Carb or worse?

[Scott Danforth]

No, a failed manifold gasket between the head and manifold would only leak exhaust and flame and would make popping noises when running

Do a propper compression teat and leakdown test

135-150 psi is a good range
115-135 psi is a worn engine range
100-115 psi is a really worn engine needing a rebuild

10psi is usually a sign of something majorly wrong

 

[alldodge]

150 is for a new motor. Needs at least 100 to run at all. Worn motor in the 135 to 140 would be good. Best to check readings after motor is warmed up, but even cold should get close

Exhaust manifold gasket will make it loud but their would be no reduction in power.

 

[nola mike]

If I can stop sobbing enough, I need to get a real compression tester that screws into the spark plug holes instead of trying to hold on the hole at correct angle. In a perfect world, 150 +/- 5 across all 4, correct?

Yes

Another stupid question but I have to ask: would a failed exhaust manifold gasket lead to these symptoms of no power or acceleration and louder than normal operation? Could this have been the cause of my woes? That would obviously be assuming I’m NOT getting an accurate compression test but not totally out of the question. Sense my optimism?

No. (Sorry)
What COULD cause it is water in your exhaust leaking back and rusting a valve open.

 

[Eric 3.7LX Alpha 1]

Yes

No. (Sorry)
What COULD cause it is water in your exhaust leaking back and rusting a valve open.

That's what I'm thinking also.. or maybe a bent pushrod, not allowing the valve to open to build compression? You could probably tell by pulling the valve cover off and looking at the valve spring/rockers. If the valve spring is compressed and the rocker is loose...

 

[nola mike]

That's what I'm thinking also.. or maybe a bent pushrod, not allowing the valve to open to build compression? You could probably tell by pulling the valve cover off and looking at the valve spring/rockers. If the valve spring is compressed and the rocker is loose...

If the valve is rusted (and not allowed to *close*), the bent pushrod is part of the deal I think.

 

[Krsowles]

So after another night of continual learning, I have more news. I tested compression with a more professional tester. Cyl 1 165, 2 and 3 were about 15 and 4 was 155. Between 2 and 3 was where manifold gasket was blown out, if important. Pulled head of (1st time so go easy!) and everything looked pretty good and clean except most of gasket between 2 and 3 was gone, completely.
I haven’t cleaned the block or head yet but both looked good. Took a large square that has not been used and tried to find any light coming under it as I moved it around and wasn’t any. I hope to clean block and head up well tomorrow evening and have a mechanic friend use a tool made for it and show how to check for the .008 tolerance (I believe) with a feeler gauge. How would I know if valves on 4 cyl rusted? That cyl has decent compression but I’m nervous because that was the cylinder that had water in it. As far as I know, engine never overheated, never “hydro locked” on a start and oil in drain pan does not show signs of water. Could bringing it back to launch slowly and not running well allow water to back up exhaust to #4? Again, manifold and riser appear to be almost new and riser gasket was in very good shape. I’ll need to confirm flapper in place but was part of service right before PO stopped using boat, according to bill. Also, there were no visible leaks of a cracked block on outside of block anywhere. I’m curious how water got in #4. The piston, plug and valves all looked quite similar to the other cylinders so I’m guessing there wasn’t water in it for long. I apologize for rambling but my pea brain is racing! Thanks again for all your input!

 

[alldodge]

Have a valve job done on the head. The machine shop will check for flatness and cracks.

Check the block for flatness using a metal straight edge, like a framing square or other.

If the head or block isn't cranked, then water came in through the head gasket

 

[Krsowles]

Alright, here’s where I lose total respect but I have to ask. It’ll be several weeks before I can get head done, summer is short and Father’s Day fishing trip this weekend. IF head and block found to be good this evening, can I reassemble and use motor if it runs? Am I risking more than just the time to take apart again and replace gaskets an extra time?

