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I'm due for a top end in a few months and I am thinking about doing some stainless valves. Are there any other things I can do to the head/top end to give me peace of mind? Stiffer valve springs? Also I have heard that you suffer a power loss with the stainless valves. My bike is a 250f so I really can't afford any power loss but if it isn't too much I figure why the hell not. Maybe ill balance it out with a port/polish? I have some help but these guys are really cool so I don't want to take advantage of them. I am still largely footing the bill myself so I need an "old chevy truck" of a bike so to speak. Up until this point I've just kept my bikes stock.

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Will is right about fixing stuff right and maintenance. I thought you were an RMZ guy? Anyway, the valve springs need to be matched to the valves. Springs for Ti valves are not as stiff because the valves weigh half as much as SS. First decide whether you need new valves at all. If your OEM Ti ones start to tighten up a lot in a short period of time they are done. SS will be less apt to fail catastrophically if, for example, you take in a lot of sand during a moto because the air filter was breached, but with proper maintenance Ti valves can last a long time. Some use alloy seats with Ti valves. Sure you need to replace? As for power loss of SS I will believe it when I see data. Any data. I have looked for it. It really does come down to basic maintenance, but one thing we do is preventative pulling and greasing bearings every few months. Lubing cables helps, too. New pistons every 30 hrs. Valve clearances and rod checked along with. Oil every other ride and air filter cleaned at least that much. Oh, and don't crash! Liam just took out a set of Renthall Twinwalls and the bracket for his stabilizer, among other things. Bill for the crash was about $1,500. SS valves held up though, lol. If you do new valves, cut the seats and do it right. If you port and polish, leave the walls of the intake tract rough. That's all I got.

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I wouldn't run steel  valves on the stock seats. They suck, known to chip around the edges with stock valves and with the extra weight of steel valves... I would run TI with better seats on the intake side. The intakes always wear out much sooner than the exhaust. I've been doing a lot of these heads lately just putting copper seats on the intake side, stock exhaust seats with TI valves all the way around and they have been working out very well.

 

Another very common problem is the intake guides cracking on the part that protrude into the intake port till they break off and get sucked through the motor. I would put bronze guides on the intake side too if you don't want to have to worry about that problem

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with all my bikes I always put in the copper seats when I take head out. sometimes its better to buy a head done then sell yours. for example

I bought a full xceldyne valve (CV4) head that they did for a mag article but the bike showed up a 450 came with there valves copper seats springs retainers keepers dlc buckets ported for 1400 with a blue CV4 hose kit Then turned around and sold the head that came on the bike for 700 - head was stock other then ported by someone - was on bike when I bought it. so for 700 bucks I got a one of a kind head and started fresh with a head that I knew instead of taking the word from the seller of the bike

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Thanks guys. Sorry about that. I thought I was posting in the general Moto forum. Somehow I ended up in the kx250f forum. I'm running the thumpertalk app so that may have done it. Anyway yeah I would be replacing the seats as well as springs keepers etc. I am also thinking of getting the tappets dlc treated for smoothness. Do stainless valves really rob horsepower like people say? I'm not really sure where my valves are at right now. They were pretty close to the top of the mark about 3-4 hours ago. I check them every 7-10 hours but I am considering going for some kibble whites because half the battle on these 4 strokes is the valves. Yes I am an rmz guy and sorry again for the mixup.

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I wouldn't run steel  valves on the stock seats. They suck, known to chip around the edges with stock valves and with the extra weight of steel valves... I would run TI with better seats on the intake side. The intakes always wear out much sooner than the exhaust. I've been doing a lot of these heads lately just putting copper seats on the intake side, stock exhaust seats with TI valves all the way around and they have been working out very well.

 

Another very common problem is the intake guides cracking on the part that protrude into the intake port till they break off and get sucked through the motor. I would put bronze guides on the intake side too if you don't want to have to worry about that problem

 

Interesting this is the first I have heard about stock seats chipping.  Definitely don't want that to happen.  Same with intake guides.  Is this a common occurrence on the KXF, or you are just aware of a couple of examples?  Either way, I will keep my eyes open for any signs.  Also, if you don't mind, which seats do you use and how much do they cost?  I would like to look into those.

