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Some cylinder head questions (with pics)
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Posted by: _JOE_---------------------

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?

Posted by: _JOE_---------------------

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

Posted by: whenfoxforks-ruled---------------------

Why did you take it apart? Vintage Bob

Posted by: 2strokerfun---------------------

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??

Posted by: _JOE_---------------------

Bob, it's a 250f, it's always apart.

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.

Posted by: _JOE_---------------------

Bob, it's a 250f, it's always apart.

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.

Posted by: Rich Rohrich---------------------

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.

Posted by: _JOE_---------------------

Quote:

Originally Posted by Rich Rohrich

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.

Posted by: _JOE_---------------------

Rich, any thoughts on that scoring?

Posted by: whenfoxforks-ruled---------------------

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

Posted by: Rich Rohrich---------------------

Quote:

Originally Posted by _JOE_

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.

Posted by: _JOE_---------------------

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...

Posted by: whenfoxforks-ruled---------------------

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

Posted by: _JOE_---------------------

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.

Posted by: whenfoxforks-ruled---------------------

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

Posted by: _JOE_---------------------

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.

Posted by: _JOE_---------------------

And the other....

Posted by: _JOE_---------------------

And the valves....

Posted by: _JOE_---------------------

Exhaust valves...

Posted by: _JOE_---------------------

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

Posted by: whenfoxforks-ruled---------------------

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

Posted by: _JOE_---------------------

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.

Posted by: Rich Rohrich---------------------

Quote:

Originally Posted by _JOE_

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

Scotchbrite, are you nuts?

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.

Posted by: whenfoxforks-ruled---------------------

We should get 89ers grandson to post some pics of his 250f, with the extra crank hole. He is good at general pics, now for some Macro? Vintage Bob

Posted by: _JOE_---------------------

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?

Posted by: mideastrider---------------------

I too have a crf250 its interesting to see the condition of another’s engine. Just curious, are those the original valves that came in the bike?

Posted by: whenfoxforks-ruled---------------------

Joe did one oem valve job, no seat cuts, yes? If you can get fuel in above ground, good. Anything below ground, not much difference, as long as its at least premium grade. Vintage Bob

Posted by: _JOE_---------------------

Quote:

Originally Posted by whenfoxforks-ruled

Joe did one oem valve job, no seat cuts, yes? If you can get fuel in above ground, good. Anything below ground, not much difference, as long as its at least premium grade. Vintage Bob

No Bob, all original parts. I have extra OE intake parts but didn't install them. I thought they were going to crap out sooner cuase they tightened up so I bought the valves while I have a few bucks. Now that I look at everything I should have bought the exhaust parts too. I want to do the Kibblewhites but I feel sorta giulty about spending the money when I should be saving for bikes for the kids.

Posted by: _JOE_---------------------

And the VP is in a 55gal drum.

Posted by: Rich Rohrich---------------------

Quote:

Originally Posted by _JOE_

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

VP has about 60 fuels in their catalog. Care to be more specific?

Posted by: _JOE_---------------------

Wish I could. I can't recall. I'll ask next time I see him.

Posted by: _JOE_---------------------

Does a new OE cylinder head come machined and ready for valve train?

Posted by: Pete Payne---------------------

Rich, what is the "scag" in pump gas ?
I really like VP C-12.
Ol' Steve 125 is hooked on VP MR-9 right now . A little too pricie for me .

Posted by: _JOE_---------------------

Quote:

Originally Posted by _JOE_

Does a new OE cylinder head come machined and ready for valve train?

Anyone?

Posted by: Rich Rohrich---------------------

Yes, a new OEM head comes ready to run. I always like to check that the seats are concentric and true them if they aren't, but you should be fine just building a new head straight out of the box.

Posted by: Rich Rohrich---------------------

Quote:

Originally Posted by Pete Payne

Rich, what is the "scag" in pump gas ?
I really like VP C-12.
Ol' Steve 125 is hooked on VP MR-9 right now . A little too pricie for me .

Pete - Pump fuel has a bunch of high distillation temp components (upwards of 400f) that never vaporize and lead to the exhaust deposits that destroy the exhaust valves. Premium pump can be even worse in this regard because some of the heavier hydrocarbons that are used to boost the octane can have fairly high distillation temps.

Automotive engines turn so slow and have such long hot intake tracts that it's not a problem. But in the super short and relatively cool intakes in the current crop of MX engines, anything with a distillation temp above about 260f is unlikely to vaporize once the engine sees the far side of about 7000 rpm.

Here's an example of a good oxygenated unleaded race fuel and Illinois pump gas that sort of shows it in graphic form.

Posted by: _JOE_---------------------

Thanks for the explanation on the fuel Rich.

From the looks of things I can get a new head for about the same price as a good valve seat machining after shipping and stuff.

Posted by: whenfoxforks-ruled---------------------

I would jet with the blue fuel Rich, nice and stable. Them deposits get hammered into the seat, rings and seals, everywhere! All horsepower robbers. Curious statement about the crappy premium pump fuels, my favorite BP even had to go and add in some invigorate, I just know its not good! And nitrogen, what?, they believe the engine IS alive? Joe, probably another good move, nothing like a spare head laying around. Vintage Bob

Posted by: _JOE_---------------------

It looks like I'll be doing the factory head and Kibbles after Christmas. I guess I'll have to take a ride down to the KTM dealer for some VP, no more sacrificing pricey cylinder heads to save a few bucks a year on fuel.

