no compression = no power

[shelikesit]

Well it's come to total idiocrosy on my part.<br /><br />A compression test showed absolutely no compression in # 1 or 5 and 30 psi in # 3<br /><br />Starboard side had 150 psi on all 3 cylinders.<br /><br />Can I get away with taking the head off and checking for valve sticking or rusting or am I going to find cracked cylinders walls and should just pull the motor.<br /><br />The latter would love to be avoided if at all possible. Someone sure did a great cover-up when selling me this boat...............

 

[Reel Poor]

Re: no compression = no power

Its most likely head problems, but I would recommend a cylinder leakdown test. This will pinpoint the problem.

 

[Don S]

Re: no compression = no power

At this point, you might as well pull the head and have a look. The leakdown test would be handy, but If there is a lot of rust around the rings, they will leak air into the crankcase, but the valves will be rusty too, so you will hear air leaking for both the intake and exhaust.<br />Pull the head, look at the cylinders for cracks. They will be obvious. If you have cracks, then pull the engine. If you have a lot of rust around the rings, the engine needs to come apart to rering it anyway, along with honing the cylinder.

 

[shelikesit]

Re: no compression = no power

Thanks, Somewhat bright side. I'm going out now to see if my setup has the drive shaft extension. If it does, the drive doesn't have to come out to pull the motor.<br /><br />Tomorrow I'll pull the head regardless........<br /><br />How do I do a leakdown test please.<br /><br />Thank You.... sounds like there's a chance in only head work. I plan to order the exhaust manifolds this week or next.<br /><br />I'm sure I'll need them anyway.

 

[Don S]

Re: no compression = no power

Don't order parts until you know what all you will need.<br />Who knows, if you need a new engine, it may come with new manifolds. To early to say.<br />Were you boating in salt or fresh water?<br />If you don't know how to do a leak down test, now is not the time to go buying new special tools when you already know the problem. WATER. You need to pull the head inspect everything and then determine what to order.<br />You could get the engine at TDC and hook air to it and listen, but my guess is you will hear air leaking everywhere. <br />Unless your engine is in the center of the boat, you have to pull the drive. That's the easy part. Takes all of 5 to 10 minutes.

 

[Reel Poor]

Re: no compression = no power

Remove all plugs. With engine at top dead center (compression stroke..one cyl at a time) put air in the cylinders and listen for escaping air.<br />Intake valve problem..air leaks thru carb<br />Exhaust valve problem..air leaks thru exhaust<br />Ring or piston problem..air leaks from crankcase

 

[shelikesit]

Re: no compression = no power

OK Great, leakdown test is not happening. Port side head is coming off as soon as the rising sun hits the coast.<br /><br />I'll then know more when I can see the inside of the coffee cans.<br /><br />Ok Don S, if your still listening because I try to follow your lead, should I at least think about getting the alignment tool if the motor has to come out.<br /><br />Thanks again..........

 

[Don S]

Re: no compression = no power

should I at least think about getting the alignment tool if the motor has to come out.

Absolutly.<br />Every time the drive comes off the alignment should be checked. If suddenly it's off, then the reason needs to be found. Mercruiser engines loose rear motor mounts, which if not caught will cost you a coupler (about $300+)<br />The drive should also be pulled yearly during winterizing and as just plain old routine maintenance.<br />If you aren't going to let the pro's do it, then you better learn how to do it like the pro's. Which includes the tools.

 

[tashasdaddy]

Re: no compression = no power

dan did you try the water hose trick? what happened.

 

[shelikesit]

Re: no compression = no power

I deleted this before I sent the last post-<br /><br />"That was probably a very dumb question and I apologize ahead of time."<br /><br />I should of just left it because it was a valid statement referring to the alignment tool. I see the modifications for that tool in both manuals, but I also seen if I ordered a new one, these days new ones don't need to be modified.<br /><br /><br />Tashasdaddy, no on the hose test. I did the compression test first and stopped when I thought the compression tester that I just bought was broke. Why, because I started at # 1 and there was zero, nada, none. What little commonsense I have left told me to jump tot the starboard side and check one of those cylinders, when they read 150 I double checked port and hit the forum.<br /><br />You gotta know when to fold em........... but I'm not ready to walk away, and definitely not ready to run....... I live in Daytona and we have the AMI institute here and ir inclides boats, I'll be 40 next week, maybe it's time for a career change........

