To ring job or not to ring job that is the question

Job

Cadet
Joined
Jul 15, 2011
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25
It's been awhile since I have posted as I am a self employed contractor and have been busy. Since my last post I have freed up the gear shift lever and put a new impeller in. I was going to bolt the head back on and do a compression test but noticed when grabbing the pistons with my fingers one seems to be a bit looser than the other. How much play should ther be and if a ring job is necessary do I have go with over sized rings etc.. Your responses are appreciated as I am going to try and get her running for flounder season if possible. The motor is a 1967 33 hp johnson.
 

Texasmark

Supreme Mariner
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Dec 20, 2005
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14,544
Re: To ring job or not to ring job that is the question

The pistons can be moved with your thumbs and they move enough to notice. Not that hard to put the head on and run a compression check at cranking speed, plugs out of cylinders, fresh battery. Compression tests are all over the place and the books usually say within 10% of each other. 100" would be a swag...my Merc manual says 120 or more with a new engine running around 150. If you are worried, shoot some 2 cycle oil in the plug holes and run it again. If the comp. leaps, do it, if just say 20% increase, then I wouldn't bother.

Mark
 

Job

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Joined
Jul 15, 2011
Messages
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Re: To ring job or not to ring job that is the question

Thanks for the response. Yeah I just didn't want to waste a head gasket and get bad results on a comp test so I was hoping someone could say how much play there should be as the upper piston makes a slight noise in the cylinder wall when I move it. The motor was froze up when I got it and had been sitting 15 to 20 years. Another question is isn't there a hone you put on a drill that just shines up the cylinder walls a bit but not enough to make you have to go to over sized rings? Whats it called and where do I get it in case I have to re-ring it?
 

robert graham

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Apr 16, 2009
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6,908
Re: To ring job or not to ring job that is the question

If the piston is really loose then you could need an over-sized piston and rings, but if it was my 40+ year old motor I'd just run it like it is. She'll probably run fine! Good Luck!
 

Job

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Re: To ring job or not to ring job that is the question

Couldn't the piston get damaged if it is too loose in the cylinder. I'd really like to do it right if I can as the boat , motor and trailer was my wifes dads and he's been deceased since she was 18 and used to ride in the boat with him when she was little so I was hoping to take her for a ride down memory lane. The boat is a 16 ft. chysler lone star skipper series year as yet undetermined and the trailer is a dilly.
 

robert graham

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Apr 16, 2009
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6,908
Re: To ring job or not to ring job that is the question

You can bore it over-size, new over-size pistons and rings, if you can find the parts for that motor. Older 2 stroke motors often have some "slop" in the pistons due to wear, but continue to run fine. Piston skirts can be knurled by a machine shop to take up some slack and help with oil retention in that area, if you can find one that can/will do it. That would keep you from boring it over and new over-sized pistons and rings. Maybe just run it like it is and it may surprise you how well it does! I mean it's an antique boat and motor and you're probably not going far out in the Gulf with it?
 

194269

Petty Officer 2nd Class
Joined
Jul 9, 2011
Messages
104
Re: To ring job or not to ring job that is the question

OMC has for years ran a straight taper on there piston skirts, and a low wrist pin location. With this combination you can rock the piston in its bore. It may seem excessive but nothing to worry about.
 

Job

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Joined
Jul 15, 2011
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Re: To ring job or not to ring job that is the question

No I won't take it out far in the gulf but maybe beach front on calm days. I do go to the jetties which is at the channel where all the ships come in and have been adrift there at night in a friends boat trying to get it going again and praying my ship don't come in if you catch my drift cause the breaks on those ships don't work so good. I've also been stuck at night in another friends boat in the inner-coastal where all the barges run and seeing the red blinking light on the end of one of those barges coming at us about 400 yrds away they don't have good breaks either but luckily that time my friend had just forgot to open the valve on the gas tank.Thanks for the replys guys I'll borrow my friends torque wrench and and bolt the head back on, do a comp test on it and pray for good results and try not to worry about the play in it though it seems a little excessive. As you can see God has shone me no small mercies before. I know parts are a little difficult to find and I'd have to get a manual which I probably will anyway. I've seen one for a 1968 which is a year later model for 19 bucks on ebay, I'm assuming it' pretty much the same if not exactly. I'll post the results when I do the test as time permits but hopefully very soon. Thanks again.
 
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