For the 10 gallons of fuel I burn a season the extra cost will be well worth it.

I guess it's time pull the chassis down and grease her up. Hopefully we stay busy at work this winter so I can the boingers serviced too.

Posted by: whenfoxforks-ruled---------------------

Quote:

Originally Posted by _JOE_

Hopefully we stay busy at work this winter so I can the boingers serviced too.

Be careful what you wish for, I have seen some forks get real pricey to service. Vintage Bob

Posted by: _JOE_---------------------

I sure hope there's no suprises, though I don't have them serviced often enough so I guess it'll be my fault if there is. They work great and I don't beat the suspension at all, so hopefully seals/bushings/oil will be all they need.

Posted by: whenfoxforks-ruled---------------------

Clunking is about 300 dollars. I am sure your fluid is black and thick, and about it. Change often, with the stupid timed drainage? Vintage Bob

Posted by: _JOE_---------------------

Lol, I get the occasional seeping seal. Nothing a liitle cleaning hasn't stopped yet. I'm sure the oil is ugly. I wish I felt comfortable enough(had the right tools) to change the oil and seals myself.

Posted by: RM_guy---------------------

Quote:

Originally Posted by _JOE_

... I wish I felt comfortable enough(had the right tools) to change the oil and seals myself.

Christmas is coming up, ask Santa for some tools

Posted by: _JOE_---------------------

Quote:

Originally Posted by RM_guy

Christmas is coming up, ask Santa for some tools

It'll be a stretch for the elves to get my valves done in time, I'm not gonna push my luck.

Posted by: whenfoxforks-ruled---------------------

Changing fork fluid has to be the easiest maintenance to perform, but the shock you need to refill the nitrogen. Good suspension fluid is a bit pricey, compared to motor oil? The seals, be ware of the cheaper seals! If the seals keep getting contaminated, maybe you just need new wipers/dust seals? Vintage Bob

Posted by: _JOE_---------------------

I think it would be silly to replace the dust seals without doing the fluid seals.

I did a fliuid change in my RM, it wasn't too bad but the suspension still sucked when I was done no matter how many adjustments were made. The shock was a b!tch, the forks were pretty simple. I'm in need of an oil level guage, cap wrench, seal drivers, and a few other tools before I'll crack into the CRF. Anyone got any used ones from a past bike they wanna part with? The Zook was old and crappy(molested) to start with. This one started out 100%, I want to stay as close to that as I can afford to keep it......

Posted by: whenfoxforks-ruled---------------------

You do not measure the fluid on changes. Only on total rebuilds. The oem has a sweet time table, and how much to put back in it, got a stop watch? How much do you weigh in gear? Vintage Bob

Posted by: Pete Payne---------------------

Thanks Rich !!!!!!

Posted by: _JOE_---------------------

Quote:

Originally Posted by whenfoxforks-ruled

You do not measure the fluid on changes. Only on total rebuilds. The oem has a sweet time table, and how much to put back in it, got a stop watch? How much do you weigh in gear? Vintage Bob

I'm around 175-190lbs in gear depending on what type of riding and what time of year...

For some strange reason I'm always heavier in the spring?

Posted by: whenfoxforks-ruled---------------------

That is definitely NOT the stock spring weights. Did you get the static sag in spec, after the race sag, to get in the ball park? Go to MX Tech's spring generator. I will bet we can find you the proper springs, cheaper? The winter thing Joe, you need to ride more in the winter? Vintage Bob

Posted by: _JOE_---------------------

I would love to ride more in the winter, unfortunately the indoor track is an hour away and costs 20 bucks an hour per rider minimum when we rent. Ice tires would be sweet, they would open up some doors for fun.

The suspension works great, it could be a bit plusher in the woods but it definately out performs me at the track. I've not had the big clunker bottom out yet so I would think the springs are fine, for now anyway. I really just wanna get the oil freshened up before it hurts the internals.

Posted by: whenfoxforks-ruled---------------------

1)No sniv'lin about them track prices, thats half price! Such a deal! 2)The ice tires are cheep, till the spoon slips, and add in the er visit? 3)You know not to transport thumpers out in the cold? Unless you carry a salamander heater to thaw it. 90mph on a open trailer or pick up, when its 20 degrees out, its froze. No way it will start. Half hour in front of the salamander, magic. 4)You are missing the entire top of the stroke, Punch in your weight with gear and see what springs go in? May know a guy with springs? The bottoming is for maniacs, or REAL portly riders. Over 200 and you could not even run a guy over with out bottoming! Vintage Bob

Posted by: _JOE_---------------------

1) I'm cheap, it pisses me off to have to pay ride anywhere.....2)I mount my tires with a machine.....3)I don't go unless it's above 35, I don't like being cold.....4)MX Tech spring generator says to use stock springs at 200lbs in gear on the MX track. And the bottoming(shock) is to let you know you shoulda been a gear higher for that double....

I dusted off the trusty 'ol manual and looked at fork oil change procedure. It has to be more complicated than just loosening the cap and flipping it over then adding the amount of oil shown in that spiffy timed drainage chart? I think I remember having to bleed the air out of the inner chamber on the RM? I think I have some oil in the garage, maybe I'll give it a go. I guess I should call around and see if anyone has a cap wrench in town.

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Some cylinder head questions (with pics)

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