75 Merc 650 - ran out of gas when WOT, then..

[casi77]

75 merc 650, 3cyc. engine., I have two gas tanks (22L) each.

I ran out of gas on one of the tanks as I was going full speed, engine stopped.. I plugged in the fuel hose on the other gas tank, primed it, tried starting it, it was hard to start, placed the smaller lever on the throttle box up a bit, it started.. I placed it in forward gear, and give it gas..it would has half the power.. its like one of the cylinders not working, or not getting spark!? etc.. didnt know what the problem was while I was on the water. Anyway I was able to make it to the boat launch and take my boat out of the water.

Came home and first checked spark plugs, found out that on 2nd cylinder (middle), the plug was covered with !? melted metal or piston ring !? someting.. like someone soldered solder onto it.. thin layer of it.

While this happened!??

I checked compression, its 140, 120, 140 ..
opened up the side intake cover, checked 2nd cylinder, top pistion ring was like not playing when pushed in with a screw driver, but other two rings on the cylinder was playing normally.

What could have caused this, ?? why on only 2nd cylinder?! suggestions what to do please...

 

[rickdb1boat]

Re: 75 Merc 650 - ran out of gas when WOT, then..

Well, I'm thinking that when you were about to run out of gas, it presented a very lean condition to the cylinders. #2 normally runs hotter than the other 2 and therefore was well overheated by the time the motor stopped. Not good to run a motor out of fuel/oil at high speed. No lube can and will seize it up. At this point, you are looking at least at tearing it down and seeing if you can salvage(Repair) the one cylinder. If not too bad, you may be able to bore it out and go with an oversized piston and rings. But when you get that far, it's usually best to do them all...

 

[Laddies]

Re: 75 Merc 650 - ran out of gas when WOT, then..

When you run tanks completely empty you can suck crap off the bottom of the tank in many cases have to clean the carbs

 

[casi77]

Re: 75 Merc 650 - ran out of gas when WOT, then..

Even if you have two inline fuel filters?

I have one on the fuel hose coming from the tank before the primer (glass see-through kind) & one on the engine.

When you run tanks completely empty you can suck crap off the bottom of the tank in many cases have to clean the carbs

 

[rickdb1boat]

Re: 75 Merc 650 - ran out of gas when WOT, then..

If you found melted metal, you need to find out where it came from before you run it again. It can only cause further harm running it like it is...

 

[casi77]

Re: 75 Merc 650 - ran out of gas when WOT, then..

Compression is at 120 psi on the 2nd cyclinder.. should I test it out with a new spark plug & maybe do a sea-foam (thinking it may clean up the combustion chamber!?) and run it see how it performs!? Or would it do more damage?

Well, I'm thinking that when you were about to run out of gas, it presented a very lean condition to the cylinders. #2 normally runs hotter than the other 2 and therefore was well overheated by the time the motor stopped. Not good to run a motor out of fuel/oil at high speed. No lube can and will seize it up. At this point, you are looking at least at tearing it down and seeing if you can salvage(Repair) the one cylinder. If not too bad, you may be able to bore it out and go with an oversized piston and rings. But when you get that far, it's usually best to do them all...

 

[casi77]

Re: 75 Merc 650 - ran out of gas when WOT, then..

i could only think it came from the top piston ring.. when I took out the intake cover, and checked with flathead screwdriver , there was no play, seems like it melted abit, but the other 2 rings on the same piston had play in it, no sign of meltdown.. it could be why the compression is lower on that particular cylinder @ 120 psi instead of 140 like the other 2?
Is this the right assumption?

If you found melted metal, you need to find out where it came from before you run it again. It can only cause further harm running it like it is...

 

[Laddies]

Re: 75 Merc 650 - ran out of gas when WOT, then..

casi, if you have spark on all 3 cyls, then I think you should rebuild the engine before checking any thing else out, thats allway the most cost effective way to do repairs

 

[casi77]

Re: 75 Merc 650 - ran out of gas when WOT, then..

ok.. if it is the case for me to go ahead and rebuild it.. what is the most cost effective way of rebuilding it?

hoan and change the rings on the 2nd cylinder?

any quick instructions how to dismantle the block to get the 2nd piston out to change the rings? ..maybe I do not need to unbolt every piece on the block?! this is a question for those whose done a similar rebuild..

thanks

casi, if you have spark on all 3 cyls, then I think you should rebuild the engine before checking any thing else out, thats allway the most cost effective way to do repairs

 

[Laddies]

Re: 75 Merc 650 - ran out of gas when WOT, then..

