Does our bike have valve seats?

[steve68steve]

Have an exhaust valve seat that won't clean up and has a small dimple in it.

I can't see a seam around the seat and partsfish.com doesn't list a valve seat in the diagram for the head, suggesting it's just machined into the head itself. Can anyone confirm this?

I'm concerned about how much material would have to get removed to clean it up.
Also, wondering if the valve is potato chipped. I don't have the means to check in my garage, but my thinking is that even if the valve is crap it's constrained by the valve guide - so as long as I'm lapping by rotating the valve 360degrees instead of just wiggling back and forth, a bad valve should still clean up the seat.

...in fact, that might be the way to check the valve itself: if the seat cleans up fully, but the valve only cleans up in small section, that means the valve cone is no longer concentric to the guide.

Looking for a sanity check.

It's a 2014 non-esa, if that matters.

 

[Thrasherg]

I am 9% sure there are valve seats, Yamaha may not list or show them, but the head material is far too soft for the valves to seat into directly. Suspect you need a proper engineering firm to remove the old seat and fit a new one, or buy another head from a breaker, but check it first to make sure the seat is not damaged.

 

[WJBertrand]

As noted above, there have to be hardened valve seats in order to tolerate unleaded fuel. Even steel heads need hardened seats.

The seats don’t appear to be available separately, rather they are integral with the cylinder head. A good machine shop should be able to clean up the seats (depending on damage) and perhaps the valve. Not too expensive to fit a new valve if necessary.

Having said all that, I’m surprised to hear your bike has valve trouble. It’s not a common issue on these bikes.

 

[AntrimMan]

To answer your question, yes, never any doubt, definitely has valve seats, image below stolen from greg the pole post for illustration purposes only.

Top end rebuild

Greetings. I finally caved and tore into my motor. Folks in the know, please chime in. High def. pics here: https://flic.kr/s/aHskQgPES5 The motor has 80k km on it. Original owner. Started using oil at 50k. Puffs blue off high throttle application. Not while on the throttle. Comp check...

www.yamahasupertenere.com

Tenere top end rebuild

80k KM. Compression on both cylinders was well below minimum. With, or without oil

www.flickr.com

Try the easy things first, maybe your seats only need to be touched up a bit.
Begin there then the shop can tell you if replacement seats are required or even possible.
All the best.

 

[OldRider]

How about a good picture of the damage. If it's not very bad any good engine shop can re-surface the valve seat.

 

[steve68steve]

Thanks for all the replies!

The backstory on this is that I pulled the engine out for valve job #2 (around 50k miles), bought another bike, and let this one sit for 2 years. A buddy I trust has volunteered to rebuild the head. He texted one of the exhaust valves is leaking (fluid test) and doesn't clean up with lapping. His pics were hard to tell if there was a seat in there and the schematic doesn't list one.

I just got back from his house.

Seeing it in person it's easy to tell there's a seat - interesting Yamaha doesn't list a replacement part or instructions in the shop manual to remove/ replace.
We lapped it until it cleaned up and it passes the leak test. It's now a bit over the .9 -1.1mm of valve/ seat contact area. It's not obvious to me what problem having "too much" sealing contact between the valve cone the seat cone would cause, but I'm going with it being out of tolerance vs. replacing the head assembly ($900) or going thru the PITA of removing the seat and figuring out what part replaces it.

 

[steve68steve]

Forgot to add: we work in a machine shop manufacturing environment, so we briefly talked about the rework path to meet all specs being to bore out the ID of the seat. This would remove material from the cone, bringing the part in spec. ...but, it would do so by reducing the wall thickness of the seat, which seems like it would be a lot more likely to be a huge problem than having an oversized "contact patch".

For engineer/ machinist geeks: I worked for a company years ago that would put MMC on tapped holes. When the holes failed position, they would bring them in tolerance by reaming out the ID to get enough bonus tolerance to pass the position.

