Failure Mode

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Model T Ford Forum: Forum 2017: Failure Mode
Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Blake, Kansas City on Thursday, June 29, 2017 - 09:38 pm:

My 31 years with FoMoCo included about 9 years in the Kansas City assembly plant where I interacted with lots of engineers. When analyzing component failures they often used the term "failure mode" which implies a part can fail in more than one way.

Which brings me to the subject of original 2 piece valves. I pulled the head on one of the two engines I purchased in Iowa and found part of one of the heads cracked off and missing. I had always assumed the entire head would pop off of the stem, one failure mode. I did not expect this (see pic) but I must admit I've never seen a failed 2 piece valve. Is there more than one failure mode, or is this the way they typically fail?

T valve


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Thursday, June 29, 2017 - 11:07 pm:

Gary, I would say there are two failure modes: non destructive and very destructive. You had the former, where the piece apparently go out the exhaust pipe. The latter is when the parts fly around in the cylinder and break stuff.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Blake, Kansas City on Thursday, June 29, 2017 - 11:14 pm:

Thanks David for the quick response.

I don't think I was clear in my question though. Do the valves themselves have two failure modes? The failure mode pictured would of course be one. But do the heads ever separate as a single piece from the stems. That is what I had always assumed happened to a valve made by joining a piece of rod (the stem) to the valve head.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Harper - Keene, NH on Thursday, June 29, 2017 - 11:19 pm:

Hi Gary,

I have had two piece valves fail. The head popped off in all cases. I have never seen the failure which you show. Good luck with your project. Bill


Top of pagePrevious messageNext messageBottom of page Link to this message  By Corey Walker, Brownsboro TX on Friday, June 30, 2017 - 12:43 am:

I shook the pieces of this one out of my muffler when it broke. I made a key ring out of it, then when people ride with you in your modern ride and ask what is on your key ring, you can tell the story of having a valve come apart while driving.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Friday, June 30, 2017 - 02:31 am:

Gary, sorry for the quick and somewhat smart-aleck response, but it's pretty true, the two piece valves usually fail by a part breaking off, or by the entire head coming off, sometimes in two pieces.
Usually, the smaller piece coming off goes down the exhaust, the full head, though most often finds its way into the cylinder and really ruins one's day.
Technically, my first answer is about right! Part of the problem in figuring it out though, is the parts flying around usually obscure the original cause of failure.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Darryl Bobzin on Friday, June 30, 2017 - 08:38 am:

Looks to me like both these valves failed from stress cracks originating in the holes formed for the valve lapping tool.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Friday, June 30, 2017 - 08:41 am:

Haven't experienced a 'popped' off 2 piece.

But have removed many, in rebuilds. Wouldn't run a T motor today without new valves anyway.

Typical from observation is valve getting stuck, the exhaust one, as heat and lack of lube. The iron head of the 2 piece will just melt away.





At times you find them mostly busted around the head.





Best to remove and discard those 2 piece iron head, steel stem valves.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Blake, Kansas City on Friday, June 30, 2017 - 09:18 am:

Thanks to all for taking the time to respond.

It did occur to me (after I made the posting) that my question is pretty much moot, as in "who cares, or what difference does it make?", since you should never use or reuse 2 piece valves.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Friday, June 30, 2017 - 12:26 pm:

Not a moot question at all, as folks will look at their valves and think, "AH! These look good, leave well enough alone" when the response should be, "Ah, these look good, replacement should be easy." And this thread tells why.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roar Sand on Friday, June 30, 2017 - 03:52 pm:

The two piece Ford valve design is not a good way to build a valve; especially an exhaust valve. The hot gases impinge on the underhead/stem right where the two pieces are joined, and this is typically the hottest part of the valve, so a failure here is likely.
The other failure mode could be thermal fatigue at the OD of the valve head. This happens when a hot valve ends up closed (in contact with the valve seat in the block (cylinder head for OHV engines). About 80% of the heat in the valve is dissipated through the seat to the colder part, that has water right behind it. The OD of the valve head therefore cools relatively rapidly and shrinks, while the center of the head is still very hot. This results in a hoop stress, and when repeated enough times, a radial crack will form, starting at the OD of the valve head. It is therefore a good idea to let an engine idle and cool down some before shutting it off quickly after working hard. Worst case scenario; climbing a hill and shutting off the engine immediately as you pull over and stop at the scenic look out.
FWIW
Roar


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Saturday, July 01, 2017 - 04:52 pm:

Roar

Good idea on over heating.

And Ford did change to all-steel valve for the T May 31, 1927.

