Broken Valve Spring

Gaz64 · #1 (**permalink**) 10-12-2021, 06:28 PM

Quote:

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 · #2 (**permalink**) 10-12-2021, 08:34 PM

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 · #3 (**permalink**) 10-12-2021, 09:02 PM

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 · #4 (**permalink**) 10-13-2021, 10:25 AM

Quote:

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 · #5 (**permalink**) 10-14-2021, 06:55 AM

Quote:

Originally Posted by eschaider

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

Ed

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

HTM101 · #6 (**permalink**) 10-14-2021, 07:22 AM

The damage can sometimes be extensive. In 2008, #2 intake valve in my 427 dropped because both springs had broken. The piston split the cylinder wall.

When the failure occurred, and before I dismantled the engine, I knew things were bad. We were stopped on the side of the road with antifreeze running out of both side pipes.

splenderleith · #7 (**permalink**) 10-14-2021, 07:34 AM

I was unsuccessful in removing the head last night. I believe the air from the compression is plenty to break the seal, but the intake side seems to have a slightly weaker bond, which leads to a gap on the intake side. It seems that the air is then able to escape before it breaks the exhaust side loose.

What I think I may try this evening is to hook up the compressed air and pressurize the first cylinder to see if I can get enough space to get some plastic shims in. I believe if I can break the head gasket on the exhaust side free, I can probably pull it off.

If that fails, I will probably have to find a way to remove the studs. I think that will involve some thin jam nuts, with the same thread as the studs.

I will report back after I try option 1.

eschaider · #8 (**permalink**) 10-14-2021, 08:05 AM

Quote:

Originally Posted by HTM101

The damage can sometimes be extensive. In 2008, #2 intake valve in my 427 dropped because both springs had broken. The piston split the cylinder wall.

When the failure occurred, and before I dismantled the engine, I knew things were bad. We were stopped on the side of the road with antifreeze running out of both side pipes.

Very impressive job there HTM101!

Ed

HighPlainsDrifter · #9 (**permalink**) 10-14-2021, 09:31 AM

The engine needs to be pulled and at least one piston replaced if it has wrecked the cylinder wall a sleeve can be installed. the connecting rod needs to be checked as it may be bent also.
Good Luck.

cycleguy55 · #10 (**permalink**) 10-13-2021, 01:02 PM

Quote:

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 · #11 (**permalink**) 10-13-2021, 03:30 PM

Quote:

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 · #12 (**permalink**) 10-13-2021, 03:45 PM

Quote:

Originally Posted by ZOERA-SC7XX

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

Make sure the parking brake is firmly set, 100PSI is also enough to rotate the engine in gear and move the car.

767Jockey · #13 (**permalink**) 10-13-2021, 03:43 PM

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

Gaz64 · #14 (**permalink**) 10-13-2021, 05:25 PM

Quote:

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.

patrickt · #15 (**permalink**) 10-13-2021, 05:36 PM

Quote:

Originally Posted by Gaz64

Bore size is irrelevant.

Uhhh, are you sure about that? Lift force (for blowing that head up through the ceiling) is found by multiplying the pressure times the area. That's why a hovercraft can get off the ground by using only 7 lbs. of pressure.

Of course, you should not just take my word for it. See: https://www.discoverhover.org/infoin...ors/guide4.htm

Gaz64 · #16 (**permalink**) 10-13-2021, 06:00 PM

No, I don't agree.

Let's assume 5 square inches.

A typical compression test might yield 180 psi, about 12 x 1 atmosphere (14.7psi). Compression ratio and inlet valve closing point are the determining factors.

And so do we get 5 times our typical compression pressure?

patrickt · #17 (**permalink**) 10-13-2021, 06:11 PM

The page I referenced gives a wonderful example, including the math, but an easy way to visualize the difference is to think of a thimble full of air at x pressure and imagine how easy it would be to hold your thumb over it. Now take the same pressure and have it inside a barrel. Do you think the strength necessary to hold the lid of the barrel down is the same as the thimble even though the pressure is the same?

cycleguy55 · #18 (**permalink**) 10-14-2021, 12:07 PM

Quote:

Originally Posted by Gaz64

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

Bore size matters. 100 PSI (Pounds per Square Inch) has a greater overall force when applied to a greater area. It would be 200 lbs force when applied to 2 square inches, but 500 lbs force when applied to 5 square inches.

That's also why a narrow bicycle tire (e.g. 700 x 25c) needs more pressure (100-125 PSI) to support a given rider weight than does a wider tire (e.g. 700 x 38c) - which might only need 60-80 PSI.

patrickt · #19 (**permalink**) 10-14-2021, 12:10 PM

Quote:

Originally Posted by cycleguy55

Bore size matters. 100 PSI (Pounds per Square Inch) has a greater overall force ...

I think Gaz gave up when I hit him with my thimble and barrel example.

splenderleith · #20 (**permalink**) 10-13-2021, 05:47 PM

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?