Stainless valves problem

[quickchange]

Local here has gone through 2 sets of mushroom stem stainless valves, has had engine rebuilt, stock with adjustable tappets, new valves, new springs ,std cam grind. stock head, engine builder gave 12 thou clearance, problem has occurred rear valves leaking, now seat where recut etc, 6000 miles on pulling down they found all valve stems bent ??? some as much as 20 thou run out, Im thinking not enough clearance as some came in at only 8 thou, they also had fitted new split guides , Now this has happened twice ?? Of course owner blaming stainless valves ??Do in fact stainless valves expand greater than original ones ??? & should have say 13-15 thou clearance ,
Anyone had this problem before ?? The vehicle has correct timing & not running lean ,The owner is a retired mechanic so no dummy , Please feel free to give us your thoughts, Thanks in advance , Derek from a hot dry NZ,

[Pete]

The problem is NOT the material the valves are made of.
Find a different guy to check and assemble the engine.

[nkaminar]

Two things can be done to check the clearance between the valves and the head. One is to put the head on the block without a gasket and just two studs but no nuts, one in front and one in back, and then see if the head lifts when the engine is turned over, by hand. The other is to use modeling clay spread on the inside of the head to see what clearances you are getting. Again put the head on without a gasket and no nuts. There should be plenty of clearance because things can sift around when the engine is running.

Double check that the guides and seats are concentric.

My question is whether the valves have the skinny stems and are copies of the orginials. The use of the split guides raises this question. Stainless can be weaker depending on the alloy used. The "modern" valves have thicker stems. If the owner is concerned about the valves, you can replace them with the modern valves sold at the vendors, like Snyders. https://www.snydersantiqueauto.com/p...8798&cat=41697

[CT Jack]

Agree with nkaminar. The suggested interference check could indicate the valve length is incorrect. This would cause bending. Your engine is a stock engine I would go with using good quality standard valves that are correctly sized.

[Bob Bidonde]

In comparison to the stock valves, stainless steel valves are poor conductors of heat. The valve material is not the problem. However, it seems that the valves are hitting something.

[Joe K]

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No gauling on those stems?


Stainless doesn't perform well in "sliding" motion. Your lubricant of choice may need examination.


Joe K

[Doug Clayton]

Stainless exhaust valves must be set at .015" clearance. The KR Wilson feeler gages produced in 1931 and later use a .015" thick gauge. I seem to remember this is also stated in the 1932 Service Bulletins.

[BillCNC]

Correct, exhaust is set at .015" & intakes are .013". The use of stainless seats and exhaust valves is to prevent them from burning.

Regards
Bill

[Pete]

Here is s good article on valve materials etc etc.

https://www.underhoodservice.com/tec...%20the%20alloy.

[dave in australia]

Wouldn't too tight of a clearance cause the valve to stay open a smidge and cause seats to burn up, and not stems to bend. Wouldn't too tight of a fit of the guide cause the stem to be tight and be a possible cause for the stem to bend?

[David in San Antonio]

Pete - Thank you for the article link. I learned things about metallurgy I wasn’t aware even existed. It sounds like the relatively low rpm, low compression stock A engine shouldn’t pose much of a challenge for valve composition choices.

[harryc]

I have my own refacing and seating machines but regardless I have always, over 50 years, made it a habit to finish up by hand lapping which I know a lot of professionals scoff at. I have never had any problem what so ever --stainless or otherwise. Maybe your problem is sloppy seating.

[ursus]

The guy that replaced the valves in my engine showed me the results of his work by demonstrating the following: each valve must be loose enough in the guide to fall by its own weight, that it should make a ringing sound when it lands in the seat. I am using stainless steel valves.

This was after another machine shop screwed things up by mixing up all the halves of the two-piece guides after grinding. I tried installing a few valves for testing with Prussian blue and found that the valve faces were not concentric with the seats. The guy that did the work couldn't seem to fathom why this could be a problem. Just a cautionary tale.

[quickchange]

Thanks all , Passing on info today when he is collecting a new set ,I think its a clearance problem , Thanks ,

[Pete]

Something few are aware of. In the old days many exhaust valves were made from an austenitic stainless steel which is non magnetic. Someone got the idea that putting exhaust valves in the intake would be an improvement in a race engine.
The intakes were easily identified as they were made from martensitic stainless steel and were magnetic.
This thinking has merit except for one flaw. Many of the exhaust valves of the old days were a 2 or 3 piece valve with the head welded to the stem and sometimes a button welded on the stem end for wear protection.
Never a problem in a stock or slightly modified engine but as soon as some guy figured out how to make an engine turn 8000 rpm with a .010 lift velocity cam, the valves started coming apart.
Something to think about if you are building a reasonably stout street engine using original parts.

[nkaminar]

Pete, Were the parts spin welded? (Friction welded)

[Pete]

Originally Posted by nkaminar

Pete, Were the parts spin welded? (Friction welded)

Yes.

[Ron Blissit]

The valves in my 1914 Cadillac had the head the valve threaded to the stem. I now have 6.25 boreCaterpillar valves with the stems centerless ground stems.