Breaking in new powerhead.

[steviecops]

Hi<br />I took my boat out for the first time since fitting the new powerhead. (Johnson 50, 2 cylinder). I had started the boat in a water butt at home previously, and let it idle for about 30-45 minutes total. Yesterday was the first time it has been out on the water.<br /><br />I did a search for the recommended rpms for break in, but found that I couldn't apply them to my boat and motor. I didn't want to put the motor under strain, so I gave it enough throttle to get up on the plane, then backed the revs down to where it would just stay planing. That gave me around 4000 rpm cruising, anything less and the boat would start dragging through the water. <br /><br />I found that when I gave full throttle to get the boat up quickly, I could only get 5000 rpm. Previously I'd get 5800 at WOT once the boat was planing. Would the double oil make the motor sluggish? Or could it be that the new powerhead needs to loosen up before I'll get full rpms? I know that I've still got many hours breaking in to do yet, and I should not try to hurry the process, but I was worried I might need to set the motor up again before taking it out for the second time. A friend of mine who knows about 2 stroke motor bike engines was out with me and said he thinks it is the extra iol and "tight" engine that is making me lose rpms. He says that when I run it on 50:1 again, it'll rev higher. Is he correct?<br /><br />I set the timing using the cranking speed method. Set at 15 degrees instead of 19. Jets in carbs are fixed orifice jets. Carbs were cleaned out and rebuilt with new kits. New Champion plugs gapped at 40.<br /><br />Any advice would be appreciated.<br />Thanks<br />Steve

 

[rodbolt]

Re: Breaking in new powerhead.

aint no such thing as a Tight motor. its mostly a myth. if assembled with the proper clearences it will be what it is.there may be a small amout of performance difference while the rings seat but its rather negligible. my advice would not to take much stock in your mates advice.<br /> double oil gets blamed for a tremendous amount of problems with a rebuilt motor but I have never seen it. if it will rev 5800 on 50 to one it will do it on 25 to 1. 4000 RPM is a tad high for breakin but I have had to do it before. the key is to back down and allow the motor to cool often. while the rings seat you may generate a bit more heat due to the wearing in of the microscopic fractures on the rings and bore surfaces. rour motor uses roller bearing,except the mottom main, roller bearings that are loose or tight die very rapidly.<br /> check the timing at or near 5000 RPM under load, it needs to be someplace near 18* check that the throttle shutters are fully open.<br /> if still in doubt pay a dealer to run it up with the correct test wheel to tell you if the motor makes power.<br /> but I would rather see the extra RPM than see the engine lug while dragging through the water.<br /> if ign timing is to far retarded it can cause as much damage as to far advanced, just takes a little bit longer.

 

[wilde1j]

Re: Breaking in new powerhead.

Double oil is not going to affect WOT rPM's. Breakin won't change WOT much, if at all. Something else is goping on. I would recheck link and sync again. Did you allow enough time at WOT to tell what RPM's were going to be? What plugs are you using specifically?

 

[steviecops]

Re: Breaking in new powerhead.

Thanks for the info.<br />I didn't really think my mates views were correct because I hadn't read anything like that when I did the search on breaking in.<br /><br />I'll check the timing under load tomorrow. One thing I did notice is that after starting from scratch and going through the throttle pick up, idle timing and then advance timing, the throttle linkage at WOT wasn't correct. I had to adjust it so that the throttle plates opened fully at WOT. After adjusting it, the throttle pick up wasn't right!! I chased my tail for a bit, then set it so that the throttle plates opened up fully, but the pick up is probably now not correct. Is there a way to get both right by following the manual? Maybe if the advance timing wasn't correct it would make it impossible to set everything up correctly?<br /><br />I'm using Champion L77J4 plugs.<br /><br />I'll check the link and sync again when I re-torque the head today.<br /><br />Thanks again<br />Steve

 

[steviecops]

Re: Breaking in new powerhead.

Just one more question before I take it out again tomorrow.<br /><br />I've noticed that there isn't any water coming out of the exhaust relief ports. Before I swapped powerhead there was a slight spray coming out at idle, once the thermostat opened up, and a gush at WOT. With this powerhead there are exhaust gasses coming out at idle but no water. At increased revs underway, there still isn't any water.<br /><br />I did the waterpump before swapping powerheads. The tell tale stream has good pressure and the motor isn't overheating. I tested the overheat alarm, and I can hold my fingers on top of the head for several seconds.<br /><br />Is this cause for concern?

 

[Solittle]

Re: Breaking in new powerhead.

Yep - you missed something in putting it back together.

 

[steviecops]

Re: Breaking in new powerhead.

Any idea what I might have missed SoLittle? I put it back exactly as the old powerhead came off. What part would have to be amiss to stop water spitting out the exhaust relief ports? <br /><br />Needless to say I didn't take the boat out today because I want to get any problem with the exhaust relief ports sorted out first.<br /><br />Soon as this problem is sorted out, I'll be taking it out to set the timing properly.<br /><br />Thanks<br />Steve

 

[Solittle]

Re: Breaking in new powerhead.

You mentioned that you fitted a new powerhead - - Did you have your old one rebuilt or by chance did you get a powerhead from a year that is different from the original engine? If so you will have to get some input from someone who knows those engines better than I. I would suppose that some years would be a good fit but some would not. I do know that it is important that the hot exhaust gasses get that cooling.

 

[steviecops]

Re: Breaking in new powerhead.

I got a different, rebuilt, powerhead. Mine was a 55 and the new one is a 50. Possibly not from the same year, but definately from the same era. The crankshaft splines were the same, and everything else looked the same. All the bits from my old powerhead fitted without any trouble. I checked that all the holes, etc, at the bottom were the same as on my old powerhead, and the powerhead gasket lined up with the adapter and new powerhead.<br /><br />I've got that doubt planted in my head now and I just know I'm going to have to take the **** thing off and recheck it now! Unless there might be any other reason why the water isn't spitting out the ports that I can check first.<br /><br />Thanks<br />Steve

 

[steviecops]

Re: Breaking in new powerhead.

Panic over!<br /><br />I back flushed the motor yesterday and ran it at idle today for 30 minutes. Water was spitting out the exhaust ports as before <br /><br />I don't know if the back flushing had anything to do with it, or whether I just wasn't looking properly before, but all seems well now thank goodness.<br /><br />Just waiting for the wind to drop so that I can take the boat out and set the timing properly.<br /><br />Cheers<br />Steve