No compression cylinder 2 and 3

Golson Molson · Sep 9, 2013

Hi new to the forum sorry if this is redundant. I have read several posts on this but haven`t found the real answer to my question I`m about to ask.

Took a new to us boat out on its second run yesterday and just couldn`t get the boat to run. The first run out, it was hard starting didn`t really warm up very well, had slight hesitation when pegging the throttle but ran fine on plane. Did a compression test when I got home on all 4 cylinders and 2 and 3 are zero.

Its a mercruiser 140 IO, Model number MCM140, serial number A344469 I suspect it is somewhere around a 1985.

Now my question: What is the major cause of head gasket failure on these engines. He had done some work to the cooling system at the beginning of August so now I suspect he may have over heated the engine.

Volphin · Sep 9, 2013

Re: No compression cylinder 2 and 3

That's more than a blown head gasket if you are reading zero for compression. You have a serious mechanical failure. I think you need to shop for a new engine if the boat is in good shape.

stonyloam · Sep 9, 2013

Re: No compression cylinder 2 and 3

Zero compression on two adjacent cylinders is a symptom of the head gasket blown between them. Overheating, or a warped head or crack can do it. Time to pull the head and find out.

Volphin · Sep 9, 2013

Re: No compression cylinder 2 and 3

I'd go with a cracked head, but a blown gasket would show at least some compression (10-15psi) IMHO. Regardless, the head must come off to find out.

I hope it IS just a gasket for you OP.

Golson Molson · Sep 10, 2013

Re: No compression cylinder 2 and 3

Thanks for the reply's.

Well I found the problem with the no start at least. The green wire leading to the coil was broken inside the wire at the coil connection. Stripped it back solder it back on, hooked up the hose and it fired up. After warm up it ran fairly smooth at 900 rpms. A marked improvement from Sunday when it would barely idle. Redid a compression test and the compression had increased to 120 on cyl. #1, up from 90 and 115 on cyl.#4 up from 60. Still 0 on cyl's 2 and 3. There was a little blue smoke from the exhaust and the water was warm, indicating my water temperature sending unit or the gauge is broken. Took the valve cover off to inspect the lifters and everything appears normal. The oil is at full and has no indication of water in it. All the spark plugs when pulled were warm and have a slight rusty brown appearance to them.

Full tune up today, all the wires are cracked, distributer and rotor show signs of burning and the plugs are well worn (it was a cheap boat). Add some engine and gas additives and move on from there if there is no improvement.

Could sticking rings show no compression?

Volphin · Sep 10, 2013

Re: No compression cylinder 2 and 3

Low compression, besides the obvious mentioned previously can be caused by:
Worn cylinders
Improper ring clearances
Stuck rings
Burnt Rings (Hot combustion gases leaking by rings and piston)
Valves improperly adjusted (too tight)
Valves not seating (worn seats, burnt valves, etc)

One remedy for stuck rings I have used in a pinch is Marvel Mystery Oil or GM top end cleaner. (Not sure if the GM stuff is available to the public)
Remove the spark plugs on the offending cylinders and fill them up with the MMO.
Let sit overnight at least.
Roll the cylinder by hand to get the majority of the oil out, then use the starter to do so.
Careful... you can make a mess real quickly.

Install plugs and run the engine. Recheck compression.

Another way to test where compression is being lost is to apply compressed air to the cylinder.
Put 80psi to the cylinder. Then listen at various points and tell where the problem is.
Air escaping out the exhaust indicates an exhaust valve problem.
Air escaping out the valve cover or engine crankcase breather indicates a piston or ring problem, Etc.

Golson Molson · Sep 10, 2013

Re: No compression cylinder 2 and 3

Excellent advice. Thank you

stonyloam · Sep 10, 2013

Re: No compression cylinder 2 and 3

Remove the plugs from 2 & 3. With the valve cover off, turn the engine until both valves on 2 are closed. Put compressed air into the #2 sparkplug hole and listen to see if it comes out of #3. If it does you are blown between the cylinders.

Southtowns27 · Sep 10, 2013

Re: No compression cylinder 2 and 3

Don't spend any money on tune up parts or oil additives. None of those things are going to fix a zero compression issue. You need to pull the head and find out what is going on. As others have stated, it is likely a blown head gasket between cylinders 2 and 3.

bonzoscott · Sep 10, 2013

Re: No compression cylinder 2 and 3

Stoney's was a good suggestion. I was going say a leak down test. But Stoney's comment would be quicker. If you're not familiar, you can buy adapters at auto parts store that come in a set. They are threaded for different spark plug sizes and you can hook you compressor hose to them.

Golson Molson · Sep 10, 2013

Re: No compression cylinder 2 and 3

Compressed air in #2 and out #3. Manual is on order for the engine and should be in tomorrow. How many hours approximately for a tear down for a reasonably handy backyard mechanic?

