Measuring valve wear and clearance...

[bpu699]

So, got my 930 motor apart, heads off, valves out...60k miles on it. Question of head rebuild by po.

Several questions please

Cylinders are nikasil, look great, still with visible hash marks .

Measured the valves, and they were all below minimum spec for shaft size...

Weird, I thought. Valves look newer, valve contact area on the valve seat is nice and shiny, no pitting...

I was using digital calipers to measure, Titan brand. Pretty much what all the auto places sell...

So, went and bought a new micrometer. Don't laugh, it's harbor freight. Reads to .0001. Calibrated it to some feeler gauges, seems spot on.

Went and remeasured....readings now better, more consistent. Getting about .353 inches, which is just over minimum...

But when I measure just under the collet, top of stem, I also get .353. And that's an area where in theory there shouldn't be any wear....

The narrowest is .352 near the valve... So I have .001 taper, if I am doing this right.

But here's where I am confused. Are replacement valves manufactured at the very bottom of what minimum spec is??? I would think the valve stem should on a new stem should be the same top to bottom. Yet, at its thickest, it's at minimum spec...

I was going to buy new valves, one intake one exhaust to measure...

Or, do I have two micrometers, both inaccurate?

As an aside, if one replaces the exhaust valves on a 930... Do you use the sodium filled originals? Or just the aftermarket pelican carries? Or something else? Pelican has valves from $25 to $300 per valve...?!

Also, how does one measure valve guide tolerance? I thought you wiggled the valve and measured, but can't find it in the pelican rebuild book...

Thanks

Bo

[bpu699]

Ok, answering my own post....

Other than buying a $300 gauge, you can buy a split ball gauge for $20. Fit to bore, take out, and use micrometer to measure...

Also ordered a cheap aftermarket valve to measure as new spec of a new valve, and verify micrometer accurate...

I can very slightly wiggle the valve...I assume that means it's worn...

Oddly, the car doesn't smoke. Ever. I would think with worn guides it surely would...

Uses 0.5 -1 quart of oil per track day...

Heads are very carboned up though... Can this be due to the car running silly rich under boost? Or does this unequically mean oil was getting by?

Any thought appreciated..

Bo


Addendum... I love you tube...

Watched some Porsche videos will 911s and 993s with valve guide wear. Holy krap. The valve wiggled a mm or more!!!

Mine move an imperciptible amount. Will measure with a dial indicator at the valve head... The tech in one of the Porsche videos was explaining that you take the movement with the valve open 1/2 inch, and wiggle. Measure the amount, divide by two, and that your valve guide clearance...

[Trackrash]

I just went through this on my SC. Don't know if the valves for a turbo differ.

What I found is the original valves from my motor had no taper on the stems, and were in spec as far as their stems measured.

I ordered new OEM (TRW) exhaust valves from our host, since a couple of mine were bent.

The new valves had tapered stems. I had read that valve stems should be tapered. I could find no mention of this in any of my manuals.

The TRW valves were not expensive, around $30 each IIRC. They do have the P in the triangle stamped on them, so it seems they truly are OE.

As far as I know all the exhaust valves are sodium filled for these motors.

Maybe some of the experts here can offer more insight.

The way to measure your guides is to carefully clean out the guide. Make sure there is no carbon or oil in it. Put a dry valve in the guide and measure how far you can move the valve back and forth. This is outlined in the workshop manual with the spec. IMO, unless you are certain the guides are as new, I would replace them. A turbo with 60K miles probably will need new guides.

[bpu699]

Originally Posted by Trackrash

I just went through this on my SC. Don't know if the valves for a turbo differ.

What I found is the original valves from my motor had no taper on the stems, and were in spec as far as their stems measured.

I ordered new OEM (TRW) exhaust valves from our host, since a couple of mine were bent.

The new valves had tapered stems. I had read that valve stems should be tapered. I could find no mention of this in any of my manuals.

The TRW valves were not expensive, around $30 each IIRC. They do have the P in the triangle stamped on them, so it seems they truly are OE.

As far as I know all the exhaust valves are sodium filled for these motors.

Maybe some of the experts here can offer more insight.

The way to measure your guides is to carefully clean out the guide. Make sure there is no carbon or oil in it. Put a dry valve in the guide and measure how far you can move the valve back and forth. This is outlined in the workshop manual with the spec. IMO, unless you are certain the guides are as new, I would replace them. A turbo with 60K miles probably will need new guides.

Thanks for the info...

