'73 115 merc. No compression in #3 cylinder

[FoolOfAFisherman]

Well, like the title says, got a 115 inline 6 motor with no compression in cylinder 3. And also, as my name suggests, I'm a fool of a fisherman for buying this boat without checking the compression first. The guy said it needed a new starter (which it does), but it ran fine before it went out. I figured since the boat ran, it had to have compression. Wrong. Anyway, has anyone done this type before and how hard is it to hone and get an oversize head for this motor assuming that's the prob?

 

[Gomer50]

Re: '73 115 merc. No compression in #3 cylinder

Famous words (ran fine last season).Dont feel bad your not the first nor will you be the last been there done that.
You can check to see the number three piston/rings by taking the middle fuel port cover off.There are three of them on the starboard side of the motor.
If not all jacked up it can be rebuilt fairly cheap.I redid my inline 6 same cylinder #3 bad rings.
I honed out all 6 cylinders and put in new rings and she is good to go.
A good service manual and some time is a must.If all the rest of the motor is in good condition I would say its worth it.Take into consideration that parts for these motors can be expensive (especially Ignition parts).

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

Thanks for the reply. I think it'll be worth it then. The guy before replaced all the wiring, the carbs, the throttle assembly, distributor, all fuel hoses. Far as I can tell, the motor will be in good shape once the cyl is good and I get a new starter. I gotta get a manual and then I'm gonna dive in. Any tips for me I should know like what not to do lol. Thanks.

 

[Gomer50]

Re: '73 115 merc. No compression in #3 cylinder

Make sure you have 6 plastic baggies numbered from 1 thru 6 so all the needle bearings you remove from the piston rod/crankshaft are put in the baggy reffering to the cylinder/crankshaft it came off of as well as the needle cage.So when putting it back together each has the same needles on the same piston rod / crank. Notice when unbolting the piston rod from the crank they fit together one way (perfect) mark them.I would recommend getting a complete set of gaskets as well.Check your upper and lower bearings on the crankshaft.Be carefull when removing the exhaust platte cover those bolts have been on there for awhile and can snap off real quick.All in all a pretty simple operation if you got the time and patience.I also used a 3 inch flex hone if I remember right works like a charm.

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

Thanks for the tip! I was already thinking about needing to be meticulous about what goes where just didn't have any plans yet. Good tip, I'll do just what you say. Also, any comments about what brand of service manual I'll need. I've heard that seloc brand covers to broad a spectrum to be detailed enough to be informative. I have one for my 4.5 merc and although this is true, it was still informative and detailed enough for me to everything I needed. But this project will be a little bigger than that.

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

Also, is that hone the kind you chuck in a drill?

 

[Gomer50]

Re: '73 115 merc. No compression in #3 cylinder

Yes the flex hone can be used in a drill. I would suggest a genuine service manual for your motor.Very detailed and leaves no questions unanswered.The folks here on this forum will also point you in the right direction should you ge lost.

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

Where could I pick one of those manuals up at? I've looked and can't find any.

 

[Gomer50]

Re: '73 115 merc. No compression in #3 cylinder

you might get lucky on ebay or look on the sticky notes here on iboats forum for manual download.I will give a look see and let you know.

 

[Gomer50]

Re: '73 115 merc. No compression in #3 cylinder

This is the one I use. Works okay...
https://docs.google.com/fileview?id...hkYTUtZTBkNDNmOTNiY2Iz&authkey=CPmdsO8K&hl=en

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

Can't view link. I think it's only viewable by you.

 

[Gomer50]

Re: '73 115 merc. No compression in #3 cylinder

Its not for viewing its for downloading.When you click on the link in the upper left hand corner of the page it say's download 205mb click on that and follow and save to your computer.It then opens as a PDF file.

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

Got it! Thanks a lot! There's a lot of good information in that manual. I like the "Good" and "Bad word" information. That is gonna be helpful to know what to look for. Btw, i have reason to believe this motor may have been in saltwater. Anyone have any experience with old saltwater motors and tips to getting things unstuck? I'm worried about breaking heads off bolts.

 

[jbjennings]

Re: '73 115 merc. No compression in #3 cylinder

I like to use heat, but some of the bolts are just not going to come out. The advice I would give is that when some do break off, DO NOT under any circumstances use an "EZY-OUT", no matter what you hear. And don't be too proud to visit a machinist, either. They have all the tricks and tools to get sheared bolts out correctly. It will be worth the money to avoid boogering it up worse to pay the machinist. Remember too, that aluminum melts at about 900 degrees without any warning whatsoever. It will go from solid to liquid in an instant without turning color at all, so be very careful with the heat. You can also warp parts with heat as well. Getting it really warm, then cooling, then warm, then sudden cooling can be helpful, though.
JBJ

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

thanks for the tip. I may have an advantage being that I am a machinist. However, I'm just wondering, I broke 4 bolts on the exhaust cover. I thought that was pretty good considering there's about about 24 or so and the motor is almost 38 years old. If there's a good bolt then a broken one then a good one and so on, anyone know if it will seal properly? Also, I tried to take the bolts out of cylinder block cover but i couldn't get any to budge. I felt them turn slightly but didn't see the threads on the other side turn so I stopped. Being that I'm a machinist, are there any machinists that can tell me the procedures and tool required to extract a broken bolt besides putting it on a mill and drill them out?

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

I believe i found the cause of my compression leak right here. Piston 3 rings are no good. You can see scoring wear the ring is wore down. Now...to get the cylinder block cover off....

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

A thought occurred to me...can I hone the cylinder without taking the block cover off? Hone it from the crankshaft end since I'm going to have to take it apart anyway?

 

[Gomer50]

Re: '73 115 merc. No compression in #3 cylinder

That is the only way.This is a 1 piece block beside the intake/crank cover.On the spark plug side is just a water jacket cover.Some might not agree but when I did mine I left the jacket on so not to tear off any bolts.I did not have a water leak there anyway.Once honed out and cleaned real good with soap and water dried her up and sprayed her down with 2 cycle oil to reinstall the pistons (make sure all the carbon has been removed from the piston/piston ring slots pop the new rings on and here comes the fun.I didnt even mess with a piston ring compressor I used my hands,its a little tight and you have to be carefull not to bust a ring and you will end up with some minor cuts on your fingers at least I did.Pop each piston in there cylinder and you can pull them up and down to make sure there in correctly.Leave them all the down and drop in your crankshaft.Pull each piston up some and drop in half your needle cage onto the piston rod I greased mine up good so I could keep the needles from falling out.After the needles are in the bottom half I pulled the piston up to meet the crankshaft.I then put the other half of the needle cage on the crankshaft with grease.Put the rest of the needles on and put the rest of the piston rod together.Remember I had mentioned in my earlier post that each piston rod where the bearings ride are very smooth if you put them on backwards they do not create a smooth surface where they are joined (you'll see).Then off to the next piston.Take your time.1 needle slips or falls into the motor it can be real pain to get them back out.Good luck...

 

[FoolOfAFisherman]

Re: '73 115 merc. No compression in #3 cylinder

Thanks for the instruction, im gonna try heat to get the block cover off but I'm telling you I'm about 99 percent sure those bolts are gonna break. Who knows, maybe I'll be surprised. Anyway you look at it, that covers got to come off. I can take it to work and mill em out if I need I guess.