Top end tear down

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TWMOODY
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Top end tear down

Post by TWMOODY »

Tore down the top end on my 05 200 today just because.
What I found inside was a piston with scouring on the intake
side,not from heat but sand possibly from my K&N air filter
allowing it through.
Cylinder looked good but the rod showed some heat tempering
only in the very center 3 inches or so. At the ends it looked
fine.
I put a new piston and rings in it cleaned everything up and
it runs just as good as when I tore it down.
Jetting seems on the money with a 42/152 DEK#4 and the RB carb mod
My questions are........

Even though the rod showed signs of heat nothing else did.
Piston,cylinder and head showed no heat damage.
Is this normal ??



Also, I would bet the K&N breathes better than most filters BUT
breathes sand and small dirt also.
Anyone else have this happen with this type of filter??
Last edited by TWMOODY on 09:52 pm May 24 2007, edited 2 times in total.
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Post by Colorado Mike »

I've never used one, but I have heard of people complaining of that.
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Post by canyncarvr »

'Heat tempering' meaning it's a different color?

Didn't happen to took a pic...?

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TWMOODY
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Post by TWMOODY »

No I didn't take a picture but both ends of the rod were
the normal silver color but the center 3 inches or less
showed the tannish red/brown of heat tempering.
No signs anywhere else of excessive heat.

Seems like I would see something else heat related but
I didn't
I will post a pic of the piston which has not been cleaned or anything
to see what you think of that.
I don't think I'm to lean.....

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Post by kawagumby »

I've used K&N filters on other brands of bikes...never had a contaminant infiltration problem, even in dusty desert races. Is it being coated properly? Is it sealing tight at the carb boot connection?
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Post by TWMOODY »

Yep fresh every other ride AND greased at the mounting base.
I pulled the air box apart today and all was sealed very good
I did reinstall and use rtv on the boot to box connection.
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Post by canyncarvr »

A good bit of blow-by on the piston...a sign of rings not seated very well. You might consider an alternate break-in procedure... Rings have to be loaded to seat...it takes pressure to do the job. Old hat, but it's combustion pressure getting behind the ring, forcing it against the cylinder that mates the surfaces. Any escaping gas is lost power. If it (mating) doesn't happen right off (break-in) it's not going to happen.

...and preheated intake charge...more lost power. Maybe detonation, too. I know about that! :neutral:

How about the brown color on the rod is additive deposits (the normal stuff in pump fuel..not anything you put in) maybe related to some of that blow-by...not heat. Enough heat to change the color of the rod would certainly show up in other places on the piston wooden it?

Rule of thumb: Intake side seizure is FOD or oil failure.

Someone that knows (IC?) could tell you for sure, but I believe a too-lean condition will show on the exhaust side skirt..and there will be a considerably larger carbon buildup on the underside of the crown.

K&Ns are storied for passing dirt. I don't know if they do or not. Doesn't seem logical to me that a gauze filter that was oiled would pass much of anything damaging.

You going to use a Pro-X for the redeaux?

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Post by IdahoCharley »

Basically some comments.

FWIW - Most RTV sealants on the boot to box connection will break down over a short period of time when exposed to gas/oil mixture. I would suggest resealing area with a rubberized weather strip sealer within the next month or so.

It looks to me like you experienced a slight piston seizure at some point it time. Although the top of your piston appears you are jetted safe the underside of the piston indicates that the piston experienced some high temperatures at some point in its life.

Note also that your rings were left in a little too long period of time as can be seen by the blow-by on the piston. When the blow-by increases less heat is transmitted to the cylinder wall and more is retained by the piston. Excessive heat retained by the piston is never good looks to me like your timing for a top-end rebuild was well "timely".

EDIT - I see CC posted - he may be correct in that the rings never did seal due to inadequate loading on the engine. I made the assumption that the rings were left in too long. Most times the end gap on the rings is a good indicator of wear and measuring the ring fitment to the ring landing on the piston is the second measurement. You can also loose some of the temper strength in the rings if the engine is overheated for extended periods on some bikes. I don't know if this happens on the KDX rings but it does on the some of the OEM KTM rings of years gone by and some of the older air cooled bikes. CC is correct on the rod - heat tempering of the rod just will not happen in a running 2-cycle engine. The fuel mixture is cool and wet relative to everthing else in this area. Deposits from fuel/oil is very likely the source of the discoloration if in fact the rod wasn't already colored do to the manufacturing stress relieving process.

The light scratches on the intake side are normally indicative of dirt passing the filter like you mentioned in the thread. However the full length scraping on the piston is not from dirt - its from contact with the cylinder wall.
Last edited by IdahoCharley on 10:44 pm May 22 2007, edited 2 times in total.
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Post by canyncarvr »

Yes...no carbon on the underside without some heat to stick it...but it doesn't look like a pervasive condition...right?

How do you tell the diff between rings that never seated well and those that wore out?

Thanks for the input!!!

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Post by IdahoCharley »

>|<>QBB<
canyncarvr wrote:Yes...no carbon on the underside without some heat to stick it...but it doesn't look like a pervasive condition...right?

That my thought also - maybe jetting a couple of sizes too lean at one time during testing or maybe a size too lean and a hard ride where the engine was on the edge of siezing.

How do you tell the diff between rings that never seated well and those that wore out?

Supposedly some say you can look at the face on the ring and visually see wear on the ring sealing surface (change of taper, color and shape)- I've never been able to tell anything that way.