 

[shelikesit]

Re: no compression = no power

An inch of the head gasket between 1 and 3 was gone. The exhaust valves in none of the 3 cylinders on port side were seating and looked burnt and rusted on the valve shaft.<br /><br />Had a mechanic look at the cylinders and cylinder walls and said they looked fine, maybe can get away with replacing head gasket and having head redone and move on successfully.<br /><br />As for the exhaust manifold on that side, if there was suppose to more to the stem of the riser, it's nowhere to be found. It looks like a big megallon shark tooth about 3 inches long. The rest of it is probably down around my shutter plate or in my bellows.<br /><br />Thanks for all the help, looks like head work and manifolds may get this boat back on the water. Oh yeah, and cleaning of the white milkshake substance has to fit in somewhere too........................what a mess.............. did someone say to use seafoam ??? well, if it's suppose to turn oil into foam, it worked............. if it's suppose to break matter down and help clean........ try something else when it comes to your crankcase oil................<br /><br />Questions-<br /><br />Will a head from a 90 model 4.3 from the scrapyard work on my motor if this head is actually bad???<br /><br />Would the valves and rockers be the same or would I need new ones from Mercury?<br /><br />Since I'm doing this alone, would it be easier to take the lower unit off and then the upper unit to make the sterndrive disassembly lighter or should I get some help and take it off in one piece. <br /><br />I have to replace the trim tab bolt anyway, that's why I wanted to separate it.

 

[Reel Poor]

Re: no compression = no power

Definately replace the manifolds. Water leaking in from them is probably the cause of the gasket piece missing (cant compress water so it pushed the gasket thru). I think you would be ok with the scrapyard head if its from a truck, I usually like to match up casting numbers though. If the head is the same the valves and rockers will work also. <br /><br />Your choice on the drive. While you have it apart replace the water pump assembly also, and service the drive. Be sure to check bellows and hoses, might also check shift cable while its apart.

 

[Don S]

Re: no compression = no power

If you are going to replace the head, at least get one of the same casting number to match the one on the other side.<br />You mentioned a 90 one, but you never mentioned what year you engine is. So can't say from that discription.<br />Are you sure the old head can't be repaired? Maybe a couple of new valves to replace the rusty ones, clean them up and ......?????

 

[shelikesit]

Re: no compression = no power

Thanks for both replies. I'm looking at BARR manifolds from marineparts.com They're in Jupiter, Fl a couple hours below me.<br /><br />A bit pricey @ $760 shipped but seem worth it. 3 year warranty and the guy says they don't get many returns.<br /><br />As for the heads, I'm in the process of taking the other side off now. Bolts broke on the risers from the port side so I couldn't separate the manifold. I got all 4 to come out on starboard and Don S, there's about 3/16" at the most in the thickest part, so thanks on that tip. Less than 1/4" and they're trash <br /><br />I took pictures of most of my steps and bagged all my bolts and parts. Can't wait to get a good look at the mess in the bilge and get the boat clean the way I want it, from the bottom up. I'd like the bilge to be as clean as the dash if that makes any sense.<br /><br />Someone said anal about cleanliness in the motor compartment, I'm learning down here you have no choice.<br /><br />Thanks A Million Times!

 

[shelikesit]

Re: no compression = no power

Wait a minute, you never said the other head had to come off.<br /><br />I can get one machined and leave the other alone??????<br /><br />If that's the case I have tools to clean up. The manifold had to go anyway, especially before it does blow that gasket from going bad.

 

[Reel Poor]

Re: no compression = no power

Not that it has to come off...but if I were doing it I would do both sides. Really no additional cost either except fo the machine work that it may need also. The gasket kit will come with enough gaskets to do both sides.

 

[shelikesit]

Re: no compression = no power

Ok Great, I'll sleep on it, the starboard side was showing 150psi in all 3 cylinders.<br /><br />I think since I'm this deep I may take the head off and have it done anyway.<br /><br />Anyone else ??????

 

[shelikesit]

Re: no compression = no power

Sorry to keep this going but after looking at this head closer, the # 3 exhaust port has less than 1/16" of mating surface. If there's a tollerance to that mating surface, this head has none. It looks like it may have been wearing away and rattling manifold to head for awhile.<br /><br />Will a machine shop be able to get more surface there or are they just going to say it's trashed just from that? That valve was rusted the worst also.<br /><br />If it's done with I'll go straight to the scrapyard. <br /><br />The numbers I found on this head say<br /><br />14094768<br />H259<br /><br />It's 1990 V-6 GM 262, if I go to a 1990 truck and only buy one head should something match those numbers?<br /><br />Thanks!

 

[Reel Poor]

Re: no compression = no power

I think Bondo's the man for that question. He has a lot of experience with the truck to boat motor conversions.<br /><br />If the heads are exact matches that number(14094768) will also be on the head your looking for.

 

[shelikesit]

Re: no compression = no power

forgot to thank you reel poor, yes i found the casing match and both the one from the scrapyard and the good one from the boat are going to the machine shop tuesday.<br /><br />the guy at the machine shop took one look at the mating surface and said the head from the boat was trash.<br /><br />mating surfaces have tollerances, i really like learning this stuff if boat mechanics wasn't so costly, it'd be pretty fun to do for awhile