YZ 250 piston?????

[Rcannon]

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]

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]

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]

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]

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]

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]

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]

You guys are great. I appreciate the replies.

I am going to sit back and learn some more.

 

[bigred455]

R cannon run a different oil with the same jetting and ratio and you will see I am correct.

 

[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.

 

[Rcannon]

Bigred, I thought about doing this, but I have had such good luck with the R that I am afraid to switch!

 

[Rich Rohrich]

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.

 

[Rcannon]

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]

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]

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.

 

[jmics19067]

I will continue to use it out of fear.

having more than adequate protection is always a good plan. There is a marketing plan behind that fear though. Just take a look at the the gear box or four stroke oil dilemna with that bike specific wet clutch conspriracy.

Yamalube 2s is specific for oil injected two stroke bikes <as far as I know only trail bikes> but can be premixed ,add in the fact that a lot of old bikes have the oil injector blocked off for a cheap fix and then dedicate to premix. the 2R is specific for premix for racing conditions ,

So what would happen if you put a trail designated premix into a race bike that is trail ridden? There is only a few things I would have to guess is ok.

1 would a high performance engine recquire more protection then a low tech engine or is the load the engine sees that determines the protection needed?

2 is the load I am placing on the engine greater than what the low performance engine could handle?

If I exceed the intentions of the low performance engine more protection is needed but if I don't come close to the full extent of the race engine how much protection is recquired?

I know this is backwards thinking since most people want to get the most out of their engine and protect it to the best of their ability<very smart> but if it is not needed is there any benefit?

I am not so sure if I am going to try it but just bouncing around ideas in that vacant lot between my ears.

 

[bigred455]

Originally posted by Rich Rohrich


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.

....

Not true yamalube 2-r will not leave a burn pattern on the piston crown like other oils. 98 kx 250 running 32:1 with pump fuel piston crown had no carbon at all bike was JETTED SHARP.I switched over to super m WITH A NEW TOP END pulled the head after 20 hrs and the crown was covered with a burn pattern same with 927.I also seen the same results with a 98 yz125 like I mentioned using 2-r.Remind you that pump fuel was being used.

 

[Studboy]

:|

Bigred,&nbsp; What makes 2-R so special that it won't stick to the piston crown, all other factors being the same???

 

[Rcannon]

BigRed, I am thinking of another bike we just rebuilt. The CR 80 had been running Yamalube R as well. The piston was allowed to stay in the bike for over a year of hard riding. Finally the intake skirt let go.

Despite all the hours, there is no burn pattern on this piston.

The powervalve on my YZ was also spotless. I know this is just two examples, but I would have a hard time argueing with what you say.

 

[Rich Rohrich]

Originally posted by bigred455
....

Not true yamalube 2-r will not leave a burn pattern on the piston crown like other oils.

I guess all those pistons I took out of our road race bikes running 2R must have just had phantom burn patterns, or maybe it was just a mirage. :silly:

 

[bigred455]

I totally believe you, seeing burn patterns using 2-r . I am just telling you what I have seen using unleaded pump with 2-r. I also believe not all motors will react the same (burn patterns) with certain oils.

 

[Rich Rohrich]

If you don't see a burn pattern with Yamalube 2R then the chamber is too cold, PERIOD. The look will change with different fuels, but it will be there regardless, IF the engine is run hot enough. A properly jetted MX bike that is being ridden hard should always show a pattern with this oil. If you don't see a pattern then you know there is free power just waiting to be unleashed from the engine.

The oil/fuel mix doesn't know or care what engine it's reacting in , the chemistry is the same regardless of the color of the bike.

 

[Chili]

Not that Rich needs backup from someone like me but on the last rebuild on my son's KX80 which was run exclusively on Yamalube 2R from the outset there was a definate burn pattern.

 

[bigred455]

Originally posted by Rich Rohrich
If you don't see a burn pattern with Yamalube 2R then the chamber is too cold, PERIOD. The look will change with different fuels, but it will be there regardless, IF the engine is run hot enough. A properly jetted MX bike that is being ridden hard should always show a pattern with this oil. If you don't see a pattern then you know there is free power just waiting to be unleashed from the engine.

The oil/fuel mix doesn't know or care what engine it's reacting in , the chemistry is the same regardless of the color of the bike.

.......
....

I have modified some of the ports on my 03 kx250 won't say how or how much,but I was running a 160 main before the change, she was running so rich the power down low was affected tremendously after the change. I did not have any mains below a 158. This was a new top end put in the same time I changed the ports. I came home and pulled my pipe, put the piston BDC and had a look with a flashlight I had the total piston crown covered with a dark brown burn pattern. I purchased a few more main jets down to a 145,right now a 150 is working great 60 degrees,the summer months a 145 probably will take care of it.MY POINT, I was running way too rich and moving the main down from a 160 to a 150 proved it. I had a burn pattern from running rich with 2 hrs on the top end. I would never jet by looking at the piston crown color, all oils and fuels are far to different,leaving different deposits on the piston. I was not using yamalube 2-r, Klotz r-50 is being used with av fuel.

 

[Rcannon]

Guys, thanks again for this thread. I think I am starting to learn a slight amount about jetting.

My bike did not bother to read MXA to see what the correct jets for it were! Tomorrow I think I will search for leaner stuff.

My plug is still quite dark. The bike has a nice brown plug when the stock jetting is used with the stock reed cage. If I use my Rad Valve or V force, the jetting is rich everywhere and the plug goes black. Still, I like the way the machine runs with the aftermarket reeds.