YZ 250 piston?????

Rcannon

Subscriber
Joined
Nov 17, 2001
Messages
1,886
Likes
0
#1
I spent last weekend tearing down the top end in my YZ 250. The bike is a 1997 that I have owned for about two years. There was nothing wrong with the bike, but it was due for the annual ring change.

I was shocked to see the weisco piston after 1 years use (over 60 hours of riding time). The piston looked brand new. There was a slight polishing of the piston on the intake side. There was also a slight dusting of carbon on the tp of the piston. One easy wipe with a towell removed this.

Most of the used pistons I see have a decent carbon build=up on the top. Why was mine so clean? I use pump gas mixed with Yamalube R at 32 to 1. The jetting, as confirmed by Studman (name promotion) is slightly rich everywhere. There was no build-up of carbon on the powervalve. zero. It looked perfectly clean.

The last several months on the bike have been at the local track. It is my first time ever on an MX track...therefore, old ladies pass me on a regular basis. Could the easy riding have something to do with the lack of build-up?
 

jmics19067

Lifetime Sponsor
Joined
Jan 22, 2002
Messages
2,097
Likes
0
#2
You are describing the exact situation I go thru. I run yamalube 2r at 32-1 with c12 ona 94 yzwr 250. I talked a little bit with Rich R about this and basicly , if you dont foul plugs, not dripping splooge everywhere, the bike pulls relatively clean, and you are happy with the power just set back and smile.


If I do any modifications to the bike over the winter I will usually rejet in the spring<cool weather> on a sand track <high load> as best I can. 90% of the time that will carry me over being on the rich side for trail riding in the summer. I am usually somewhat close enough so I dont foul plugs in all circuits but if I ever really put the bike under a load I know I am going to be relatively safe. Of course if I fouled a plug I will reset.

I assume the heat of high rpm/load I guess is what cooks the carbon hard and if you are jetted too way too rich for those situations is when you have the buildup problem.
 

Studboy

Thinks he can ride
Joined
Dec 2, 2001
Messages
1,818
Likes
0
#3
Rcannon,
Name Promotion???? I am happy just as I am!!! :debil:
I have seen pistons in 250's that aren't revved very hard and well maintained look great after a long time also.
Your bike was a little rich, but not too bad. Just enough to make it spooge a little. The bike ran excellent though IMO, it wasn't quite as SNAPPY as my bike, but there weren't any glitches and the bike pulled well.

I am in progress of installing a Wiseco piston in my 02 YZ, so I'll let everyone know how that goes as soon as I get my forks back from MX-Tech.... :). I'm still a little unsure about the "one size fits all" Wiseco compared to the sized OEM pistons.

BTW I have seen Wiseco's come out of 250's that were run for over 4 years!!! A little loose, but they still ran. (I'll bet a little low on compression though.) :)
 

bigred455

"LET'S JUST RIDE"
Joined
Sep 12, 2000
Messages
782
Likes
0
#4
Yamalube 2 r is the reason why the crown of the piston is clean. That is all I ran in my 98 kx 250 and the piston crown looked just like you described every top end I did. I just had a look at a 98 yz 125 piston and power valves the crown was spotless and the valves were really clean.Just because the crown of the piston does not show a burn pattern does not mean the jetting is lean. Different oils show different colors or no coloring. Yamalube is the only oil I have seen that does not show a burn pattern on the piston being your jetting is close. Then again some motors may show a burn pattern using yamalube 2 r.
 

marcusgunby

Lifetime Sponsor
Joined
Jan 9, 2000
Messages
6,450
Likes
2
#5
Ive read a rich engine will wash the top of the piston-so its not really a oil thing at all.When its leaned out it will run hotter and may have a bit of carbon build up.
 

viking20

Sponsoring Member
Joined
Aug 11, 2002
Messages
428
Likes
0
#6
Originally posted by marcusgunby
Ive read a rich engine will wash the top of the piston-so its not really a oil thing at all.When its leaned out it will run hotter and may have a bit of carbon build up.
I have to agree with Marcus. My sons Honda 125 was extremely clean inside,untill I started leaning the jetting out,it looks much more normal now!
 

jmics19067

Lifetime Sponsor
Joined
Jan 22, 2002
Messages
2,097
Likes
0
#7
Going to get nitpicky here , but I wouldnt think an extra rich mixture will "wash away" the carbon. I am more inclined that the lack of a good tempature from either being too rich or the motor not working hard <probably a combnation of both> is the reason why hard carbon deposits don't form.