Buy a manual

 

[Silvertip]

Re: 75 Merc 650 - ran out of gas when WOT, then..

Pull the plug and using a small pen light or bore scope, check the crown and edges of the piston. Bet you see damage. Chances are the ring lands are gone and you see pitting on the piston crown. If so, its rebuild time. And don't run the engine after rebuild until you clean and rebuild the carbs.

 

[jaymasta]

Re: 75 Merc 650 - ran out of gas when WOT, then..

casi, if you have spark on all 3 cyls, then I think you should rebuild the engine before checking any thing else out, thats allway the most cost effective way to do repairs

that has to be the stupidest thing I have ever heard and no where near the most cost effective, he isn't even 100% sure what is wrong with it yet, and he should also figure out EVERYTHING that is wrong with it before he goes ahead with a costly repair, that way he can fix evertyhing at once and have a solid running engine with no problems at all or he can scrap the whole thing and go with a newer motor if it is more cost effective....

 

[Laddies]

Re: 75 Merc 650 - ran out of gas when WOT, then..

To those of you who are so inept at things mechanical that you could not figure out my remarks on rebuilding an engine without checking out any other possiblities was anything but jest. The best advice I could give you would be to not check the engine out (as I did) and not buy a manual (as I did) but save yourselves time and embarrassment and pay someone with experence to do what ever needs to be done

 

[casi77]

Re: 75 Merc 650 - ran out of gas when WOT, then..

Manual is on its way.. ordered it from Amazon..

Im going to test it out tomorrow hopefully.. I just put in a new spark plug, cleaned it up a bit.. will put in "Seafoam" in the gas.. and try it out.. at this point I do not care if it really blows up.. since looks like I will be dismantling it and rebuilding it either way.. I guess I'll take the chance..
Will keep you all posted...

Buy a manual

 

[briannh1234]

Re: 75 Merc 650 - ran out of gas when WOT, then..

Casi77 -

If it were me I would not run that engine like that.

Right now you know you have low compression and probably a broken ring. If you run it like that you risk damaging more parts. That ring can come loose from the pistion and start bouncing off other parts before being blown out the exhaust. That piston could melt down and get stuck in the bore. The the connecting rod can break and come flying out the front of the engine.

In the best case you would just have more parts to replace during rebuild. In the worst case you would kill the block and be looking for a new motor...

Just my 2 cents.

- Brian

 

[rickdb1boat]

Re: 75 Merc 650 - ran out of gas when WOT, then..

Well. is it alive???

 

[casi77]

Re: 75 Merc 650 - ran out of gas when WOT, then..

havent had time to bring it out tonight.. will for sure tomorrow.. I also bought some Sea-foam, will put that in the tank as well.. got 2 spare spark plugs and spark plug wrench.. after reading Brian's comment.. ..ohhhhhhh man!!
i have a little kicker motor too but I got no room to put it on the transom, was thinking of bringing it but going to have to leave it & its short shaft too!! if i get stuck on water, gotta paddle I back I guess!! will keep you all posted...



quote time=1155325744 user=rickdb1boat uid=9947 fid=29 tid= rid=15]Well. is it alive???[/quote]

 

[casi77]

Re: 75 Merc 650 - ran out of gas when WOT, then..

took it out tonight.. runs great!

havent had time to bring it out tonight.. will for sure tomorrow.. I also bought some Sea-foam, will put that in the tank as well.. got 2 spare spark plugs and spark plug wrench.. after reading Brian's comment.. ..ohhhhhhh man!!
i have a little kicker motor too but I got no room to put it on the transom, was thinking of bringing it but going to have to leave it & its short shaft too!! if i get stuck on water, gotta paddle I back I guess!! will keep you all posted...



quote time=1155325744 user=rickdb1boat uid=9947 fid=29 tid= rid=15]Well. is it alive???

[/quote]

 

[MortenH]

Re: 75 Merc 650 - ran out of gas when WOT, then..

Well, I guess you were lucky, but I am quite sure that the melted metal on your spark plug comes from the crown of the piston, and I dont think it is a good idea to run her like this. I am also quite sure that it is not the piston ring that have melted - the piston have a melting temperature way below the rings. You are probably sitting on a ticking bomb. My suggestion is to tear her down and check before the big bang. You might get away with just a new piston with rings, and a hone of the #2 cylinder.

-M-

 

[casi77]

Re: 75 Merc 650 - ran out of gas when WOT, then..

its been 2 seasons now.. still rungs great!!