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

[nikki]

Well just a quick update... drained the oil today before tearing it down and again, it smelled like gas a little bit (oil had 1 hour on it).

So got it all apart and everything appeared pretty normal. I measured the valve clearance again and all in spec although I couldn't measure the middle intake valve (might cut a feeler guage in half to measure it at a later time).

First thing I noticed was that the top intake ring was angled the wrong direction with the ring gap directly under the middle intake valve right where the gas enters the cylinder. According to the manual, the ring gap should be more at 8 o'clock with 12 o'clock being facing the front of the bike (It was around 5 o'clock). This could possibly explain the gas in oil problem in itself I think? Something like the gas comes into the cylinder and as the ring forces the gas up to the combustion chamber, some gas goes right through the ring gap before combusting. Also, could be another place for unburnt gas residue to sneak through. The cylinder looked like new, as it should, with no wear marks whatsoever in the cross hatching. The top ring was slightly out of spec - limit is .12mm and it was around .13mm so more reason making me think the top ring could be a problem. There was very little carbon build-up except a little bit again around the middle intake valve. Rod has no up-down play and very little side-by-side. The crank did have two dark brown spots around the rod at TDC but didn't look to be all around the crank just TDC. The piston had no blowby spots or discolorations.

I will try to snap a few pictures tomorrow. I have a new piston but think I might just do the rings right now and see if it helps the problems. I also took apart all the oil lines and cleaned out the oil strainer under the frame guard (which had tiny pieces of tree looking stuff in it). Will take a look at the carb tomorrow and clean that too. For kicks, I might take a look at the clutch too.

Ol'89er - you bring up a good point about valve float as what I think happened last weekend with the power stopping earlier than normal at high RPM's did kinda respond similar to hitting the rev limiter. Also, my valves are on the low end of the clearance range. For instance, if the intake range is .10mm-.14mm, then I am right at .10mm. If the bike responds like that again, I will definately consider new valve springs and maybe shims.

Another "possible" reason for the high RPM power deal might be related to gearing. I did go up one tooth on the rear sprocket back in March before the weekend that I got injured and I have rode hard just a little bit since then. But I just know it didn't feel right last weekend. I plan on riding Monday and paying close attention to how the bike reacts.

Thanks everyone for your help and comments and thoughts as it is very appreciated. Wrenching on four-strokes is a whole new thing to me.

And jimyz - I am 99% sure I will never ride a 125 again. This 250F is amazing (aside from a little mechanical paranoia).

 

[truespode]

Originally posted by nikki
Wrenching on four-strokes is a whole new thing to me.

learn


Wrenching on 4-strokes intimidate the hell out of me but reading your stuff and vicariously learning a little is giving me a little more confidence.

Keep coming with the updates.

Thanks
Ivan

 

[Ol'89r]

Originally posted by nikki
If the bike responds like that again, I will definately consider new valve springs and maybe shims.

nikki.

If you have the engine apart, you may want to replace them now. The valve springs in this engine are not much bigger than a throttle return spring in a fitty. With the high rpms that the engine turns, I would think they would weaken pretty fast.

If you shim them, you have to be careful not to pack them too tight. This can cause 'coil bind' and damage your cam. There should be a few thousands clearence between the coils at full valve lift. Also, notice the springs. Some valve springs have a heavy end. Or, in other words they are wound tighter at one end than the other. The heavy end or tight end has to go against the head and the light end goes against the collar. Sometimes you have to put them in a vice and sqieeze them down a little to see which end is wound tighter. Cant remember if the springs on the YZF are wound that way or not, but it's worth checking.

Another little tip. When you install your cam, be sure to set the cam in the TOP cam holder journals first. DON'T set it in the head and then try to put the top cap on. Set it in the top cap and check to be sure the locating circlip is in place. Then, while holding the cam together with the top cap, place the whole assembly down into the head using the dowel pins to locate it. If you do it the other way, it is too easy to dislodge or get the circlip out of place thus causing misalignment of the cam and damaging the cam journals.

Also, be very careful when torquing down the cam journals. Use a inch pound torque wrench for this. It only takes about 7.sumthin foot pounds torque for these caps so, it's hard to get an accurate reading with a foot pound wrench. Check your manual for the proper torque and don't go over this figure. This can distort the cam journals and damage the cam.

Good luck. :thumb:

9r

 

[SFO]

The valve springs are progressively wound on the yz-f.
The tighter portion of the coil is also painted. This side goes against the base washer, with the more open part of the coil against the retainer.

Maybe Mike Perry can pipe in and talk about the seat pressure issue... :worship:

 

[Rich Rohrich]

Originally posted by nikki

First thing I noticed was that the top intake ring was angled the wrong direction with the ring gap directly under the middle intake valve right where the gas enters the cylinder. According to the manual, the ring gap should be more at 8 o'clock with 12 o'clock being facing the front of the bike (It was around 5 o'clock). This could possibly explain the gas in oil problem in itself I think?

Nikki - The rings on a four-stroke are design to turn in their grooves. It's sort of a self-cleaning mechanism. The idea behind staggering the gaps is an attempt to keep them from lining up during the normal movement that will take place.

 

[nikki]

CRAP!!!!


Just put everything together and now it has very little compression. I can kick it over with my hand. 50+ kicks and it hasn't fired. Very little back-pressure coming out the exhaust too. It does have spark.

What could be wrong? Compression ring? Auto-decompression? Timing? This sucks - supposed to go to Michigan for LL regional practice tomorrow.