RCannon, I wouldnt worry or try too hard on making the jetting real crisp for casual trail riding. Or I should say jet for the most demanding situation and then live with it for the cow trailing. Whats the worst that can happen?foul a plug and a little splooge? Having it jetted for little load and then working the engine hard could spell disaster.


I'm still a little unsure about the "one size fits all" Wiseco compared to the sized OEM pistons.
That is why it is imperative you do the heat cycle thing for breaking in the top end and letting the bike warm up nice before you get on it hard.
 

Rcannon

Subscriber
Joined
Nov 17, 2001
Messages
1,886
Likes
0
#8
You guys are great. I appreciate the replies.

I am going to sit back and learn some more.
 

bigred455

"LET'S JUST RIDE"
Joined
Sep 12, 2000
Messages
782
Likes
0
#9
R cannon run a different oil with the same jetting and ratio and you will see I am correct.
 

bigred455

"LET'S JUST RIDE"
Joined
Sep 12, 2000
Messages
782
Likes
0
#10
R cannon run a different oil with the same jetting and ratio or the oils company recommendation and you will see I am correct.
 

Rcannon

Subscriber
Joined
Nov 17, 2001
Messages
1,886
Likes
0
#11
Bigred, I thought about doing this, but I have had such good luck with the R that I am afraid to switch!
 

Rich Rohrich

Moderator / BioHazard
Joined
Jul 27, 1999
Messages
22,748
Likes
546
Location
Chicago
#12
Originally posted by bigred455
R cannon run a different oil with the same jetting and ratio or the oils company recommendation and you will see I am correct.
I've run lots of different oils and ratios including Yamalube R in roadrace and drag bikes for a lot of years. Deposit severity always comes back to piston crown temperatures, the jetting (how much carbon remains after the fuel reaction), combustion temps(again related to jetting) , and the amount junk in the fuel (this can play a larger role than many realize).

There is nothing magical about Yamalube R, other than it being a very good general purpose oil. :silly:

If an engine is jetted sharp and it is run hard Yamalube R leaves a nice thin brownish layer of carbon on the piston when it's mixed with clean race fuel at ratios from 16:1 all the way up to 40:1. The color and the overall look of the deposits will change some when you change over to unleaded race fuel, but the carbon layer is otherwise pretty similar.
 
Last edited:

Rcannon

Subscriber
Joined
Nov 17, 2001
Messages
1,886
Likes
0
#13
So...trying to read something into this using the finest fuel available from Habibs market is fairly meaningless, right.

I like the way the bike runs. I may work on jetting in the pilot and needle area, but overall I am very satisfied.

I think a lot of this boils down to me not being able to ride this bike hard enough to create any heat. I suppose I should remember this as the 04's are starting to look very nice!
 

jmics19067

Lifetime Sponsor
Joined
Jan 22, 2002
Messages
2,097
Likes
0
#14
There is nothing magical about Yamalube R, other than it being a very good general purpose oil.


well if yamalubeR is for racing I was thinking of going to yamalube S since I am slow :confused:

seriously though the S at 3.95 a quart compared to 4.95 a pint for the R is seriously making me think about how much of a load I am.... errrrr how much load I am putting on the engine and switching.
 

Rcannon

Subscriber
Joined
Nov 17, 2001
Messages
1,886
Likes
0
#15
I dont like the cost either, but honestly it is nothing compared to fuel for the truck (30.00) and the cost of my mental pain if something oil related happens when I use cheaper stuff.

I will continue to use it out of fear.