Weird issue merc 3.0

[kd7isf]

Hi,

Got another strange issue for ya'll.

Got a merc 3.0 that seems to be "working against itself"

When you crank this one, it will act like it almost can't push past a certain point in it's rotation -- and if you release the key, it will blow back through the carb.

Compression is 120 120 180 180

I'm thinking valves (i.e. sticking valves) are the cause.

Any guesses?

Thing is, it runs fine above about 800 rpm's........... I would think a sticking valve would make it run worse at higher rpm?

Thanks

 

[CobiaXL]

Re: Weird issue merc 3.0

Wow 180lbs on a 4-banger..Does it smoke when running?Could be valve spring guides leaking oil in cylinder.

 

[Don S]

Re: Weird issue merc 3.0

When you crank this one, it will act like it almost can't push past a certain point in it's rotation -- and if you release the key, it will blow back through the carb. Compression is 120 120 180 180

Sounds like water in the back two cylinders to me.

 

[CobiaXL]

Re: Weird issue merc 3.0

Sounds like water in the back two cylinders to me.

Great minds do think alike....Some kinda of liquid in the cylinders either oil or water..I would double check that.

 

[kd7isf]

Re: Weird issue merc 3.0

Hi,

Ok, sorry, I guess i should have listed them in the correct order: 1 = 180, 2 = 180, 3 = 120, 4 = 120.

No sign of water in the oil, no significant blow by (wouldn't oil in the cylinder cause lots of blow by?)

What would cause enough oil to get into the front two cylinders to increase the compression so high?

Note, I thought about the possibility of the head gasket being blown between the 2 front cylinders -- so I pulled out all of the spark plugs and redid the compression checks. Same results. First check was with just one plug pulled at a time.

Plugs all look good -- no sooting or anything else out of the ordinary.

Thanks

 

[kd7isf]

Re: Weird issue merc 3.0

No smoke when running.........

 

[kd7isf]

Re: Weird issue merc 3.0

Too bad I didn't think of that about 4 months ago.......:facepalm:

Badly leaking valve seals would account for several indications I am seeing:
-In about 2-3 hours of runtime on the hose, it's lost a little over a quart of oil with no visable leak
-Now that I'm thinking about it, it does smoke a little, mostly on startup and sudden accelleration. Blueish smoke.
-The front two cylinders (the ones with the insane high compression) have soot in their exhaust ports, the back two do not.....

Being that the boat sat for 3 years before I got to it, my guess is the seals probably rotted away -- I'll check and post results.........

 

[kd7isf]

Re: Weird issue merc 3.0

Well,

that didn't pay out as well as I'd hoped.
The valve stem seals on the two cylinders with the really high compression looked just fine -- identical to the ones on the other two cylinders......

Also, the plugs in the two cylinders with 120 are nice and clean, the plugs in the two cylinders with 180 are covered in nasty black soot (these are new plugs I put in a few weeks ago).

How can I have black soot (I assume black soot = burning oil) if the valve stem seal is not the entry point?
Valve guide wear should be equal across cylinders, and this is a low hours engine (probably 45-50 hrs tops) so i can't see valve train wear being severe enough to cause this.

There is no source of pressurized oil in that head -- so where's it coming from?
Can't be rings -- that would cause a loss of compression, not an increase.
Can't be water -- that would show signs of water intrusion -- such as rust, brown deposits on spark plugs, rust trails on the exhaust ports, and water in the oil -- all of which we do not have...........

Any thoughts?

Thanks!!

 

[CobiaXL]

Re: Weird issue merc 3.0

Can't be rings -- that would cause a loss of compression, not an increase.

If only the oil rings are broke that will not cause loss of compression ,matter of fact it would make compression higher due to oil seating in compression rings.

 

[kd7isf]

Re: Weird issue merc 3.0

Hmmm...

Would I still get extra high compression from that?

Also, why would the oil rings just sorta like break?

Thanks

 

[CobiaXL]

Re: Weird issue merc 3.0

Hmmm...

Would I still get extra high compression from that?

Also, why would the oil rings just sorta like break?

Thanks

If oil is leaking into cylinder because oil ring is broke,cylinder pressure would be higher.

 

[CobiaXL]

Re: Weird issue merc 3.0

If only the oil rings are broke that will not cause loss of compression ,matter of fact it would make compression higher due to oil seating in compression rings.

Fixed above post...Sorry i was buzzed posting.