The dilemma I have is that the head was supposedly rebuilt 5000 miles ago... I don't want to redo work that was recently done... But I have no way to verify...

The valve seats and valve head where contact is made is nice and shiny, no pitting. Supporting the notion of a recent rebuild. Otherwise, at 60,000 miles, I would expect it to look worse.

Also, where the head contacts the cylinder, the machining marks still look good. You can "see" the machining cuts.

Will measure valve stem wobble today, if I have time. They move an imperceptible amount, but I can "feel" it more than see it. Again, at 60,000 miles without a prior rebuild, I would assume it would look way worse...

The rocker faces look brand new, with the exception of one. That's the one with the pitted cam...

I will check the WSM, I looked at Bentley and the Pelican rebuild book. Pelican just said that the valve needs to be above spec along its entire shaft. I am puzzled, as the valve stem, in a noncontact area, is already at minimum spec...

The TRW valves for the 930 are 70-90$ dollars each. The only ones I see for $25 is some off brand... They don't mention if they are sodium filled or not.

I don't mind replacing stuff, if its needed. I am just leery of doing a full rebuild on a motor that ran great, and didn't smoke. My 911s from years back, smoked everytime I started it. The 930 though does have tons of carbon build up...


On piston #1, on the engine mount prior to disassembly, I was getting wacky leakdowns. 15%+ leak down when first tested. Took carbon off the valve with a pipe cleaner, got the leakdown to 5%. Tested the next day... 100% leak down. Held no air. What the ?!?!? Poured oil down the cylinder, leaddown went to 3%.I was fully worried to see broken rings, scored pistons, bent valves. But, took it apart, and piston looks new, rings are all accounted for (top ring has some carbon, hard to move. Cleaned it, all back to normal. Need to measure gaps/etc.

My issues all seem "carbon" related.

But long and short of it, motor looks really good so far. 1 cam with pitting, 1 rocker with slight wear... and of course, the head studs.

I did order Henry's Supertec studs... coming soon .

Best I can tell, my issues are simply from running really rich under boost, due to mods the PO made...

[safe]

Originally Posted by bpu699

I can very slightly wiggle the valve...I assume that means it's worn...

Any thought appreciated..

Bo

In spec they do "wiggle" a bit.
Kind of redneck, but it will give you a hint:
Try to wiggle them "up and down" and "side to side", if you understand what I mean.... They usually wear the guide oval and mostly so towards the combustion chamber. So if they are still round there is a big chance that they are in spec, but you really need a special tool measure it properly.

[bpu699]

Thanks guys...

Looked in the WSM... don't see any specs for a "wiggle test" that someone mentioned...

Also, the WSM only has one spec for the valve, and its midshaft....

[bpu699]

Ok, here is what I have so far...

Cylinder #1, exhaust valve open 1cm (about normal, I would think). Dial indicator to its edge.

.006 inches wiggle if I do it gently. 11/1000's if I do it forcefully (I assume the valve "bends" some in this scenario).

Pelican book saws .2mm, or .008 is acceptable shaft wear, if I read that right... Internet gurus on youtube say to take the wiggle number and divide by 2 to get clearance. If thats right, its .003 to .006...

Does that sound right?

Rennlist has some posts that the wsm states .5-.8mm wiggle is considered in spec... That seems like an awefully lot...

Likely will send the heads off to Cgarr get them done and be sure... But that seems "in spec"? I would feel silly rebuilding heads that were just rebuilt...

Split ball tool on order...

[prschmn]

There needs to be some clearence between the valve and guide for lubrication.
From the sound of it you're fine. If the fit is too tight you risk the stem biting the guide when it gets hot which will try to pull the guide in the head-not at all good.

[Mark Henry]

To me with a new valve .015" is the wear limit, so .5-.8mm is WTF.
I put the valve in both the right way, then backwards and measure. I do this because one end of the guide is often in spec and the other is out. I find that you almost always have to replace the exhaust guides. Guide must be reamed and finish honed to size after installing, the bronze actually collapses slightly during install. If the valve sticks anywhere it will cause problems, it must glide.

[bpu699]

Originally Posted by Mark Henry

To me with a new valve .015" is the wear limit, so .5-.8mm is WTF.
I put the valve in both the right way, then backwards and measure. I do this because one end of the guide is often in spec and the other is out. I find that you almost always have to replace the exhaust guides. Guide must be reamed and finish honed to size after installing, the bronze actually collapses slightly during install. If the valve sticks anywhere it will cause problems, it must glide.

.015 inches is .4 mm...

