no fuel to 2 cyinders?

[stonyloam]

Re: no fuel to 2 cyinders?

Well to check the head gasket you could try this (don't know if it will work). Remove the plugs from 1 & 2, bring it to TDC (both valves in #1 closed), and with your compressor (use one of those air guns with a rubber end) pressurize #1 and see if you can hear air coming out of the #2 plug hole. That will tell you if you have a break between them. There is no oil or water flow through the narrow area between 1 & 2. IMHO I don't think the valves or lifters are the problem.

 

[alldodge]

Re: no fuel to 2 cyinders?

Stonyloam, do you think there is a possibility that the valves got bent from being adjusted to far down and taping the piston? OP said it was running fine at first and only ran for a little while this year.

 

[rainman01]

Re: no fuel to 2 cyinders?

Sure can not hurt to try that. Take a little doing to get the compressor close enough for the hose to reach, but the theory makes sense.

 

[rainman01]

Re: no fuel to 2 cyinders?

Even more so, my compression tester is a multi with a quick connect in it so I can screw it into the cylinder and run air pressure straight inti the cylinder through it. A fine idea! Will let you know if it works.

 

[Bt Doctur]

Re: no fuel to 2 cyinders?

Never solids on the inlines or V`s.If the valve train is normal then try injecting air into the cylinder and listening for it. out the intake manifold =bad intake valve. out the exaust=bad exaust valve, air into #2 and air coming out of #3 is head gasket.

 

[rainman01]

Re: no fuel to 2 cyinders?

Stonyloam,
Could not get my compressor down there by myself, (had surgery a couple weeks ago and still mending), but filled my air can up to90psi and took it down there. Put the tester in #1, pulled the plug from #2, hooked the quick-connect to #1 and listened to the air merrily coming out of #2 cylinder. Even to an old shade tree mechanic like me, that's not good. If my basic knowledge is correct it either has to be a blown headgasket or a hole blown through both pistons. Top and sides of the head pass close inspection, not a hint of a crack. Guess there could be inside but the air was coming out just as fast as it could go in, so I would think a crack that size would have to be visiable.
Anyhow, head has to come off. Right? And also, I would think that little trick with the air pressure may work with a hung valve also. The air pressure has to go somewhere, right?
Alldodge, I was with you, gasket was new and shouldn't be bad. All I have to say is HORSE HOCKEY!!! I can not even have an hour of "underway" time on this.
Any other suggestions, pointers would be greatly appreciated, and THANK YOU VERY MUCH!!! All of you, Alldodge, Stonyloam , BT Doctur & achris.
Dennis.

 

[alldodge]

Re: no fuel to 2 cyinders?

Either way sounds like the head has to come off. Once off it should be clear what happened

 

[stonyloam]

Re: no fuel to 2 cyinders?

Sure can not hurt to try that. Take a little doing to get the compressor close enough for the hose to reach, but the theory makes sense.

I don't know, it is basically a truck six, not some high compression ratio hi performance engine, so I doubt that the valves are hitting the piston. That head is going to have to come off IMHO.

 

[tank1949]

Re: no fuel to 2 cyinders?

Hello again,
Pulled valve cover, all looks good. No obvious bends in rods & rockers travelling back and forth just fine and valves APPEAR to be traveling just fine. BUT... a second compression test shows 0 pressure on either cylinder. Other 4 between 90 - 95. I checked each cylinder 3 times just now. Roger checked last nite and said all was fine. We were 4 to 5 beers into it at that point, did something wrong I guess. Maybe not release pressure from gauge? Anyhow, there is no pressure on these two. A hung valve on each? Can they be freed without pulling the head? The motor sat in garage over the winter before it was put in. Could this be what caused them to hang?
Sorry for the original mis-info.
Dennis.

Had a defective shreader valve and bad O ring one time on cylinder compression tester that almost fooled me into pulling motor. Also, unlike auto motors that have very flexible motor mounts to provide soft ride, marine mounts are a lot stiffer and sometimes you really can't notice out of kelter vibrations, ie plug not firing. With that said, perhaps cam lobe worn down? You not gettig at least one cylinder providing 150+ psi seems too odd?

