Some cylinder head questions (with pics)

_JOE_

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In the first pic there is scuffing where the outer race of the cam bearing sits. Is this normal?

In the next two pics the one exhaust valve looks much cleaner. Any reason for that?
 

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_JOE_

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And what's this little guy for? (the one with the blue dot)
 

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2strokerfun

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Interesting scuff pattern. Almost looks like it goes up, loops and starts back down. I once tore down an aircraft engine that had spun a cam bearing; much much more damage than your scuff. So I guess I'm really just typing and not answering any question... Maybe bearing was installed with some trash under it??
 

_JOE_

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Bob, it's a 250f, it's always apart. :nener: Seriously, it's due for rings and the stock pancake showed a little skirt wear so I was interested to have a look. And it's super crappy weather here so I stuck her in the basement for a good once over. Got any tips for suspension fluid change?

2stroker, it's a roller bearing. The outer race is clamped by caps. I would say the outer race was spun for sure. Maybe cold start issue? We do run them a few times over the winter but I usually run 0w40. The cap bolts were reasonably tight coming apart. The cam looks great, no scuffing inside the inner race of the bearing.
 

_JOE_

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Bob, it's a 250f, it's always apart. :nener: Seriously, it's due for rings and the stock pancake showed a little skirt wear so I was interested to have a look. And it's super crappy weather here so I stuck her in the basement for a good once over. Got any tips for suspension fluid change?

2stroker, it's a roller bearing. The outer race is clamped by caps. I would say the outer race was spun for sure. Maybe cold start issue? We do run them a few times over the winter (20*) but I usually run 0w40. The cap bolts were reasonably tight coming apart. The cam looks great, no scuffing inside the inner race of the bearing.
 

Rich Rohrich

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Joe - Take a close look at the valve seat contact area and you'll likely see the reason for the difference in the exhaust valve deposits and coloring.
 

_JOE_

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Rich Rohrich said:
Joe - Take a close look at the valve seat contact area and you'll likely see the reason for the difference in the exhaust valve deposits and coloring.
Uh oh, you think the seat is burnt? I'll pop the valves out today and have a look.
 

whenfoxforks-ruled

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If it was not for the valves, I thought it was a 2 stroke. Rich, oil, coolant or man you are getting some bad fuel. The loose seat makes for a really crappy burn. New valves, recut the seats, you got the lap and run deal. Do you know for a fact the "scoring" was not there before? If the cam is not scored, burnt, then the "scoring" in the race could be there to begin with. The marks could be from the original machining, the shiny is the worn area. Measure the id. No skirt pics? How about side to side, small end of the rod bore? How are the thrust washer clearances? Vintage Bob
 

Rich Rohrich

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_JOE_ said:
Uh oh, you think the seat is burnt? I'll pop the valves out today and have a look.

Well, the seat contact area is where the majority of the heat transfer takes place between the hot exhaust valve and the relatively cool (by comparison) cylinder head. If the exhaust valves are running at substantially different temperatures, then it stands to reason they would react to what's happening in the combustion chamber differently. It's similar to the way different heat range spark plugs color differently. If oil is entering the chamber, and on a worn 250F it definitely is, then the effect will tend to be more pronounced in the same way a two-stroke shows more color on the plug from the oil.

As for the cam cap, it looks to me like the bearing is spinning. When the valve springs are worn those cams whip around like crazy, so there is no telling what type of motion is being transferred along the shaft to the bearing end. I've seen lots of 250 Hondas with similar markings.
 

_JOE_

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I didn't get a chance to pop the valves out today, hopefully tomorrow.

Glad to hear the scoring is a pretty common thing. I keep the valve springs pretty fresh, around 20hrs or so.


Bob, it's so black in there cause I let it idle itself out of fuel before I brought it in the basement. It's not had any valve or seat work yet at about 80hrs on the clock. Lower end is tight in the middle, I have yet pull side covers. A .020" guage fits on one side of the crank between it and the rod. I have no specs? Guess I need to buy the actual service manual huh?

