Topic: So this happened today

[josherr]

Happy Sunday to me !
After a long break from working on my build I finally ordered some bolts to continue building and while I dropping the pistons into the cylinder this happened



Im installing 836 Wiseco pistons and didn’t notice the last thin oil rings bent while I pushing in the piston

What would be the best option going forward ?
I doubt I can hone that out, the scratches are deep
Do I have to push in a new cylinder and have it boned out again ?
Should I just sell everything ?!

Thanks for any replies


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[The Lone Builder]

Ouch! I feel for you!

No idea what you can do though

[bryanj]

Polish the high bits off, the highest part of the mark is below the lowest poinr the rings get to so only the piston skirt is there except for when installing the piston

[754]

 Like he said, it will buff right out.. take your time.
 is the piston ok, ?  you will need a new ring.
 what ring compressed were you using for the very last time ever ?

[maxheadflow]

Do me it looks like something got smeared in the cylinder while it was running. I doubt that happened during assembly unless you were driving the pistons in with a BFH.  Looks more like a cast iron piston stuck in the cylinder while running but I guess it could be aluminum. I would see if you can dig it out then run a fixed hone through the bore.

[HondaMan]

That's nasty(!).
That's a lot of displaced material: it likely damaged the piston in that site, too, would be my guess? In the front, on the exhaust side of the piston, the skirt will be the hottest. If you manage to remove the high parts of it and leave just the groove, it will likely burn oil in that cylinder at upper RPM because the oil collected there will be too much for the oil ring(s) to control.

[Ace Blackwell]

From the picture, it looks like some thing is smeared on the cylinder. The debris looks proud of the cylinder wall, but the wall underneath doesn't look like it has a depression.  Are you confident that the piston / ring isn't missing material that been embedded on the wall?

[754]

 Don't hone it, it will enlarge the hole.  just work down the high spot.

[Tracksnblades1]

jos,

You may have a chance.

Your stock stroke is 63mm (2.5"). Add the measured length from top of piston to a little past bottom oil ring land to your stroke.
With your measurements totaled, measure down from the top off the cylinder and mark cylinder near the damage area. This should indicate whether the damage is within the ring travel at the bottom of the stroke in the cylinder bore. If the damage is outside of the ring travel it shouldn't affect the rings sealing.

I tried loading a picture of a used cylinder on eBay so you can visualize this easier. But our net is crawling tonight.

If someone has a used cylinder apart they might chime in with a measurement from the bottom of the cylinder up to the worn/polished area of the ring travel at the bottom of the stroke.

I'll try to dumb down my picture and attach it when things speed up.😩

[754]

just measure  lower ring to end of piston, cuz the skirt stays in the cylinder at BDC

[Tracksnblades1]

just measure  lower ring to end of piston, cuz the skirt stays in the cylinder at BDC

Good idea,

Do,you know if the skirt is flush with the bottom of the cylinder sleeve at BDC..?

[754]

 Not really but when you put the heavy bevel on an 836, they don't get down that far.. I would hope.
 Someone will have a run in cylinder to measure soon. . i think he is ok so long its not on a thrust surface, ie 12 or 6 oclock.

[josherr]

Hello
I will have to measure it out tomorrow and see if I’m good
This a picture of the piston, it is slightly damaged

Should I lightly sand where the damage is ?




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[Tracksnblades1]

Check for protrusion. You'll have to remove any to maintain piston to wall clearance.
I would make sure the oil ring, ring lands are not damaged. Sometimes the damage can close up the ring to land clearance. This can be tougher to verify on a three piece oil ring. I would push the complete oil ring assembly, by the damage, into the groove checking for resistance or the inability to turn it while seated back in the lands as it would if it was compressed in the cylinder.

If you are able to use the piston and cylinder. I would prolong the breakin period a bit longer for caution.

[754]

 I just noticed it seems to be on the thrust area of the piston path.
 if you heat the barrel you can turn the sleeve damage to 3 o'clock position , just make sure all sleeves finish flush. 
 Piston looks better than I imagined.  , just make sure the ends of the ring are away from there.