250F ring time, loss of power, gas in oil, cont...

[nikki]

Thanks Rich for warning me in the "250F oil kinda smells like gas" thread about the whole cheap gas, burning temp, ring blowby, crank problems, etc. issue.

The bike has approx. 25-30 hours on it and this weekend I noticed that when I would rev it out in 2nd gear to do jumps I have always done in 2nd, there was a slight loss of power when 3/4-full throttle. Kinda like it revved but quit making power earlier than normal. I assume that coupled with the oil smelling like gas and the hours on the bike all point to worn rings.

Red and I checked the valve clearance on both the 250F and CRF on Friday (thanks AJ and Lou for the instructions) and both bikes were on the low end of being in spec. So that was a good thing.

We will be doing rings on the little piggy this week. We're thinking all we have to do is take the cam chain off then we can pull the whole cylinder/valves in one piece? Is this true? I think Red said on the 426, you could not do this. If so, I think this will make our lives a little easier.

Would anyone recommend replacing anything more than rings? And can I measure the rings to verify they are worn or anything else to check if there are any other problems (ie. rod play, piston, etc.)?

Also, Rich or other knowing gurus - what type of race gas would you recommend to extend the life of the rings/crank/etc.? I am not looking for top of the line but something better than pump and something easily accessible and available in a 55 gallon drum or something.

So much for low maintenance four-strokes!! I guess the big bore bikes might be a little better though or Red has gotten REALLY lucky with his bikes. He had an '01 426 for 1.5 years and put tons of time on it and just did a top end and clutch right before he sold it for fun but it didn't need it. Never did anything with the valves or carb or anything and ran 93 pump gas. Now he's had the 450 for a year and the power is still great and the valves are in clearance and he hasn't touched a single thing. Pump gas in that, too.

 

[Rich Rohrich]

Nikki - The 250 and 426 are virtually identical from a top end replacement standpoint. Very simple and clean. The new Wiseco forgings are a bit lighter than OEM so it's worth considering them as a piston replacement.

While you have it apart toss the cam chain. It's only $16, and it might save you from prematurely wearing the crank sprocket when the chain starts to develop tight links.

Make sure and check the crank main bearings for excessive play. The mains should be replaced at the end of the season along with the pulling the valves and redoing the seats. At 30 hours they should be OK, but it's worth checking.

As for fuel, Phillips B35 and VP MR2 are IMO best choices in terms of price/performance ratio in both the 250 and 426 but keep in mind they will require richer jetting. VP C12 Phillips B32, will give good results as well for a bit less money per gallon and will tend to richen the total fuel curve across the board which isn't such a bad thing in the low speed circuits on the 250F. Just try and stay away from automotive specific fuels with high temperature distillation curves. If you need a source for Phillips fuels let me know. They can be purchased in 15 gallon drums which is about as big as you should go from a safety and storage standpoint.

 

[jmics19067]

Nikki,
here are a few things that I would check/ look at.

clean everything extremely well before, during , and after. before so you cant knock dirt off the frame into the motor, during so you can see what your looking at when you are inspecting, also right before assembly so you dont build dirt into the engine and after all complete to easily see if there is any leaks.


when you first pull of the jug see if the piston is discolored below the rings. How big the black spot is below the rings is a very good indication of how much blowby you have. a little bit of black right by the ring ends shouldn't be too much cause for alarm , there could easily be just a tad of blowby because of the gap.

take off the "compresion rings" the top one<s> place into the cylinder and use the piston to push it down straight into the bore about an 1" and measure the end gaps. compare with your manual these two things should easily tell you if your rings need replacing or not. The oil wiper ring is actually 3 pieces, 1 spacer and 2 wipers on each side of the spacer. The compresion rings keep the fuel/ power on top of the rings, the oil ring keeps the oil below the rings.

measure the piston skirts at the bottom front to back, and measure the cylinder bore in 6 spots, top, middle, bottom, front to back and side to side. this will give out of round ,taper , and when you subtract the piston measurement from it piston to cylinder clearance. compare to manual. make sure the cross hatch of the cylinder is in good shape.

The manual will probably state rod side clearance you can check.

always check new ring end gaps before installing you might have to file the ends a bit for them to be correct. If need be secure a file in a vise and carefully open the ring ends over top of the file, slowly,carefull work the ring ends over the file teeth checking ring end gap often, make sure edges are deburred.

be careful placing the oil wiper rings on the piston. spacer < springy looking thing > goes on first then the actual wipers. make sure that the ends of the spacer are not over lapped. Make sure that the none of new ring end gaps are not in a straight line over top of each other. Your manual might even say a specific pattern. If the is no ring pattern I take the number of rings and divide it into the circle ie 2 rings 1/2 way around from each other 3 rings 1/3 of the way from each other. The oil wiper spacer end gap is not critical as long as it isn't over lapped or directly inline with the wipers.

these are generic four stroke things that I look for /at. Sorry I cannot help with specifics but your manual should include all you need to know on removal, inspection, clearances, and reassembly. As a mechanic<not bike> these things will help you get the bike back to stock shape. As a tuner I have lots to learn so I can't help with anything beyond interpreting a manual. I am sure Rich will help you with the fuel issue and anything specific that you should look at.

