Maintenence-Head Rebuild


15 replies to this topic
  • ca_101

Posted May 19, 2009 - 09:19 AM

#1

I'm thinking it might be time for a head rebuild, for maintenence purposes, on my '00 426. I just bought it this spring with a bad big end bearing, rebuilt it, the bike runs great and I love it (first 426). I can't remember right off hand what the I shimmed the valves to, but they were low (thin pads), nothing over .65 on either side. I will have to check tonight.

I want to freshen up the head, nothing crazy, just an OEM makeover. I have done everything else in an engine but nothing past shimming in a head. My questions are:

1) What parts do I order? (need to be replaced)

2) How much can I do myself? (wouldn't mind investing in some special tools, very mechanically inclined and eager to learn the head)

3) What all needs to be done for a maintenece rebuild? Not looking for a walkthrought, just an overview.

  • TIG88

Posted May 19, 2009 - 12:33 PM

#2

You will need a valve spring compressor. You will also need to cut the seats, but I suggest you send this out to someone to do. Its nothing you wanna tackle on your own. And the equitment is kinda expensive.

You will need:

1) Valves
2) Springs
3) Valve Retainers
4) Valve Cotters
5) Valve Guide Seals
6) Appropriate Shims

These can usually be bought from the TT store cheaper than just about anywhere else. Most people agree that when it comes to Pistons or Valves, OEM is the way to go.

  • 642MX

Posted May 19, 2009 - 06:28 PM

#3

For the price MXTIME does them for, its not worth messing with. This guy does exellent work. Here's the link: http://www.mxtime.com/

  • matt4x4

Posted May 20, 2009 - 05:55 AM

#4

valve spring compressor can be made for about 20 cents from an angle bracket - see the tips section of TT

  • grayracer513

Posted May 20, 2009 - 06:17 AM

#5

valve spring compressor can be made for about 20 cents from an angle bracket - see the tips section of TT

So that means you can disassemble and reassemble the head yourself. What's your solution to a homemade seat cutter set?

Changing seals and valve springs is one thing. Properly replacing the valves is a precision machining operation, best done by a competent machinist.

  • matt4x4

Posted May 20, 2009 - 09:12 AM

#6

I Didn't say that he could then install new seats and cut them, Grey - just wanted to give him the heads up that he can disassemble and assemble the head without a valve spring compressor.
However, should he plan on doing this often he may want to invest in a seat cutter for about 1000 and it'll serve him well if he knows what he's doing or he can just send the stripped head out to MXtime and get them to do it for under 100.

  • grayracer513

Posted May 20, 2009 - 09:59 AM

#7

I've been looking for a good used set of cutters for a while now. I could so easily pay for them with a few side jobs. I know lots of Honda riders.

It is nice to be able to tear down one's own head in order to clean carbon and inspect things, but it doesn't save any money on valve jobs around here. The shops charge the same amount whether it's assembled or not.

  • matt4x4

Posted May 20, 2009 - 10:55 AM

#8

detected a little sarcasm in that post! :doh: :snore: :lol:

you thinking a used Serdi or a hand operated Neway?

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  • grayracer513

Posted May 20, 2009 - 11:05 AM

#9

I very much prefer powered grinding stones for doing seats, especially for finishing them. Hard to find for small engines, though. The Serdi units do offer great accuracy and control, which are important, but they would be out of my range unless I were opening a shop. However, if one is careful, he can do a good job with hand units also.

  • ca_101

Posted May 21, 2009 - 09:03 AM

#10

I didn't really expect to be able to cut the seats my self. I've read about it enough to know that it is a pretty precise procedure. I would like to be able to disassemble and assemble a head confidently.
Another question....In what instances do the valve guides need to be removed and replaced? Is that routine head maintenence? Also, what is the purpose of "lapping" valves?

  • grayracer513

Posted May 21, 2009 - 09:26 AM

#11

Guides in a YZ head very rarely need to be replaced. This is simply because the bucket tappet design puts virtually no side load on them as a rocker arm would. The guides are very important to an engine running titanium valves, though (yours does not), and they need to be inspected just the same. Replace if the show excessive wear.

It is always best, when the valve guides are in serviceable condition, to leave them undisturbed. The reason for that is that no matter how carefully and precisely the guide is replaced, doing so will always find the new guid slight off center of the old seat, which means more than th enormal amount of material must be removed from the seat to restore it, shortening the service life of the head overall.

Lapping is the process of applying an abrasive paste between two mating parts and running them against one another so that they grind each other into a state of perfect match. ABSOLUTELY NEVER DO THIS to any engine using titanium valves under any circumstance. Titanium valves depend on a very hard, but extremely thin coating on the valve faces in order to have any reasonable durability, and lapping degrades that coating.

You can lap stainless valves such as those in the 2000 YZ426 IF they are through hardened, and not hard coated, as several brands now are. If the valve job is done right, you won't have to. The truth is that a good machinist should be capable of refinishing a valve seat that will seal perfectly without lapping.

  • GCannon

Posted May 21, 2009 - 12:38 PM

#12

Gray:
I have been thinking that I could purchase a new SS exhaust and Intake valve for the purpose of lapping the seats before installation of new titanium valves.
I understand the risk of not lapping with the valve that will be in service however I was thinking this may be acceptable for freshening the seat and installing new valves.

In other words buying two new SS valves and using them as a tool.

Please comment.

  • TIG88

Posted May 21, 2009 - 01:56 PM

#13

Gray:
I have been thinking that I could purchase a new SS exhaust and Intake valve for the purpose of lapping the seats before installation of new titanium valves.
I understand the risk of not lapping with the valve that will be in service however I was thinking this may be acceptable for freshening the seat and installing new valves.

In other words buying two new SS valves and using them as a tool.

Please comment.


I seriously doubt that would work, I understand my screen-name isnt Grayracer, but I grew up working and messing with engines. If there is a tiny, undetectable flaw in one of the ss valves, you are out the cost of the valves, the lapping compound, and most importantly time. Also, I cant swear to it, but I think lapping works both ways, removing tiny bits of material from both surfaces, but I'm not entirely sure about it. This is really one of those jobs you just have to bite the bullet and have it done right! :doh:

  • grayracer513

Posted May 21, 2009 - 03:08 PM

#14

GC,

There is some merit to the idea, but TIG is correct in that lapping will wear both sides of the equation, the softer or more machinable of the two will wear first.

While you could do that, there really is no risk in not lapping the valves at all if they are done correctly. Then again, if I had a 426 of any year, and was rebuilding it, I would use the OEM SS valves without giving it a second thought. Way cheaper. Just be sure to use the appropriate springs.

  • matt4x4

Posted May 22, 2009 - 05:15 AM

#15

I really don't see enough of a performance gain to justify the extra cost of Ti valves, I'm with grey on this - go with SS and don't look back.

Funny thing is - all my buddies with hondas switch to SS when their valves go. (notice I said "when", not "if")

I can see your idea of using an ss valve as a pretty decent idea - at worst, it will help smooth the seat just enough to save some innitial wear on your Ti valves because they no longer have to perform this duty. I'd be the same as sanding something with 2000 grit when before, it would only have been done up to 1000.

normally, you lap valves and seat to match both surfaces, you'd be attempting to match one surface to another by usung a "supposed" identical shaped dummy tool - I've heard of that being done in the automotive industry sometimes.

  • TIG88

Posted May 23, 2009 - 07:05 AM

#16

Funny thing is - all my buddies with hondas switch to SS when their valves go. (notice I said "when", not "if")



We'd all have SS valves too if they only lasted 30-50 hours :doh:





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