Looking to get a little fishing in before the end of the season,

Bondo · Sep 10, 2013

Re: No compression cylinder 2 and 3

Golson Molson said:
Compressed air in #2 and out #3. Manual is on order for the engine and should be in tomorrow. How many hours approximately for a tear down for a reasonably handy backyard mechanic?

Looking to get a little fishing in before the end of the season,

Ayuh,.... Welcome Aboard,... Poppin' the head off shouldn't be more than a few hours,....

Take Pictures, 'n post 'em up,...

The Odds are, Not in yer favor,...
Chances are, you'll need a head, or maybe mill that 1 to clean it up,...
Ditto the Block,...
Generally speakin', 1 or the other, or both get fried by the combustion gases passin' through,...
If there's No cracks, machinin' might Fix it,....

Yer Machinist can tell ya what ya got to work with,...

Good luck, 'n keep Us posted,.... We'll walk ya through it,.......

Btw,.... The Factory manual can be found by followin' the links, found in Don'S Adults Only section, at the top of this forum,...

Golson Molson · Sep 11, 2013

Re: No compression cylinder 2 and 3

Head is now off and sure enough, 1.5" gap missing between cyl 2 & 3. Took about 3.5 hours with at least .5 hours cataloging parts and taking pictures. Minimal scaring on the block and minimal scarring on the head. I will take the head to our marine shop and get their recommendation. However, it is slightly more scarred than the block. No scarring in the cylinders and oil pressure was good last time it ran. Question, should I wet paper sand the block to remove the minimal scarring or should I just leave it? I'm thinking machine the head and lightly wet sandpaper the block with 600 grit just to remove the roughness. Thoughts?

Bondo · Sep 11, 2013

Re: No compression cylinder 2 and 3

Golson Molson said:
Head is now off and sure enough, 1.5" gap missing between cyl 2 & 3. Took about 3.5 hours with at least .5 hours cataloging parts and taking pictures. Minimal scaring on the block and minimal scarring on the head. I will take the head to our marine shop and get their recommendation. However, it is slightly more scarred than the block. No scarring in the cylinders and oil pressure was good last time it ran. Question, should I wet paper sand the block to remove the minimal scarring or should I just leave it? I'm thinking machine the head and lightly wet sandpaper the block with 600 grit just to remove the roughness. Thoughts?

Ayuh,.... Bring yer head to a Machine Shop, not a Marina,....

Usin' a good sized flat file should give ya a Flatter surface on the block,...

Golson Molson · Sep 11, 2013

Re: No compression cylinder 2 and 3

Bondo said:
Ayuh,.... Bring yer head to a Machine Shop, not a Marina,....

Usin' a good sized flat file should give ya a Flatter surface on the block,...

Would minor scratches in the block be a concern after I file it?

stonyloam · Sep 11, 2013

Re: No compression cylinder 2 and 3

It is called draw filing, pretty easy to do and should leave a smooth surface. Watch this video: https://www.youtube.com/watch?v=9cxYnsJRM_c

ricohman · Sep 12, 2013

Re: No compression cylinder 2 and 3

Golson Molson said:
Would minor scratches in the block be a concern after I file it?

Unless you have done this before, I would suggest getting some experienced help here. I have seen some perfectly good blocks ruined by filing and sanding. Unless you can lay down the 60-120 microinches with sandpaper and a file.
It's not difficult, but experience can count in this situation.

Volphin · Sep 12, 2013

Re: No compression cylinder 2 and 3

That's assuming the file is a perfect straight edge, which they are not. Leave the block alone, except to prep it for the head gasket. I use a medium 3M pad on a air powered 90 degree gasket scraper. A drill gun works as well in a pinch. The head is where warpage occurs more readily due to its thickness and torque loading. The machine shop will mill it flat. Might as well do a valve job too.

Southtowns27 · Sep 12, 2013

Re: No compression cylinder 2 and 3

Post a couple pictures of the block

Golson Molson · Sep 12, 2013

Re: No compression cylinder 2 and 3

I used 4 different files on the block after cleaning to remove residue gasket crap with very light pressure. There is no scoring, it was just the residue from the gasket. They were all fine files used for ski sharpening. Put my 12" carpenters square on every inch of the block and it is flat. The head was sent in to Ideal supply (our only place to grind the head within 50 miles), New head gasket, exhaust/intake gasket, exhaust gasket, t-stat housing gaskets have been ordered along with 2 rubber mounts for the exhaust and missing water return flap in the exhaust.

Good news. I spoke with the gentlemen who sold the boat to me and he feels very bad about it. He has agreed to pay for the parts as I am doing the work myself.

Will post pictures later tonight when I figure it out.

No compression cylinder 2 and 3

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