I pointed out on my first day that the fastener will locate on the pitch diameter, and reaming out threads is just reducing the pull-out strength of the fastener. "That's how we've always done it."

 

[Jlq1969]

The service manual does not mention anything regarding valve seats because Yamaha mechanics and official workshops are not oriented to that type of work. It is only mentioned in the manual, the checks (of the valve, the seat, the springs)... any check that is outside of that specification, ends in a replacement, in this specific case, replacement of the cylinder head... If you think In replacing “a single seat”, it is not the work that a top-level workshop would do. A job “well done” entails the replacement of all seats, valves and valve guides. The springs can escape replacement if they are not "twisted"... you mentioned before about "valve rotation", the rotation is expected, but it is not a rule that they should rotate, they probably tend to rotate in a regular regime. very high and constant revolutions (at full load)...in normal use they tend not to rotate (in touring or work vehicles, which use rocker arms that directly hit the valve stem, it is common to find grooved wear on the valve stem). tip of the stem, if it rotated, the wear would be round)

 

[Jlq1969]

The purpose of valve rotation is to ensure even cooling. At very high RPM, the cooling of the valve seats is uneven (there are hot areas and others less so)... the same would happen in the valve if it did not rotate. By rotating, it is ensured that the valve dissipates heat evenly….but the speed of rotation of the valve compared to the speed of rotation of the engine is minimal (0.004%)…..and the moment of rotation is also “controlled”. ”….if the valve rotated too fast it would make a groove in the valve seat. The design of the disc that goes between the spring and the cylinder head determines in a certain way the moment and speed of rotation.

 

[steve68steve]

The service manual does not mention anything regarding valve seats because Yamaha mechanics and official workshops are not oriented to that type of work. It is only mentioned in the manual, the checks (of the valve, the seat, the springs)... any check that is outside of that specification, ends in a replacement, in this specific case, replacement of the cylinder head... If you think In replacing “a single seat”, it is not the work that a top-level workshop would do. A job “well done” entails the replacement of all seats, valves and valve guides. The springs can escape replacement if they are not "twisted"... you mentioned before about "valve rotation", the rotation is expected, but it is not a rule that they should rotate, they probably tend to rotate in a regular regime. very high and constant revolutions (at full load)...in normal use they tend not to rotate (in touring or work vehicles, which use rocker arms that directly hit the valve stem, it is common to find grooved wear on the valve stem). tip of the stem, if it rotated, the wear would be round)

Understood. And it's not hard to imagine that the price of rebuilding a head with competent labor would quickly exceed the price of buying a whole new assembly. In a for-profit shop environment, that's a no-brainer.

But this thinking contributes to the disposability of ...everything. This bike is at a point in its life cycle where the replacing major engine assemblies is probably not worth it. It's 10 years old, 50k+ miles, and a "second" bike. It's not worth a lot of money RUNNING. It's a gamble that getting it back into running order won't cost more than it could be sold for. If repairing it risks losing money, it's hard to justify not just scrapping it.

...but if motivated, resourceful, DIY guys could restore it on the cheap, it's a win - and at that, I'm already $400+ into seals, gaskets, and fasteners just to do the job. We're maybe a special case in that we have access to a machine shop. It would cost us nothing to bore out the seal and press in a new one. A few hours on a Saturday is << $900.
/rant

Re: valve rotation, I might have miscommunicated - I was referring to rotating the valves while lapping. The idea was that even a BAD valve (with a high spot) would clean up the conical seat evenly, provided the valve was rotated fully thru 360degrees when lapping. Just swinging the valve back-and-forth thru a "comfortable" range (say, 30 - 45 degrees) would cause the lapping to only occur in that "swept" range under the bad valve's high point.
...all moot since it cleaned up and holds fluid now.

Your reply makes me think that the spec of .9 - 1.1mm of valve/ seat engagement might be a heat transfer thing. Too little won't seal; too much transfers too much heat between the valve and the seat?

