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Autopsy findings
https://slantsix.org/forum/viewtopic.php?f=30&t=64498
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Author:  SpaceFrank [ Sun Feb 16, 2020 1:26 pm ]
Post subject:  Re: Autopsy findings

That first picture looks familiar; that's exactly where the '64 block in my Lemons Dart cracked. Not sure exactly what caused it. It may have been frozen a couple years before then, but we first noticed it (about 1" long) at the same race where we blew a head gasket into the water jacket for the first time. After that, the crack grew about an inch a year until we finally stopped throwing Barr's Leak at it and pulled the engine.

DadTruck wrote:
power ported the pistons (that involves drilling small holes from the piston crown
to the top ring groove to put pressure behind the top ring groove).

:shock: I've never heard of this mod before. What's the benefit?

Author:  DadTruck [ Sun Feb 16, 2020 5:25 pm ]
Post subject:  Re: Autopsy findings

the top ring and ring groove on a piston is designed so that gas pressure from the combustion in the cylinder gets trapped in the gap behind the piston ring to force the ring outward and seal against the cylinder wall. Piston porting gets more pressure behind the top ring to increase the sealing potential of the top ring.

I was working with a 140K mile slant that has a ridge worn in the very top of the cylinder that you could feel with a finger. The remaining bore was worn smooth.
The bore as ran was out of specification for size for a standard size piston and out of specification for taper for any size piston. The rings sets used were also the OE 140K rings, so they also likely had tolerance issues.

The piston porting would put additional outward pressure on the top ring to assist it with overcoming the out of tolerance bore.
Modern thin metric piston rings are much better at conforming to the bore and modern piston ring grooves are developed and machined to much closer tolerances so I would not piston port a new engine that has components matched and in specification. But on older designs and certainly and engine with worn pistons and worn bores it is something that may help, for a while anyway.

this article has an accurate description of piston ring sealing and piston porting
https://www.jepistons.com/blog/vertical ... as-porting

Author:  GregCon [ Mon Feb 17, 2020 6:42 am ]
Post subject:  Re: Autopsy findings

Gas porting is generally a race-only trick for two reasons:

1) It wears the ring out faster so it's not a 100K mile setup

2) The gas ports, aka holes, get clogged up with carbon pretty fast

Author:  Rob Simmons [ Mon Feb 17, 2020 7:10 am ]
Post subject:  Re: Autopsy findings

I got a couple sets of pistons from Howard Davis years ago with this done to them. Now I better understand the purpose of all those holes drilled in the ring groove. I’ll have to dig those back out for a look-see...

Author:  MadScientistMatt [ Mon Feb 17, 2020 9:34 am ]
Post subject:  Re: Autopsy findings

GregCon wrote:
I have a 225 I'll give you. Houston is very close to Georgia, so just drive over and I'll even load it for free and give you some cashews.


Thank you for the offer! Is that Houston, TX or a different Houston?

Author:  GregCon [ Mon Feb 17, 2020 10:43 am ]
Post subject:  Re: Autopsy findings

Texas!

Author:  MadScientistMatt [ Tue Feb 18, 2020 6:04 am ]
Post subject:  Re: Autopsy findings

I've confirmed I should be able to make it to the Pigeon Forge event.

Author:  Rob Simmons [ Tue Feb 18, 2020 6:19 am ]
Post subject:  Re: Autopsy findings

Will you be in a vehicle that you can haul a builder motor back with?

Author:  MadScientistMatt [ Tue Feb 18, 2020 6:50 am ]
Post subject:  Re: Autopsy findings

Rob Simmons wrote:
Will you be in a vehicle that you can haul a builder motor back with?


Yes, I went and got a mini-truck when I realized a lot of things on this year's to-do list would be a lot easier with one.

Author:  Rob Simmons [ Tue Feb 18, 2020 11:32 am ]
Post subject:  Re: Autopsy findings

I shot you a PM about the block and crank Gary has. :wink:

Author:  MadScientistMatt [ Mon Feb 24, 2020 6:36 am ]
Post subject:  Re: Autopsy findings

More pictures. The other rod bearings are pitted. May have been water in the oil from my last head gasket failure - or just 200,000 mile wear?

Image

And the main bearing caps. A couple grooves there...

Image

Author:  Charrlie_S [ Mon Feb 24, 2020 6:47 am ]
Post subject:  Re: Autopsy findings

MadScientistMatt wrote:
More pictures. The other rod bearings are pitted. May have been water in the oil from my last head gasket failure - or just 200,000 mile wear?

Image

And the main bearing caps. A couple grooves there...

Image


Hell, just polish them up with some scotch brite, and put her back together. Good for another 200,000 miles. :lol: :lol: :lol:

Author:  volaredon [ Mon Mar 30, 2020 3:35 pm ]
Post subject:  Re: Autopsy findings

MadScientistMatt wrote:
The 225 has developed rod knock on a dyno pull after making around 120 hp to the wheels on 5 psi of boost. So I've pulled the motor, and following Doctor Dodge's book, I've started a teardown. First find... this may be a sign I should be looking for another block to build instead of keeping the bragging rights that it's the original engine.


the last /6 that I rebuilt had that same crack.... was a running pullout, crack was not discovered til it was assembled, installed and ran. as I was debating what to do with it, and had decided to send my other block I had (the one that came out of the car) for machine work to match my new pistons that were in that cracked block, when the car was totaled pretty drastically.

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