gbalias

I think its time for head rebuild...

21 posts in this topic

couple questions regarding my 08...

 

its time to replace valves (or maybe even seats) as i belive they have reached their operating limits in terms of clearnces. 

 

 

I was able to adjust all my intakes to proper tolerance with the exception of the furthest right side one.  Im guessing it gets most of the mixture since the carb is slightly angled in its direction.  I was only able to get it to juuuuust above .10mm ( i prefer closer to the looser end of the range).  I deduced this because if i continue to go in order of shim sizes and begin to reduce the shim thickness and check clearances, it stops at about .065mm clearance.  Right now its got a 140 shim in there with a .10 clearance.  If i put a 135, clearance goes to .065, if i put a 130, its still .065.  So what is happening is the cap is contacting the spring retainer and not the stem of the valve.

 

So whats next?

 

pull the head and replace valves (im guessing for sure i should do this)?  What about seats and guides? Springs?

 

Replace with stainless?

 

I guess I should also do timing chain, cyl, and piston while im in there.  the bike has 179 hours on it.  all original!!!  I like to maintain my stuff....

 

 

 

ps- exhaust valves havent moved in a loooong time.  Should thay also be replaced?  I guess might as well...

 

 

ok, thats all the questions I could think of so far. 

Share this post


Link to post
Share on other sites

Hey,

Here is what I would do:

Replace all valves, stem seals, and have the cylinder head inspected at a machine shop to check tolerance on guides and also check for cracks.

I would also see if they can cut the seats to get a fresh edge.  if they are too worn have them replaced.

 

Going to steel valves will be a durability up option and you will be shimming less.

 

Also shimming your valves on the loose side does you more harm then good as you spend less time on the ramps of the camshaft and thus is more violent during operation.

 

Kibblewhite sells kits that comes with springs and valves, I would just do it all right one time and ride on.

 

For the piston and cyl, have a look to see if its scored, if it is, bore it a little bigger and get it re honed for a new slightly larger piston.

 

timing chain?  yup!

 

While you have the top end off, check the play in the crank bearing (manual will have specs)  if its out of spec, now is the time to get that crank rebuild and put in fresh bearings.

 

With all that work you will have a great engine that will last you even longer!

Share this post


Link to post
Share on other sites

It is NOT true that any of the aftermarket stainless valves last any longer than the OEM titanium parts.  It is also not true that they are cheaper, necessarily.  The valves themselves quite often are, but stainless vales weigh roughly 40-45% more than Ti, so they need special heavier springs, and teh spring sets often more than make up for the savings on the valves.  It is my considered opinion that for 95% of all owners, the OEM valves will last as long or longer per dollar spent than most any other option.

 

Bear in mind that a good many of the SS valves out there are hard coated rather than actually hardened at the faces, so they become subject to the same pattern of hours on hours of no adjustment or very little required, then suddenly start sinking quickly.

 

 

For the piston and cyl, have a look to see if its scored, if it is, bore it a little bigger and get it re honed for a new slightly larger piston.

 

This one is a non-starter altogether.  There are no slightly larger pistons available.  Some of the aftermarket pistons are available in multiple sizes to allow some degree of custom fitting, but only in increments of .0001", so it changes very little, and the wear limit on the bore is only .002".  If the bore is actually within this tolerance, a new OEM piston will fit well enough to be serviceable, and a quick cleanup with a bottle brush hone is all that's needed.  Precision honing a Nikasil bore requires a diamond grit hone, is quite expensive, and I don't recommend it.  Rather than that, you should follow the prescribed procedure of replacing the cylinder, or having the bore replated and finished back to its correct original size.

Share this post


Link to post
Share on other sites

Oversized pistons seen here:

http://www.ebay.com/sch/i.html?_odkw=yz450+pistons&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xyz450+oversize+piston.TRS0&_nkw=yz450+oversize+piston&_sacat=0

Can bore and sleeve, re-plate...etc

Up to the owner to determine what is right for them, options are out there for their application and budget. 

 

There are many options for valves as well, and there is no golden rule solution that works for everything

A common upgrade on the early CRF450's for example was the steel valves as the Ti wore faster.

