Posts
2080
Joined
3/12/2012
Location
San Antonio, TX
US
Edited Date/Time
11/18/2020 7:27pm
The bike has 90 hours on it now. This past weekend the pipe cracked on me so I decided since I had to replace it I might as well tear it down for a rebuild. That’s 90 hours on the stock top end for those of you who haven’t seen me mention it before in other threads that I haven’t cracked it open yet.
After an hour this is where I’m at.
I did a compression test before pulling the engine. I’m still at 200psi which is exactly the same as I tested at 50 hours.
Then I pulled the cylinder off to see what the piston and cylinder looked like. I’d say running amsoil dominator at 55:1 has been the best oil for this engine for sure. No scoring, scuffs, wear marks or heavy build up. Inside the pipe is also very clean and no scaling or build up. The ring gap measured .53mm for the top ring and .45mm for the bottom ring and spec. is .40mm, but that’s at 20mm down and I measured about 7mm down so I’ll have to recheck it tomorrow. For being out of spec. the bike sure did run amazing.
Plans for the rebuild; new grapics, plastics, pipe, repack the silencer, Boyesen rad valve, top end rebuild, suspension rebuild, grips, grease, replace wear parts.
Done so far; replaced the wheels with DID dirt stars and stainless steel spokes, front and rear SKF wheel bearings.
After an hour this is where I’m at.
I did a compression test before pulling the engine. I’m still at 200psi which is exactly the same as I tested at 50 hours.
Then I pulled the cylinder off to see what the piston and cylinder looked like. I’d say running amsoil dominator at 55:1 has been the best oil for this engine for sure. No scoring, scuffs, wear marks or heavy build up. Inside the pipe is also very clean and no scaling or build up. The ring gap measured .53mm for the top ring and .45mm for the bottom ring and spec. is .40mm, but that’s at 20mm down and I measured about 7mm down so I’ll have to recheck it tomorrow. For being out of spec. the bike sure did run amazing.
Plans for the rebuild; new grapics, plastics, pipe, repack the silencer, Boyesen rad valve, top end rebuild, suspension rebuild, grips, grease, replace wear parts.
Done so far; replaced the wheels with DID dirt stars and stainless steel spokes, front and rear SKF wheel bearings.
Very impressed with how it's running! Seems like you've got it right in the design window (A:F, track conditions, maintenance, fuel). Nice job.
The Shop
The engine was reassembled with a vertex B piston kit. I’ll do a compression test on it tomorrow as I wanted to break it in and get a broken in reading.
With the engine back together I upgraded to a Boyesen Rad Valve. The stock reeds looked to be in great shape other then the gap everyone complains about and obviously when the engine is running doesn’t affect anything.
The parts stock pile in all its goodness.
So here’s a rebuild list; repack the silencer, clean and grease bearings, suspension was sent out to be rebuilt, new Pro Circuit Works pipe, chain sliders and blocks replaced due to wear, frame guards, new grips, brake pads replaced, oil change in the steering damper switched to 15w40, Boyesen Rad Valve, new plastics, BNG with a 2004 Factory KTM vibe, and a new seat cover to finish things off. I’ve already replaced the rims, spokes, and wheel bearings a few weeks prior.
While the bike was apart I decided to test some sprockets. Ping mentioned something in his Ask Ping post about chain angles and freeing up the rear suspension. After a lot of research I found that really is a thing and it really does help. I also found Keefer talking about it some too. I was running 13/49 vs. the stock 13/50 for a little more pull in each gear. That put me at a 3.77 ratio. I wanted to pull 2nd and 3rd a few feet longer and I also wanted to run a 14t because of the research I did on the suspension and sprocket sizes so I went to a 14/52 and a 3.714 ratio. .056 ratio change isn’t very much, but maybe it will be enough to get over this triple at 3 palms cleaner in 3rd. 14/53 would have given me 3.79 so I would have lost some pull in each gear.
Anyways, here’s the finished product ready for a ride this weekend.
Bike looks good, BTW.
Pit Row
ps- my top ring end gap was right at the limit and my bottom ring was still in spec.
This piston replacement interval should be adjusted to compensate for dirty intake/poor fuel/lesser oil/detonation etc. But for you, keep on doing what you're doing!
https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/17-TC250-Jetting-…
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