I use end gap and ring landing spacing to say - yep the ring has served it time. Sometime if the cylinder is oil glazed in one or two area you can fairly well assume (IMO) the rings never sealed. It seems to me that img 300 and 301 show areas between the ring landings where blow-by past the top ring was exposing the second ring to the blow-by which stopped the blowby. But then 301 shows blow-by pass both rings on the exhaust side. In my experience blow-by most commonly starts near the ring locator pins when the rings have seated well. [/b]
Hey cool - I screwed up your quote CC - sorry. :sad:
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Post by canyncarvr »

IC wrote:I screwed up
your [quote="IC]quote
[quote/]
[/quote]


The edit police are on the way! :shock:

IC wrote:..blow-by most commonly starts near the ring locator pins when the rings have seated well.
The cleanest part of the piston IS at the ring pins.

..which I wondered at. Sensibly, the ring is going to contain less pressure where it's in two pieces (both ends). This piston looks like it should (ring-wise) ONLY at the pins.
IC wrote:I use end gap and ring landing spacing to say - yep the ring has served it time.
End gaps on any pistons out of my bike generally spec to 'it's time' ...(well, or WAS some time back). I've not checked ring-to-land gap to know one way or the other. The reason I'm taking it apart is to replace stuff...not for a look-see. I'm not that energetic! :wink:

Just thought of this...TW..do you use the spacer UNDER the ring?

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Post by TWMOODY »

I agree with the blow by past the second ring but the weird thing is it had
145lbs compression at tear down.
Engine had about 1100 miles on it at tear down also so something caused the ring failure.
The boot to air box connection is from what I could see a very tight connection (rubber still very flexible) so I just added a tad of rtv to make sure.
Cylinder looked excellent above intake port (in line with piston damage)
but slightly marked below which a abrasive pad cleaned right up.
I did use a hone to put cross hatch on cylinder but slow speed and
only seconds cause I know your not supposed to hone.
Just thought of this...TW..do you use the spacer UNDER the ring?
Ok what spacer you speaking bout???
You going to use a Pro-X for the redeaux?
You mean for the piston CC ?
I had a weisco on the shelf waiting for me to put in.
I like to keep any part that will fail on hand so I'm not down
for more than the time it takes to fix it.

Another thought on oil failure on the intake side......
I have ZERO spooge, none, zippo,nuttin.
I haven't sense I started using Amsoil interceptor.
I mix 40:1 and am using 16oz of toluene per 5 gallons of gas
and pump 93 octane
The 16 oz is PART of the total 5 gallons.
Guess I should mix 32:1??
I put the original foam filter back in and notice absolutely
no difference in performance.

Didn't think to measure ring end gap on tear down but the new rings
are .011
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Post by IdahoCharley »

Do you always warm-up your bike prior to riding it hard?

If you look at the pictures on the intake side of the piston it is clear (to me anyway) the left side and right side of the piston is lightly scuffed. Looking at the exhaust side of the piston in-line with both sets of oiling holes is also clear to me that scuffing of the piston is likely evident although to a much lesser degree. These four areas are the classic areas which would indicate a four point seizure most of the time from a "cold seizure" (piston expanding quicker than cylinder wall). That was my basis for thinking the piston had lightly seized or been scuffed.

If a person wonders about lack of lubrication seizure on the intake side I suppose they could also say the oiling holes on the piston on the exhaust side provides some evidence of lack of lubrication due to the scuffing starting to take place. Rational being the fuel oil mixture either lacked sufficient lubrication in the fuel/oil mixture or the engine ingested some water momentarily preventing proper oiling of the piston skirt. I can't argue one scenario over the other but I believe it is more likely the engine was not sufficiently warmed-up and ran too hard OR that water was introduced into the intake system during a ride or maybe while washing the bike and then sucked into the cylinder.

Bottom line - I don't believe that you running 40:1 had anything to do with the failure of your piston/rings. Normally you can evaluate whether or not you have adequate oil in the fuel mixture by examining your bottom end (oil residue) in the case/oil residue on the piston skirt and oil residue on the wrist pin bearing at disassembly.
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Post by TWMOODY »

Do you always warm-up your bike prior to riding it hard?
I have been known to ride 2 or 3 minutes and give her hell
and did that very recently when a friend came over with his
friend riding some 400 enduro thumper and had a coment
about my little 200.
Once around the yard before hitting the dirt road and giving
the 400 a spanking.
I topped at 74mph and let off.
I didn't tell him he could of took me top end though :lol:
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Post by TWMOODY »

Had a long time 2 smoker look at the piston today and first thing he said
was COLD SEIZE...

I did a plug chop with the jetting at 40/152 and DEK4
the posting earlier said a 42 pilot but was a 40.
My chop is posted and I think looks good.

I put a 155 main in and tried it but by the seat o the pants I lost
a considerable amount of midrange torque.

Plug chops all the same plug

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Post by IdahoCharley »

I think that plug chop looks PERFECT! :grin: :grin:
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Post by m0rie »

Looks just about right to me.
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Post by canyncarvr »

If I may re-address this..I missed the question earlier.

The spacer? I mean the wavy-crimpy looking thing that commonly comes WITH rings..to be placed underNEATH the ring.

I've heard more complaints of those spacers causing stick than anything else.

That is the 'spacer' I was referring to.

I like that plug!!! YEehAW!!

Re: 155 lost some...

Funny ain't it? One plug size can actually make a difference you can that readily feel!!

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Post by TWMOODY »

No spacer was with the original (OE) piston or the weisco.
Bike running great and I do allow a little bit of warm up time.
Yes the jet sizes make a huge difference.
One jet size can take away lots of power and cause
a good amount of sputter !!!!
I can say I have learned to jet a bike properly and to
do it again would be a breeze.
One thing I would have to say is that the DEK needle on
#4 seems much better than the CEK on #3 or #4.
Wider power band with the same or better hit.
Thats IMO
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Post by Indawoods »

I like the wimpy DEK too! :lol:
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