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top end inspection, (noise) athena gasket kit

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Since I have had my bike 2004 YZ250, I have thought it's had excessive engine noise. (I put a fresh Wiseco piston in it, about 8 tanks ago) it seems to have just as much power,  starts nearly the 1st kick every time, it's just the noise I hear is bothering me. I recently noticed a rattling sound as I'm getting into the power band in 5th. (with 93 at a 32:1 mix with Klotz Supertechniplate, even tried the same oil mix with a 50/50 mix of 110/93). Jetting is stock,  I'm  at 400ft elevation.  

 

I decided it's time to pull the top end off  to inspect it, I should have time this week end.  I was just hoping you guys could help me determine what it could be and give your  suggestions on setup. I will be keeping this thread updated and posting pics until I figure it out,  If nothing else I will try a OEM piston.I went ahead and ordered Athena base gaskets, and head o rings. does anyone know if these will be ok? it also comes with a high compression base gasket, does anyone know how much of a difference in compression it makes?

Edited by yz250474

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The noise would drive me nuts too.  I am still not used to it.  If you are going to have the jug off, check the rod for vertical play and side to side slop.  REally, move it around and see if there is any play.  shouldn't be any, just sliding a bit side to side on the needle bearings.

 

Noise can come from a lot of places.  See if you can isolate it to the motor or case(clutch).  Put you hand on the jug and see if you feel anything.

 

Some pistons actually are more "noisey" than others.  Look for detonation.  Rule of thumb with 2cy, run a tad on the rich side.  Plugs are cheap.

 

Let us know what you find.

 

Ride hard, take ibuprofen, repeat as necessary.

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The noise would drive me nuts too.  I am still not used to it.  If you are going to have the jug off, check the rod for vertical play and side to side slop.  REally, move it around and see if there is any play.  shouldn't be any, just sliding a bit side to side on the needle bearings.

 

Noise can come from a lot of places.  See if you can isolate it to the motor or case(clutch).  Put you hand on the jug and see if you feel anything.

 

Some pistons actually are more "noisey" than others.  Look for detonation.  Rule of thumb with 2cy, run a tad on the rich side.  Plugs are cheap.

 

Let us know what you find.

 

Ride hard, take ibuprofen, repeat as necessary.

I did check for up and down play and found none last time, side to side play was in specs. I did notice the noise changed a little if I put my hand on the clutch cover. it sounds like its coming from the bottom of the cylinder/sleeve. Im going to get my local dealer to measure it again to see if its out of specs...seemed like they didn't measure it to good last time.( was quick), and I'm going to ask some questions, they didn't say anything about a A,B,C,D piston. it was at idle I noticed noise if I reved it I cant hear it. by the way my plug looks now it is a little rich, but maybe I should try a size up main? all it has done to it is a pro circuit platinum pipe,r304, and boyesen power? reeds (fiber glass) are the OEM reeds better?

 

 Does anyone know of anything else I should check while it's apart? power valves?   and if I cant find anything I'm going to install OEM gaskets and piston. Would it be ok to go ahead and order a D piston? or should I have it measured first?

Edited by yz250474

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I should of mentioned this before, with the cylinder bolted down and the head off. when I spun the crank the piston would make a little knocking sound after it reached the bottom of its stroke and started to come back up (i will post a video) I thought maybe it was normal for a forged piston and wouldn't do it when warmed up...maybe not normal?

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I wonder if the piston is rocking at the bottom of the stroke??  Might measure the base of the cylinder to see if it is out of round.  Just a SWAG here

 

You mentioned the noise was by the clutch cover...is the basket loose or something else in there wrong?

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I wonder if the piston is rocking at the bottom of the stroke?? Might measure the base of the cylinder to see if it is out of round. Just a SWAG here

You mentioned the noise was by the clutch cover...is the basket loose or something else in there wrong?

I got that fixed, can't find nothing else...

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if everything goes as planned I will have the cylinder off by noon tomorrow. I plan on taking it to my local Yamaha dealer to have it measured, anything I should mention?  I seen a thread a little while ago about the bushing? wearing out for the power valve shaft... didn't have time to read it all.... just if you guys can think of anything please let me know. I will post pics tomorrow.

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Might have them check for roundness of the cylinder.  Before you take it to them, do the solder/ squish band measurement if you want to get the head cut.  Do a search, you will see what I am talking about.  Make the motor more predictable and easier to jet.  Makes it snappier too.

 

OH!  Did you check the timing?  With today's fuel, that could be an issue.  I am old enough to remember when we could get REAL gas.

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Might have them check for roundness of the cylinder.  Before you take it to them, do the solder/ squish band measurement if you want to get the head cut.  Do a search, you will see what I am talking about.  Make the motor more predictable and easier to jet.  Makes it snappier too.

 

OH!  Did you check the timing?  With today's fuel, that could be an issue.  I am old enough to remember when we could get REAL gas.

