Why did this part of my motor break?

[sflsurfrider]

do u have another crank or case to mock up that you can use for process of elimination?

 

[WaveDemon]

do u have another crank or case to mock up that you can use for process of elimination?

I do but it's in an assmbled short block. I might pull it appart this weekend. Ollie may also take the crank and mesure it on his lathe.

 

[Ollie Rastabean]

I have a spare set of cases I will bring too so you dont have to break that shortblock.

-O

 

[Rockstar]

OMG that sucks big time dude. Im sorry. You can ride my SJ over the weekend all you want.

 

[WaveDemon]

OMG that sucks big time dude. Im sorry. You can ride my SJ over the weekend all you want.

thanks bro, I was planning on it. :wink:

 

[WaveDemon]

this is what that little peice of crank ring did to my motor in about 10-15 seconds of total run time.

 

[Mouthfulloflake]

hold on....

is this the same motor that you posted on pwcnowhere.com?

the one that according to everyone had a 'great' crank in it?

hmmm

you might want to put that on some V blocks and check it.

something is WAY wrong there.

 

[keefer]

I agree, if the cases were not tight, there would be a major air leak not to mention massive failure because of the crank rattling around. It just dont work like that. Are you sure that is not a piece of one of the thrust bearings on the big end of the rods? Truly bizarro. Hope you figure it out.

 

[douglee25]

Just throwing out some things that came to mind:

1. Could the wrong bearing be pressed on the crank?
2. Could a wrong retainer ring been used?
3. Could the retainer ring have been pinched in the cases when assembly took place? Are there any marks on the case indicating that?
4. Is the bearing bad? Noisy? Rocks in the race?
5. Have you tried a new retainer ring on the bearing and mock up the engine again to see if the slop still exists?

Doug

 

[MADMAT]

This thread is depressing:banghead:

I'm about to reassemble my first motor ever. I'm nervous.

Very sorry to see what happened to your motor demon.:frown:

 

[ski4]

me too matt, my finsihed motor is starring me in the face and i am having nite mares about something like this happening

 

[WaveDemon]

It may be time for a little history on this motor. It was built by a reputable builder for JetRock. JetRock used it for only a few hours (he claimed 1 or 2 hours all on one outing) then got the bug for MX and sold it to me. I ran it for a few more hours (less than 10 total) and put in higher compression domes. It turned out to be to much compression for pump gas and I destroyed the pistons and rings. I replaced the pistons and rings and cleaned the case without dis-assmbling it (probably a mistake). I put new pistons and rings in. I did a pressure check, it had a slow leak at the carb gasket. I figured I would throw a little 1211 on the gasket and run it anyway the next morning. On the initial start up it free reved, twice. I figured I didn't seal the carb gasket well enough. I pulled the head for damage control and found what the pictures show on the first page, one busted piston (rings are intact) one busted dome and a 2" long crank ring in the head pipe.

 

[Mouthfulloflake]

ahhhh...

and now, we know...

the REST of the story.

:biggrin:

 

[Flash-FX]

Wild guess...The 2" piece is left over from the piston/ring failure. The bearing locating circlip could never jump out of that machined groove in the crankcase....unless it was split/broken.

It's a piece of ring? I never saw anything that BIG survive thru a motor...WOW!!
Good scavenging..

:frown: Just a guess..

Hope you get it back together soon.

 

[keefer]

I agree with what Flash said, I think that you had a piece of piston ring instead of the retainer ring. I bet that retainer ring was broken all along or broke when you took it apart. It is tempting to not split the cases with a top end failure but sometimes you can get all the metal out and sometimes something is hiding and bites you in the butt. Check that crank with a set of V blocks and guages and pay special attention to the big end bearings. You dont want to be right back in there again because of a crank failure. I went through that last fall on my wife's SJ Good luck.

 

[WaveDemon]

I found the crank ring in the head pipe while the motor was still assemled

 

[sflsurfrider]

could it have been a piece of piston ring from the first failure that you didnt know was in there?

 

[WaveDemon]

could it have been a piece of piston ring from the first failure that you didnt know was in there?

it could have been but why is there a big chunk missing from the crank ring? Does that ring not close? is it supposed to be that open?

 

[sflsurfrider]

i just took a look at a trashed sbt crank (is there any other kind?) in my shop and that ring has about a 1/8" gap. i would think a stocker would be the same, hmmmm.

id defenately put that crank on some v blocks.

 

[WaveDemon]

thanks for checking, it's going to be tested very soon.