 

[alldodge]

Get a straight edge and check flatness. If both are flat then all it will cost ya if it fails is another head gasket

 

[Krsowles]

Ok, thanks. I will confirm block and head flat and within the .008 spec., confirm exhaust flapper in and working and check valves and make sure they’re seating (flipping head and pour fuel on them and check for leaking?) as well as confirm 4th cyl valves moving freely and not stuck/bent. If all good, I’ll try it . If it fails again and I’m only out my time and the gaskets, I’ve learned more than the price! I’ll update results and also, plan on having head checked professionally, when possible. Thanks for all the input, it’s been very helpful!

 

[alldodge]

Bit late, but push rods and lifters should be kept in original position. Probably still be ok, but always best to keep them in order

When installing rocker arms, the valve must be fully closed. Once closed zero lash is determined and then 3/4 of a turn more

Zero lash is found by holding the push rod in position, and moving it up and down. As the rocker nut is slowly tightened, the up/down will get less. Once there is no more up/down felt with your fingers, this is zero lash. Now turn 3/4 more and your done

 

[Krsowles]

I kept pushrods (and head bolts) in order so they go back in same location they came out of. I found a video this afternoon about adjusting valve lash, was very similar to what you said. It also gave an order of which valves to do at TDC and which I should do after 1 revolution of motor, after doing the valves from TDC. From what I’ve “learned” so far, timing off could build pressure and blow out head gasket. Thoughts? If so, anyone have specs or directions on how to do a 1998 3.0? May be different for years close to 98 and some discussion about not doing it right could do it again.

 

[Krsowles]

Timing hasn’t been touched, to my knowledge, but who knows. Checking it may not be a bad idea.

 

[Krsowles]

I’ve done some more “learning” today. I cleaned up the head pretty well. Not all uniform color but definitely as smooth as I was going to get it. Flat bar and feeler gauges told me there were several spots that .009 would try to slide through. Put head aside to contemplate sending to machine shop in couple weeks or put it together and see if it’ll hold a couple weeks. Pulled manifold to clean and prep that. Inside cyl 2 looks to be a large crack I missed the other night when I pulled it. Guess I won’t quit my day job! So this is probably where my water is coming from. My question for the brain trust is this; if water comes into cyl 2, can it build enough pressure to blow head gasket out between 2 and 3? Then enough pressure to blow out manifold gasket in same location? I’d feel much better knowing what caused this to occur rather than just putting back together and praying it’s better. I’m picking up a used manifold tomorrow that’s supposed to be excellent shape () and I also found a shop to do my head and will have it back by Wednesday, so doing that as well. Thanks again for your input!

 

[alldodge]

Don't know how it cracked, could be a defect or maybe got to hot.

if water comes into cyl 2, can it build enough pressure to blow head gasket out between 2 and 3?

Don't see water from a crack manifold to blow a head gasket, but if a head gasket blows it can build enough heat to crack the manifold

Then enough pressure to blow out manifold gasket in same location?

Same as above, if it gets hot enough maybe, or if the manifold was not torqued to spec, or not flat

 

[Krsowles]

Thanks, alldodge. I don’t know if it overheated but I believe PO would’ve told me if he knew about it. That said, I don’t know. I’m guessing the crack from poor winterization and was hoping for a sequence of events from that, that would explain all this.

 

[Krsowles]

Update: had head flattened and reassembled motor, what fun! Torqued the head to 95 ft lbs, in 30 lb steps. 95 came from the Mercruiser bulletin 98-14 and plug gap set to .035. Adjusted valves at TDC, rotated one turn and then did the ones not done at TDC. Go to fire it and some times it sputs and coughs with the occasional backfire but won’t start. Looking for any insight, thanks!

 

[Krsowles]

I have checked spark and fuel, both good. Timing hasn’t been touched except by valve lash adjustment.

 

[Bondo]

Ayuh,....My guess is, the distributor is 180* outa time,....

 

[Krsowles]

Thanks Bondo. I have a follow up then. Can the distributor get 180 degrees out if I never removed it? I also have the distributor wired 1-3-4-2, how it was when it was running. The spark arrestor has written on it 1-4-3-2. Can anyone set me definitively straight on the 98 Mercruiser 3.0 firing order? I’m 95% sure it was 1-3-4-2 when I took it apart but my antique brain may be slipping. Good news is I can’t remember! Thanks again