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New valves in my 02 XR250R

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So i bought new stainless steel valves for my dirtbike and i wanted to know if before i intall them do i need to get my valves seats honed or do anything to the valve seats? The new valves are standard size i did not get oversized valves so can i just intall them or is there anything else i need to do. Any information helps. Thank you.

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You don't just install new valves. You need to cut the seats, install new seas, new springs, new keepers, and measure the seat pressure from the springs.

 

If you don't know how to do all of this, or have the tools, take the head to someone that does.

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When I did mine I bought valve grinding compound. I slid the new valve in and attached the back of the shaft to my drill and spun it untill it cut the seat and made a full seal wit the valve. Hope it helps. If you do it this way u dont have to buy a bunch of tools.

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Thank you guys much. My problem was when i went riding my bike broke i took apart the top end & found that my valve retainer broke which caused it to lose that intake valve & the piston hit it. So i ordered wiseco stainless steel intake valves and got everything else fix but didnt know exactly how to install them. And what installing them entails. So ill make sure i get the seats cut and get new seats. And ill definitely look to buy that valve grinding compound man. Thanks!

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When I did mine I bought valve grinding compound. I slid the new valve in and attached the back of the shaft to my drill and spun it untill it cut the seat and made a full seal wit the valve. Hope it helps. If you do it this way u dont have to buy a bunch of tools.

This is completly wrong. Although not absolutely necessary it is not bad to replace valve guides if installing new valves. Then seats need to be cut again and valves lapped with grinding compound. If you have not done it before, and I assume you have not from your post, I strongly suggest going to a specialist.

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I lap my valves occasionally but would never use a drill motor.  I attach a piece of rubber hose onto the tip of the valve and twist it with my fingers periodically lifting the valve. I inspect the surface with a high power magnifying glass.  The sealing surface should be no more than 2mm wide.

 

There is no need to lap valves that are freshly and properly ground. 

 

As BTR said, take it to a good machine shop.

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This is completly wrong. Although not absolutely necessary it is not bad to replace valve guides if installing new valves. Then seats need to be cut again and valves lapped with grinding compound. If you have not done it before, and I assume you have not from your post, I strongly suggest going to a specialist.

 

 

The assembled head also needs to be measured for spring height, coil bind, and seat and open pressure, and adjusted if necessary. Not doing so risks premature seat wear, cam wear, spring failure or short valve life. Or any combination of those things.

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The machine shop/bike shop I took it to to check the seating said they were properly seated although it may be technically wrong it worked and I didn't have to spend $300 dollars on a $400 dollar bike to do it. If it was a new bike and I was racing yeah I probly would have taken it to the machine shop and had them do it. If your poor like me and need to do it it works. The valves seated with no leaks new valve guides are in new springs and keepers and seals and the bike is running great with the right amount of compression.

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I understand. Im 17 in high school & need to save every bit of money for college. So if i were to do it your way exaclty what would i do. Ive never done anything like that before. How much should i cut?

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I understand. Im 17 in high school & need to save every bit of money for college. So if i were to do it your way exaclty what would i do. Ive never done anything like that before. How much should i cut?

Ur not really cutting your using the valve grinding compound to get the same result. U do it untill the valves are properly seated. I used a product called perrusian blue that shows you how well its seated. If the seats are too far gone you might need to replace them. If u got a pic i can tell u better. U dont have to use a drill u can do it by hand. The guy at the bike shop told me do it untill no light shines thru from the back and it will hold gas with no leaks. U just want to watch the valve and seat and look where its making contact. It needs to have contact all the way around the valve and seat evenly.

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Do you people ever look at Honda (or Clymer) service manuals?  They state explicitly "The valve contact surface cannot be ground and the valve must be replaced if this area is damaged."  Grinding includes lapping the valves.  The contact area on the valve is specially treated or Stellite, for temperature protection and wear resistance.  Any form of grinding or lapping will diminish this treatment.  The valve seats can be reground, preferably with a 3 angle treatment.  The angle and width of the seat to valve contact area is critical to long term performance of the valves.  I have previously lapped many valves on motorcycle and automotive engines but that was 20 years ago.  The introduction of unleaded fuels and improved metallurgy has eliminated the need for this practice. Valve lapping should only be considered as short term fix for as set old valves until they can be replaced.

Edited by Flycast47

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Half true,The people that wrote the manual (like the Honda Manual) are the same Idiots.That made the stock valves with thin hard coat.So the manual is talking about,putting in stock valves.It says nothing about  the fact that the stock intake valves are junk (late Xr250-Crf 250/450). So the manual,knows a little,but leaves out the most important part.Dont use stock Honda intake valves.

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The manual states nothing just take it to a qualified dealer. Let me tell you i have worked at several machine shops. How do you think they would do it. They either cut or grind the seats either way do what u want. Mine is running fine the dealer checked it said it was within spec. The clymer manual says nothing except one  line about stock valves and not grinding them. The motorcycle shop here said they would be cuting the seats and them lapping them.

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I'm thinking it would be extremely difficult to accurately measure the angle on the 2mm wide surface on the valve and then grind the exact same angle on the seat.  Keep in mind that the seat angle is dictated by the angle of the tool itself and the valve angle, by the angle setting on the valve grinder.  

 

Also, what exactly is this magic surface treatment on the inferior '96 and later xr250 valves?

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It is probably:

Stellite alloy is a range of cobalt-chromium alloys designed for wear resistance. It may also contain tungsten or molybdenum and a small but important amount of carbon.  Stellite was a major improvement in the production of poppet valves and valve seats for the valves, particularly exhaust valves, of internal combustion engines. By reducing their erosion from hot gases, the interval between maintenance and re-grinding of their seats was dramatically lengthened.  

 

Note the Stellite face on the valve:

 

e_valve1.gif

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where did u get that valve diagram? I admit the way i did it was probly not the best method. My seats were only in need of a small amount of lapping to get the valves to seat correctly. What I did may not work depending on your seat wear. As far as my 84 xr350 it was all it needed. Thanks for all the other info. I made a post asking this info but no one answerd that post glad someone answered this one. 

 

Anyone have any links to seat cutting tools that are somwhat portable and inexpensive. We should make a full valve abnd seat tutorial as there isnt much info for this for the do it yourselfer that doesnt want to pay a machine shop. Theres a lot of what not to do in this post. Does anyone have any info on exactly how to cut seats and placing valves correctly.

Edited by f1tzg3r4ld

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According to Kibblewhite's website, their Black Diamond stainless steel valves can be re-faced.  

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BR it is true that Honda does have hard coat on valves.It is useless on intake valves.Ask any body that owns over 15 Xrs. Or ask the guys that run tour companys in Baja.What they have to do with the junk intake valves in the Crf 250/450x

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