For the engine masterminds - Page 2 - PeachParts Mercedes-Benz Forum

Diesel911 · #16 07-09-2017, 12:49 PM

[QUOTE=Carpenterman;3727610]I really don't want to pull the head again. The engine runs OK, as I said.

I didn't think it was a good idea to file the top nut, as I assumed it was hardened. If Diesel911 is correct, I can get the nut off to file the valve stem without removing the camshaft. I suppose if I have to, I can depress the valve to get it off. I figure I can get a Dremel stone in there to do the filing.

Yea, it's the machine shop's fault. They should have at least run a straight edge along the end of the valve stems. But the first valve adjustment after reinstalling the head went fine--the problem developed over a year later at the second adjustment since the re-work. So I'm sort of on shaky ground with regard to making claims.

Also, this is the only machine shop in my area, they are very reasonable, have done other excellent work for me, and I want to measure good will against any perceived liability.[/QUOTE]

Like my story about the Ford gasser Cylinder Heads if the Shop does not have the specs for the job they just do what they know how to do.

When you bring them a Vehicle that they would not normally have expertiese on bring a copy of the specs or proceedures with you.

Note that out here Chilton, Motors or other manuals in Libraries are considered only for reference and they cannot be checked out. Shops are not paying to send a Man to the Library to get the specs.

Well equipped shops will have an online subscription to something like Mitichelle manuals which would have likely told them how to do the head correctly. But, often Mechanics do not like to read unless they have been told the job needs special attention.

The other issue is the vehicle owners. I have often told Vehicle owners they should have at least a Haynes type Manual for their vehicle and they throw back that they don't know anything about Cars and are not going to work on the Car themselves. I tell them they need to read them manual to familiarize themselves with common procedures so they don't get screwed by the Shop. But, that still does not penetrate thick Skulls.
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t walgamuth · #17 07-09-2017, 01:53 PM

A good machine shop will take an equal amount off the tops of the valves to what was taken off the head to make it all work with the same geometry

leathermang · #18 07-09-2017, 04:09 PM

Quote:

Originally Posted by t walgamuth

A good machine shop will take an equal amount off the tops of the valves to what was taken off the head to make it all work with the same geometry

I am not sure that would be standard procedure on a valve with threads on the top AND a slit down the side in that threaded area...

Most valves do not have the adjustment built into their top... so the machine shop would assume the geometry adjustment would be made by the cap nut...and it WAS for the first year....

Those threads were cut before the valve was hardened... even cleaning up those threads after grinding the end would be tricky.

Are the valve rotators working properly on this engine ...and that particular valve .. were they installed new when the head work was done ?

Carpenterman · #19 07-09-2017, 09:05 PM

Thanks to everyone for your expertise. This is an interesting problem.

When I took the head in, I was only looking for a check up, not a total rebuild. Told him I would consider a rebuild if things were really wacked. The head had about 280k miles on it.

I asked the machinist to do the following:

1) check the trueness of the deck

2) check the seats and dress any that needed it

3) check the valve guide wear

4) install new stem seals

I didn't specifically say anything about the rotators nor did he say anything about them to me.

I left him with a printout of the valve and deck specifications from the FSM. Not sure if it included valve height.

When I picked it up he said the guides were worn but not bad. Two of the exhaust seats needed dressing and he told me that he had to adapt or "make" the tooling, as the shop didn't have the specific ones. I suspect this is the cause of the problem.

I think I will remove the rocker assembly and the cap nut, leaving the bottom nut on the stem to clear the threads after grinding a minimum off. If it seems like a lot of force is required to chase the threads using the bottom nut, I'll use a die.

I guess I'll have to buy the special third valve wrench that I've never needed until now. It's the forth cylinder exhaust valve and it's right up against a cam tower, so I couldn't get anything else to work to keep the valve from spinning.

Originally, I did consider a total rebuild, which of course would have been best given the mileage. I was referred to a rebuilder in Ft Wayne, Indiana which is an hour away. He was very opaque about whether he had actual experience with MB diesels, how much it would cost, or how long it would take.

So I decided to gamble with my local guy.

Diesel911 · #20 07-09-2017, 11:39 PM

Quote:

Originally Posted by t walgamuth

A good machine shop will take an equal amount off the tops of the valves to what was taken off the head to make it all work with the same geometry

Besides the surface grind issue all valve seats are not ground to the same depth or the Valve Faces have the same amount removed from them. So not all valve stems will have the same amount protrusion.

Also there is a limit as to how much you can remove from the top of a Valve Stem. Which of course is why you need to have some specs to go by.

