1977 Merc 2.5L 153 cid 120 hp head troubles

c00ljim

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Jun 1, 2004
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Well shame on me. When I got this boat the engine was siezed, so I poured all kinds of gunk into it to free it up, eventually with the use of a pry bar I got the engine to take its first steps towards life. After a few other new parts were installed, she purred like a kitten, and I was on the water. Howerever, flash foward to today. I did a compression test, and I got 120 on the 2 outside cylinders, and only 35 on the 2 inside ones. Just this morning, I pulled the valve cover for the first time. There was a broken push rod laying there. (This probably happened, when I forced the engine to free up). Next up I am starting to remove the head, but I am a little lost. I see there are 10 bolts that have to be removed, and here are my actual questions. What is the recommeneded torque settings for installation, what is the tightening pattern? I'll be sending the head out to check it for being warped, and have the valves looked at the same time. Yes I am replacing the head gasket, as that seems to be the general consensus of whats wrong. While the head is off, I will do a good look see of the pistons as well.
 

ron7000

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Jul 10, 2004
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Re: 1977 Merc 2.5L 153 cid 120 hp head troubles

I'm not familiar with that year and model, but it sounds like it's just an inline 4 cylinder?<br />If that's the case, the tq pattern would be same as my '02 3.0L, which is:<br /><br /> 8 4 1 5 9<br /> 7 3 2 6 10<br /><br />the idea, same as with any cylinder head, is you tighten from the center outwards.<br />I don't forsee the torque setting being any different than mine, I belive they are 1/2" bolts which is 90 lb-ft final setting.<br />Make sure you use a marine head gasket, such as felpro marine.
 

c00ljim

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Jun 1, 2004
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Re: 1977 Merc 2.5L 153 cid 120 hp head troubles

thanks ron7000,<br />for the speedy response, and the heads up, heh no pun intended...... :)
 

c00ljim

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Jun 1, 2004
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Re: 1977 Merc 2.5L 153 cid 120 hp head troubles

Well now, my bolt size is .75, or 3/4 of an inch bolt head, will this now make a difference in the torque setting?
 

Airpacker

Seaman Apprentice
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Jul 27, 2004
Messages
35
Re: 1977 Merc 2.5L 153 cid 120 hp head troubles

3/4 is the head size, not the thread size. A 1/2 inch bolt will have a 2/4 inch head.
 

c00ljim

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Jun 1, 2004
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Re: 1977 Merc 2.5L 153 cid 120 hp head troubles

Airpacker thanks, but I did say head size, and ron7000 simply said bolt size, which I won't know for sure until I extract mine. You say a 1/2 inch bolt will have a 2/4 inch head size, well forgive my asking but doesnt 2/4 = 1/2????<br />Anyway, maybe I should just wait, until I extract mine, and then we'll know for sure.<br /><br /><br />Anchors Away m8ty
 

xltier

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May 20, 2004
Messages
636
Re: 1977 Merc 2.5L 153 cid 120 hp head troubles

very possible that the piston rings are stuck in the ring grooves.as the rings wear they need to expand to keep the compresson up.i think the 2/4 is a misprint and he meant 3/4.the bolts are 1/2 inch thread size.
 

c00ljim

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Jun 1, 2004
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Re: 1977 Merc 2.5L 153 cid 120 hp head troubles

xltier <br /> <br />Are you saying that may also be why the compression is shot for those 2 inside cylinders?<br />Would there be any others symptoms, say like, oil fouled plugs, for those cylinders? I'm not exhibiting anything other than a power under load failure. We have already ruled out the fuel circuit in its entirety, and I did the compression check, then I removed the valve cover, as well as side dust cover. We we're going to do just a visual of the pistons, but I'll also take a peek at whether or not the rings are stuck as well. Will post more in a day or so. This being my first attempt at any of this. :)
 
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