Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

[xjma]

Starting a new thread since I either un-seized it or it never really was 'seized' in the first place!! Here is original thread
http://forums.iboats.com/showthread.php?t=536184

Motor now turns with ease using 6" rachet or pull cord (muffs and fuel tank are 45 miles away), took off water jacket (busted two bolts, found one that had already been busted and rigged up), successfully removed exhaust cover and I'll let the pics tell the story. Looking for feedback. To me, it looks like it could be run as is, but bottom cylinder not 100%. Wanting some feedback on the best course of action....and I'm not opposed to putting it back together and running it as is until the lack of power gets annoying. Would use this basically as a back-up motor for lakes/ponds, etc. and just for fun, not out on the open ocean where a tip top motor is 100% crucial.

Specs. Although the motor hasn't seen a lot of hours, it's seen a lot of miles bouncing around in the back of a pickup.

Plugs. Had R&Red them so many times adding oil to cylinders when we thought it was seized that who knows which is which, but these are the plugs that were in it.

Top and middle right are my bad, top left is previous prick....who covered it up by trying to drill the SS fastener out and then putting a wood screw in there!! I'm nowhere near redneck enough to use a wood screw on a machine!!

So the two center bolts plus this bottom front bolt on the exhaust cover were a bear, but worked them out successfully.

 

[xjma]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Continued:

Notice pre-mix hanging around in exhaust ports from me adding tons to the spark plug holes.

Looks good from here, although strange no carbon right next to cylinder...must have run hot?? Or is this what it looks like when straight gas is run through the motor??

 

[xjma]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Continued:

Bottom cylinder (No. 2). Piston looks fine, rings are fine and not stuck, some good scratching at the bottom half of the cylinder...I would assume on bottom half of piston as well.

 

[xjma]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Continued:

Top cylinder (No. 1). Piston is great, little exhaust treatment on the side but I'm fine with it, very minor scratching on the bottom, but otherwise mirror finish on the cylinder walls. I still need to get the compression tester to get numbers but my thumb compression gauge says that no. 1 is pretty close to 100%, where as no. 2 is less than 100 but still fairly strong.

Looks to me like it will run as is, but could benefit from a bore on bottom cylinder....maybe get away with cleaning up the scratches and hone it?? Rings move freely.

Anyone know of a place where I can find a good price on a complete gasket kit and/or complete rings kit all together rather than buy each part individually??

Oh, and thanx again for your help!!

 

[xjma]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Also, does a "piston assembly" come with rings?? I would think so but the parts lists aren't clear. If it did, that would be sweet....107 for a piston assembly, could get the bottom one over, and just hone out the top....but new rings, which come in a set of 4 are like 150 . Still, 260 plus gaskets in parts then a bore and hone (say 30 bucks +/-) and then the cost of some bolts, new impeller, new fuel filter, and a few heli-coils ain't bad.

 

[sutor623]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Still, 260 plus gaskets in parts then a bore and hone (say 30 bucks +/-) and then the cost of some bolts, new impeller, new fuel filter, and a few heli-coils ain't bad.

Right! And the best part is if you do this you will have a great running motor for life (if you decide to keep her). The work and $ is well worth the peace of mind when heading out onto the water. I have been on sinking boats, and stranded with a lazy motor. I will do everything in my power to prevent that from EVER happening again. especially when I do a ton of my fishing in the winter when the water is 40degrees, the air temp is 30 or lower, and the coast guard is off the water!

 

[xjma]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

These sites with the parts aren't the best I've dealt with...hard to determine exactly what all comes with each item (like do rings come with the piston, and which gaskets come in a gasket kit), but I THINK that I've got it figured out.

Looks like about 95 for the full gasket kit (guess I should call and make sure it has crank seals), and 225 for two pistons (which appear to come with rings, pin, clips, and two washers and a pile of needle bearings instead of a caged needle bearing?).