 

The post above is correct for the steel valves having more weight, and that does require a heavier spring which can take some power away from the additional requirement of spinning that stuff.

 

Whatever is decided good luck on your build!

Share this post


Link to post
Share on other sites

Ok.  Good info guys.

 

So would it be recommended to change only the intake valves and leave the rest alone or just do everything?  And if i just put in OEM Ti, do i keep old springs as well?  Will new valves be needed in order to check whether or not the seats need work?

 

When i say the looser side of the tolerance im talking i prefer .13-.14 instead of .10. If i have to make a sacrifice due to the gap in shim sizes, i shoot for the looser....i dont think that does any harm to the cam lobes. 

 

 

I can measure the cylinder when its apart and decide from there i suppose in terms of that part of the repair.  The bike has been flawless, even with as many hours are on it.  Most people dont even believe me when i tell them ive never had it opened besides the regular clearance check and adjustment.  It still runs fantastic, i would just like for it to go another 8+ years!

Share this post


Link to post
Share on other sites

This is one of those things where you just have to pull it apart, clean it, and inspect. There are many service type measurements that are outlined in the factory service manual. I say do that and simply see whats needed and go from there.

Share this post


Link to post
Share on other sites

 

Yes, that's another option, but honing to a slightly larger size, as you suggested earlier really isn't.   Big bore kits come with their own set of problems, and while they do have their merits, it's rarely as simple as dropping them in place.  I haven't seen one yet that didn't need to be re-balanced, for one thing. Then there are tuning issues.

 

Honda 's valve problems are its own.  The YZ never went there.  It's not in the least uncommon for the original valves to go well over 200 hours without even needing an adjustment.  Mine's at over 300 now.  Nothing in the aftermarket beats that for the money. 

1 person likes this

Share this post


Link to post
Share on other sites

OEM it is then

 

In that span of the 300hrs....have you changed anything in the valvetrain or cyl/piston?

Share this post


Link to post
Share on other sites

I was in the engine to do a transmission modification and top end inspection.  The piston was pretty worn; the ring lands were starting to drag on the bore walls.  So it got new rings and a new piston, the bore was OK once honed.  Of the 5 valves, only the center intake needed any adjustment, but it had enough wear on the face of the valve that I decided on a new one in that port.  The others were in good shape.  Mains and big end were tight.  

Share this post


Link to post
Share on other sites

when you did the valve was anything done to the seat or just swapped out and reassembled?

 

 

after looking at valve prices....its crazy a set of oem valves alone cost $450 on a bike thats worth maybe $2500! lol add in timing chain, piston, cylinder, gaskets......whew.  tough pill to swallow.

Share this post


Link to post
Share on other sites

I feel your pain... I just dropped the middle valve on my 06 YZ. My fiancé has an early model CRF and I'm probably fixing valve issues every 18 months. I ride more often and more aggressively than she does and haven't done anything to the YZ (besides basic maintenance) until now...

 

It is expensive to rebuild these things but I couldn't be happier with how much life I got out of mine, I just hope I get as much the second time around....

Share this post


Link to post
Share on other sites

when you did the valve was anything done to the seat or just swapped out and reassembled?

 

I practice what I preach: Absolutely always have the seats refinished when replacing valves.  Always. 

Share this post


Link to post
Share on other sites

copy that....in my experience i have never installed a valve on anything without doing seat work, but ive never dealt with Ti valves before. 

 

i guess we're adding that to the price list, Alan.  lol

 

 

yea..i cant complain either.  this poor bike has gone through some desert racing, then supermoto in vegas and socal, and now woods and mx in texas. 

Edited by gbalias

Share this post


Link to post
Share on other sites

So question since we're on the topic of valves.

How do you know when your valves need changing other than knowing by the valve adjustments.

2. When installing new valves, is it ok to "lap/seat" these Ti valves? If not qhats the correct way

3. Grayracer said he has his seats refinished, what does that mean?..How to know when seats need to be changed?

4.What about valve springs?

5. What about valve guides?

Share this post


Link to post
Share on other sites

So question since we're on the topic of valves.

How do you know when your valves need changing other than knowing by the valve adjustments.

