Steel valves, or titanium?

[jakeeee]

Im in a sticky situation in what to get, and iv always wanted to know how do you seat a titanium valve, is it the same as a steel valve with some fine and coarse or can it only be done with a machine ect?

[grayracer513]

If by "seat" you mean how are the seats to be refinished, and by "fine or course" you are referring to lapping compound, stop right there.

Titanium valves should not ever be lapped with abrasives under any circumstance regardless of what old information is left in any manual. The problem is that Ti is a very strong metal, but it is not hard enough to survive as a valve face, and can't be made hard enough by any practical means. The solution then, is to coat the finished valve with layer of some derivative of titanium nitride (off the Rockwell scale at somewhere over 85). This works very well, but the coating has to be applied in an extremely thin layer, often less than .0005", because it's too hard to machine. The use of abrasives raises the possibility of damaging this coating in such a way as to bring about premature failure of the valve face. Seat refinishing with this type of equipment must be done only by cutting and then preferably grinding to a fine finish as precisely as possible without any lapping of the valves.

[jakeeee]

Yeh i meant lapping, i i know you can do this on car valve, im assuming the same with stainless steel for bike?

With ti i would need the valve seats to be recut?

thanks for your input, im just trying to decide what valves to get for my 09 kx450f

[grayracer513]

When ever replacing any valve of any material, the seats need to be refinished with precision hand seat cutting tools at the least. The more precisely this is done, the longer the new valve will last. Lapping, if it is done at all, is only for the very last finish on the sealing.

[Chuck.]

I would add to the above that some Honda steel valves are Stellite coated and while harder than Ti or SS the coating is very thin. All valve prep, contrary to automotive, must be done on the seat and not the valve. Final check, after Prussian Blue checks, is with a fine compound and only about a half turn of the valve. I suspect with Ti or SS valves, while softer, the same applies.

[grayracer513]

I would add to the above that some Honda steel valves are Stellite coated and while harder than Ti or SS the coating is very thin. All valve prep, contrary to automotive, must be done on the seat and not the valve. Final check, after Prussian Blue checks, is with a fine compound and only about a half turn of the valve. I suspect with Ti or SS valves, while softer, the same applies.

Exactly, but stellite is not as hard as titanium nitride. It's also not particularly commonly used to coat stainless valves anymore as TiN is less expensive and more effective, the downside being that it is impractical to machine, whereas stellite can be ground using ruby stones or harder with relative ease.

[kx450f63]

I think the bigger issue at this point is the seats now that you understand not to use lapping compound. At the rpm ranges we operate these engines, the valve face and seats become work hardened. If one hardens at a different rate (like the 07 250f Honda's) you will see diminished operating life. I believe in most cases for longevity purposes you should replace the seat along with the valve. I also believe the materials Kaw is using are more than acceptable in the OE state.

If you are just looking to make one run again after finding the face of a valve is beyond its service life. You certainly can just drop a new valve in and it will probably operate as designed. I would at least check to make sure the new valve will seal on the old seat before I put it together. Save yourself some headache and check the seal now and if need be you could have the seat cut to seal it up.

[grayracer513]

If you are just looking to make one run again after finding the face of a valve is beyond its service life. You certainly can just drop a new valve in and it will probably operate as designed. I would at least check to make sure the new valve will seal on the old seat before I put it together.

I will guaranty you that won't, or if it does, it won't last long. Such a thing should only be done when one understands it to be a stop gap measure, and when the wear to the valve and seat in question is in the very early stages. When new, the face of the valve is cut to a precise angle, normally 45º to the stem. Many engines are built with the faces cut at a slightly different angle than the seats (44º at most, usually less of a difference with Ti valves) as an "interference angle" so that the valve seats the best at the interior edge of the seat, and any wearing in of the fit improves the seal rather than reduces it. In modern HP MX thumpers and the like, encouraging even that much wear is not favored, though. The seats are cut at 45º and the width and position of it against the valve face are determined usually by 60º and 30º cuts above and below the seat.

This creates a conical, precisely flat 45º seat defined by 15º corners on both sides, against which a precisely flat conical valve face must sit and seal. As wear proceeds, it does so from the edges of the seat inwards, which eventually creates a "half" rounded groove of wear in the valve face, and rolls down the edges of the seat, making it become more rounded in cross section than flat. Even it this wear appears to be very slight, it needs to be corrected before a new valve is used on it, or the new valve will be quickly worn.

[kx450f63]

I will guaranty you that won't, or if it does, it won't last long. Such a thing should only be done when one understands it to be a stop gap measure, and when the wear to the valve and seat in question is in the very early stages.

Have you noticed that some valves tend to wear more rapid than the seat?

