Valve stem finish & valve guide wear

[burgermeister]

I have been having a rather annoying issue with valve guide wear. I had my heads refurbished at the end of 2010, with new valves, guides, and springs - everything stock. Mid-2012 I had to get them refurbished again, as all the exaust valve guides were quite shot, with one being really really shot.

We figured is was a bad batch of valve guides, got a new set from a different source, and got 'er running again using the same valves. Well, I'm getting better, because this time one of the guides is totally gone after just 1800 miles. The others are worn, but probably still serviceable - obviously not for much longer.

The question is why. Another set of bad guides seems unlikely. The seals are the black rubber ones, so lubrication ought to be reasonable. I am wondering if the finish on the valve stems could be the issue - I would expect the exhaust guides to be more sensitive to this, as they are pretty short of lubrication, and the exhaust guides are wearing much more than the intakes.

Here is a picture of a current exhaust valve. Note the visible machining marks.



Here is a pic of one of the current intakes. Same thing.




And hee is one of the old 163K mile exhaust valves. The valve stem finish seems smoother.



It seems to me a valve stem ought to be perfectly smooth, almost polished, but I've never seen a new valve before.
Are the machining marks normal for new valves?
Did the factory valves have them, and they're just worn away?
Has anyone else had experience with valves that have machining marks on the stem - in other words, are they OK, or ought I get some new valves?

[TimT]

Are the machining marks normal for new valves?

No

Every new valve I have ever seen the shaft looks to be finished to a mirror polish...

[Walt Fricke]

And TimT has seen a lot of them. All I have seen are old ones, but they also are mirror finished, or close to it with a little wear perhaps interrupting the mirror part. Certainly never machining marks.

Lubrication of the exhausts can be improved, I think, by omitting the guide seals. No suction in the exhaust port to speak of, and no gravity to help move the oil along. I can't say I have done SAE quality testing, but have not noticed any excessive oiling issues with the motors I have assembled without them.

What brand are the new ones? Looks like TRW stamped on the old one.

[HawgRyder]

Even when using Teflon (white) seals..I used to pass a triangular file (one pass) through the hole to give it a little notch.
I know the seal is supposed to keep the oil out of the guide...but as you have experienced...no oil is just as bad as too much.
There are guides that have a sort of spiral look to them on the bore...and if I remember correctly...you can sort of "tap" an old guide oversize and screw in a coil of bronze ... then broach it to size to give the oil a place to reside for lubrication.
Hope it helps.
Bob

[AlfonsoR]

Just wondering...

in regards to potential direct causes: What material are the guides and valves made of? Brand? What condition are the rockers in?

In regards to in-drerct causes: do you have the restricter upgrade installed? Do you do a lot of low rpm (city) driving? Any signs of high temps in the top end? Heat shields installed correctly? Fan not pulling in enough air? Did you remove the engine tray? Oh wait, that's 993, ha.

Oh yeah, and what did the valves look like that you pulled out in 2010? Any other prior history or evidence on valve/ valve guide wear prior to 2010?

[chris_seven]

I think that the combiation of finish and clearance will point the way as there are several variables to consider.

The surface finish of the valve is clealry important and I would think a 'polised' valve should have an RA of around 0.15microns.

http://sg.misumi-ec.com/pdf/tech/press/pr1167_1168.pdf

The clearance between the valve and the guide is also important and there must be a cross over which means very smooth finishes may need more clearance than slightly rougner finshes as they don't hold an oil film and then a point where roughness dominates and causes wear.

There is a trend in modern engines to use 'texturing' on valve stems to help retain oil films

Valve-stem texturing - snake oil or snake skin? Ğ RET-Monitor

Seal design is also interesting and there is some quite good data being published:

http://www.skf.com/files/004641.pdf

[burgermeister]

Originally Posted by AlfonsoR

What material are the guides and valves made of? Brand? What condition are the rockers in? ...

The valves are marked with +IVS+, which I think is Intervalve SA, a small swiss manufacturer. Guides - Phosphor bronze AFAIK. Rockers are fine (rebushed & refaced 1800 miles ago). Cams look good. No idea re. oil restrictors - they are whatever the factory put in in 1988. The bottom picture at the top is an original valve, which was removed at 163000 miles.

Driving is probably 60% freeway, and 8 or so days of track operation per year.

Chris, neat info on valve stem seals et al - thanks!

[Walt Fricke]

I don't have a camera capable of such good close-up resolution. But I have a bunch of valves on my bench at the moment, some out of my race motor (though I bought it used, so don't know how long the valves have been in use - at least 125 track hours, I think), and some used ones of completely unknown provenance but all likely pretty old and well used.

A couple of these show circumferential markings sort of like yours Valves start out as a forging, don't they? Some parts are obviously machined on a lathe (the heads), as those machining marks remain. I have no idea how the shafts are made so smooth - can you centerless grind something with one big end? Can wear reveal what was beneath some kind of polishing operation?

You ask a question, and all you get are more questions. Sorry. For sure you are getting way less use from your guides than you should be getting.

Bob - I remember (from a misspent youth reading Hot Rod magazine and dreaming of things I couldn't afford) a drag race valve guide system much like what you describe. Something like a Helicoil (though of different material of course) was inserted into the guide. When it wore, you yanked it out and put in a new one. Perhaps honed it, and good to go. Much quicker and easier R&R of guides, and arguably had lots of space to store lube. I asked some of my engine builder friends about this once, but they hadn't heard of it and didn't think it would work on our Porsche motors. Though I think more because they hadn't heard of it. If it is not still in use in drag race circles, where rebuilds are very frequent, perhaps it had some flaws.

