SuperMoto Junkie banner

1 - 15 of 15 Posts

·
Registered
Joined
·
63 Posts
Discussion Starter · #1 ·
Check out the pic. I'm not done disassembling the case yet so I don't know for sure but I have an idea or two, but I'd like to see what the forum thinks just from looking at the pic. (Yes I had metal in the oil and filter and around the flywheel (magnetized), bottom of case, ect but i don't think all of it was from this piston, but certainly some). The scoring is on the other side of the piston (looks exactly the same) all scoring is below the bottom ring, all rings are in perfect condition. Also, the cylinder walls, well any area around the piston that could possibly come in contact with this part of the piston for that matter. (no joke, cylinder walls are perfect)

So what do you think caused this piston skirt scoring?

Ok hint at what I think happened: I don't have it all apart yet but I'm 85% sure the bottom connecting rod bearing blew out, filling the case with metal flakes and flinging them all around, but could all these little particles really score the piston skirts that bad?:hmmm: Like I said everything else looks pristine in there(I will say there was quite a bit of metal in the oil/case)

And how about this one just for fun, since the rest of the piston/cyl. is in great shape, can i put this piston back in the motor once everything in the bottom end is fixed?

Nate
 

Attachments

·
Premium Member
Joined
·
4,683 Posts

·
Registered
Joined
·
849 Posts
Correct me anyone if I'm wrong but the bore sleeves are harder than the piston and yeah, it'll score easier. Depending on what you find, for the cost of a piston v the ass-ache of stripping the motor again, I'd replace the piston/rings. Or at least clean it up good.

If the bottom end has let go then it's a full strip and clean out job :headshake
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #4 ·
Thanks guys, sorry I kinda forgot about this post since I was workin on the bike so much. I've totally torn the motor down and am in the middle of a rebuild. Turns out, the conrod bearing blew out, lots-o-metal in the motor, seems that the metal flakes flying around in the oil caused the scoring as the piston skirt moved down into the crankcase. Def getting a new piston. Also under better light it did score the cylinder ever so lightly, but not that bad. Rehone and it should be good to go.

Nate
 

·
Premium Member
Joined
·
4,683 Posts
Very true.. the piston is aluminum vs. the Nikisil coating on the cylinder.


Moto, No I havent:damn: Ill update my thread here in a bit so I dont clutter up this thread..
 

·
Registered
Joined
·
849 Posts
Very true.. the piston is aluminum vs. the Nikisil coating on the cylinder.


Moto, No I havent:damn: Ill update my thread here in a bit so I dont clutter up this thread..
Cool, granted, just a Stella induced flashback.. :D
 

·
Registered
Joined
·
913 Posts
i'm not 100% sure, but i think honing is not advised since it removes the nikasil coating........

since the conrod bearing blew out, are the crankshaft and conrod ok?
 

·
Registered
Joined
·
106 Posts
For sure do not hone out the cylinder, just use a nylon ball "hone" to get the crosshatch, just a few seconds max. By the way, the lower con rod bearing going out is what caused your piston to slap around in the cylinder and score it up like that. Bearings are pretty soft and wouldn't dig into the piston that bad
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #10 · (Edited)
Crank is good, i have a new conrod kit coming, which includes a new rod, needle bearing, and the shaft the conrod rotates on that is pressed into the two halves of the crank.

Glad you gave me the heads up on the honing craiggriep, can you point me in the direction of one of these nylon ball hones? The only hones i have found for the do it yourselfer is the hone you can buy at the autoparts store and the flex hone ball that rocky mountain and other sell(this one is not nylon i'm sure)

I assume i would still use honing oil for this?

Nate
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #12 ·
No problem, i would have probably been in a big mess had you not said anything at all, thanks!!!! :D
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #13 ·
Craig, after looking at that website... quick question

My cylinder is 96.94mm or so, so i guess i get the 105mm ball? Also, i assume 320 grit since im looking to just get the cross hatching?

Nate
 

·
Registered
Joined
·
106 Posts
Sounds good.. Nikasil is pretty damn hard, all you're really doing is removing the glaze so your new piston rings will seat right. Im sure you'd be ok with a common hone, but I really wouldnt chance it.. anything worth doing is worth doing right
 
1 - 15 of 15 Posts
Top