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Interesting this is the first I have heard about stock seats chipping.  Definitely don't want that to happen.  Same with intake guides.  Is this a common occurrence on the KXF, or you are just aware of a couple of examples?  Either way, I will keep my eyes open for any signs.  Also, if you don't mind, which seats do you use and how much do they cost?  I would like to look into those.

 

Its common, the first things to fail on these heads. Just did one Friday and I'm sure before this week is up, I'll have another one in with the same problem. I will take some pictures of the next one so you guys can see what happens. I've been using the cv4 seats. I've also used the kibble white seats but I don't like the fact I have to cut that much extra material out on those and I feel the material is better on the cv4s. Trying to save the cutters here.

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Its common, the first things to fail on these heads. Just did one Friday and I'm sure before this week is up, I'll have another one in with the same problem. I will take some pictures of the next one so you guys can see what happens. I've been using the cv4 seats. I've also used the kibble white seats but I don't like the fact I have to cut that much extra material out on those and I feel the material is better on the cv4s. Trying to save the cutters here.

 

Thanks, pictures would be cool.  I'll look into the cv4 seats.  Never replaced a seat, but I have a cutter and, to your point, they aren't cheap.  Appreciate the heads-up.

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Thanks, pictures would be cool.  I'll look into the cv4 seats.  Never replaced a seat, but I have a cutter and, to your point, they aren't cheap.  Appreciate the heads-up.

 

My seats are done cnc with a newen contour BB. Single point cutter at 2800 rpms, any angle or radius from the bowl out to the chamber.

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Just pulled a head off a 2011 bike that has the beginning stages of the intake seats chipping around the outer edges. I will clean it up and take some pictures to post for you guys.

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the kibble white seats are cheaper however there a different copper alloy

kibble white seats are

Copper-based material designed specifically for use with titanium valves in high performance applications

 

where cv4 is copper beryllium witch is better

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Thanks guys. Sorry about that. I thought I was posting in the general Moto forum. Somehow I ended up in the kx250f forum. I'm running the thumpertalk app so that may have done it. Anyway yeah I would be replacing the seats as well as springs keepers etc. I am also thinking of getting the tappets dlc treated for smoothness. Do stainless valves really rob horsepower like people say? I'm not really sure where my valves are at right now. They were pretty close to the top of the mark about 3-4 hours ago. I check them every 7-10 hours but I am considering going for some kibble whites because half the battle on these 4 strokes is the valves. Yes I am an rmz guy and sorry again for the mixup.

if you are replacing the seats you wont get the best benefit of them by using steel valves titanium would be better set up with the copper

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Here we go. It will continue rapidly at this point into the 45 and so on.

 

 

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2965.jpeg

2968.jpeg

Edited by Yves Edge
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if you are replacing the seats you wont get the best benefit of them by using steel valves titanium would be better set up with the copper

 

Correct. There are different seats to use for the SS valves. I still prefer the TI and copper beryllium seats.

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So you think ti valves with copper seats would last longest?

By far the best performance. Really to many variables to say on longest between ss & ti... riding style, brands, combinations of seats and valves... I believe my set up is the best way for many reasons all things considered.

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Well the thing is I am on a 250f from a 450. I really hadn't ridden a 250 before I owned this one and it turns out that I should have stayed on a 450 because I run the shit out of this 250. It doesn't feel right to bash on it that hard. I know that the valve train aside from the crank is what really takes the brunt of the beating with these high revving bikes so I figure that maybe ss valves may be right for me. I'm an intermediate level rider and lately I have really really improved. I have help but not a whole lot so money is an issue but if it saves my ass in the long run it's worth it. I have heard some guys say that the ti valves are tougher than they used to be but are they just as tough as as valves?

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Well the thing is I am on a 250f from a 450. I really hadn't ridden a 250 before I owned this one and it turns out that I should have stayed on a 450 because I run the shit out of this 250. It doesn't feel right to bash on it that hard. I know that the valve train aside from the crank is what really takes the brunt of the beating with these high revving bikes so I figure that maybe ss valves may be right for me. I'm an intermediate level rider and lately I have really really improved. I have help but not a whole lot so money is an issue but if it saves my ass in the long run it's worth it. I have heard some guys say that the ti valves are tougher than they used to be but are they just as tough as as valves?

If your ringing it out all the time I would stay away from SS. Go Ti with some good seats.

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