exhaust valve failure analysis

[rebelrouser]

I have never quite seen failures like this, maybe you guys with more experience have. These are exhaust valves, mopar 440 with Edelbrock Victor JR. heads. 11/32 stainless steel valves. Spring pressure is 265 at seat and 600lbs open. Mechanical roller cam, first valve is 710 lift, second one is 740 lift, same spring pressures, but new springs for the extra lift of the second cam. Springs do not coil bind. First picture is a valve purchased from Edelbrock with around 600 runs, It has three hair line cracks coming from the center of the valve, also seen this on a Indy 440-2 head with same size valves, both heads take the same size. Seats look good as well. Had the first version on the dyno, had 1,300 average exhaust temps, engine made 725 HP, never ran either versions over 7,000 rpm. Have 3/8 manton pushrods.

Second two pictures are from same engine with Manely standard race valves, replaced on the freshen, engine expired with two passes on it. On the cylinder that lost a rod it bent the exhaust valve, this valve came from another cylinder with no damage, Valve was in the head and when I removed the springs it came out in two pieces. I could see no marks on the piston or valve where anything hit. The stem broke right below the end of the valve guide. I am repairing this engine, and have trashed all the valves and purchased Manely severe duty valves to replace them with.

Just want some advice if I am missing something, so I can keep it together.

[JoePorting]

My first thought is to blame the cam. Maybe it wasn't ground right. How do the pushrods look? Look for shinny spots on the pushrods where they could be binding on the head. Look for anything else that looks strange from the rocker arms to the retainers/locks. When you have everything together, spend extra time cycling the valve train by hand (with no sparkplugs) to see if you see anything strange.

[BillK]

What is the dark area right around the point where it broke ? Almost looks like corrosion ? Maybe heat ?

[mag2555]

Enough rust pitting combinded with enough load/ stress can start cracks .
This is why L19 grade rod bolts should not be assembled with bare hands or be exposed to moisture.

[mag2555]

Has the Exh seat moved in the head?

Heat may also have been a factor in where that valve broke.

[Rick!]

If the pic was straight on at the fracture, one could get a better story on how it broke. It appears that there are beach beach marks originating on the RH side of the stem and it went a while before it broke. The clue is the fracture origin in this case.

[rebelrouser]

Has the Exh seat moved in the head?

Heat may also have been a factor in where that valve broke.

I just touched up the seats and they came out good. It must have been something to do with the engine failure, but I can not figure out what caused it.

[rebelrouser]

My first thought is to blame the cam. Maybe it wasn't ground right. How do the pushrods look? Look for shinny spots on the pushrods where they could be binding on the head. Look for anything else that looks strange from the rocker arms to the retainers/locks. When you have everything together, spend extra time cycling the valve train by hand (with no sparkplugs) to see if you see anything strange.

When I put in this camshaft it went from .710 to .740 lift, and the pushrods did have a small shiny spot on them where they touched the heads. I have clearanced this issue. All the pushrods were straight, chucked them in the lathe. I rolled it over with weak springs, and even before I added clearance in the head for the pushrods it spun freely.

[vwchuck]

I would bet that your valve seat moved in the head and you had very tight clearances in the valve guide. It appears to have broken off at the end of the valve guide due to side loading. Probably had an inclusion in the stem and the side loading exacerbated it.