221 cu in 1939 Failed No4 Piston 1

[Phil Gillespie]

Originally Posted by Charlie ny

The post on #40 showing the underside of the failed piston shows a border area around the hole. This border area could indicate a bad pour during the casting process. omho.
Charlie ny

Charlie I noted this also the border area around the hole and had similar thoughts.
When i sent a couple of pics to Egge their comments were the piston was like theirs but had been modified??? These were Egge pistons from Reds Headers. Having all pistons and rods and bearings checked.


What alternatives for pistons for a 3 1/16 plus 80 thou. Any recommendations?
Thanks
Phil

[Phil Gillespie]

Originally Posted by Charlie ny

The post on #40 showing the underside of the failed piston shows a border area around the hole. This border area could indicate a bad pour during the casting process. omho.
Charlie ny

Originally Posted by Bored&Stroked

Here are some pictures that will give you an idea of how a consistent radius dome compares to a multiple radius (pointy) dome.

I made 3D CAD models of both of these variants - such that I can CNC the domes of heads to match pistons. On a recent build, I had to take a brand new set of Edelbrock heads (like the one from this post) and CNC the domes to match the 3-radius piston design that the engines Jahn's 4-ring pistons had - otherwise they would touch in the middle crown area of the Edelbrock heads. Also, I wanted a consistent squish area of .040 above the piston - so a new chamber was needed.

Edelbrock Standard Dome - Matches Ross Pistons:

Attachment 354457

Multiple Radius Dome - Matches a lot of cast pistons:

Attachment 354456

Sketch - Edelbrock Standard Dome - Ross Pistons (based on a .1875 crown height and 3 5/16 pistons):

Attachment 354459

Sketch - Multiple Radius Dome - 3 5/16 cast pistons (4 ring Jahns):

Attachment 354458

Note: On some of the early 4-ring Jahn's pistons, they used the multiple radius dome . . . on the 3-ring versions that a lot of the racers used, they had a consistent radius dome.

Hope this helps you all visualize the differences.

B&S

Yes I can visulise the difference for sure as you really want the profile of piston crown and head profile to match to give consistent clearance between surfaces.
Thank yu for your time to put this together.
Phil NZ

[Mart]

Were they prepared to say in which way they were modified??

Mart.

[JSeery]

I have never dealt with Egge, but there would be no reason for Reds to modify Egge pistons (just added cost if nothing else) and that does not look like heat damage to me. There is a second crack partly through the piston to the side of the hole in the top! Might contact Reds and see what they have to say.

[Brian]

I think the 'modification' refers to what appears to be a chamfer machined around the outer top edge of pistons, possibly to clear a head gasket protruding over edge of cylinder?
Compare with Seth's photo...

[Phil Gillespie]

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Originally Posted by Brian

I think the 'modification' refers to what appears to be a chamfer machined around the outer top edge of pistons, possibly to clear a head gasket protruding over edge of cylinder?
Compare with Seth's photo...

Was not aware this had been done, but would not the answer to have gone to the larger bore sized gasket?
Phil NZ

[flatjack9]

I have seen pistons with that exact same top. They were not in the original box so I don't know their history.

[Phil Gillespie]

Just did some measuring for Con Rods:
Con Rod Bore Less Brg: 2.215. Brg OD: 2.222. Brg ID: 1.958. C/Shaft dia: 1.955.
Wrist Pin dia .744. Wrist Pin bush: .748.
From these measurements this would be a 40 thou over sized brg for bottom end?
All pistons are showing scuffing at L to R locations on pistons. Presume my rods are 21A. See pic. no castle nuts with pins, no self locking nuts??

[Phil Gillespie]

Some more pics for above post. Cant see how these pistons have been modified as per Egge comment.
Phil NZ

[40 Deluxe]

Do you have any photos of piston pieces that ended up in the pan?