 

[rainman01]

Re: no fuel to 2 cyinders?

Alright gentlemen, The head is off. The test with air pressure did indeed ID the problem. The head gasket is blown between the 2 cylinders. Quite a nice hole also, 1" plus. Mystery is solved. Now to replace the darned thing. I can replace the head gasket for about $30.00 which I can get tomorrow and have her on the water this weekend. My gut tells me to order in the full kit ($80.00 and a week to get it) and replace all gaskets involved in removing the head. Any opinions?
Tank1949, I have 2 testers with spare O-rings. Had that happen to me once also. 1 has a shredder valve, 1 is old school without the valve. Compression came up on the 4 good cylinders when I started fooling with the valve lash. Did not fine tune them as I suspected I might have to remove the head. I believe that compression will come up when adjusted properly. Again, I am not even close to being an expert, but what I can find suggests that 120 to 125psi is excellent compression for this motor. Is that wrong?
Wish I had asked questions here when we replaced the motor. We re-did the out drive at the same time ourselves. I'll bet you folks would have saved me a ton of time.(and irritation). I am sure I will be back as I re-install the head.
You folks are all great,
Thank you,
Dennis.

 

[achris]

Re: no fuel to 2 cyinders?

Great to hear you found the problem... Now you need to find out why the gasket blew. If you don't fix the root cause, you'll be replacing that head gasket fairly soon...

Before you put the head back on, check the block and head for flatness and twisting. And while the head's off, verify the timing marks on the crank pulley line up to TDC when #1 piston really is TDC.... Then when the heads back on, check the timing.

Chris.....

 

[tank1949]

Re: no fuel to 2 cyinders?

Great to hear you found the problem... Now you need to find out why the gasket blew. If you don't fix the root cause, you'll be replacing that head gasket fairly soon...

Before you put the head back on, check the block and head for flatness and twisting. And while the head's off, verify the timing marks on the crank pulley line up to TDC when #1 piston really is TDC.... Then when the heads back on, check the timing.

Chris.....

Rainman, thought you said motor recent rebuild? Or, at least implied it. Perhaps I misundestood. If that re-built has been in salt h20 since early 80s, You may want to find a good auto core at junk yard and retrofit to marine. While out look inside water passage ways for excess rust. Just a suggestion.

 

[rainman01]

Re: no fuel to 2 cyinders?

New gasket set to arrive tomorrow AM. Would one of you kind sirs know the FLB torque and sequence. I have always torqued from center outward, equally to both ends. Does this hold true on this motor? Also Manifold torque specs if possible. I am totally unfamiliar with them.
And yes, again, it was re-built last fall. stored over winter and put in early July. Head was checked Sat. at NAPA shop and is good. Block, am going to have to take my chances on. Boat is still tied to dock, in no position for removal.
Thank you gentlemen,
Dennis.

 

[stonyloam]

Re: no fuel to 2 cyinders?

Info for your engine should be in here: Boatinfo - Mercruiser Service Manual nr. 3 - 1978-1984 - All 4 cylinders, L6 & V8 Engines

 

[tank1949]

Re: no fuel to 2 cyinders?

Rain, what caused head to blow gasket???????? Clogged water jacket. Please don't throw good money and not check out other potential issues. Just a suggestion. Been where you are more than I care to admit!

 

[rainman01]

Re: no fuel to 2 cyinders?

The info I have been given is that slop (wear), in the distributor is most likely the culprit. I have not heard of this before but the local marine dealer/shop and the mechanic at the NAPA machine shop both said that is the most likely reason. Apparently it will cause too much pressure to build??? I am told it is a somewhat common problem with the older engines. I have the distributer from the old engine which seemed to be fine so I am going to put that in. Also am considering going to an electronic set up. Any thoughts on this. And by the way, the mechanic who re-built this motor seems to be laying low at this point. Can not gat ahold of him. Interesting......
Thank you for the link on the engine Stonyloam.