 

[Thrasherg]

I am 9% sure there are valve seats, Yamaha may not list or show them, but the head material is far too soft for the valves to seat into directly. Suspect you need a proper engineering firm to remove the old seat and fit a new one, or buy another head from a breaker, but check it first to make sure the seat is not damaged.

It was meant to say I am 99% sure!! Not 9%

 

[Jlq1969]

It was meant to say I am 99% sure!! Not 9%

At least, the drawing in the ss manual, the seat is drawn

 

[Jlq1969]

Su respuesta me hace pensar que la especificación de .9 - 1,1 mm de enganche de válvula/asiento podría ser una transferencia de calor. Demasiado poco no se sellará; ¿demasiado transfiere demasiado calor entre la válvula y el asiento?

Only the manufacturer knows the reason for these values, but I think that the ideal in terms of heat transfer would be to transfer the “greatest” amount of heat….
I also think that if the drawing of the valve and its seat, adjust to reality... it is clear what the working range of the valve is, depending on the shape of the seat.

 

[steve68steve]

Only the manufacturer knows the reason for these values, but I think that the ideal in terms of heat transfer would be to transfer the “greatest” amount of heat….
I also think that if the drawing of the valve and its seat, adjust to reality... it is clear what the working range of the valve is, depending on the shape of the seat.
View attachment 110690

This is exactly the image that I referred to above. The .9- 1.1mm contact patch of "a" seems odd to me. Lapping will obviously increase the size of "a", but it's not immediately obvious why that would be a problem - so much so that it's only allowed a .2mm tolerance window.

I was telling a coworker about this today and how I thought it the only downside would be having to shim appropriately (and maybe the correct shim not being a standard size). He pointed out that as the valve gets moved up towards the camshaft, the spring force would change. I hadn't thought of that, but removing material at "a" would only cause the valve to go deeper by the sine of the chamfer angle. ...maybe my math's wrong, but it's not a 1:1 thing.

Also, while this drawing does a great job of depicting what "a" is, it does a lousy job representing the rest of the seat surface. AFAICT, the seat is just a thin-walled cylinder with an ID chamfer. Those surfaces shown adjacent to "a" don't depict reality.

 

[steve68steve]

@Jlq1969 I noted your location is Argentina and was impressed by how well you speak English (mi Espanol es muy, mal, a pesar de tres anos de Espanol en escuela cuando era el chico)

Then I saw your quote of my post was in Spanish.

If this means that you and I are reading the forum in different languages and having a conversation, I can almost forgive the internet for all the damage it's done to our society.

THIS is what we thought the internet would be for: having the world at your fingertips. No borders. Exchange of ideas and information.
Instead we got mostly porn, memes, and conspiracy theories.

 

[Jlq1969]

I was telling a coworker about this today and how I thought it the only downside would be having to shim appropriately (and maybe the correct shim not being a standard size). He pointed out that as the valve gets moved up towards the camshaft, the spring force would change. I hadn't thought of that, but removing material at "a" would only cause the valve to go deeper by the sine of the chamfer angle. ...maybe my math's wrong, but it's not a 1:1 thing.

The spring is not progressive, so as long as it is pressed, the pressure is always the same. The problem with lapping the seat, beyond the limit (1.1), is that the original valve could no longer be used. The maximum indicated by Yamaha is for “The Yamaha replacement valve”... If there is no other option, and the lapping exceeds those 1.1, you have to look for a valve on the market for that seat and match both (valve and seat) using the lapping…..In that case, it will always be a better option to change the seat, rectify it according to the manufacturer's standard measurement, install new original valves and twin both with lapping…..
…My English is not even that good...using the translator I can understand some things better, but there are many words or phrases that, being technical (mechanical), as well as idioms/customs specific to each country, which complicate things more . I think I write English quite well, I try to use the translator as a backup so that I'm not writing something wrong...But what you say about the internet is true, not everything is bad, it helps knowledge, you just have to know how to differentiate between what is true and what is not…