Then on most engines you need to worry if the valve seats are deepened and Valve Faces are re-ground it decrease the tension on the Valve Springs and the Springs need to be shimmed.

snapped_bolt · #21 07-10-2017, 12:59 AM

...should have been correctly in the first place. I believe there is no such "fix" in the FSM as grinding of valve train components for "proper" geometry.
The head should be pulled, and the seat that was "repaired" should be repaired correctly.
I am not certain about the components in the head- whether the parts are hardened through, or just surface hardening. If you grind through a surface-hardened part, the remainder will be soft and wear away, perhaps even self-destruct.
The last time I head something like this- the 70's- when my brother assembled a Cadillac 390 in his high school shop- among other things, he used washers on the lifters because the push rods he found weren't long enough! Then engine ran, but I don't think anyone wanted to install it in anything!

"the problem developed over a year later at the second adjustment since the re-work."

I would really be concerned if this had happened to my engine. If you initially had clearance, and now no longer have that clearance, why do you think that would be? Seems rather unnerving! Almost as if the valve is becoming deformed- maybe the seat was also cut at a slight angle? What is making the valve stem longer? You are losing clearance, right? The stem is coming up, either by eroding the seat, or deforming as it rotates.
Since this is an SLS head, I would not start it again until properly repaired.

"Also, this is the only machine shop in my area, they are very reasonable, have done other excellent work for me, and I want to measure good will against any perceived liability."

If this is a decent machine shop, they will accept responsibility for errors. If it were me, I would contact them and tell them what has become of their valve job. You would be a better friend to them by being straightforward about what you are dealing with. If they are worth their salt, they will correct it promptly. If they can't, they need to pay for having it done by someone who can.

Gaskets, new valve seat, and new exhaust valve- that should do for parts.
If good SLS heads grew on trees, maybe not a problem.

Anyhow, this is what I would do.

Regards,

snapped_bolt

t walgamuth · #22 07-10-2017, 07:08 AM

Quote:

Originally Posted by snapped_bolt

...should have been correctly in the first place. I believe there is no such "fix" in the FSM as grinding of valve train components for "proper" geometry.
The head should be pulled, and the seat that was "repaired" should be repaired correctly.
I am not certain about the components in the head- whether the parts are hardened through, or just surface hardening. If you grind through a surface-hardened part, the remainder will be soft and wear away, perhaps even self-destruct.
The last time I head something like this- the 70's- when my brother assembled a Cadillac 390 in his high school shop- among other things, he used washers on the lifters because the push rods he found weren't long enough! Then engine ran, but I don't think anyone wanted to install it in anything!

"the problem developed over a year later at the second adjustment since the re-work."

I would really be concerned if this had happened to my engine. If you initially had clearance, and now no longer have that clearance, why do you think that would be? Seems rather unnerving! Almost as if the valve is becoming deformed- maybe the seat was also cut at a slight angle? What is making the valve stem longer? You are losing clearance, right? The stem is coming up, either by eroding the seat, or deforming as it rotates.
Since this is an SLS head, I would not start it again until properly repaired.

"Also, this is the only machine shop in my area, they are very reasonable, have done other excellent work for me, and I want to measure good will against any perceived liability."

If this is a decent machine shop, they will accept responsibility for errors. If it were me, I would contact them and tell them what has become of their valve job. You would be a better friend to them by being straightforward about what you are dealing with. If they are worth their salt, they will correct it promptly. If they can't, they need to pay for having it done by someone who can.

Gaskets, new valve seat, and new exhaust valve- that should do for parts.
If good SLS heads grew on trees, maybe not a problem.

Anyhow, this is what I would do.

Regards,

snapped_bolt

Good points about why is it apparently "growing".

Carpenterman · #23 07-10-2017, 09:41 PM

Good info, SnappedBolt.

As for "growing" valves being a cause for worry, why is this valve so unusual, if as reported by many people and observed by myself, exhaust valves are always tight, adjustment after adjustment, and never loose?

Diesel911 · #24 07-10-2017, 10:19 PM

Quote:

Originally Posted by Carpenterman

Good info, SnappedBolt.

As for "growing" valves being a cause for worry, why is this valve so unusual, if as reported by many people and observed by myself, exhaust valves are always tight, adjustment after adjustment, and never loose?

Ya, on Engines with valve rotators often every time the valve rotates there is a slight amount of wear to the seats and the valve face. Because of that the valve sits higher due to wear.