With some other misc crap it looks like 400 bucks plus a bunch of my time (and hopefully not too many bloody knuckles if I remember to keep my mechanix gloves on) will get us a brand new powerhead on a motor you can't buy new anymore. Just have to see if thats what my brother wants. If we like this motor maybe run it instead of '07 20hp honda, which would fetch more $$ used I would assume??

Not really looking forward to drilling out the three busted SS bolts!!


Also, can anyone confirm from the pics that this is what it looks like when someone runs straight gas in a 2stroke??? I'd like to just make sure before I go ahead and rebuild it just incase something else caused the issue.....there was no thermostat in the housing,haven't checked impeller, yet.

 

[sutor623]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Are you in spec when you check compression? If your numbers are within 10% of each other, and the higher number is 100, you will more than likely be okay. Like you said, rings look like they are in good shape. Id try and do some basic maintenance on this motor (water pump, carb kit, spark plugs) and see how she runs. If it doesnt run like you want, then pull the powerhead. I dont see any deep gouges on the cylinder walls, just some scoring. I have run motors with a lot worse scoring than the one that you are posting about, and had no issues at all. Maybe a little fuel/oil blow by, but other than that, good to go.

 

[xjma]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Thanx sutor, that's the type of feedback I'm looking for (hence the huge post with tons of pics, haha). Wasn't sure if this was bad for an outboard. I haven't done compression test, yet, but hope to this week. I'm pretty sure the top one is going to be very close to 100%, and the bottom less, but hopefully serviceable. Might be wise to get it running and work kinks out before rebuilding the whole top end.

One thing I noticed when I ran out there this morning to hit the bolts with some PB, top center of exhaust manifold, there are three holes in the block for one bolt location. Top hole appears to be un-used (maybe was intended for locating dowel or different application of same block), middle hole as you can see is threaded, then the bottom hole I noticed I can see the piston through it....it goes right into the top cylinder!! What is the point of this?? Must get a little early relief of pressure before the actual exhaust port opens.

Also, while trying to come up with a reason for scoring on the bottom of the bottom cylinder, isn't that where the fresh water hits the cylinders first?? There was no Tstat in this motor...could that be the cause? Even with no Tstat there is barely any carbon build up in the exhaust manifold.

 

[sutor623]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Well, couldn't tell you about those extra holes there. But, some motors ( like my johnson 4 hp) actually fill the water jacket from UP TOP, and the water pushes downward and out of the motor. There is a chance that there are some pieces of impeller or debris inside of your water jacket, down lower. Both of my 4hp motors actually were scalded (you can see the paint wearing off) in the BOTTOM cylinder. So some motors cool the top cylinder first, and other the bottom. I am guessing FWIW your motor cools the top cylinder first. Here are some pics of paint gone on bottom cylinders in both to give you an idea.

 

[sutor623]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

If I were you, Id hook up the water input tube (in the lower unit) to a connector from the water hose and see how much water flow you are getting. Motor may have heated up and caused the piston to swell. Typically from what I have seen, if there is scoring on the PISTON wall itself, there was a water delivery/ cooling issue. It means the piston got so hot that it swelled up. If the rings are toast, and piston wall (not cylinder wall) looks okay, it is often a bad fuel/oil mixture. It seems to me that if the motor was run on a bad fuel/oil mix, both cylinders would look like the lower one does. Just my past experiences......

 

[xjma]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Ok figured out red circled hole from manifold directly to cylinder is the auto decompression feature!!! Cant find any good info on these systems for 2stroke, only the manual ones and the ones for 4strokes. I'm inclined to want to plug the hole as it seems like it could be robbing some Hp.

 

[oldman570]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Not a good idea to plug any holes as they are there for a good reason. It will not help the HP any. They probbly are there to help drain the water out of the motor when it is not running and in storage in cold weather. That way the block will not fresse up and break. Motors are made to be sold thurout the world and not just in warm climents. Don't buy any parts till a compression test has been done and the readings are less than 10percent diffrence. If 10 or more a total rebuild is needed. Thermostats need to be inplace inorder for the motor to run at its best. No stats mean poor performance and more fuel used.
Doing things right the first time will be easier than doing them everytime you turn your head.
Oldman570

 

[sschefer]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

The commpression relief has no effect on HP but those scuffs on those pistion and the aluminum stuck to the side will. Rebuild it and be happy.