I cleaned the goo off of everything and got a skirt pic for you...
 

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whenfoxforks-ruled

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Rich, Is there a reason 1 exhaust valve gets crud-ed up and not seal, like more unburnt particles goes to one side? Or like I stated earlier, skipping the recut strikes again? 20 seems a lot Joe, I have no idea where our old book went, they never go with the bike, suckers! My library of information, unlike my cluttered desktop from saving sites from Rich? Joe, did you inspect the small end id? Vintage Bob
 

_JOE_

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Ok, I pulled the valves this morning. Cleaned the head up a bit so you can see. The seats look OK to me? I'm having trouble getting a good pic with this camera, I'll grab my other one from work this afternoon and see if that's any better.

Bob, I didn't measure anything yet. I have to run the cylinder and stuff up the shop some time for that. The pin fits the rod with no looseness so I'd assume that's ok. It's not like this thing is a high hour ragged out race bike.
 

whenfoxforks-ruled

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Just the opposite Joe, adult trail ridden? The pic was iffy, how much skirt wear. All Juniors rods clearly showed wear patterns like the wrist pin cage was wobbling. How much do you dance on the rev limiter/cash register? 8 years and that sound still makes me cringe. Vintage Bob
 

_JOE_

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I know the rev limiter but don't hold it there. The motor is much more effective about 2k rpm shy of the limiter. I upped the compression a bit to help the midrange so I could keep from having to wring the piss out of it all the time. The piston looks great, the coating isn't worn through at all.

Anywho, here's some more pics.
 

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_JOE_

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And the other....
 

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_JOE_

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And the valves....
 

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_JOE_

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Exhaust valves...
 

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_JOE_

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Does this stuff look normal? Well, besides the hair on the first intake valve and the carbon on the other.
 

whenfoxforks-ruled

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Man at the power robbing deposits! Even the seats have them. Joe, you need to drop 5 or 6 grand on that pro circuit stage 8 racing head? Not funny? You have been running pump premium gas, got a few dirt/particle scratches, and 80 hours on a stock oem rebuild, except for the piston, and replaced the springs 4 times, sound about correct? You put in the 14:1? That sounds to me like the oem rebuild paid off, for you. Too bad I know what that motor can look like at the other end of the scale after 15 hours. How many shim sizes from stock were you at? Vintage Bob
 

_JOE_

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I know Bob, I need to get that carbon cleaned up. Can I use a ScotchBrite pad on the valves/seats? The valves were shimmed when I did the piston, .001/.0015 smaller shims on the exhaust and .001/.002 smaller intakes. They're still right on spec where I set them. The piston is 13.5:1.
 

Rich Rohrich

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_JOE_ said:
Can I use a ScotchBrite pad on the valves/seats?

Scotchbrite, are you nuts? :ohmy:

Even with the lack of detail in the pictures it's obvious the exhaust seats are trashed and need to be re-cut. The exhaust valve faces are clearly eroded and need to be reground, or replaced (the scag in pump gas is likely the root cause here). Valve replacement is probably easier and maybe end up cheaper than getting them properly reground.

It's hard to tell for sure from the pictures, but it's unlikely the intakes are in much better shape. The intake seats look bad (hammered to an unacceptable width) in the pics.

Get a real valve job from a shop that has the proper (read big $$$$ ) valve seat cutting equipment and the skill to use it on small valves and replace the valves and springs. Given that you don't live on the limiter you'd be well served by going to a full Kibblewhite stainless steel valve kit with their double valve spring race kit. Starting with a proper valve job most riders in applications similar to yours get a couple of hundred hours out of the Kibblewhite valves and the springs.

Money well spent for most. :cool:
 

_JOE_

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Well, at least I have a bunch of months of snowy weather to save for a valve job. I have a set of factory intake valves/springs if I have to go the cheap route I'll use those and buy some factory exhaust valves, though I would LOVE to drop in the Kibbles.

Rich, would running VP car fuel be better than pump gas?
 
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