bearing is spun, could be a few things

Just take it apart and see what things look like

 

[wrench 3]

With the knock and the blow-by, I'm thinking that maybe something's on top of a piston and hitting the cylinder head. It could be a piece of broken piston or some thing that came in from outside. You'll really be kicking yourself if you left a stray bolt in the intake manifold.
Pulling the cylinder head will probably give you a good idea of what's going on but you'll still have to pull the engine to do any repairs.

 

[Oldpos]

Ok so I got around to the motor today, it’s storming so it’s hit or miss working on it. But I did run a compression check.
the results were taken at 1st reading cylinder dry as in nothing added since last run, second reading was after I put oil in each cylinder, third after I rotated the motor for 5 minutes with the plugs out and oil in cylinder.
nbr 1 140,170,150
nbr 2 0,0,0
nbr 3 130,200,160
nbr 4 120,165,150

obviously nbr 2 rings are blown and it explains the blow by and having to advance timing to compensate for a dead cylinder, but not so sure about the noise, bad rings wouldn’t make a knock sound. I did not run the engine but as I was spinning it with the starter with no plugs I did not hear any knock. Maybe good news? Head gasket is good, maybe rob bearings good, maybe just pull the one piston and put new rings on it?


thAnks again for all the help, any suggestions are always welcome

 

[Grub54891]

With the knock and the blow-by, I'm thinking that maybe something's on top of a piston and hitting the cylinder head. It could be a piece of broken piston or some thing that came in from outside. You'll really be kicking yourself if you left a stray bolt in the intake manifold.
Pulling the cylinder head will probably give you a good idea of what's going on but you'll still have to pull the engine to do any repairs.

Anything's possible. Seen it happen twice in my life. One was a screw came out of the choke plate, didn't totally destroy the piston, but hammers it up pretty good. The guy shut it down quickly when it happend.
The other was a guys motor he just rebuilt. His girlfriend put the carb on and dropped a nut. She figured it would be ok, upon starting it immediately destroyed a cylinder and valves. Funny part is he kept the girlfriend and I think they got married also.

 

[Grub54891]

Well the head is most certainly going to have to come off. At this point I'd pull the motor and get it on the stand as I'm sure the pan has to come off to inspect all of it also. Dang, that stinks.