 

[Faztbullet]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Also, does a "piston assembly" come with rings?? I would think so but the parts lists aren't clear. If it did, that would be sweet....107 for a piston assembly, could get the bottom one over, and just hone out the top....but new rings, which come in a set of 4 are like 150 . Still, 260 plus gaskets in parts then a bore and hone (say 30 bucks +/-) and then the cost of some bolts, new impeller, new fuel filter, and a few heli-coils ain't bad.

Dont know where ya"ll get these prices buy my pistons comes with rings ,clips and wrist pin is $130( not a Wiseco) and gasket set is $89. This is a Mercosil block and it takes a special cutter bit to bore and diamond hone to hone these cylinders and most auto machine shops cannot do this. Try to hone it with a ball hone or a regular stone hone and cylinders will look like they are coming apart or it was honed with sand , they have to be almost polished looking with a very very fine crosshatch.

 

[xjma]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

I quoted prices from a combo of these two sites http://www.crowleymarine.com/mercury-outboard/parts/368_140.cfm and http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=18583+94 The first one was recommended to me, second one I found through google.

When I asked the question it wasn't clear to me whether the pistons came with the usual parts or just bare....150 for just a set of rings?!?! Crazy for 2 cylinders!! I think Wiseco was like 145/piston....not sure wiseco is necessary or even the best option for this application. How do they do on OB motors?

Anyways, for now I think I'm going to button this thing back up, new impeller, plugs, fuel filter, make sure the carb is all clean and see how she goes. I haven't gotten a compression tester yet, waiting for a friend to bring one on saturday to test the cylinders. As long as they're decent I'll see how it runs. If the bottom cylinder is no good, I'll tear into it and rebuild it. A local dirtbike shop does lots of cylinder machining as they're very involved in racing, I'm sure they can do it. If not, I know a motorcycle machine shop a little further away that can do it for sure.

 

[sutor623]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Anyways, for now I think I'm going to button this thing back up, new impeller, plugs, fuel filter, make sure the carb is all clean and see how she goes. I haven't gotten a compression tester yet, waiting for a friend to bring one on saturday to test the cylinders. As long as they're decent I'll see how it runs.

This is what I would do.

 

[xjma]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

So I finally borrowed a compression tester from a mechanic friend. Both cylinders were at 75 psi give or take a psi or two!!! This is not at all what I was expecting!! I was expecting one to be in the 120 range and the other to be somewhat less. It is an old matco gauge and there is some electrical tape on the hose....maybe it's not reading the correct psi?? The fact that they were consistent when one cylinder looks 95% and the other is 75-80% good is strange.

Wondering if the compression relief system (no valves, just ports that dump to exhaust up higher in the cylinder than the actual exhaust ports) could be the reason it's reading 75???

I'd like to hear from a few of you guys to hear what yall think. Even though I'm kinda disappointed I think I'm going to get the seals, fix the busted bolts and try to fire her up. I'm not convinced that this motor won't run. My thumb compression guage tells me she's good...

 

[Faztbullet]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Those are idle relief port and they bleed off some compression at idle to make the engine idle a tad smoother, the compression should be around 100-115psi....

 

[CharlieB]

Re: Rebuild, Rings, or Run it as is?? 25 hp Merc 2cyl 2stroke (pic heavy)

Suspect the guage and or hose is old and inaccurate.

If the motor starts and runs, then compression is not your issue, it 'may' limit your WOT HP a little

Try retesting with another gauge, and/or running the motor on the water to find out if it will perform before spending for a rebuild, UNLESS you intend to keep the motor and just want the additional security of KNOWING that has been rebuild and is in a NEW condition.