:debil: :whiner:

Guess I'll go pull the valve cover and take a look. Or the pipe and try to peek in the cylinder.

 

[High Lord Gomer]

Oh Nikki, sorry to hear that! Mine is also apart right now and I'm trying to figure out how to find when the bottom end thinks it is at TDC on the exhaust stroke instead of the compression stroke.

If I had to bet, I'd put money on the timing being a tooth or two off.

Good luck!

 

[SFO]

I might try double checking my cam timing and then check the decompression cable free play.

 

[nikki]

CRAP - again...

I think the timing was a tooth off but now we have both the punch marks on the cam sprockets and the TDC mark on the case aligned and still have a problem.

The intake valves measured .10 and .11mm (in spec) 1 ride ago, yesterday before disassembly, and now after reassembly. I can't get to the middle intake valve with the feeler but assume it's okay.

However, something funky is going on with the exhaust valves. Both measured .18mm (in spec) one ride ago and yesterday. Right now - the one closer to the clutch lever side still measures .18mm BUT the one on the brake lever side is showing like no clearance (can't get a .05mm under it at any time in the stroke). Also, we noticed when you take the exhaust rocker arm/cam sprocket off, the cap that goes over the shim on the problemed exhaust valve always sits higher than the other in spec exhaust valve now. Does this sound normal? What could have happened in between yesterday and today to make this one exhaust valve have very little clearance between the cap and the lobe?

Damnit this sucks!

 

[nikki]

DOH!!! She's runnin!!


I wonder if ANYONE has ever seen this before... pull off the cap on the out of clearance exhaust valve... and what do ya know - the shim wasn't in the shim groove! It was making the valve cap sit about 50% higher than it should taking away all clearance and making the exhaust valve always open hence no compression on the compression stroke cuz it all went out the exhaust.

Problem solved!! :thumb:

 

[truespode]

Congrats!!

Good luck at LL.

Please give us a ride report!!

Ivan

 

[SFO]

Originally posted by nikki
DOH!!! She's runnin!!


I wonder if ANYONE has ever seen this before...

Problem solved!! :thumb:

Sixteen clumsy and shy, I moved to London and died.
I booked myself in the Y, WMCA.
Thank Ala your yz-f is barking fire now.
Problems, all I know, have preexisted. :silly:
Super glad you sorted it out.
Good luck manana :thumb:

 

[jmics19067]

Originally posted by nikki
DOH!!! She's runnin!!


I wonder if ANYONE has ever seen this before... pull off the cap on the out of clearance exhaust valve... and what do ya know - the shim wasn't in the shim groove! It was making the valve cap sit about 50% higher than it should taking away all clearance and making the exhaust valve always open hence no compression on the compression stroke cuz it all went out the exhaust.

Problem solved!! :thumb:

Nikki,

If the shim moved while inspecting/assembling a little engine assembly lube or white grease can help "glue down " parts like that to keep them from shifting.

If you took apart the engine and found that I would start to suspect valve float. What can happen if the valve springs get weak or you overrev the engine is that the valves don't follow the profile of the camshaft on the way closing. If the valve can't react to the downslope of the cam there will be a gap that parts "can" bounce around unintentionally. You would probably find something that was "hammered" though.

From your post I believe you meant on assembly but I just wanted to point that out.


sorry about not being fully understandable about the rings , they will move a bit. Atleast you know they werent sticking :thumb:

 

[Smit-Dog]

Originally posted by SFO
Sixteen clumsy and shy, I moved to London and died.
I booked myself in the Y, WMCA.

...As the flames rose to her Roman nose and her Walkman started to melt...

Anyone that quotes The Smith's in a post.... :worship:

 

[biglou]

Hey Nik-The coolest thing is, you now have a much greater understanding of what is going on inside there, and hopefully feel confident with your new-found knowledge. And yours doesn't even make the "whirring noise"! Great job! :thumb:

 

[Rich Rohrich]

Originally posted by nikki
DOH!!! She's runnin!!


I wonder if ANYONE has ever seen this before... pull off the cap on the out of clearance exhaust valve... and what do ya know - the shim wasn't in the shim groove!

Nikki - If it makes you feel any better. I've done a bunch of YZFs over the last few years and I still have that happen now and again. :eek: Don't feel bad about getting caught by it on your first try.

It's a great feeling to hear it bark back to life isn't it? Good Luck at the qualifier. :thumb:

 

[nikki]

Man... what an experience this weekend! Actually, I'm kinda happy that it didn't go smooth because we got LOTS of practice playing with the cams and cam chain and valves. I think might be able to beat BigLou's cams in hand at 5 minute mark. :moon:

I'm curious to take a look at the oil tonight and see if it's still gassy. I haven't converted to race fuel yet but plan on it in sometime soon here. The bike ran great yesterday but I was on a 3rd-4th gear track and didn't get a good feel for the cutting out at high RPM's in 2nd gear that I noticed last weekend. I'll ride at our friends' track sometime in the next few weeks again and see if it's still funny.

The Loretta Lynn regional is in 3 weeks - yesterday was just practice at the track (Dutch Sports Park in MI). Unfortunately it's a pretty rough track and I had a hard time with my shoulder but hope to give the regional a whirl anyways. I think there are almost 50 girls who qualified in my class for Dutch so it'll be interesting. Go figure out of 7 regionals, this one had the most qualify in the big bike women's class. :silly:


Thanks again everyone for the advice and help!!! :thumb: