Any ideas on what would cause this?

[pcmandevon]

I finished installing the rebuilt engine in my sportster over the weekend. It fired right up and ran great on the hose. I put it in the lake today and we were following the break-in methods I have read about here. for the first few minutes it ran fine, then the engine kind of sputtered out and died. I checked the plugs and they looked pretty oil fouled, so I installed new ones. The boat still wouldn't start so some folks passing by towed us back to the dock. The boat still wouldn't start on the trailer so I just took it home. when I got home I checked the compression just to make sure everything was okay. I have 150 or so in the MAG side and nothing in the PTO side. the engine didn't run for over a minute in the water.

I also reinstalled the oil injection, but I had premix in the tank that was only about 2 weeks old mixed 35:1. I know that the engine was getting oil, and it didn't run long enough to overheat. the rebuild was done with a Wiseco kit by a good 2-cycle guy. Does anyone know what might have gone wrong? O-ring? Rings? Thanks for the input. Devon

 

[Badboyr6]

where did you get the motor from?

 

[Dr Honda]

1) Did you figure out why your engine melted the first time?

2) If you did just a top end... did you have a leak-down done on the lower half? If you had a bad crank seal, it would have gone lean, and melted a piston.

3) If you did just a top end... did you check the crank index?

4) Did you check the ignition timing?

5) Did you rebuild the carbs, and verify the jetting?

6) the clearance on the pistons could have been wrong. (Wiseco clearance is different than stock)

7) Just because the person who did the engine was a "2-stroke" guy... was he a "Rotax" guy??? Unlike most 2-stroke engines, the Rotax/SeaDoo engines have to get the Squash-band set properly, or else the engine will eat it self. (they make 8 different base gaskets)



I'm sorry it happend... but there could have been a bunch of things that caused the problem.

 

[pcmandevon]

1. I think the engine died the first time because of the way it was rigged with the wrong ignition system. (this was the wierd 787 with 717 electrical)
2. My thinking was that the bottom end should have been fine. It was nearly new SBT rebuilt engine.
3. The guy that put the engine back together for me checked the bottom end and the crank.
4. It's a 787 so the ignition timing should be a given. (I think)
5. I took the carbs apart and cleaned everything up, but they are the 38mm carbs so I was only guessing on the jetting. The plugs were oil fouled so I think the jetting is okay.
6. I will check this again.
7. I will check this as well.

Thank you for the help, I'll check into these things. Devon

 

[Dr Honda]

1) May or may not have been a prob, but OK... I remember now.

2) Can't "think" on this one... you have to verify. A seal can be destroyed during the build.

3) A crank can be pulled out of index if handled improperly, and people don't check them. (takes special tools to check) I know I only check if I have a reason to think it's been twisted. When I see a PTO melt down... that's a reason to check.

4) Nope... not at all. You have to check the timing, and set it in the MPEM. (that takes a "BUDS" tool)

5) Just because the plugs are dark doesn't mean a thing. They could be dark from too much oil, or an extended rich idle. (in a no wake zone) But if it's lean up top... you will melt a piston before you burn the plugs clean.

6) OK... but you really can't on the jug that melted.

7) OK... but it's not easy once the engine has run since you will build carbon. BUT... since the good jug is only 150 psi, I don't think it was the issue.


My gut is telling me you have a crank that is slightly out of index, timing that may be a little high, and a carb that is a little lean. If you have just a little of any of those 3... you will melt a PTO jug, and have a perfect MAG.

One last though. Almost all of the 800 engines have differential jetting because the crank will twist under a load. From the factory, either they would open the high needle a 1/2 turn... or go 1 size bigger on the main jet. (did you do that with your 38's?) The reason I ask, is because almost none of the 720, or smaller engines need that. (the engines 38's would come from)

 

[RFoster130]

I think i would be heading back to who did the work on it.

 

[pcmandevon]

I took the PTO jug off...

After taking the head off I figured I would take the PTO jug off. The MAG side looked great, like it was brand new. The PTO side looked pretty bad (See Pictures).

 

[Dr Honda]

Doesn't look like there is any damage to the crown... so it's not timing or a squash band that was too tight.

Since it's only on one side... I'm thinking lean run. If both sides are melted... then it could be lack of oil.

Is the RAVE clearanced properly? It doesn't look like there was contact, but I figure I would ask.

 

[pcmandevon]

Yeah, the clearance on the RAVE is okay I checked it when we took it apart, so no contact. I'm think about replacing the 38mm carbs with the proper 40mm carbs. I had the low screws set at 2 turns out and the high screws set at 1/2 out. I thought this would give it too much, but I guess not. I didn't know about the PTO side needing to be set richer. This engine is starting to feel like it's made out of glass. Devon

 

[Dr Honda]

I wouldn't go as far as saying the engine is made of glass... but with a 2-stroke, the "deadly sin" is... don't run lean, and since you were running carbs that most people DON'T run... you were on your own with the jetting.

If it was me setting that up... I would have opened the high needles at least 2 turns, and only given it enough throttle to see if it was clearing out, or running rich.

When experimenting with a 2-stroke... go rich enough on the main, where it seems as if the engine has a high RPM miss. Then, lean it out until it runs smooth. From there, you can fine tune by reading the plugs, or piston wash.

FYI... unless you needed the low needle open that far to get a stable idle, it doesn't do much past 1/4 throttle.

On a good note... you can probably scrape the aluminum off the cyl wall, re-hone the jug, and just replace that one piston.

 

[Dr Honda]

Just a thought... look down into the crank, and see if you can see any oil on the bearings.

 

[pcmandevon]

I will check it as soon as i can, the guy that rebuilt it the first time has it right now. what should I be looking for? Thank you for all the help. Devon.

P.S. I did buy a set for 40mm carbs and the guy I bought them from is doing a rebuild on them with a Mikuni kit. What should I look for when i get them from him?

 

[Dr Honda]

While he has them apart... have him verify that the jetting, needle and seat, and the pop-off is correct for your boat.

 

[pcmandevon]

will do, I'll check them myself when they get here as well. What is it I'm looking for in the crank area. There didn't seem to be any oil where there shouldn't be. Devon