Help! Piston replacement recommendations

Questions and Answers about the best carb and Head mods available for the KDX.
Post Reply
akagalford
Member
Posts: 9
Joined: 11:36 pm Jun 14 2010
Country:

Help! Piston replacement recommendations

Post by akagalford »

So I have a big trip planned this weekend up to Taylor Res. and decided I should probably make sure the KDX is in top form for the trip. I bought a project bike last season and only got around to tearing into it in the last month or so. Come to find out the top end was blown. With all that I am learning from the experience I realized the piston and rings in my KDX had never been replaced. (and I couldn't even begin to guess how many hours are on it, way beyond 200 for sure) I had the top end off a few years ago and I could still see the thatching in the cylinder. I ordered up new gaskets and a Wiseco piston kit and pulled it apart tonight. After running things through the parts cleaner I realized it was a good thing I pulled it apart as the bottom edges of the piston cone have started to chip and you can see its time for a new one. I can't see any thatching in the cylinder anymore and some of the edges in the ports are sharp. Because of all of this now I may not make the trip. What is my best coarse of action from here?

Can I just hone the cylinder and be ok with the new piston and rings? Is the cylinder in a 1991 KDX 200 Electroplated?

I'll try to get some pictures in the morning.
User avatar
Julien D
KDXRider.net
KDXRider.net
Posts: 5858
Joined: 07:53 pm Nov 07 2008
Country: USA
Contact:

Post by Julien D »

cylinder is plated. Clean it up really well with a scotch bright pad and some solvent. you can use wd40, kerosene, etc. See if the cross hatch becomes visible as you scrub the old aluminum deposits from the cylinder. If not, it should be re-plated. Langcourt, millennium, powerseal, etc. will hook you up with a new piston and match the new plating to it for a decent price. A standard strip and re-plate is not too bad, and the aftermarket plating is far superior to the coating that kaw used originally.
Image
User avatar
kdxmaniac
Supporting Member
Posts: 595
Joined: 09:01 pm May 24 2010
Country:

Post by kdxmaniac »

if you are using the wiesco piston.....it is forged, and will need a few thousants clearence more..........so, if your cylinder is not scard{deep lines going up and down}.... then i say run the piston like it is, because as the cylinder wears {wore out as you say} the clearence is already their for the weisco piston.....................make sence??
my bikes
-------------
96 ktm 300
96 XR400R
07 hayabusa
77 kz 1000
85 goldwing 1200
02 BIG DOG PITBULL

gone but not forgotten
96 kdx 200
98 ktm 380 "because it dang near killed me!"
97 ktm 360
96 ktm 250
93 wr 250
94 dr 350s
93 kx 250
07 gsxr 1000
99 bandit 1200
Budget_89KDX
Member
Posts: 241
Joined: 04:38 am Sep 11 2010
Country:

Post by Budget_89KDX »

Or you could do as the previous owner did with mine and sleeve it.knowing what I know I wouldn't go that route.those coatings are tough.the machine shop I did my apprenticeship at in college said they're not setup to be able even bore them out the coatings are that tough.
User avatar
Indawoods
Creator and Founder
Creator and Founder
Posts: 9951
Joined: 09:59 am Jun 12 2003
Country:
Location: Midwest

Post by Indawoods »

I have never seen any cross hatching on an electroplated cylinder. This is the case for unplated cylinders but nor plated. You will see a spiral scuff from top to bottom on a fresh cylinder but that's it.