Part # 3052B2 All Steel valve, (Factory No. 424D)

Price increase for the steel valve was $.25 each, the older 2-pieces still available as #3052 (Fac. No. 424B) @ $.15 each!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Saturday, July 01, 2017 - 05:07 pm:

Gary,

Not sure if it's been indicated already above, (no time to read it all), but to my recollection there are 3 failure modes I know of.

1. As you show.
2. Stem comes out of the valve head.
3. Stem breaks off below the head.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eckensviller - Thunder Bay, ON on Saturday, July 01, 2017 - 07:05 pm:

Why would they switch to an all steel valve so late in production? Surely they knew they were just a couple months away from shutting the whole line down, no?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Blake, Kansas City on Sunday, July 02, 2017 - 06:28 pm:

Tim

I mentioned in my opening of this post that I worked for Ford. I was employed by the parts and service division and in the position I had in the plant I could sometimes become an advocate for engineering changes based on the real world performance of vehicles. Sometimes engineering would agree to part revisions for the production and the service parts, in other cases they would agree to changes to service parts only. Considering that Ford continued to produce T engines up until the start of WWII making that change would make sense for production and service parts despite the imminent end of the production of complete cars. I'm sure Ford had been aware of the propensity of those valves to fail, in one of the 3 failure modes discussed above for some time. The real question is what took so long?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Sunday, July 02, 2017 - 06:42 pm:

Gary

in answer to your question, I would surmise that the answer is "the Lincoln Highway" and other paving and road improvements that was taking place at the time. I would wager that later "T"s were seeing a whole lot more miles and much higher speeds as roads improved, improved roads became more common, and speeds and running duration increased along the way.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Sunday, July 02, 2017 - 08:40 pm:

An ironic thing is, that with all the years, miles, and model Ts I have been around? The worst valve failure I ever saw wasn't a two-piece valve, and wasn't even a model T.
My dad had a Chevy pickup with an extremely low geared rear end, and a small block V8. At highway speeds, that poor thing wound up so high, that over the 25 years he drove that thing, he blew up three engines.
The worst one. He was going up a long steep hill, knowing him, probably about 70 mph. A valve stem broke and dropped the head of the valve into the cylinder. Pieces found their way out through the intake manifold into the adjacent cylinder. The valve head punched a hole into the water jacket in the head, broke the piston, bent the rod, and put three cracks the full length of the cylinder. The adjacent cylinder was also cracked, rod bent, piston broken. The crankshaft sustained visible damage from the bent rods, and two cam lobes were visibly damaged by pieces jamming their way between the rising valves and the head above. At least three push rods were bent.

The block, one head, and a fair number of moving parts were basically destroyed.
So, even replacing these old two-piece bi-metal valves does not guarantee no failure. One-piece valves can and do break. I headed off a likely failure on one of my model T engines when I was freshening it up and discovered a flaw in the stem that likely would have eventually failed. And it was an otherwise nice old one-piece valve.
All that said. Changing two-piece valves I put right behind replacing Babbitt thrust washers as a model T MUST do. Such a simple job, and can save you so much trouble and damage.
The silly thing is, that often, when a valve loses its head in a model T engine? Little or no damage is done. I have known several people that got lucky that way. Then again, I have seen model T engines destroyed by losing a valve head. One knocked the center main bearing web right out of the block, and bent the crankshaft.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Vern (Vieux Carre) on Sunday, July 02, 2017 - 09:16 pm:

Gary,
Thirty years ago I removed a spark plug only to find the side ground electrode missing, replaced the plug and went on with life. A year later when I pulled the head, I found a valve with a smaller piece missing than the one you show but looking more like a burned hole than broken. To this day I don't know which (spark plug or valve) failed and caused the problem.
Vern


Top of pagePrevious messageNext messageBottom of page Link to this message  By Burger in Spokane on Sunday, July 02, 2017 - 09:46 pm:

On my maiden voyage, after pulling the old dog out of winter hibernation,
winter before last, I had a sudden loss of power about 2 miles out. The
beast could not manage to push itself along in high, and I limped it home
standing on the low pedal. A little poking around showed an outward chuffing
of gas from the carb, and it became apparent I have compression pounding
backwards out the intake. Time to pull the head. Someone suggested I check
compression before I did anything, and upon pulling No.3 plug, found it to have
a peculiarly smashed finger. No sense in even checking compression at the
point.

Pulled the head, and guess what ? No.3 exhaust valve was nothing but a shaft.
And no head to be found anywhere ! No damage to the piston, but no valve
head anywhere. I presume it now hides in my muffler and provides one more
operational rattle.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Blake, Kansas City on Sunday, July 02, 2017 - 11:18 pm:

Burger

That valve head no doubt fragmented, so you probably have several pieces in the muffler. Model T's have lots of room at TDC in the combustion chamber so I'm not too surprised a broken 2 piece often leaves little to no damage.


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