[burgermeister]

Well, I think TimT answered the big question with the first reply - those marks are not normal. Abnormal marks, abnormal wear with 2 different sets of valve guides - that is a pretty big "X" hanging over the valves. So Thanks Tim!

I've sent an email to Intervalves with the pictures attached - I was hoping to hear back from them, but no luck so far. Well, time will tell - I'll post if I hear anything.

I thought valves were sintered (powdered metal) or made as 2 pieces (stem & head) and then friction welded together ... I suppose I could look it up online, but I find I don't care enough to bother! Must be the getting older thing....

I have wondered why guides aren't screw-in affairs - maybe it's too tough to keep them from loosening, maybe it has to do with heat transfer, or - even more likely - it's just cheaper to press them in. Aftermarket service is not really of any concern to a mass market manufacturer - they will gladly save 2 cents even if it means everyone who keeps the vehicle past 150K miles would need to spend $500 as a result.

I vaguely remember my autoshop teacher having a tool that would somehow knurl the inside of a valve guide. It was used to cheaply restore cast iron heads (without separate guides) so they'd run another 40 or 50 K miles.

[Walt Fricke]

The cam oil line restrictor didn't come in until the 964s at some point. So a stock 3.2 would not have them, and valve/guide wear could not be laid at the feet of a design which lessened the amount of oil squirted out of the bar at rockers and valves.

[burgermeister]

I purchased a couple of Intervalves valves from our host - they are an interesting comparison to the original valves.

The valve stem appears to be somewhat rough - definitely not a mirror polish.


Here it is with a factory valve in the background.


Here is a valve guide. I simply took the 2 Intervalves valves and "sawed" at the guide at 2 spots with the valve stem. I took the factory valve and did the same, in the middle between the 2 prior locations. The IVS valves clearly wore away the machining marks (red circles) , the factory valve just polished them a bit (green circle).



I then moved the IVS valves inside the old valve guide while applying lateral pressure (maybe 10 - 15 lbf). No oil, which is probably about right for the head side of the exhaust valve. Note the bronze colour on the valve stem!


Here it is again. The dark stuff on the paper was wiped off the valve stem (and they were clean before I started). The line where I stopped wiping is clearly visible.



So ... is the first picture indicative of typical new valve stem finish? Is the type of abrasiveness I am seeing intentional? Doesn't make sense to me, but sometimes things are counterintuitive.

I'm no expert in tribology, but I do think there is some evidence that the IVS valves would cause more wear than the factory valves. I have searched, but I cannot find anything bad about them online, and it seems everyone carries their valves these days. My unscientific attempts at finding causality suggest the IVS valves suck, and badly - yet if they did, others ought to have issues with them, but I read nothing of the sort. So I must be missing something - any clues welcome.

[pete3799]

Very interesting results.
I hope someone here has an answer for you......i sure don't.

[E Sully]

One of the problems I see with the comparison, the factory valve has been used, and could have become more polished from use. You would need to compare new to new. I used the intervalves from our host with new guides in my '86 3.2 rebuild, and no issues at 3,000 miles.

[TibetanT]

Hello There:

I am no expert, but just wanted to add my observations for reference.

Every new valve, or set of valves, I have ever purchased has a smooth mirror finish to the shaft. Hope this helps.

[crummasel]

I did not make bad experiences with surface roughness, but some time ago i bought a set of valves with a roughness which appeared really bad to me.
It simply "felt" awful to me to install them as they were
I polished them prior to installing and there were no problems.
They lost about 0,015 mm in diameter but they were OK with tolerance to inner diameter of the guides after reaming.

[Walt Fricke]

I have 8mm stem Intervalves in a race motor of mine. I don't remember the stems looking anything out of the ordinary. Not that I inspected them for that, but I had a couple of them on my desk for some months and, since I would expect a mirror finish, I'm pretty sure I'd have noticed. As would the engine buider I had install the the guides for them, and install the valves and springs while he was at it. That hazy, 2,000 grade sandpaper look really stands out.

Bad batch? Bad QC? If this were the latest and greatest innovation, they'd have advertised it. IV has reasonable market share, I think. Worldpack carries them. Sounds like something to get Wayne and his crew on, as they sell them and won't want to have dissatisfied customers.

[manbridge 74]

Your test with no oil would lead me to believe your oil spray bar holes might be clogged.

[burgermeister]

Walt, I'm not sure that's QC. It almost appears as if that finish is intentional - the part of the stem where the keeper goes does not have it. I just don't get it - but I don't know anyone in the valve design business. My various engine & machinery design books contain basically 3 pages on tribology between all of them, and they can be summarized as "harder parts wear slower" ...

manbridge, my cams & rockers were fine. I'd think the cam would go pretty quickly if the spray bar was clogged. I also tested the spraybar in the parts cleaner, and all orifices sprayed as intended.

[Walt Fricke]

Yup - a clogged spray bar hole will cause the rocker to wear the cam lobe down to a circle in short order. I saw the result of that once in a shop - each side of the lobe had a full lobe profile maybe 1mm thick, and the middle of the lobe was worn down the width of the rocker. Couldn't have machined things better if you had tried.

[burgermeister]

Just for completeness sake, I ordered a TRW valve and looked at that. Smoother finish than the IVS, but still abrasive enough to rub a bunch of bronze off. I tried chucking an IVS into the lathe and sanding it with 600 & 1000 grit. Those valve stems are pretty hard stuff - they don't like to be sanded ....

Alas, just to confuse the issue further, I borrowed (commandeered?) my daughter's microscope and made an attempt at taking pictures.

Here is a set at 100x

Factory 163K miles


IVS Sanded


TRW


IVS as received