'68 Merc 650 4cyl - To buy or not to buy...

[joblo33]

My '69 650 broke a rod and I went in search of a powerhead and found a complete '68 650 for $100 Canadian. The only problem is the compression is 140-50-110-140. I opened the inspection plate and it looks like cylinder two just has 2 of 3 rings stuck, no scoring. I couldn't get at #3 to take a look. I've rebuilt a '75 Merc 500 and it turned out great, but it started with all cylinders above 100psi. I'm looking for opinions as to whether or not I should take this on. I'm a student with a very limited budget (no summer job except fixing motors in the garage) and a few weeks left before school starts again. The motor is in almost perfect cosmetic condition with lots of chrome and would look sweet on my boat.<br />Eric

 

[joblo33]

Re: '68 Merc 650 4cyl - To buy or not to buy...

Just to add to this. The motor is being sold for $100 because the rotor had fallen apart and destroyed itself and the cap. The cap and rotor are discontinued parts. My '69 has a good cap and rotor. The owner was amazed when I showed him the compression.

 

[joblo33]

Re: '68 Merc 650 4cyl - To buy or not to buy...

Is it possible for compression to be this low from just stuck rings?

 

[Nos4r2]

Re: '68 Merc 650 4cyl - To buy or not to buy...

1) Can you use it to make one good one<br />2)Do you want the hassle of a possible full powerhead rebuild?<br /><br />If the answer to either is no, then I'd stay clear-but that's just my personal opinion.I'd stay clear with figures like that.

 

[joblo33]

Re: '68 Merc 650 4cyl - To buy or not to buy...

The predicament is I can't say no to either of those as long as I know the end result will be nice. I have a good set of everything on the motor with the broken rod and I'm always looking for something to do at night at the summer cabin, where I have all the necessary tools. The problem is I need to determine whether or not the walls are gonna be scored. Has anyone here ever seen a motor with 50psi where the only problem is stuck rings? from the inspection plate I see no scoring or metal filings, just two of three rings seem to be stuck. The local Merc shop is going to call me tomorrow morning with a price quote for the rings, so that should help with my decision.<br />Eric

 

[joblo33]

Re: '68 Merc 650 4cyl - To buy or not to buy...

Someone finally said what I've been waiting to hear for days: Go ahead and buy it, it's only $100. So I'm going to pick it up tomorrow. I'm going to see if I can get away with using some pistons out of my 1969 instead of buying a ring set.Hopefully it'll only cost hours of my life and the cost of a gasket set. *crosses fingers*

 

[JasonJ]

Re: '68 Merc 650 4cyl - To buy or not to buy...

You may just need to do a good decarb to break those rings free. I would do that before tearing into anything. That is the wole point to decarbing, is to free up piston rings that get stuck over time. Good luck....

 

[joblo33]

Re: '68 Merc 650 4cyl - To buy or not to buy...

Thanks JasonJ. They look too far gone for a decarb to fix, but I guess there's no harm in emptying a can in there to see what happens, if it works it'll save me a lot of hours work.<br />Eic