snapped_bolt · #25 07-10-2017, 11:42 PM

are never a good sign.
If the "growth" continues, what is supposed to be done once there is no thread left to adjust? What, broken camshaft time?
If the valve is being closed by the spring, and the seat is not close to uniform, the end result will be that valve stem being deformed- that is, gradually lengthening, all the while gradually narrowing the valve gap. It has been on it's way since the repair, and has gotten to this point. If allowed to continue, you may wind up with the valve breaking away from the stem, a bent/broken stem, or broken camshaft if allowed to continue.
The Roto Cap allows the valve to turn in it's seat. If the seat is uneven, (at an improper angle), the valve strikes the seat partially, allowing a slight bending force to be applied to the valve/stem area. Imagine a nail head- it can withstand some uneven force, but eventually the nail head will break away. I know, not the same materials, but it's the same idea- if you have an uneven seat, you are essentially prying the head off the nail, bit by minute bit, at every closing of the valve onto the uneven surface. First symptom would be a rough idle, as if the valves were not adjusted properly, because that valve would not completely close. This would likely remain as the only symptom until the valve had lengthened from this working to the point that the gap could not be maintained at a valve adjustment. It is as if the engine is being used as an efficient machine to destroy one valve- it is working away at it, slowly, until it cannot go any further.
My bet is on an improper repair- perhaps the seat was cut totally wrong. Perhaps another seat was installed improperly. The seat could not only be too deep, but also cut at the wrong angle of degrees- and also cocked at an angle to the valve plane! The red light for me is the diminishing clearance. This doesn't happen if the work is done correctly. I can think of quite a few scenarios that could cause this seeming "growth"- none of them are self-correcting.

Key statements for me- "The upshot being that I can no longer get enough clearance to the cam follower"-

"But the first valve adjustment after reinstalling the head went fine--the problem developed over a year later at the second adjustment since the re-work."

This has been a "developing" problem.
Valves do end up naturally "tight" don't they? Seems the default end condition between adjustments.

How did you know the valve was ground too deep? Did the mechanic tell you, or did you notice it while looking at the deck? If I had seen that I would have had a lot of questions, and required twice as many answers!

You have already told us this has taken time to make itself a problem. This would not have been a problem if the job was done properly. The head should be removed and inspected to find out why this is happening, and the source is inside, on that valve seat.

If you are sensible with the machine shop, they will work with you. Maybe offer "free QA" for the process (I would). Instead of reporting another bad shop to the list, we can add another one where we can send a head for a valve grind.

I did a 5.9 Cummins for a guy a while back. The machine work, completely undocumented, appeared as if done at a tech school run by Gumby. I sent it to another shop that actually engaged me in conversation and rattled manufacturer's specs off as a first language. Possession of the space and machinery does not make a good machine shop. Request the work as documented, and check the final measurements yourself!

Damn. Nobody likes pulling a head. Fewer than nobody want to do it the second time! My concern is that sooner or later, you will HAVE to remove it, and there may be a lot more to repair in there by then!

I hope this helps, it may have confused me, but there is no way you can get a diminishing clearance without that valve coming up, by slowly lengthening the valve, or hammering it's way through the valve seat- one thing for certain is it's coming, it's on it's way; like the scene in Monty Python and the Holy Grail, with Sir Lancelot attacking the castle, seemingly so slow he will never get there- then suddenly, destruction is unleashed!

Or at least, that's the way I see it.

Regards,

snapped_bolt

leathermang · #26 07-11-2017, 01:11 AM

Quote:

Originally Posted by Diesel911

Ya, on Engines with valve rotators often every time the valve rotates there is a slight amount of wear to the seats and the valve face. Because of that the valve sits higher due to wear.

Since on a 617 Turbo engine BOTH intake and exhaust valves have the rotators....
I think your statement is not supportable.
Exhaust valves are subject to much higher temperatures than intake...that affects the rate of wear of the seat and the valve backside.

Diesel911 · #27 07-11-2017, 12:04 PM

Quote:

Originally Posted by leathermang

Since on a 617 Turbo engine BOTH intake and exhaust valves have the rotators....
I think your statement is not supportable.
Exhaust valves are subject to much higher temperatures than intake...that affects the rate of wear of the seat and the valve backside.

The material the Exhaust Valves are made of is different at lest on their face and I believe they valve stems are partially filled with Sodium to aid in heat transfer.

Exhaust is dirty and has some carbon in it. Carbon articles between the seat and valve face when it rotates kind of grind a little.

On the other hand the intakes Air is clean and cools the Valve and Seat and neither get contaminated with the Carbon particles that are in the Exhaust.

On Engines with out valve rotaors the clearance stay closer to what they were set to over the same period of use. That is an observation from the time when I worked as a Mechanic.

leathermang · #28 07-11-2017, 02:12 PM

Quote:

Originally Posted by Diesel911

The material the Exhaust Valves are made of is different at lest on their face and I believe they valve stems are partially filled with Sodium to aid in heat transfer.

Exhaust is dirty and has some carbon in it. Carbon articles between the seat and valve face when it rotates kind of grind a little.

On the other hand the intakes Air is clean and cools the Valve and Seat and neither get contaminated with the Carbon particles that are in the Exhaust.

On Engines with out valve rotaors the clearance stay closer to what they were set to over the same period of use. That is an observation from the time when I worked as a Mechanic.

You are making the assumption that the rotation caused by a rotator happens while the valve is in contact with the valve seat.... I do not know that that is the situation. Valves rotating keep the valve seat and the valve round...and keep carbon from sticking to those particular locations...