[flatheadmurre]

Originally Posted by Phil Gillespie

Was not aware this had been done, but would not the answer to have gone to the larger bore sized gasket?
Phil NZ

When dealing with 21 stud engines there´s no big bore stuff available so that is perhaps why they modified the pistons.

[Lawrie]

That looks like detonation to me,
Lawrie

[Phil Gillespie]

Originally Posted by flatheadmurre

When dealing with 21 stud engines there´s no big bore stuff available so that is perhaps why they modified the pistons.

This is a 24 stud engine and checked out when removed heads and plenty of clearance from observation.
Phil NZ

[Phil Gillespie]

Originally Posted by Lawrie

That looks like detonation to me,
Lawrie

This will occur in just one cylinder like this? A single stromberg 97 with 45 jets and 65 pv should not be leaning out surely. Plus am using 95 octane.
Distributor recently rebuilt and set up as per machine.
Phil NZ

[JSeery]

Originally Posted by Phil Gillespie

This will occur in just one cylinder like this? A single stromberg 97 with 45 jets and 65 pv should not be leaning out surely. Plus am using 95 octane.
Distributor recently rebuilt and set up as per machine.
Phil NZ

Well, if anyone would be familiar with detonation in a flathead, my guess is it would be Lawrie! This should be a more common occurrence in a high performance engine.

Could a couple of mixed up plug wires be the cause, firing that cylinder early?

[Charlie ny]

Casting flaw, casting flaw, casting flaw........I'll bet insiders at EGGE know it too !
Charlie ny

[B-O-B]

Had the heads on my f-500 6 cylinder milled & torqued back on. I was pulling a grade with a load of gravel when there was a puff of white smoke. Yep it burned a hole right thru the top of one of the pistons. The exhaust was pretty loud & I didn't hear it pinging for help. Piston kinda looked like yours with a hole in the top.

[DocJohn]

Whilst the crack in the piston might have started at a small casting flaw, that's not the root cause of the failure. Those cracks are driven by a stress perpendicular to the plane of the crack - so a radial stress in the piston crown in this case. The most likely cause is a severe hot/cold cycle so that the centre of the crown gets very hot then is trying to cool faster than the outer rim and is restrained, setting up a radial tensile stress. The region around the hole has clearly been very hot, looking at the surfce condition.

Cause of the hot/cold cycle? Air leak into the No 4 port somewhere - runs lean and hot especially under load, and repeated quenched by the incoming cool mixture off load?

Of course, it's not helped by a thin crown or internal casting defects, but all the pistons will have those so the question comes down to the origins of the excess stress cycle.

[Phil Gillespie]

Originally Posted by B-O-B

Had the heads on my f-500 6 cylinder milled & torqued back on. I was pulling a grade with a load of gravel when there was a puff of white smoke. Yep it burned a hole right thru the top of one of the pistons. The exhaust was pretty loud & I didn't hear it pinging for help. Piston kinda looked like yours with a hole in the top.

Yes kinda like it happened with me the puff of smoke.
Do you find a cause or just a replacement piston?
Phil NZ

[Phil Gillespie]

Originally Posted by DocJohn

Whilst the crack in the piston might have started at a small casting flaw, that's not the root cause of the failure. Those cracks are driven by a stress perpendicular to the plane of the crack - so a radial stress in the piston crown in this case. The most likely cause is a severe hot/cold cycle so that the centre of the crown gets very hot then is trying to cool faster than the outer rim and is restrained, setting up a radial tensile stress. The region around the hole has clearly been very hot, looking at the surfce condition.

Cause of the hot/cold cycle? Air leak into the No 4 port somewhere - runs lean and hot especially under load, and repeated quenched by the incoming cool mixture off load?

Of course, it's not helped by a thin crown or internal casting defects, but all the pistons will have those so the question comes down to the origins of the excess stress cycle.

Thanks for your insight. The cause of the hot/cold cycle? Could this be a fault perhaps in inlet manifold. Although in saying that it had a good steady idle vaccum of 20 inches.
Phil NZ