As long as the plating is not worn away... scuff with a scotch-brite and re-piston it with a fresh piston.
*** Administrator //***
****'95 KDX 200/****

"People ate cows a thousand years ago for the same reason we eat them now. Cause they are easy to catch.We're not savages,we're just lazy. A cheetah could taste like chocolate heroin. But will never know. Those bastards are fast!!! "
User avatar
kdxmaniac
Supporting Member
Posts: 595
Joined: 09:01 pm May 24 2010
Country:

Post by kdxmaniac »

i think its plated...........you should be able to scuff it like inda said, put a new piston and rings in it, and be good to go.
my bikes
-------------
96 ktm 300
96 XR400R
07 hayabusa
77 kz 1000
85 goldwing 1200
02 BIG DOG PITBULL

gone but not forgotten
96 kdx 200
98 ktm 380 "because it dang near killed me!"
97 ktm 360
96 ktm 250
93 wr 250
94 dr 350s
93 kx 250
07 gsxr 1000
99 bandit 1200
heckler
Member
Posts: 243
Joined: 11:15 pm Apr 06 2010
Country:

Post by heckler »

re: scuffing the cylinder with scotchbrite pad

I'm replacing my stock '05 220 piston (it has a "C" stamped on it) with a Wiseco 69.0 mm piston. I don't see any damage - heck, I don't even see any marks in the piston and only a slight buffing on one side of the cylinder. The motor runs great, it's just because the internet told me the 220 piston will crack that I'm replacing it.

The cylinder feels perfectly smooth to the touch, and my fingernails can't detect any scratches at all.


Is there a certain pattern or direction of scuffing that I should do to the cylinder? I'm tempted to just leave it as is since it's perfectly smooth - I don't see any aluminum deposits.



Another question - why did RMATV only have one Wiseco piston size for sale? Measuring the cylinder ID seems pointless if there's only one piston size available.
Last edited by heckler on 02:24 pm Jan 04 2011, edited 1 time in total.
heckler
Member
Posts: 243
Joined: 11:15 pm Apr 06 2010
Country:

Post by heckler »

also, if I were just "doing the top end", is it common to clean up the exhaust ports and replace just the piston rings and gaskets? My stock piston seems brand new and I don't think I'd should replace it at this point (although I will to prevent the OEM grenade problem).

How do I know that the "top end" needs to be done next time around?
User avatar
kdxmaniac
Supporting Member
Posts: 595
Joined: 09:01 pm May 24 2010
Country:

Post by kdxmaniac »

>|<>QBB<
heckler wrote:re: scuffing the cylinder with scotchbrite pad

I'm replacing my stock '05 220 piston (it has a "C" stamped on it) with a Wiseco 69.0 mm piston. I don't see any damage - heck, I don't even see any marks in the piston and only a slight buffing on one side of the cylinder. The motor runs great, it's just because the internet told me the 220 piston will crack that I'm replacing it.

The cylinder feels perfectly smooth to the touch, and my fingernails can't detect any scratches at all.

Is there a certain pattern or direction of scuffing that I should do to the cylinder? I'm tempted to just leave it as is since it's perfectly smooth - I don't see any aluminum deposits.

Another question - why did RMATV only have one Wiseco piston size for sale? Measuring the cylinder ID seems pointless if there's only one piston size available.
the reason you want to "scuff" the cylinder is to get the glaze off, so the rings will seat better and quicker.

we usually go in a cross ways, up and down while going aroud the cylinder.


wiesco or "foged" pistons needs a little more clearance than a cast piston. a forged piston swells more than a cast piston when its heated up. if you dont have the right clearance the piston will not get the oil it needs and will seize.
my bikes
-------------
96 ktm 300
96 XR400R
07 hayabusa
77 kz 1000
85 goldwing 1200
02 BIG DOG PITBULL

gone but not forgotten
96 kdx 200
98 ktm 380 "because it dang near killed me!"
97 ktm 360
96 ktm 250
93 wr 250
94 dr 350s
93 kx 250
07 gsxr 1000
99 bandit 1200
User avatar
fuzzy
KDXRider.net
KDXRider.net
Posts: 3437
Joined: 01:29 pm Jun 18 2003
Country:
Location: Fredneck, MD

Post by fuzzy »