 

[kd7isf]

Re: Weird issue merc 3.0

So,

I did I leak down test -- sort of..... I connected an air line to each cylinder (connected to one at a time, via the spark plug hole)

naturally 1 and 2 had no issues. 3 and 4 (3 much worse then 4) both leaked quite noticibly through the exhaust valves.

Guess it's time to take the head in for a valve job

I'm thinking my compression tester is simply so cheap that the gauge is not aligned properly.
Instead of 180 180 120 120 I'm thinking I'm probably more like 140 140 80 80

Clinder walls are nice and smooth -- no scoring or anything...

I'll post results.......

 

[kd7isf]

Re: Weird issue merc 3.0

Hi all,

Ok, so we got the head back.

They replaced the intake valves (pitting) and the exhast seats...

Compression is now 180-180-165-160

It runs better, but still not right.

Still vibrates a lot -- especially at idle.

Tried to take it on the water -- NO power -- lucky to get to 1200 - 1300 rpms and died when backing off the throttle.....

Also should mention that we heard some dull, very low pitched thuds from the back end when we tried to give it throttle. Sounded like a bad ujoint.

We pulled the drive and the ujoints seem to be just fine. Seemed really stiff though -- I was under the impression the input should turn freely -- not require as much force as I could possibly make with both hands to turn it -- so we sperated the upper and lower drive -- turns out the water pump was making the whole thing very hard to turn. We are going to install a new impeller (parts on order) and see what happens......

Also notices that all four plugs (new this weekend) are covered in black soot -- which to me indicates running too rich -- but if I turn the idle screw in any more than it already is, it will not idle....

Currently have the idle screw at 1 1/4 turns out, for max vacuum of 15.....

Also thought about timing -- timing mark rusted off the timing cover long ago, so I set it by vacuum. If I advance or retard it any from where it is now, it will not idle or it shakes the boat and the trailer and the truck!!! Somehow that doesn't seem quite right to me.................

Any ideas?

Thanks!!

 

[kd7isf]

Re: Weird issue merc 3.0

???

 

[kd7isf]

Re: Weird issue merc 3.0

Hi,

Ok, I think I got it figured out now.

Somebody please shoot the idiot that laid out the print screen for the flame arrestors on the late '90's 3.0's.....

The firing order listed as part of the specs printed on the Flame Arrestor is WRONG!!!!

The CORRECT FIRING ORDER IS 1-3-4-2

The WRONG FIRING ORDER (AS PRINTED ON THE FLAME ARRESTORS) IS 1-4-3-2

I am positive that this is the primary cause of 97+% of the problems I have seen on this board that start with "after tune up, 3.0 will not run right".......

This explains the crap idle, the inability to get the timing right, the bouncing needle on the vacuum gauge, and the extreme lack of power on the water!!!! .......

Merc should have to supply us all with properly printed flame arrestors -- or at least a corrected sticker to apply to the ones we have....

I am going to put it in the water again this weekend and will post the results.

Thanks + reccommend adding this to the must have technical info for DIY'ers....

 

[kd7isf]

Why your MERC 3.0 won't run after tune up [Solved]

Why your MERC 3.0 won't run after tune up [Solved]

Hi,

Just a bit of advise for the many (to include myself) who have done a spring tune up only to find that their engine either no longer runs, or no longer runs correctly (i.e. very hard to start, no power, choppy idle, no idle, etc...)....

The problem is simple.
Most of us take the wires off, then replace the cap & rotor (& points when applicable), then re-install using whatever guide we have.

In the case of the Mercruiser 3.0, Mercruiser did us a "favor" and printed the tuneup information on the top of the flame arrestor.

A nice "favor" since it makes it possible to do a tune up without pulling out the book (or buying one if you don't have one).

EXCEPT, it's NOT a favor in our case since they MISPRINTED THE TUNEUP INFO on our Flame arrestors!!!!

Our engines don't want to run after a tune up because we assume the info printed on the Flame Arrestor is correct and we get the firing order wrong because of it.

THE FIRING ORDER ON THE FLAME ARRESTOR IS WRONG (PRINTED AS 1-4-3-2)

THE CORRECT FIRING ORDER IS 1-3-4-2

Correct your firing order and your engine should run fine....

Sure would be nice if Merc would send us some kind of a sticker to put over the incorrect info (even better if that sticker had the right info on it).

Hope this helps!!

Please post this to the must have techical info for DIY'ers section!!!
I see post after post about this and now that I have finally figured it out, I'd want to make sure everyone knows....

Thanks!!!