The wiggle test indirectly measures clearance. Clearance is actually much smaller than the distance that the valve wiggle, as the exposed shaft is a distance multiplier and the measured distance exaggerates the actual clearance...

I hope to measure a new valve stem diameter soon. The shaft size is 9mm. A new stem is supposed to be up to 8.997. I don't think that they are manufactured to that spec. I think they are cut thinner. Much like new piston rings are cut in the middle of spec, rather than on the large end.

Like I said, my valve stem, in a nonwear area, are at minimum spec... so, they were cut that way new.

Can anyone else measure their stems just below the retainer collar and see what you get? New stem, vs old?

Bo

[targa72e]

I went thru this recently with my 964 rebuild. Engine looked like recent rebuild , most parts measured as new. Valve stems one exhaust were at low end of specs but like yours the area that should never wear was the same diameter as middle. Purchase one new valve to test size. New valve was actually under spec so reused old ones.

john

[bpu699]

Ok... Now I am scratching my head...

Got the new exhaust valve and new valve guide...

My existing exhaust valve guide, cylinder number one...is 0.352 inches... Low end of acceptable...

The brand new valve, is 0.3515 inches!!!!

The new valve, with no wear is thinner than the old one...

Redid the wiggle test, valve fully extended so it's stem is flush with the guide, so it's stick out really high... Way beyond normal.

Old valve and guide... .008inches

New valve in new guide.....005

Old valve, in new guide .003

But all within spec???

Shocked a new valve is more under spec than the old one? Any other folks notice that?

[bpu699]

Alright, did more measurements... 2 different tools. Micrometer and calipers... Keep in mind one tool is inches, one is mm...

New valve is under spec as new...

Used the expanding ball tool to measure the valve guide opening... Supposed to be 9mm new...

Well, the new one is 8.97 mm. Old guide is 8.98 mid guide...

Old exhaust valve is 8.92-8.93 mm on the calipers.

That's a difference of 0.05 to 0.06mm... Well within spec of .05 to .08. Max is .15 per pelican rebuild book...

Basically, valves seem within spec, at least on the worst cylinder...

I suppose I can have 2 tools, both inaccurate...though unlikely.

Odd that the valves and guides measure smaller...

Surprised the new valves measure at the very low end of spec...

[bpu699]

Originally Posted by targa72e

I went thru this recently with my 964 rebuild. Engine looked like recent rebuild , most parts measured as new. Valve stems one exhaust were at low end of specs but like yours the area that should never wear was the same diameter as middle. Purchase one new valve to test size. New valve was actually under spec so reused old ones.

john

Well, that makes two of us...

Any of the pros on here find the same?

[safe]

Its up to the machine shop to ream the guides to the right valve clearance.

[bpu699]

Originally Posted by safe

Its up to the machine shop to ream the guides to the right valve clearance.

Good to know...

But if a new valve is 8.92 and the shaft is reamed to 9.0 to 9.01 which is spec... Then you are just about out of spec for tolerance with a brand new valve... You have .08 to .09 right there...

The new valve was nowhere near 8.97 or new spec...

If you don't ream it, you are in spec.

Are manufacturers intentionally making valves on the loose side? Like I keep hearing ring gaps are loose brand new too???

[Mark Henry]

What brand is the new valves?

[bpu699]

AE from our host. Bought an inexpensive one to measure against....

[Trackrash]

From what I can figure, as I went through this recently, Porsche has changed the spec on its valve stems. At least it's exhaust valves.

The new valves have a TAPERED stem. Not sure why, maybe to offset the thermal expansion.

I read something about it in another post.

Perhaps one of the experienced pros on this board can chime in. Perhaps Porsche has a Service Bulletin about this?

[bpu699]

Originally Posted by Trackrash

From what I can figure, as I went through this recently, Porsche has changed the spec on its valve stems. At least it's exhaust valves.

The new valves have a TAPERED stem. Not sure why, maybe to offset the thermal expansion.

I read something about it in another post.

Perhaps one of the experienced pros on this board can chime in. Perhaps Porsche has a Service Bulletin about this?

Pelican book says there should be no taper?

New valve has no taper...just undersized?

I just need to figure out what to redo and what to leave alone... Teetering on that slippery slope...

If it were totally out of spec or smoking decision would be easy... But motor ran great prior to broken head stud being found...

Found some threads suggesting new clearance is supposed to be .01mm. Book says .05 to .08.

A new valve with a reamed out guide to 9 mm gets me the same clearance I have now...

Anyone have a new Porsche or trw valve they can measure?