The clearance for an F piston in an A cylinder is still within clearance spec, and the differences are also nearly immeasurable with standard garage tools. A wiseco is like an F, and again will go into any stock-bore cylinder...This is why they only sell one. You can get 'closer to perfect' by using the ABCDEF pro-x progression which is just a layman's way of making up for plating wear. No choice on the 220. What does all this mean? If you use a wiseco you will likely be REAL close to the lowest clearance spec. This is good. HOWEVER MAKE SURE YOU COMPLETELY WARM UP YOUR WISECO-EQUIPPED BIKE BEFORE RIDING IT. This is how they got the nickname siezeco as lots of cold seizures have occurred. Truth is if I had the control over it I'd want my top-end this tight even with a cast piston. You shouldn't set clearance to prevent cold-siezure, just warm the thing up.
'91 KDX 200 Project $300 KDX
'95 KDX 200 Project $600 KDX
'94 WR 250 Always a project
User avatar
kdxmaniac
Supporting Member
Posts: 595
Joined: 09:01 pm May 24 2010
Country:

Post by kdxmaniac »

fuzzy.........im either reading you post wrong, or you are thinking wrong. a forged piston swells under heat, so on startup you have a smaller piston, as it heats up the piston swells. this is why the seizer happens when you dont have enough clearance, and the bike is warm. thats why alot of times a engine will un-seize after it cools down......but the damage has already occured.... it wouldnt seize cold.............not wanting to argue, maybe i read your post wrong?

btw.....if your using a stock size piston is a used bore, you will be fine one the clearance"if its not wore out"........what you have to watch for is on a new plated cylinder.
my bikes
-------------
96 ktm 300
96 XR400R
07 hayabusa
77 kz 1000
85 goldwing 1200
02 BIG DOG PITBULL

gone but not forgotten
96 kdx 200
98 ktm 380 "because it dang near killed me!"
97 ktm 360
96 ktm 250
93 wr 250
94 dr 350s
93 kx 250
07 gsxr 1000
99 bandit 1200
User avatar
kdxmaniac
Supporting Member
Posts: 595
Joined: 09:01 pm May 24 2010
Country:

Post by kdxmaniac »

here is a article on forged and cast pistons.


http://www.glmmarine.com/castvsforged.html
my bikes
-------------
96 ktm 300
96 XR400R
07 hayabusa
77 kz 1000
85 goldwing 1200
02 BIG DOG PITBULL

gone but not forgotten
96 kdx 200
98 ktm 380 "because it dang near killed me!"
97 ktm 360
96 ktm 250
93 wr 250
94 dr 350s
93 kx 250
07 gsxr 1000
99 bandit 1200
heckler
Member
Posts: 243
Joined: 11:15 pm Apr 06 2010
Country:

Post by heckler »

does the 220 have an "exhaust bridge"????

Wiseco says to drill two holes into the piston if you have an exhaust bridge. WTF?

http://www.wiseco.com/PDFs/Manuals/MSeries.pdf


Thanks for the help! I'll be breaking in my piston slowly.
User avatar
fuzzy
KDXRider.net
KDXRider.net
Posts: 3437
Joined: 01:29 pm Jun 18 2003
Country:
Location: Fredneck, MD

Post by fuzzy »

No, you're reading right, and I agree w/ you. Difference between what we're talking about is that there is a difference between a cold seizure, and a seizure due to incorrect(tight) piston clearance. When clearance is on the tight side of acceptable, and a forged piston is in there, and you go flog your bike(expanding the piston) before the bore is warmed up as well as the piston, you may very well experience a cold seize (this is even more common with methanol and/or iron bore cylinders). When speaking factory plated KDX cyl's in particular, the wiseco is safe in any-size factory bore....WARM IT UP though. Granted, if you send a wiseco and your cyl to a replater, you're likely going to end up with slightly more piston clearance than the above example. Slightly in this case, just like the ABCDEF differences are like .00002. :mrgreen:

The KDX does not have a bridged exhaust port.

There is a picture of a bridged exhaust port a few posts down in this link:
http://www.bannedcr500riders.com/board/ ... n+drilling
'91 KDX 200 Project $300 KDX
'95 KDX 200 Project $600 KDX
'94 WR 250 Always a project
Post Reply