 

[jmics19067]

oops abit late

 

[cujet]

See what happens? You post a simple question and next thing you know the engine is all apart!

All kidding aside, regular maintenance is the best way to long engine life. Changing piston rings keeps the oil cleaner too. Even if the rings are not worn out, the ring tension may be slightly lower, allowing some blowby.

Yeah, it is odd how some folks get away without doing regular maintenance. I have a friend like that, he never takes anything apart and it keeps running. As you would expect, he ends up riding a worn out slow bike! But it still runs (for now).

I have had success with certain engines by taking them apart shortly after break in and inspecting every aspect carefully. Often times getting better life from the engine by taking care of the issues I find.

Chris

 

[Ol'89r]

Originally posted by nikki

Would anyone recommend replacing anything more than rings? [/B]

nikki.

While you have the head apart, you may also want to replace the valve springs. If your power is dropping off before you hit the rev limiter, your valve springs may be weak. This will cause 'valve float' at a high rpm.

The real problem with weak valve springs is the danger of damaging the engine. If you were to miss a shift at a high rpm, the valves could float and tangle with one another. This can bend the valve stems and cause major damage to the top end.

Just my $ .02

Ol'89r

 

[SCHLAVA]

Guys this is an '03 with maybe 30 hours on it! Shouldn't this not be happening to a bike this new?

 

[Rich Rohrich]

It's a 13,500 rpm slipper skirt pistoned RACE BIKE that is being raced by a multi-time state champion. It's completely normal to replace a piston and rings at the 30 hour mark under these circumstances. This isn't an XR250 and it can't be treated that way. ;)

 

[SCHLAVA]

Agreed to a point...It may be completely normal to replace a piston and rings after that many hours but I don't think you'd notice such a power loss so quickly on a new bike. I'm a multi time year end place winner in the A class for enduros and have ridden my 01 250 for two and a half seasons. Thats 18 enduros plus i play ride every weekend(30-40 miles a day) except around christmas on my '01. I just replaced the rings for the first only because I had the head off to check my valves. The leakdown test was perfect and my valves look as good as new. They show absolutly no wear.

I'm not trying to be rude or snappy but I know that regardless of rider lever or multi time state whatever, that just seems to premature to "feel" the power loss of a brand new bike. What about jetting with the weather changes or clutch slippage? 30 hours? Thats 6 sundays in a row for me. I could never see replacing piston and rings that soon or that often??!! Rich I apologize if I'm coming off as rude!

Mark

 

[SCHLAVA]

Oh yeah I perform normal maintenance to Nellie. She gets airfilter and oil changes after every race or two weekends back to back of trail riding. I also every month or so just to a compression/leak down test to see if anything changes drastically. So I really don't abuse her maintenance wise.

Mark

 

[Rich Rohrich]

Originally posted by SCHLAVA
Rich I apologize if I'm coming off as rude!

Mark

Doesn't seem rude to me. You stated your opinion based on your experience. :thumb:

It's easy to forget that reliability is inversely proportional to rpm. While I have nothing but respect for the designers of these engines, the simple fact is they had to produce them at a specific price point and it shows.

Having seen the wear patterns of a lot of YZF4s and 250Fs it's IMO unwise to not pay strict attention to the service intervals. Okie's 250F is a good example. He has two seasons on it of riding every weekend on a tight SX style course that never gets the bike on the rev limiter, mixed in with a handful of longer track days on the bike. It sees good regular maintenance but we still had planned on doing the crank over the winter. Prior to DW02 I put a new top end in the bike. The old piston looked good, ring wear wasn't excessive and the valve clearance was within spec but it was clear that it needed to be freshened up.

Anyone who was at DW02 knows that Okie's bike dropped a valve. It wasn't until I got it apart that I realized why. The crank main bearings wear on these engines and it allowed the piston to valve clearance to close up at the sustained high rpm it saw at Cooperland. On one of the longer sections a valve kissed the piston and popped the keeper dropping the valve.

The tough part of this is, on a cold engine in the shop the crank and rod APPEAR to have no excessive clearance, and give no indication that it's going to cause problems. The g loads occurring at 12000+ rpm apparently had other ideas. This type of failure is extremely COMMON on the 250Fs, along with valve failures and rod failures. I'm extremely cautious about not stretching service intervals and this still caught me be surprise. Okie isn't some rev happy teenager, and he still had the crank bearings fail which lead to a failure that should have been a lot more expensive than it ended up being.

I have two junk cylinder heads that I use for flowbench development that came to me after similar crank failures, and Eric Gorr has collected a whole box full of trashed 250F parts in a similar fashion.

My point here is this, fatigue life on these parts is finite and it can get really expensive to try and stretch the life of these parts if your engine sees high rpm on a regular basis. In roadracing we kept engine hour records and tossed cranks at specific intervals wether they APPEARED worn or not because the consequences of trying to stretch the intervals was well documented and respected. IMHO, a 250F that is regularly raced needs to be treated in a similar fashion, but the exact intervals are still a matter of some debate.

