Starting the rebuild, broken bolts???????

[physicistkev]

As I posted a few months ago, the PTO cylinder in my 717cc in my 1996 Sportster, lunched itself. Turns out it blew off about 1/3 of the top edge of the piston near the exhaust port. Everything from my experience, tells me a lean condition, but I will keep investigating as I tear the engine down.

At this point, I have the nut off of the MAG flywheel and the PTO flywheel is off. The engine is out of the boat and getting it out was rather easy. Just had to apply a decent amount of force to the flywheels to get them off. I used the Dr Honda method of snaking some rope down the spark plug hole and using that as a stop. Pretty simple really, and quite effective.

The only real issue I have run into is I broke 2 bolts getting the cylinders off. One from each cylinder. The bolts on the inside, closest to the exhaust. I got the PTO piston one about 2 full turns before it broke and I got the MAG piston about 1 turn before it broke. I don't think I could have gotten them out any other way. Anywho, I now have to get the remnants out. Any special tricks to this? I think I have 2 options. Drill and use some type of "screw out" tool or just drill and Heli-coil the hole. Any other suggestions or methods?

I have done enough Heli-coils in my time, even for head bolts on motorcycles, but I am open to suggestions.

Also, when it comes to investigating the cause of the damage, what should I be looking for? I have seen 4-strokes melt pistons from a lean condition and I had an outboard melt a piston, but I haven't seen a piston "chunk" like this. There are scratches and impact damage on the dome of the head on the PTO piston. The anode and cathode were crushed together on the spark plug. So, there was debris flying around in the PTO combustion chamber. The motor actually spins quite smoothly and there doesn't seem to be much if any debris in the bottom of the engine. i am just peaking down through the openings in the case where the connecting rods are so I will have a better view as I break the motor down.

Any help or knowledge is greatly appreciated.

Thanks,

Kevin

 

[Dr Honda]

Wellllllllll................................................


If the engine was older... the ring may have just failed... and when that happens... it will take a chuck of the crown off because the top ring design is "Exposed." Also... the exhaust port is the largest... and where all the heat is concentrated... so that's the normal fail point.


As far as the broken bolts... I'm assuming that there isn't enough to grab with vice grips. If that's the case... I would file/grind the bolt flat... spray on some PB blaster, (let it sit overnight) and use a left handed drill. Normally, the bit will grab, and roll the screw out. I would start with a pilot hole, and then use a lefty drill at just under the minor diameter of the bolt. That's the way I do it at my shop... and 9 times out of 10... the stud will come out.