89 Johnson 70, rebuild yes or no?

[Lowranger]

I have 1400 hours on my 89 Johnson 70. It powers my 22' C-Dory Cruiser. Total weight about 3500 pounds. 13 3/4x 15 uncupped Michigan prop. Top speed about 23 mph @ 5400 rpm. Information gleened from this site seems to indicate that my Johnson is happiest @ 5800-6000 rpm full throttle. My mechanic says my rpms are ok, BUT, I should have overhauled my motor @ 1000 hours and that I'm running on borrowed time. I've had this engine since new and it still runs perfect. My question; is my mechanic correct that I must rebuild my motor?

 

[Solittle]

Re: 89 Johnson 70, rebuild yes or no?

If you have 1400 hours on a 14 year old motor and it is presently still running well that is reliability of the first order. Whatever you are doing to that motor just keep doing it.<br /><br />Of course your mechanic wants to rebuild your motor. That is money in his pocket which is why he is in business. I would bet that if he is also a dealer that he will tell you that your motor is too old to be rebuilt and you need to buy a new one.

 

[Hooty]

Re: 89 Johnson 70, rebuild yes or no?

Do a compression check. Readings should be in the 100psi range and the cylinders should be within 10% of each other. If you've taken good care of the engine, maintained it properly and the compression looks good, run it another 1400hrs. I would get the revs up 4-500rpm though.<br /><br />c/6<br />Hooty

 

[alcan]

Re: 89 Johnson 70, rebuild yes or no?

Unless you are soley depending upon this motor and won't be near a repair shop for months. My opinion is, no need to. If it ain't broke don't fix it. So long as you properly maintain and care for your engine. That motor will tell you when it's ready for an over haul.

 

[ezeke]

Re: 89 Johnson 70, rebuild yes or no?

There is little difference with OMC Motors, but virtually every OMC Owner's Manual and Service Manual has a "Specifications" page. On that page is listed the "Full Throttle Operating Range". It is best NOT to exceed the upper limit of that range.

 

[Hooty]

Re: 89 Johnson 70, rebuild yes or no?

My manuals also have the "Full Throtle Operating Range" specifications. They also show the rated horsepower for a given engine speed but I'm unable to find where they specify a maximum engine speed. Am I looking in the wrong place?<br /><br />c/6<br />Hooty

 

[P.V.]

Re: 89 Johnson 70, rebuild yes or no?

I would agree that 1400 hours is quite a good amount of time on this engine. You are lucky ??? to have gotten this amount. He's not saying that you now need to rebuild it, just that any additional time is counting down on the clock. How much of THAT time is left is anyones guess. If you believe that you have 2, 3 or four years (100,200 or 800 hours left) on this motor, I'd like you to buy me a lotto ticket sometime. It can be rebuilt, I'd just wait till you "hear" a good reason to do so. Then I'd consider a 4 stroke as a replacement....

 

[ezeke]

Re: 89 Johnson 70, rebuild yes or no?

To Hooty,<br /><br />I will be the first to admit that I don't have a clue where these ideas come from, but my father, who died in 1972, told me to prop the Evinrude so that I did not exceed the "Full throttle range". My 1976 115 has 5,000 hrs plus on it without a rebuild or a major problem. I have 135 PSI on all cylinders when I put it away for the winter last week.<br /><br />The motor that Lowranger is using has 1,400 hours on it.<br /><br />I am convinced from a lot of stories like mine and his, that there is no reason to push it.<br /><br />But, I'm always willing to learn!-?

 

[Lowranger]

Re: 89 Johnson 70, rebuild yes or no?

Thanks for all replies. A compression test seems like a good idea but a search of this site presents conflicting recomendations. Motor, hot or cold? Plugs, in or out? Throttle, open or closed?

 

[DJ]

Re: 89 Johnson 70, rebuild yes or no?

lowranger,<br /><br />First off, there is no way to do a compression test with the plugs in. <br /><br />Hot or cold, that's your choice.<br /><br />Throttle open, yes.<br /><br />As said before, the important thing is the closeness of all three. In your case, I'd say you'll be fine.<br /><br />Just keep her decarbed and run it until it dies. It may last a lot longer than you expect.<br /><br />Good luck.

 

[rodbolt]

Re: 89 Johnson 70, rebuild yes or no?

hello<br /> I have a crabber with a 95 50 hp 3cly. he had it converted to non-vro at the purchase in 96. he has over 5000 hours on it and so far I have replaced the pugs and water pump/tstats every year. changed the gear oil 3 times a year. 3 control boxes and 4 sets of cables over hauled the carbs once and replaced a regulator. other than mostly maint. it just runs every day of every month except febuary.<br />I have another that runs a 120/140 frankenstein jonnyrude that were not sure of the hours but he has reciepts of just over 10,000 gallons of gas since 98.I redid the powerhead for him in 98. so do the maint dont overheat it change pumps tstats and vro's before they are needed make sure the alarms work as designed and go boating<br /> good luck and keep posting

 

[bonitoman]

Re: 89 Johnson 70, rebuild yes or no?

RE-Prop the boat and get it close to 6 Grand and Say "NO TO FOUR STROKES"

 

[BillP]

Re: 89 Johnson 70, rebuild yes or no?

Saying you need a rebuild and are on borrowed time at 1400hrs is just plain bunk...expecially on a 70 omc. The ones who believe motors are shot at 1400 hrs evidently have little experience around well maintained motors. As noted on above posts, motors can go high hours and it isn't luck. I suppose most were also done on "non-synthetic" oil which debunks other myths too. The only preventive maintenance I'd do would be related to age...water pump, fuel pump diaphram, black box, wires, seals, tstat, etc. You are doing the right maintenance so keep it up.