Piston wear on valve cut out

[Dougyb]

Guys, I am in no means an engine expert, but I can follow directions and replace top ends, etc. Today, while doing an air leak test, I found massive amounts of wear/ chipping/ erosion on the cutouts on the bottom of the piston. Compression is suprisingly still a solid 150 psi. Engine starts easy, obviously doesnt run good because of the air leak but that could change. My question is 1) what caused this
2) should I replace the piston
3) should the cutout in the bottom of the piston be flush with the exhaust port opening, or should it be of to the side of the port like shown in the video. Thanks guys, Dougy B

 

[Larry's Shee]

There should be no hole on the ex side of the piston. You need to tear it down and find where the rest of the piston went

 

[Larry's Shee]

DON'T even run this any more, only cause more damage. Could either be sloppy piston/bore clearance or sucked something in (reed screw)

Air leak could be broken case from broken piston.

By off chance you weren't running it in "reverse" were you?

 

[blasterdemon7]

Oh crap ! Time to split the cases.

 

[Blaner]

of dear, no more riding for you! your cylinder/bore clearance is too big resulting in the broken skirt

 

[blasterdemon7]

The air leak may be a hole in the cases do to the missing part of that piston.

 

[Dougyb]

wow, thanks for the heads up guys. I didn't know exactly what I was looking at or where the bottom of the piston with cut outs would be positioned as to the exhaust ports. By bore/clearance issues Im guessing your saying my piston was too small for the cylinder wall?

 

[Blaaster]

wow, thanks for the heads up guys. I didn't know exactly what I was looking at or where the bottom of the piston with cut outs would be positioned as to the exhaust ports. By bore/clearance issues Im guessing your saying my piston was too small for the cylinder wall?

Yup the piston and or the bore has worn beyond specs, causing the piston to flog around, cracking it, eventually dropping a bit into the crankcase.

 

[Dougyb]

Made a video just to show the damage, so I guess I have to split the bottom engine and try to find that piece?

 

[blasterdemon7]

Time to pull the motor and split cases to clean and inspect for damage.

 

[Larry's Shee]

For everyones info, the carbon on side of piston below the rings is from severly worn rings. They were allowing the fire of combustion to shoot past them, severely overheating the piston. Which could also be cause of carbon build up on underside of piston. Plus possibly inferior oil.

 

[Awk08]

the side cases you are refering to in the last video are just the clutch and stator covers, removing them does not get you inside the engine where that piece of broken piston is
the engine must be removed, completely disassembled and the center cases split. look under the exhaust port, or below the intake and you will see the split in the center cases, thats where it has to be split apart, and requires about $150 in specialty tools to do it, and although some on here promote buying those tools, for possibly a one time only use, i find it much easier and cheaper to just allow a reputable shop to do it
i've had a local dealer install a new crank for $75, but they fudged it
I now send all my work to ken oconnor racing
http://kenoconnorracing.com/index.html

 

[Blaaster]

For everyones info, the carbon on side of piston below the rings is from severly worn rings. They were allowing the fire of combustion to shoot past them, severely overheating the piston. Which could also be cause of carbon build up on underside of piston. Plus possibly inferior oil.

Can also be caused by mild detonation, causing the piston crown to overheat, which can cause the rings to be pinched in between the lands causing blowby.

Carbon buildup on the underside of the piston can also be caused by detonation, overheating the piston crown, and cooking the oil on the underside.

My guess is that you had an air leak before the carnage happened, causing detonation, or the jetting was too lean.

 

[Dougyb]

Blaaster, I did have an air leak before it blew up. I was nieve and unknowing at the time, I just knew that the bike revved irraticallly when under less than mid throttle. Compression always checked out good so I thought I'd be ok....

In any case, here's a video of my unfortuanate findings. I'd like to thank every single poster on this thread, you guys were spot on and I learned from every post. Thanks a ton!

 

[Triple_B]

Looks to me like that chunk of piston dropped down into the crank case, and punched the wall of that the crankshaft sits in, causing that huge piece of case to be "pushed" out. Your definitely going to need to take the bottom end apart and get that case repaired or replaced.

 

[slickerthanyou]

Blaaster, I did have an air leak before it blew up. I was nieve and unknowing at the time, I just knew that the bike revved irraticallly when under less than mid throttle. Compression always checked out good so I thought I'd be ok....

In any case, here's a video of my unfortuanate findings. I'd like to thank every single poster on this thread, you guys were spot on and I learned from every post. Thanks a ton!
Cracked case - YouTube

That has sicivicdude written all over it! Contact him he reapirs them if your not able!

 

[Dougyb]

slick, I ordered your air test much too late, lol

I just looked him up and ill send him a message after i open the cases and see what the internals look like

 

[Dougyb]

Split the cases today guys, I couldn't find the peices from the psiton but did find other things in the video. My main concern is the hairline cracks that are in the crank roundout part of the case. In order to fix them I would have to also remove the crank, which is a pain, so I was hoping a little gluvit (epoxy for aluminum that settles and seals into cracks/spaces) would do the job. And then maybe see if sicivicdude is interesteded in repairing the other side of the case, which has a few hairline cracks and a big chunk broken.

Case's split - YouTube

 

[sicivicdude]

I am physically getting sick to my stomach watching that video. Do you have a water lens on that thing?! It looks like we're looking through the ocean at a blaster engine!

 

[slickerthanyou]

Those cases are junk. You need a new set. That one main bearing you rolled around is junk also. Epoxy isnt gonna hold up at all. You will need a set of cases I'm sure sicivic has a good set, then have the crank area machined to fit that +4. That is the correct way of doing it.