Broken Valve Spring

[eschaider]

Originally Posted by Tommy

For my own curiosity and the OP, what is the likely root cause of a bent valve?

Contact with a piston.


Ed

[t walgamuth]

Originally Posted by eschaider

Contact with a piston.


Ed

I would expect it was over revved. With all the rev limiters available today this is less likely but I would still think most common. It could be done by downshifting at too high rpm also.

[eschaider]

Originally Posted by t walgamuth

I would expect it was over revved. With all the rev limiters available today this is less likely but I would still think most common. It could be done by downshifting at too high rpm also.

Best efforts not withstanding, sadly there is always a way to circumvent safeties we attempt to build in. That said, it does not matter how high you overspin the engine or even float a valve. If a piston does not hit the valve, the valve will not bend.


Ed

[Gaz64]

Originally Posted by eschaider

Best efforts not withstanding, sadly there is always a way to circumvent safeties we attempt to build in. That said, it does not matter how high you overspin the engine or even float a valve. If a piston does not hit the valve, the valve will not bend.


Ed

Yes, that is exactly correct.

A valve head has to contact the piston to be bent. This could occur at ANY engine rpm, either from valve float at high rpm, or from valve spring failure, which could happen at the next startup, idling etc.
In the owners case, the valve spring has broken into many pieces, the valve drops to full open, the moving piston smacks the valve head, and keeps smacking it until the valve head snaps off, wedged into the valve seat. 50% of the time the piston could be damaged, especially from large valves.

[splenderleith]

I was able to remove the intake and all 10 of the head bolts. I can definitely see a bent valve from the intake port.

I haven’t figured out how to get the head loose. Any ideas?

[Gaz64]

Refit 2 head bolts, one each end, at about 4 threads in.
Refit the spark plugs for that head, leave the other bank out.
Spin the engine on the starter. Head should break from the headgasket.

Otherwise, a large prybar, waterpipe etc down the intake port, and pull over.

[eschaider]

Originally Posted by splenderleith

I was able to remove the intake and all 10 of the head bolts. I can definitely see a bent valve from the intake port.

I haven’t figured out how to get the head loose. Any ideas?

This picture is exactly what Gary described / predicted in post #15.


Ed

[undy]

Originally Posted by eschaider

This picture is exactly what Gary described / predicted in post #15.


Ed

...or what I said in post #6.

[cycleguy55]

Originally Posted by splenderleith

I was able to remove the intake and all 10 of the head bolts. I can definitely see a bent valve from the intake port.

I haven’t figured out how to get the head loose. Any ideas?

You might try using air. Make sure all the head bolts are loose or removed. Put a fitting in one of the spark plug holes in an end cylinder (not the one with the broken valve) and pressurize it. Area of a 4.36" bore is 4.75 sq inches, so 100 PSI is 475 lbs pressure pushing up on the cylinder head.

2021-10-17 Edit: 460 CID standard bore is 4.36", so (4.36 ÷ 2)² x 3.14159 = 4.7524 x 3.14159 = 14.93 in² x 100 PSI = 1,493 lbs.

My earlier numbers were incorrect.

[ZOERA-SC7XX]

Originally Posted by cycleguy55

You might try using air. Make sure all the head bolts are loose or removed. Put a fitting in one of the spark plug holes in an end cylinder (not the one with the broken valve) and pressurize it. Area of a 4.36" bore is 4.75 sq inches, so 100 PSI is 475 lbs pressure pushing up on the cylinder head.

Sounds like a good plan. However, you should leave at least two head bolts loosely attached. 100 psi is quite a bit of air.

[767Jockey]

That piston is likely going to be ugly. Hopefully your cylinder walls were spared.

[Gaz64]

Originally Posted by cycleguy55

You might try using air. Make sure all the head bolts are loose or removed. Put a fitting in one of the spark plug holes in an end cylinder (not the one with the broken valve) and pressurize it. Area of a 4.36" bore is 4.75 sq inches, so 100 PSI is 475 lbs pressure pushing up on the cylinder head.

Bore size is irrelevant. 100 psi from an air line into the cylinder will still be 100 psi.

[splenderleith]

Thanks for all of the help this far. I am sure I wouldn’t have gotten this far without it. Diagnosis spot-on Gary.

I put the plugs back in, cranked it and saw the head move. With some very light prying pressure, it seems to move a little on the intake side. However, I can’t get much more than that. I am wondering if I might be missing something. I can’t get the exhaust side of the head to budge, even the slightest bit.

Valve covers removed, intake manifold removed, headers removed, rocker arms and push rods removed (rocker arm studs and 6 of the valves still in place), 10 head bolts removed, spark plugs removed.

There are 3 large Allen head screws/plugs in the head, between the valves, which I assume are something to do with the machining process. I haven’t messed with them. Does it seem like I missed some fastening device?

[Gaz64]

Originally Posted by cycleguy55

You might try using air. Make sure all the head bolts are loose or removed. Put a fitting in one of the spark plug holes in an end cylinder (not the one with the broken valve) and pressurize it. Area of a 4.36" bore is 4.75 sq inches, so 100 PSI is 475 lbs pressure pushing up on the cylinder head.

I'll say my interpretation of Brian's statement lead to some confusion.

I read it as 100 psi is 475 psi, as in 100 psi becomes 475 psi, which is impossible while you have a shop line connected to the cylinder.

100 psi would create 475 lbs of force, not pressure.

The theoretical force output of a cylinder is the usable piston area multiplied by the applied air pressure (F = PA). For example, a cylinder with a 11⁄2-in. bore and an extend force of 80 psi generates 141 lb of force (1.767 × 80 = 141).