FWIW, two seasons on Okie's bike wore the following parts and required replacement.

- new crank assembly (the ground bearing surfaces on the crank ends gall when the mains start to fail)
- new crank main bearings
- new trans shaft bearing (the one behind the clutch pusher wears quickly)
- the OEM Ti valves are of suspect quality for the cam dynamics used and the faces were worn to the point of needing replacement. As soon as they are available I'll be replacing the OEM Ti valves with Kibblewhite Stainless Steel valves and the matchjing springs, which will last much longer and should flow a bit better.
- balancer shaft needle bearing (I've heard from a couple of engine guys that this is pretty common)
- cam chain
- valve springs were replaced as a safety measure
- piston & rings


Just for the record I don't think any of this maintenance is unreasonable on a 13000+ rpm RACE engine. To this day I'm still amazed they can build these bikes as good as they do while selling them as cheap as they do.

One last thing, before any of you KTM zealots start yipping and humping each others legs, your engines have similar issues, the only difference is you'll need to take out a second mortgage to deal with them. :confused:

 

[zcookie49]

maybe I should get that YZ250 I was thinking about the other day... :think:

 

[whyz]

A Read from Gary Virgin,,

Today's Hyper-Thumper's can actually pound the valves into their seats,reducing clearance between the cam and valve,costing HP and possibly burning the valve due to the poor seal. T-Valves are notorious for this and thats why we've gone back to stainless on the Evansville Superbike Shop 540.

(Is this True ??) Thanks.. Cause I dont know..Just reading..

Even it you keep up on adjustment,the seats get pounded so much they distort and lose that nice 45 deg. angle.

Dirt and carbon passing through the engine gets hammered into the seats,creating pits for combustion gasses to escape through.

(Could this also be a reason for fuel to contaminate the oil too?

A leaking intake valve actually lets some fuel escape back into the intake on the compression stroke,which richens the next charge of fuel. This now super rich condition causes sluggish performance and washes the oil off of the cylinder walls,which can lunch a motor. Your valve springs also lose their ability to maintain the correct seat pressure,which doesn;t close the valve quick enough,so it can make very expensive contact with the piston.
Result??> Bent Valve. :think:
and is that why,also, that people go to Stainless??

Thank You. :silly:

 

[cujet]

God I love those big bore 2 strokes. So powerful, easy to overhaul and cheap too!

Chris

 

[Rich Rohrich]

Originally posted by whyz

Even it you keep up on adjustment,the seats get pounded so much they distort and lose that nice 45 deg. angle.

This was certainly the case with Okie's 250F. I've seen similar behaviour on a number of other Ti valve 426 engines and 250Fs. My 98 400F did the same to it's steel valves after a couple of seasons, even with fresh valve springs each year.

Do a search on Mike Perry's name hear in the Thumper forum. Mike is the head of R&D at Kibblewhite (the makers of Black Diamond SS valves), and had been kind enough to share a wealth of information on a similar issue that is plaguing the CRF450 engines.

 

[Rich Rohrich]

Originally posted by cujet
God I love those big bore 2 strokes. So powerful, easy to overhaul and cheap too!

Chris

The AF500 looks like a bargain when you look at the costs over the life span of the bike. :thumb:

 

[jimyz]

Nikki, are you thinking of taking up smoking again (two stroke) ?

 

[DEANSFASTWAY]

So Nikki What did you ever find ? Let us know were all interested.

 

[SFO]

Originally posted by Ol'89r


If you were to miss a shift at a high rpm, the valves could float and tangle with one another. Ol'89r

The valve to valve clearance is pretty dramatic with these new shallow included valve angle engines.
Perhaps Ol'89r is still thinking hemi style 2V valve to valve?
What a valve is going to touch in these badboys is the piston, not another valve but you could put some huge valves in it and start worrying about v to v but I think that might be for another thread.

 

[SFO]

Originally posted by Rich Rohrich



The AF500 looks like a bargain when you look at the costs over the life span of the bike. :thumb:

An AF500, my secret fantasy.
No valves to touch though :eek:

 

[Ol'89r]

Originally posted by SFO


What a valve is going to touch in these badboys is the piston

You are correct as usual SFO. :thumb: Thanks for catching that.

My main concern about valve float is nikki's statement about losing rpm sooner than normal. This is an indication of valve float. Feels just like hitting the rev limiter, even in engines that don't have a rev limiter.

9r

 

[Okiewan]

What a valve is going to touch in these badboys is the piston

Been there, done that. :(

 

[bk_thrasher]

hey<

Is it a tough job replacing valve springs??

 

[Rich Rohrich]

Originally posted by bk_thrasher
hey<

Is it a tough job replacing valve springs??

If you have experience with 4 valve japanese motorcycle engines and the valve spring tools required then no it's pretty straight forward. If you don't then it's a job worth sending out to get done.

 

[SFO]

The valve spring cotters, or keepers, is different in/ex.
Be advised.