Gray, I am not encouraging... so called band aid repairs. I will however question your guaranty. Have you ever tested your theory by only replacing a suspect valve and nothing else? I have tested it with automobiles and motorcycles alike, high HP and low HP of both. I have replaced just two valves that burnt on a 200,000 mile plus small block chevy when I was in my early teens, because the farmer said If I can make it run I can have it. That truck still ran 10 years later, grant it, it was just a farm truck. I even reused the gaskets just to see if it would work and of course I didn't have any money. Most recently a few years ago I was trying to sort out a friends honda 250f and I put together just about every combination of valve and seat that was available. The bronze seat and Ti valve ended up working quite well but in the mean time we put used valves on used seats, new valves on used seats, and used valves on new seats. Even the worst combination lasted at least 60% of the life span of the OE new pieces.

You may ask, why would one do this? I would answer, when I want to get the next ride or practice in and it's after hours, if there is any way possible to make it run, I would, for the next day.

Do I believe this is the preferred fix, absolutely not, but can it be done with reasonable success, absolutely.

[grayracer513]

Have you ever tested your theory by only replacing a suspect valve and nothing else?

I'm not speaking of theory. In over 40 years of working with engines, I have to see a new or refinished valve seat correctly on a used seat.

[36MotoMarc]

Wow I'm with Gray on this one. Given the high probability of failure and the often catastophic damage (and bodily harm) that can occur, I would never compromise by using known-bad parts. 60% the life? Forgive me if I'm wrong but that seems like an arbitrary statistical number not based on actual data.

In the context of the OP's question, the advice MUST be to have the seats cut by someone familiar with modern MX fourstrokes. Regardless of valve material chosen. Gray's explaination of the process is spot-on.?.

[noslo33]

if you need to use valve grinding compound on your head,you should use a sacrifical valve to do this procedure.i personally have cut hundreds or valve seats with my neway valve seat cutters,and if done correctly,they leave a velvety smooth finish that requires no lapping to seal.peace and wheelies.

[36MotoMarc]

if you need to use valve grinding compound on your head,you should use a sacrifical valve to do this procedure..

And I've seen the ERONEOUS advice given on TT to use an "old" valve to lap a TI valve's seat. To do so is foolish and worthless, and damaging. As you say, it must be a "sacrificial" valve, as in NEW. However it is unnecessary on a modern Ti valve with a properly cut seat.

[funkinalive]

gray, firstly i would like to say that i really enjoy (and understand) your explanations and you obviously have a lot of knowledge. but as much as i hate to say it, i have also experienced and had success with such backyard fixes to the valves, on various machinery. granted that their service life is greatly limited.

[grayracer513]

i have ...had success with such backyard fixes to the valves, on various machinery. granted that their service life is greatly limited.

I guess if you're willing to accept limited success, that's OK then. That's my point here, that lapping a valve onto an unrefinished seat doesn't last. Especially when it's coated titanium valve.

[kx450f63]

I guess if you're willing to accept limited success, that's OK then. That's my point here, that lapping a valve onto an unrefinished seat doesn't last. Especially when it's coated titanium valve.

I think it also depends on your definition of success.

[funkinalive]

for all intent, i believe the context was that it will work, not whether it would last. in the end you are correct: it is not good engineering practice, and will give you less than "sucessful" results. but it WILL work for the desperate.

[grayracer513]

for all intent, i believe the context was that it will work, not whether it would last.

Looking back to the original post in the thread, noting of the sort can be assumed from the questions asked by the OP. Since he did not state that he was looking for a quick or emergency repair, the normal assumption is that the was asking how to correctly do the job, specifically which valve material to choose.

When a single valve can cost $100, it seems to me that longevity is a relatively important element of the total picture.

[jakeeee]

Looking back to the original post in the thread, noting of the sort can be assumed from the questions asked by the OP. Since he did not state that he was looking for a quick or emergency repair, the normal assumption is that the was asking how to correctly do the job, specifically which valve material to choose.

When a single valve can cost $100, it seems to me that longevity is a relatively important element of the total picture.

I meant exactly this, i dont get why anyone would look for a short term solution when rebuilding a bike, the less i have to tear into it the better really!

Ill get valve seats properly refurbed!

[kx450f63]

Im in a sticky situation in what to get, and iv always wanted to know how do you seat a titanium valve, is it the same as a steel valve with some fine and coarse or can it only be done with a machine ect?

A reasonable person of average intelligence could assume many questions, either presumed or intended from this one quote. I think that is what we did, and do for conversational purposes.

If what you want is the dry version of the answer we now know the OP wanted, here it is: One would need to cut or grind the proper angles on both the valve and seat and yes, same for a steel valve.

Longer version: Buy new valves and seats from an experienced reputable manufacture. Give them to an experienced reputable mechanic/machinist to have them installed. Do not lap them after your choice of mechanic/machinist gives the completed cylinder head back to you. As far as the material to purchase, the phrase, "You get what you pay for" applies here. The more you spend the better the intended outcome should be, within reason.

Now if your interested in installing your own seats and valves, I say have at it. It will be a great learning experience.

Now, any one care to elaborate on the lapping process used and recommended in years past and the reasons why it is not recommended in this case other than the coating issue. As we know the coatings were not intended to solve the problems that lapping were intended to solve.