I have read about squish,  a little... so it don't change at all after changing pistons?? I have not checked the timing, I remember seeing a gauge for sale on a website for $45 I was looking the other day but couldn't find it. I will buy it for sure if I can find it. I don't really want to retard timing because  I like the power.... I want more really. I thought a 50/50 mix would stop detonation but idk.

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Naw, squish should be the same for the pistons.  Thing is, you need the jug on to measure it.  Just lay on a piece of soft solder, put the head back on, torque, cycle the piston to "smash" the solder, be gentle, and that is what you measure and maybe send to the shop who will cut the head for ya.  Yup, makes more power.

 

 

Do some searches, you will get videos on youtube.  easy to do.  Heads are not made the same.

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I don't ride much so I wouldn't mind setting it up for 100% race gas, this noise has to go first... something's not right. I  plan on getting the squish ( prefer 93/ but when I put 50-50 of 93 -110 it seemed to have a lot more power), jetting, and suspension setup, none of that matters if it sends the crank thru the cases. so that's why I been putting it off, I guess.  if it has been detonating a little would I be able to tell with a forged piston? 

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Naw, squish should be the same for the pistons.  Thing is, you need the jug on to measure it.  Just lay on a piece of soft solder, put the head back on, torque, cycle the piston to "smash" the solder, be gentle, and that is what you measure and maybe send to the shop who will cut the head for ya.  Yup, makes more power.

 

 

Do some searches, you will get videos on youtube.  easy to do.  Heads are not made the same.

thanks I will do for sure, but I got to figure out the cause of this noise first... I don't mind taking it back apart, that's half the fun of owning a bike to me. working on it.

 

 

I really think the cylinder is out of round.... I will post a video of the sound it makes with the head off when I spin the crank.

Edited by yz250474

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snappier..... that's probably how I should of described it with the 50 50 mix, every time I upshifted the front wheel came up. It didn't do it with 93.. makes me think it is something with the fuel/timing.

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That might be an issue.  Kinda looks like blow buy of the rings.  The spot on the bottom of the cylinder is an area where the rings didn't make contact i.e out of round.  Looks like the piston could have been sloppy in the bore too, (banging noise)  skirt slap.  You might have saved a grenade motor, whew.  See if you need to go with a replate (cross hatch looks good) or if you have the wrong size piston.  Check skirt clearance!!

 

Think you are onto something here.  Chime in everyone!!

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That might be an issue.  Kinda looks like blow buy of the rings.  The spot on the bottom of the cylinder is an area where the rings didn't make contact i.e out of round.  Looks like the piston could have been sloppy in the bore too, (banging noise)  skirt slap.  You might have saved a grenade motor, whew.  See if you need to go with a replate (cross hatch looks good) or if you have the wrong size piston.  Check skirt clearance!!

 

Think you are onto something here.  Chime in everyone!!

I took the cylinder to a engine shop and the guy said it looked ok, just to hone it (which he did for $20, I think that made it worse)  and install a "standard piston".... local dealer said the same thing. ( they both supposedly measured it)   I should of sent it for a replate and saved myself from buying another piston. Pretty disappointed with both shops.

Edited by yz250474

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I took the cylinder to a engine shop and the guy said it looked ok, just to hone it (which he did for $20, I think that made it worse)  and install a "standard piston".... local dealer said the same thing. ( they both supposedly measured it)   I should of sent it for a replate and saved myself from buying another piston. Pretty disappointed with both shops.

Well, now, don't take my word for it over the internet and me not having any gauges to measure it.  Did you see them measure it?  Have you shown them the cylinder recently?  Just for gits and shiggles, measure the skirt clearance and see what you have.  When I got my last cylinder back, the skirt clearance was VERY tight, WELL in specs, actually on the very end of being tight.  Had whopping compression!!

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Maybe write up another post ans ask for opinions on the cylinder and possible noise from other gurus on here.  More eyes see better.  Mention you have pictures, we love pictures.

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There is a lot of blow by. Did you check the ring gap when you installed the piston? If you wanna see if it's out of round check the ring gap in various places (top,middle,bottom) and see if the ring gap is the same. The noise at bottom dead center would concern me. Check the rod for play at more than just top of the stroke check at various points all the way around and make sure your small end bearing is good that could be the issue as we'll. I only made all the previous statements because you already have it apart. The fact that you are hearing the noise when the motor is under a heavy load and race gas made it better makes a lean main jet a prime suspect.

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Never thought of the ring trick, been a while, but that will work too

 

The knock improving with better fuel makes me think of timing too.  If there is a bearing going, better fuel won't heal it up either.  The piston crown looks rich from here.  Is there any pitting on the piston or in the head?  Detonation will sound like a hammer whacking the piston and shows up more or better when under a load or lugging the motor.

 

I am still leaning toward correct piston size, rings(duh), check timing, and think about getting the head cut.  Could be that you have too much compression and timing both. 

 

Keep asking questions and keep looking.  Keep us informed of how it goes.  These guys on here are a great source of info. and experience.

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