Posts
698
Joined
6/17/2016
Location
Ogden, UT, USA
Gentlemen, I just wanted to get your opinion on the health of this cylinder. I have the engine opened up for other reasons (here). While I have rebuilt several motors, I have always started from beyond blown up. The previous owner says the top end was done at 200 hours, the bike now has 240 hours. Just so I can learn and better gauge wear in the future, my questions would be...
1. from 1-10, how worn is this? 1 being not worn at all, 10 being total throw away
2. If this was your bike, what would you do? if anything, before installing it again
The grooves in picture one are the worst of them, you can barely feel them and they do not catch your nail if you run it across them. Thanks!
I'd say a 6 or 7 on the scale. If it were my bike I would replate that cylinder and clean the head up/valves.
Crosshatch looks good even though the scratched area. I’d buff it with scotchbrite and oil and run it.
You can see the cross hatching through the scuffs. I would hone the cylinder and reassess. I'd also verify all of your valve seats are fully intact and not chipped. Are you running an oem piston?
Yes, looks like OEM part number is stamped on the underside.
I'll check those valves as well. That's another question I had. Is it a good or bad idea to lap the valves just for good measure?
Here's a picture of the skirt of the piston where it was rubbing.
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You can put some gas in the ports and see if it leaks out around the valves. If the valves leak you can lap them if they arent titanium. If the valves are titanium do not lap them, you will wear the coating off.
Check the cylinder tolerance with a gauge and check its still in spec.
Not sure if this helps but I rebuilt a yz250 and had the head replated. I ended up having to take it apart again after the break in cycle bc it wouldn’t shift into 3rd. I saw the same vertical scores on my fresh cylinder and emailed the people who replated the head. They said it’s completely normal
Very encouraging actually, thank you!
Dude is mistaken he missed the point that he replated his cylinder. When you have a cylinder replated you're supposed to clean the cylinder throughly. Because the honing process will leave debris.
If you fail to clean it properly you will end up with these nasty looking. Dark marks that look like seizure lines. That are only visible but not bad harmful.
Big difference between those and the marks on the cylinder you're showing. The marks on your cylinder are from either dirt or excessive piston ring wear.
Run it like you stole it Bro. Looks like the previous owner ran some sand through it then put it up for sale. Piston and rings are jacked. You can see the rings took the biggest hit.
It doesn't look pretty.
It's definitely worth running a hone thru it and reassessing, but if I was planning to the keep the bike (50+ hrs), I'd probably replace the piston and cylinder. You'll find a few guys upgrade their 350 to 365 kits ... you might be surprised how cheap the cylinder actually is, especially if you consider it's probably original and it's got a lot of time on it. They are nowhere near as expensive as 2-stroke cylinders and especially if you get a new take-off or barely used OEM cylinder.
As a side note, for your primary gear issue, I'd look at replacing the oil pump gears (driven and idler) at a minimum with the current parts. 2017 parts were superseded and your stock gears chewed all that clutch cover and piston ... uhhh!
You'll also want to clear the oil galleries as best as you can. LOTS of compressed air, contact cleaner, check the owners manual for a map of the passages.
That is an OEM piston and rings. You can tell by the unique style of oil ring KTM uses that is unlike all other 4-stroke pistons you'll see.
You're good, Ball hone and surface plate that thing and you'll be fine. But, reasoning for those marks is just some sand/dirt that went through the filter. Valves are likely leaking. Quick lap and they'll seal up fine.
That's the plan, new metal oil pump gears and large and small metal oil pump rotors!
I think you are right, the goal is to actually keep this bike for as long as I can, might as well face the facts now while its all apart. I found a cylinder works/weisco piston combo on sale for $525, I think that is as good as it will get. Thanks everybody for the input!
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