3 cyl johnson/evenrudes

[jim_in_day]

We have 3 blown up 3 cyl johnny rudes of various vintage and hp at the shop and they all lost the middle cyl. My question is, (since I have a 76 70hp rude) why? What is it about the middle cyl. that causes this problem, all 3 have zero compression on that cyl, and that is the lowest reading on mine (although i'm still in spec). Is there something inherent about the middle carb that causes a lean condition on that cyl or is it heat?

 

[WillyBWright]

Re: 3 cyl johnson/evenrudes

You have heat from the top and bottom cylinders contributing some heat to the middle. Otherwise, heat rises and takes out the top cylinder in some other motors (mostly Forces). It's more likely that carbon build-up behind the rings and did the damage. I think it was before 1974 that the top ring was too close to the top of the cylinder making the dome rather weak. Your 76 shouldn't have a problem with that.

 

[StarTekh]

Re: 3 cyl johnson/evenrudes

tell me more information.. how do they burn gas ...<br />oil in tank or inside motor/vro. then il be happie to tell u why they blew up

 

[rickdb1boat]

Re: 3 cyl johnson/evenrudes

Then all the pistons would have fried.....

 

[seahorse5]

Re: 3 cyl johnson/evenrudes

Originally posted by jim_in_day:<br /> We have 3 blown up 3 cyl johnny rudes of various vintage and hp at the shop and they all lost the middle cyl.

The middle cylinder does run hotter if the rest of the systems are not up to snuff. <br /><br />Back in the late '80's and early '90's there were a number of service bulletins about improvements to the cooling systems. See a knowledgeable dealer.<br /><br />Back then they also came out with an improved water pump impeller kit that included a heavier spring for the themostat and instructions for re-locating the overboard tell-tale water to help bleed out any trappped air.

 

[clanton]

Re: 3 cyl johnson/evenrudes

What Seahorse said and overproped. Prop engine to turn 6000 at full throttle.

 

[Dhadley]

Re: 3 cyl johnson/evenrudes

Are all the blown ones the newer 56 cid style?

 

[jim_in_day]

Re: 3 cyl johnson/evenrudes

Thanks for all the responses, 2 of the blown up ones were a 70hp VRO and and a 60hp VRO from the late 80's, and one was a late 60's early 70's 55hp. The only thing in common is that they are 3 cyl. The 55hp and my 70hp didn't even have a tell-tale, so there was no relocating it (altho I added one to mine) and yes I am familiar with that service bulletin. Dhadley, I'm not sure when the 56 CID style came into being so not sure how to answer your question. hopefully the above did.

 

[Dhadley]

Re: 3 cyl johnson/evenrudes

The 56" motors had one plate on the exhaust. The 49's had 3.

 

[StarTekh]

Re: 3 cyl johnson/evenrudes

jim ..thanks for the extra info... I wanted to see VRO... now i can tell you for sure the vro's faild<br />causing meltdown.. SeaHores information is also a factor.... mix 50to1 in tank ,,ditch the vro...Iv see omc dealer . do just what i said...3 cyl 30Hp<br />...good luck

 

[seahorse5]

Re: 3 cyl johnson/evenrudes

Originally posted by John_Star:<br /> I wanted to see VRO... now i can tell you for sure the vro's faild<br />causing meltdown..

If the middle cylinder failed and the others were OK, then it was NOT a "VRO" problem. You might want to read up on it at:<br /><br /> http://continuouswave.com/whaler/reference/VRO.html

 

[Dhadley]

Re: 3 cyl johnson/evenrudes

Agreed. Even water in the oil injection tank cannot pick on one cylinder only.<br /><br />What we've found it that if the 3 cylinder motors are driven hard they last forever. If they are cruised, especially the 56 motor, in the mid range for an extended period they tend to score the middle cylinder. All the things Seahorse mentions have to be done.<br /><br />Think about what happens in the mid range. You have full timing advance and little fuel. The 3 cylinder motor was one of the most popular motors OMC made. Getting it to run as lean as possible earned them a lot of EPA credits. <br /><br />Everytime we've seen a 56" motor score #2 we've done all the afore mentioned things and richened up the mid range slightly. No more problem.

 

[seahorse5]

Re: 3 cyl johnson/evenrudes

Originally posted by Dhadley:<br /> <br /><br />What we've found it that if the 3 cylinder motors are driven hard they last forever. If they are cruised, especially the 56 motor, in the mid range for an extended period they tend to score the middle cylinder.

There was a service bulletin years back that referred to the 1991, 92, and some '93 motors that needed a carb jet change and a timing change.

 

[boatster]

Re: 3 cyl johnson/evenrudes

Seeing that all three were 3 cylinder ~70hp range motors I'm a bit nervous.<br /><br />I've got a 1996 Johnson 70 2 stroke. I'm going to run premix. I just bought the updated impeller kit with thermo spring/cover, and indicator nipple replacements. Are there any other bulletins I need to look for? Thanks.

 

[Dhadley]

Re: 3 cyl johnson/evenrudes

The oil injection is the last thing to be worried about to the point of eliminating it. You're doing all the updates. Just make sure the motor is set up right. You want it capable of at least 5800 with an average load. Use fresh 87 octane, TCW III oil and Champion plugs. <br /><br />If yours is a 96 and has had no problems so far, I doubt you have much to worry about.

 

[boatster]

Re: 3 cyl johnson/evenrudes

Sounds good Dhadley. I think I'm still going to run premix though. Just a kink or a misfitting line and well I don't like the thought of it....

 

[Texasmark]

Re: 3 cyl johnson/evenrudes

Hey D, You mentioned Champion plugs. I had an OMC 70 hp 3cyl and agree on it's attributes. One question from what you said is the plugs.<br /><br />As I recall my engine ran normal looking (like the automotive world uses) plugs with a ground electrode that you could set for a certain gap.<br /><br />My Merc, and the last 3 Mercs have run Nippendendo surface gap plugs.<br /><br />Since you've been there, done that, got any opinions about both that you might want to share with the viewing audience.<br /><br />Thanks,<br /><br />Mark

 

[koolerb]

Re: 3 cyl johnson/evenrudes

I just did the re-jet/retard timing SB, and the tell tail relocation SB. My #2 compression is 10% below #1 and #3. I'm hoping this will let me run it for a while before I have to pull the power head.

 

[boatster]

Re: 3 cyl johnson/evenrudes

Where do we find these service bulletins? <br /><br />Also where do I put the new pee indicator?? It didn't say where it should go on my 1996 Johnson 70 in the water pump kit instructions.

 

[jim_in_day]

Re: 3 cyl johnson/evenrudes

Wow, lots of comments, I've been out of town and couldn't respond, but Wow. Thanks DHadley and Seahorse. I have recently (last fall ) got it to run up above 6 grand, so I won't be lugging it. I mostly use it to get to the fishing hole, then use a kicker to troll with, so that shouldn't cause a problem. My next question would then be, as it is a 76 70hp rude, should i relocate the tell-tale to the top of the block do the rejet and retard (i think that year is at 17 degrees btdc) and change to the different waterpump? It has really strong water pressure (it will "pee" 8 ft sideways with no problems) but i really want this motor to be reliable so anything i can do. I also got the carbs of the 60hp VRO and the primer system to upgrade my carbs and make it easier to start, besides doing a very careful rebuild on them, do i need to consider the jets?