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Old 02-21-2015, 10:38 PM   #1
dbur971 OP
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YZ250F tear down, re-build & interesting issues

I'm starting to tear down and hopefully re_build a 2104 YZ250F. I'll post photos and issues in this thread as I go.

It had a cam bushing failure and filled the motor up with metal grindings. Besides the cam bushing there are some things I see after removing the head and accessing the crank timing chain sprocket.

1. Intake valves have come so close to the head there is no room for even carbon build up. It looks like there has been some very slight valve to piston contact. Notice the dull carbon on the ex valves and the more burnished look to the intake valves.

ValveFaces by dbur971, on Flickr

PistonTop-1 by dbur971, on Flickr

PistonTop-2 by dbur971, on Flickr

The compression was good before tear down, and the valves look OK with the solvent seepage test. After ~1min there is just barely any solvent film visible around the valves.

Think these valves are OK to use?

2. I can feel a little roughness and stickiness in the can chain drive teeth. The crank sprocket shows some signs of stress, though all teeth are intact.

CrankSprok-3 by dbur971, on Flickr

CrankSprok-telecentric-1 by dbur971, on Flickr

And here's a special treat, sprocket in stereo! View as cross-eyed stereo. look at the left image with your right eye and the right image with your left eye. Google 'viewing cross-eyed stereo' for some help with this. Can take some practice.

CrankSprokStereo by dbur971, on Flickr

Would you say this crank is still good to use or not?

Follow the flickr links to see more details if you like.

Thanks!

dbur971 screwed with this post 02-21-2015 at 10:44 PM
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Old 02-22-2015, 06:23 AM   #2
Kawidad
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To me, the teeth on the cam chain sprockets look good enough to run them, which what I would do.

As to the valves. Having them even kiss the piston makes me squeamish. If you're sending the head off to a professional to be renovated, then he'll give you the best answer to that question. If not, then you'll know more when you pull them out. You can't tell anything much, unless horrible bad, while they're still in the head.
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Old 03-01-2015, 12:05 AM   #3
dbur971 OP
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I completed the tear down and found the clutch basket has a broken off prong. Apparently the broken piece was removed and then the basket continued to be used. They also probably did not clean out the metal pieces from the motor so that's where all the debris came from and probably why the cam bushing went out. The oil stainer was heavily obstructed.

The crank bearings all feel good, but there's crap in others. I'll need to get them all cleaned out to see what's good and not. Two clutch friction discs are broken. The remaining clutch discs all look good. I wonder if I can find individual Rekluse clutch discs?

There is some bluing on the crank but that looks like it's not caused by the rod bearing overheating.

The wrist pin and rod bushing show some scoring. Not enough to feel but you can see it in these closeup photos. Can that still be used? More photos with different lighting here:
https://www.flickr.com/photos/dbur97...7648417318625/

Wrist Pin by dbur971, on Flickr

Rod Bushing-3 by dbur971, on Flickr

Oil Screen by dbur971, on Flickr

Clutch Basket (1 of 1) by dbur971, on Flickr

Crank Blueing by dbur971, on Flickr
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Old 03-01-2015, 07:18 AM   #4
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WOW That's crazy to run it with that kind of damage to the clutch basket.


The scoring looks significant. I wouldn't reuse it, but I suppose you could get away with it. As to the bluing. In my experience that looks normal and part of the heat treating process done during manufacturing.
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Old 03-01-2015, 07:22 AM   #5
mcma111
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That rod is toast. The bluing on the crank is normal.
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Old 03-01-2015, 09:50 AM   #6
Argus16
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What year is the yzf?
You wrote 2104... assuming a 2004.
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Old 03-01-2015, 10:14 AM   #7
larryboy
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Find another engine or throw the whole thing in the trash, it's not worth the time or money.
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Old 03-01-2015, 08:30 PM   #8
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Wicked Yz 250f??

That motor is about 1 hour tops going into a complete melt-down!! It cost about $3200 us to rebulit a 250f here local. I look for a low hour motor. Good Luck!!
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Old 03-01-2015, 10:05 PM   #9
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+1
I broke the rod on mine and.spent just about that replacing piston, rod, etc. even the flywheel.

I'd wait for a used one to show up if I had to do it again. Jist my .02
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Old 03-01-2015, 11:15 PM   #10
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Thanks for the comments everyone. I'm on the fence about repairing this, though maybe it will depend on how good of a deal I can find on decent used parts. Yes it is a 2004.

$175 min for head repair
$7-$30 for wrist pin
??? for replacement crank. I may have a line on a used one or a cheap Wiseco new one.
$30-$40 ebay for clutch basket.
$25 for a couple new clutch discs.
~$85 for timing chain and guides

Maybe ~$500 could get it done, though certainly not with new parts.

I suppose the rod could be replaced on this crank, but that's probably going to be as much as I'd pay for a good used crank anyway.

The rod and wrist pin photos actually look worse in the photos than to the naked eye, since they are blown up way large and taken with contrast enhancing lighting as well. Still I recognize that rod should be replaced.
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Old 03-01-2015, 11:21 PM   #11
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Quote:
Originally Posted by dbur971 View Post

Maybe ~$500 could get it done, though certainly not with new parts.

Looking at eBay it seems these things explode like KLR's, plenty of used parts...you'll do alright going that way.
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Old 03-03-2015, 11:53 AM   #12
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Looks like the advice is the intake valves should not be re-used since they have kissed the piston. That add's probably >$300 to the repair cost so in all likelihood this bike will end up parted out rather than repaired. Thank's for the comments you all have given.

David B
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Old 03-03-2015, 01:32 PM   #13
mcma111
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Kibblewhite intake valves are less than $33.00 each on E-Bay

http://www.ebay.com/itm/Kibblewhite-...5e6dfd&vxp=mtr
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BMW's
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79 R100s
91 R100gs

87 Harley FXRS-SP ~ 06 KTM 625 SMC ~ 72 Honda CB750/915cc ~ 92 XR600/654cc ~ 95 XR650l/675cc ~ 03 CRF450r ~ 05 CRF450x ~ 02 XR650l/675cc ~ 86 YZ490 ~ 93 YZ80 ~ 93 XR650l Project
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Old 03-04-2015, 10:39 AM   #14
dbur971 OP
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Quote:
Originally Posted by mcma111 View Post
Kibblewhite intake valves are less than $33.00 each on E-Bay

http://www.ebay.com/itm/Kibblewhite-...5e6dfd&vxp=mtr
But according to Kibblewhite they must be used with Kibblewhite spring sets and a spring set is $230-$250. I assume it would still be 3/5 that if I could find just an intake valve set.

With all the other things to repair it just doesn't add up to be an economically feasible project. :-( It would have been nice to have defeated this thing, I was beginning to see it as an enticing challenge, but practicality must be considered at some point.
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