Broken Valve Spring

[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.

[767Jockey]

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.

[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.

[patrickt]

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

[DanEC]

He’s correct - just like a hydraulic brake line. 100 psi is 100 psi. The issue might be when it’s multiplied by the cross sectional area of the bore in square inches as cycleguy55 said.

[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?

[splenderleith]

Picture of one of the Allen bolts.

[Gaz64]

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]

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?

[Gaz64]

Originally Posted by patrickt

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?

Hmm, I have to ponder over this one for a bit.

[Gaz64]

Originally Posted by splenderleith

Picture of one of the Allen bolts.

I thought you said you had head bolts.

They look like studs, after nuts have been removed.

The heads will not move sideways while studs are fitted. The studs need to be removed if the head won't break free.

The hex plug is a coolant plug. No need to remove it.

[undy]

Originally Posted by eschaider

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


Ed

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

[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.

[splenderleith]

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]

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]

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]

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]

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.

[eschaider]

OP,

What you have here is commonly called a blown engine. By and large you do not want to replace just the broken parts with new good parts, that is a formula for follow on failure.

There is a good chance your engine will look similar to HTM101's when you finally get it taken down. If you have one dead piston when you replace just that one piston you could find it challenging to get it to the same weight as the other seven for balance purposes. The upshot is a new set of oversize pistons, pins and rings, boring the block, individually fitting each new piston to its new cylinder and or course rebalancing of the rotating assembly.

You can frequently that find shrapnel from the cylinder with the broken valve has found it's way to other good cylinders and done damage over there also. This would likely also require other pistons being replaced. Just buy a whole new set and do the job correctly.

When you finally get the head off, if the valve head has been pushed into the port throat damaging the valve seat, while repairable, the short way home could just be replace the old damaged casting with a new one. The exception to this would be a head casting that had significant additional work done on it for example like a nice porting job.

If you have a cracked or gouged cylinder you can certainly bore it and put a sleeve in it. For a high performance engine however, I might begin looking for a replacement block. For FE engines with all the availability issues they currently have, this will certainly become more challenging, especially in the current economic and supply chain impacted climate.

When a valve spring breaks there can be certainly two and sometimes three or more pieces. Your broken spring has many pieces. This could be an indicator that the engine was operated for some time after the initial break because the failure was not apparent to the driver. If that is the case then there is the possibility for broken spring pieces to have found their way into the oil system and done additional damage elsewhere in the engine.

Bottom line this is an R&R for the engine with a complete rebuild not just a cylinder head repair.


Ed