2. When installing new valves, is it ok to "lap/seat" these Ti valves? If not qhats the correct way

3. Grayracer said he has his seats refinished, what does that mean?..How to know when seats need to be changed?

4.What about valve springs?

5. What about valve guides?

from what ive gathered here,

1- i am getting ready to change mine because one of them cant be adjusted anymore...other than a failure, i dont know another way to determine without disassembly

2- Ti seats are cut never 'lapped'  (im assuming its to protect the hard coating) having them 'cut' is correct

3- maybe the equivalent would be 'precision grinding' ?

4- springs can probably be left alone

5- need to be checked once new valves are on hand...so that would make it a case by case basis

Share this post


Link to post
Share on other sites

So question since we're on the topic of valves.

How do you know when your valves need changing other than knowing by the valve adjustments.

2. When installing new valves, is it ok to "lap/seat" these Ti valves? If not qhats the correct way

3. Grayracer said he has his seats refinished, what does that mean?..How to know when seats need to be changed?

4.What about valve springs?

5. What about valve guides?

Assuming we are still talking about a YZ450 (or a 426 with Ti valves:

 

1) If you have had the bike a while, you've probably had it during at time when it has gone months or longer without needing any adjustment to valve clearances at all.  As it wears, one or more will need to be adjusted one shim size smaller.  When it comes time to shim that same valve another size smaller, it's time to replace the valve.  Otherwise, physical inspection will let you see the wear condition, and a leak down test will tell you whether and how much they may be leaking.

 

2) Absolutely, unequivocally NOT.  Not under any circumstance ever.  Lapping with abrasive pastes will attack the hard coat as well as the seat, and the hard coat that the valve depends on is less than .001" thick.  Even with un coated steel valves, the seat must be precision refinished BEFORE any lapping is done.  Otherwise, the wear pattern of the used seat will be partially transferred to the valve face in the process.

 

3) Valve seats are properly refinished in three main ways: Precision cutters by hand, or better, precision grinding with specialized equipment, or best, recut in a specialized machine resembling a vertical mill.  When any of these processes are correctly done, lapping for a precise seal is unnecessary.  Cost is usually about $20-30 per seat.  With the YZF, the seats normally need little more than a light touch up, and very little material should be removed from the sealing face of the seat.  The need replacement (assuming they haven't been damaged by excessive heat or some sort of impact) when so much material has been cut away to restore their proper angle and shape that it causes the valve to sit too far up into the head, so that it can't be adjusted to the right clearance. 

 

4) OEM Yamaha springs are very reasonably priced, IMO, and are a good thing to replace just for the peace of mind.  

 

5) Valve guides in engines using bucket tappets suffer no lateral pressures on the valve stem, as rocker arms would produce, and as such they shouldn't wear very much at all.  This is the case with the YZF; the guides normally show virtually no wear even after long service, and don't ordinarily need to be replaced.  Your machinist should check these in the process of refinishing seats, and advise you as to any that need attention. 

1 person likes this

Share this post


Link to post
Share on other sites

is there anyone out there that does head exchanges? 

 

as in they have reconditioned to OEM spec heads that you trade with them (given your head is rebuildable)?

 

 

im torn in whether or not to look for something like that or take the head to a shop for inspection and repair.  would they only replace worn items or everything in there?  i would obviously like to keep it cost effective.  I dont need some crazy valve angle cuts or performance porting, etc.  just plain ol OEM is fine for me!

Share this post


Link to post
Share on other sites

I would, if any such place is nearby, take the head to the machine shop favored by the local dealership.  Have him check on the condition of the valve guides and so on, and report to you prior to making repairs.  Most of the time, a reasonably well cared for YZF head will go through a couple of sets of valves before it needs guides or seats, and most shops in SoCal charge about $20 a seat for refinishing. 

Share this post


Link to post
Share on other sites

sounds like a plan. 

 

i rode it this weekend.  its not running tip top...so my plan is to check clearances again maybe friday...if valves moved after 2-3 hrs of runtime, ill start disassembling, drop it of at a local place here (http://www.ebrperformance.com/)  and have them do a overall look.  i called them and they have all the machinery (CNC) to rebuild the head.

 

so if thats the route i take in the next couple weeks, i will update yall.

 

thanks gray.

Edited by gbalias

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now