Compression Readings

[Tony Sopranzi]

Hi All.

I have a 1962 Merc700 full gearshift.  The engine has been in storage since 1962.  It has maybe one or two hours on it.  The rings appear to be frozen.  I did get it running and after about 5 minutes of run time took compression readings on all 6 cylinders and they were between 61-62PSI.   A week later we ran it again for about another 5 minutes then took compression readings and they were all 70-71psi.  I havent started it since.  Can I continue to safely run it to loosen the rings and get the compression back up to where it needs to be. The engine is like inside and out and I dont want to damage anything by doing anything careless.  The water pump impeller was replaced before starting the first time.
Thanks

Tonino

[aquasonic]

The rings are already loose if it’s running. Compression should improve quite a bit with an hour or two of runtime as the rings loosen a bit more. Make sure you are using the recommended 2 stroke oil/gasoline mix. Because the motor hasn’t ran in years, a little extra oil in the first few hours won’t hurt. It sounds as though the motor may not even be broken in from the original owner.

[Tony Sopranzi]

thank you for the reply Aquasonic.  Much appreciated.  Yes we did enrich the oil mixture for the reasons you cited.  Its been 3 years since we ran it last.  Been too busy building a boat we sea trialed just this past Tuesday.  The Tech who went through the motor said the same thing you did that the engine has been barely run.  Now all I need is a hull to put it on – its a short shaft.  The boat I just built accomodates a long shaft and I have a 74 Merc500 on it.  Your reply gives me more motivation to continue running it.  Thanks again.

 

[The Boat House]

 

This is the result of using the oil from the 60’s and for some years later. Now that you have it running, today’s oil, along with the expansion  and contraction of the pistons and rings (why you need an end gap) the rings will free up over time. I suspect you will continue to see an increase in compression if you continue to run it. Some may still be stuck. Others may be partially stuck. It can take some time to get them all completely free. Tubs

[aquasonic]

Sooner or later we all have to do some “coal mining”. Pictured is a 1956 Evinrude Lightwin.

 

 

 

 

[The Boat House]

 

I’m 78 and  got to experience that garbage. It fouled the plugs, plugged all parts of the exhaust, pieces would drop back into the cylinders and score them and the piston’s. I get a great deal of enjoyment continuing to use stuff from the past but I don’t want any part that stuff.  Tubs

1 user thanked author for this post.

aquasonic

[crosbyman]

You may want to run some  engine cleaning products like Merc Power Tune , Yamaha Ring Free  or even  Carbon Guard made by Evinrude .

 

Some folks use Seafoam  some  don’t like it .

 

just follow  instructions

Joining AOMCI has priviledges 🙂

[Monte NZ]

Thanks for the excellent photos Tubs ……they are a real eye opener. I haven’t seen such a pile of carbon ever!

Monte NZ

[The Boat House]

 

This is out of the 1929 Sportwin NF I did last winter. Took a couple hours to get the baffle plates out so I could just scrape off what I could get at easily. This it typical for the motors I’m into. If you didn’t find your motor full of this crap, someone had cleaned it out, or you motor was never run much. Are vegetable base motor oils something that would be substituted for petroleum based products in your part of the world?    Tubs

 

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