84 mercury 150 zero compression on 1 cyl.

[tswest]

I just checked my compression and cylinder 1 has zero compression. The other 5 are around 110. The engine starts and runs fine the only real symptom is low max rpm. In the water it only runs around 4000 rpm's WOT. There is no noises coming from the engine like knocks or bangs. I went to my local marina today and talked to one of the mechanics to check on costs for rings and he said he had seen some pistons with the rings almost gone and they would get 40 psi compression. My gauge starts at 20 and it doesn't get to that and when you push the button to release the pressure there is almost no pressure at all. I hooked up a air compressor to the spark plug hole and pumped 60psi into the cylinder and it held. Not sure what that tells me but i did it any way. I also disconnected the fuel pump and the air pressure still held. I also don't seem to be getting water in the cylider. Any other thoughts on what could cause zero compression and how to I troubleshoot it.

Thanks

 

[jerryjerry05]

Re: 84 mercury 150 zero compression on 1 cyl.

Remove the head and check the gasket.Then look at the piston and walls.J

 

[tswest]

Re: 84 mercury 150 zero compression on 1 cyl.

Its worse than I thought. The piston has a chip out of the side. There is some damage to the surface of the head from fragments which imbedded themselves. There doesn't seem to be any damage to the piston wall except one line that you could barely hang a fingernail on. Checked the other cylinders and nothing. My questions is could the cyliner be honed and a new piston installed or am I toast. If you just honed the cylider would you have to change pistons to oversize and all that.

 

[MFisher]

Re: 84 mercury 150 zero compression on 1 cyl.

you should be able to go about 20 thousands on boring the block out and that should be a fairly common piston size to get for most outboards. Now if you are going to have a machine shop due the work make sure that they will stand behind their work and give some sort of warranty for the work.

 

[jerryjerry05]

Re: 84 mercury 150 zero compression on 1 cyl.

Honing out a fingernail groove is not a good idea.The parts are readily available and fairly easy to fix.
Like Mfish says get a GOOD machine shop to bore it out.If they say they can't bore it but can hone it for you RUN.Take the head with you and see if it re-surfacable.J

 

[tswest]

Re: 84 mercury 150 zero compression on 1 cyl.

I really dont know if I want to get this involved into it. I only paid 1500 for the boat 84 invader 17 ft, motor and ez-load trailer. Boat and trailer are in good shape but do I want to drop another 1000 to 1500 in an 84 motor. Any thoughts or suggestions would be appreciated.

 

[tswest]

Re: 84 mercury 150 zero compression on 1 cyl.

I'm tempted to put it all back together and run it until it stops then get as much as I can for the boat, trailer and any other parts I can scavange off it. Could probably break about even and a couple of years of family fun.

 

[Jacket4life]

Re: 84 mercury 150 zero compression on 1 cyl.

I really dont know if I want to get this involved into it. I only paid 1500 for the boat 84 invader 17 ft, motor and ez-load trailer. Boat and trailer are in good shape but do I want to drop another 1000 to 1500 in an 84 motor. Any thoughts or suggestions would be appreciated.

I'd be surprised if you ended up spending that if you did all the disassembly re-assembly yourself. You may want to check out the Frankenmerc thread, he is doing a complete rebuild with pics, you may decide you can replace the piston and rings, then you'd only be out the time, the parts (which wouldn't be ridiculous, I don't think), and the money at the machine shop. I'd get it to the machine shop, have them do the head and tell you what the tolerances are on the cylinder, then buy a piston and rings and have them machine it to that piston. Put it all back together and you're good for another 26 years.

I think if you put it back together and run it as-is, you will eventually have catastophic failure, and it would be a complete rebuild required.

 

[MFisher]

Re: 84 mercury 150 zero compression on 1 cyl.

as for running till it die's not a big fan unless you are in demo derby. Your motor minus the one cylinder issue seems to be the perfect motor to rebuild. I believe you said it runs good the boat and trailer are good. If you tear down to the block only which really isn't all to hard and could be done in a couple of hours and the same goes for reasembly. Keep acurate notes and keep things clean and tagged and you could do it with minimal amount of time and hair pulling. Don't waste a great motor you can get a lot more time and fun with it if you take your time.

 

[jmj120]

Re: 84 mercury 150 zero compression on 1 cyl.

I bet you could part it out and get most, if not all your 1500 back.
keep a watch on ebay. there's mercs on there all the time. you may have to take a road trip, but if you like the boat, it may be worth it.

 

[tswest]

Re: 84 mercury 150 zero compression on 1 cyl.

I found a used head for less than $100.00. After looking at the frankenmerc thread I think It is doable. Rings are about 200 for the set. Gaskets about 200. piston 50. machine shop 100.00. I'm thinking 800.00 or so if I do the labor. Am I missing anything major that is going to bite me in the backside.