Valve stem finish & valve guide wear

[burgermeister]

And, One more set at 200x. It does look like the TRW has a finer finish - the grooves appear smaller and more closely spaced. It also appears as if rubbing valve stems with sandpaper has very little effect. It furthermore appears that all new valves (TRW and IVS at least) have a somewhat rough, abrasive finish on the valve stem. The leftover grooves suggest the factory valve had a similar finish.

So, I'm no smarter than 2 weeks ago. Rats.


Factory 163K



IVS sanded


TRW


IVS as received

[Walt Fricke]

Next you'll be sending us pictures of fruit fly eyes. And my well used valve stems look so smooth to me.

Was this a labratory grade microscope set up for digital pictures, and many $? Or can one purchase something relatively inexpensive which just plugs into a computer?

Isn't there an engineering scale, with some guy's name attached to it, for surface finish/roughness? And some kind of instrument to measure that?

[burgermeister]

I did not do well breeding fruit flys in genetics class and extrapolating things from the wingless albino fly counts... Maybe I inhaled too much fly nap ... so no fruit fly pics from me

It's a semi-cheesy Costco - sold student microscope with a 4x3 digital screen (no traditional viewfinder), I think it was $200. Actually pretty decent considering the price. Takes pictures & movies too ... and uses SD cards, just like a point & shoot camera. One of those kid x-mas presents that got used twice and then sits in the closet, but at least it was preferred over the box it came in.

There is a roughness scale, and instruments to measure it, which I don't own and cannot afford due to owning & maintaining the "highest quality, most reliable vehicle ever made", a Porsche 911.

[burgermeister]

I do have one question I think I can get an answer to - what flavor valve guides do folks here use? Phosphor bronze or Manganese bronze?

[E Sully]

When I rebuilt mine I talked to the local Porsche shops and they all said to use the phosphorus bronze.
As far as polishing the stems, realize that the cylinder walls have a texture from honing also.

[HawgRyder]

My thoughts...
If the valve stem is slightly rough (not mirror smooth) it will hold oil film...and perhaps lube the guide better?
This requires the valve seal to admit some oil to supply the necessary amount.
Or....with a mirror smooth valve stem...the guide itself has some "wicking" properties that retain oil for lube.
If I remember correctly...there are guides made up of tiny little balls of bronze that retain oil...perhaps something like that would be long lasting.
Bob

[Walt Fricke]

Bruce Anderson says up until 1977, Porsche used a copper material for the guides. It then switched to a silicon-bronze.

Our host's book doesn't discuss the material to use, beyond noting Porsche's troubles with the early guides.

The engine builder I have used told me he learned what Continental uses in its air cooled aircraft engines, and makes his guides out of that material. Alas, if he told me the alloy I forgot it.

Bob - what you mention sounds a lot like Oillite bearings. I bought two of those in a hardware store 20 years ago to use as bushings for sway bars. Some day I ought to pull them off and inspect for wear, but they don't rattle around. Some sort of porous brass/bronze material.

But the question here is what are the engine rebuilders using as their normal material.