Unusual valve stem wear - question for the experts

[PaulProe]

We've had an engine go bad - the valve stems wore out 'literally' This is a picture of one of the valves.


The valves are the ones that come with the Edelbrock heads. Units were put into service in 2010 and have about 30,000 miles on them. The really confusing part is the bronze guides are NOT worn. They appear to be perfect and measure little to no wear. Engine was a bored/stroked 390 to 432. Not a big power motor, mild Crane Hydraulic roller cam. Never raced, used in a cobra replica for cruising and Ice Cream fetching. Rocker arms were a set of Erson rollers, springs were stiffer than the stock Edelbrock as recommended by Crane.

I heard a comment that Chevy had an issue like this years ago with some valves. Is this a metallurgy issue? Why would a steel valve stem wear and not the bronze guide? If both were worn equally or the bronze more than the steel, I would understand it.

Any ideas

Paul

[frnkeore]

What is the ID of the guild and the OD of the valve, on the unworn area?

[shady]

Chevys had some soft chrome plating on the valve stems. It's the same way with king pins sometimes the bushings don't wear just the pins.

[jayb]

What happens in a case like that is that some microscopic steel embeds itself into the bronze, and then that acts as a file on the steel part, so that it wears and the bronze doesn't.  I think those valves are the issue, probably substandard material or plating, and the guides will need to be replaced also, because they probably have the steel embedded in them.

[pbf777]

     This issue that you have brought is not really answerable here on a forum, but if we wish to discuss reasonable possibilities well..............

     First, lets' say that often a failure will have more than one parent, so be prepared to realize that perhaps no one subject addressed may solve the issue.

     Next, don't think that all bronze alloys are soft, some of the aluminum-silicon bronze guides that are available will outlast the stainless steel chromium valve stems!  What those particular Edelbrock heads might have in place?   

     Are the valves defective?  Definitely suspect but this would prove complicated to establish, rather this would generally be determined via historical service record of in service performance in comparison with other production runs, and this information would generally be best acquired from Edelbrock via feedback from customers, if they were willing to share such, this being questionable particularly if it were to present their product in a bad light.   

     Insufficient lubrication?  Sure seems a possibility looking at the damaged, mauled valve stem surface.  This could be caused by the guides being to tight thereby not permitting adequate oil passage (it does sorta appear that maybe the top of the guide might be without a chamfer on the I.D.?, which I would prefer to be present to aid in oil migration); oil seal function failure, say for example if not defective in some way perhaps a mixture of 11/32" seals with 3/8" valve stems stuck thru them; excessive oil contamination from overly rich fuel mixture defeating the lubricity value of the oil; how-a-bout bad valve train geometry leading to among other things excessive side-loading of the valve stem in the guide causing displacement of the film thickness required to keep the two surfaces apart; or even maybe overly restricted oil delivery to the upper valvetrain area thereby there's just not enough lubrication to dole out?   

     But no, I can't answer the question with any absolute, particularly from here, and the culprit may very well prove to more than one issue at hand?   

     Scott.

     

     

[Barry_R]

With a "nod" toward the factual information provided by Scott, I am going to agree with Jay on likely cause. 

Pretty much all the steel valves we see these days are offshore supplied, and claim to be some sort of  "stainless" steel alloy and one piece in design.  Edelbrock used to source valves from Basso (AKA BBB).  No idea any more.  Pretty difficult for a normal guy to prove/disprove the alloy, but almost all the one piece claims are false.  With the notable exception of Ferrea's induction hardened race stuff, all the common valves have a hardened steel wafer tip friction welded to the top, along with a really thin chrome wear layer plated to the stems.  If the are equally as factual about the chrome plate quality - or if its even present - you can get some significant wear. 

No or inadequate plating would cause what you area seeing, while poorly done plating can kill a guide quickly.  Chrome itself is extremely hard and does not wear much.  Poorly adhered chrome plate will break apart and embed in the guide as Jay noted, filing away at the softer steel valve material.  A rough plating job becomes a file and cuts up the guide in short order.  In an ideal world the QC Department would be random inspecting valves as batches arrived, looking for flaws in production.  But in the current cost driven environment those guys simply don't exist anymore outside of OEM.

[frnkeore]

There appears to be a scar, above the wear line. Pretty much inline with the major damage. Could that have started the problem?

[Dr Mabuse]

There appears to be a scar, above the wear line. Pretty much inline with the major damage. Could that have started the problem?

It seems that the problem was with all 16 valves?