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Diagnosing damage

General engine tech -- Drag Racing to Circle Track

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Racing68
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Diagnosing damage

Post by Racing68 » Wed Mar 18, 2020 11:54 am

This is a 590 BB Chevy pull truck engine that just came in for freshening. I've watched some of his pulls and the truck bounces down the track loading and unloading and bouncing off the rev limiter at 8400 on almost every pull may have something to do with this or tuneup is off i don't know for sure but any thoughts would be helpful.
Pistons Left to Right 7, 1, 4 Checked rings and show no signs of butting.
download/file.php?mode=view&id=23989

Pistons Left to Right 7, 1, 4
download/file.php?mode=view&id=23988

Rest of pistons look the same as #4

Main Bearings Dart Big M, ARP main studs, Callies Magnum Crank new last year, Fresh line hone last year
download/file.php?mode=view&id=23990

Rod bearings #7 on top #1 bottom
download/file.php?mode=view&id=23991

Front cam bearing the rest look like new, was not tight on assembly, Rollmaster timing chain was not overly tight at assembly, chain is normal tension for 1 season.
download/file.php?mode=view&id=23992
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prairiehotrodder
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Re: Diagnosing damage

Post by prairiehotrodder » Wed Mar 18, 2020 12:10 pm

Is it on alcohol ?

I have the pistons out of a 540 BBC with 12.5 CR on my shelf that had one season of running excessively rich / or maybe not warmed up enough on alcohol that are scuffed like that. I think alcohol motors want higher CR than the 12.5 this engine had but nobody will tell me for sure.

If your motor was really rich on alcohol could be that it had alcohol in the oil as well contributing to the black bearings.

I'm not an expert but thats my 2 cents

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Racing68
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Re: Diagnosing damage

Post by Racing68 » Wed Mar 18, 2020 12:42 pm

It's 15.5 cr on VP c-15 gas. The bearings are coated. There is a pan heater for the oil and it the engine is warmed to 150 before the start of the pull.

MELWAY
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Re: Diagnosing damage

Post by MELWAY » Wed Mar 18, 2020 4:29 pm

Does it spend any time on the rev limiter?

Does crank have centre cW?

What ignition system does it run?

Those main bearing look to has some distress from crank flex
I have seen similar main bearing on blown alky engines that are rich and or have weak Ignition system
3370lb Sedan 9.89@136MPH 358chevN/A

Racing68
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Re: Diagnosing damage

Post by Racing68 » Wed Mar 18, 2020 4:48 pm

From the pulls i watched he was on the rev limiter several times in each pull anywhere from a quick touch to a couple of seconds duration. Yes center counter weight callies magnum. Runs a MSD 7 AL3 with HVC 2 coil. This is a single carb, NA, with 15.5 cr on gas making about 1050 hp, limiter is set at 8400.

Dutchman
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Re: Diagnosing damage

Post by Dutchman » Wed Mar 18, 2020 8:42 pm

The mains are definitely showing crank flex regardless,un loading and staying in it would be my guess.
Other than chassis tuning and driver improvements to keep it in power without unloading.not much will help that crank.
What oil system and clearance.
Top alcohol motors will rattle if you shake them dry.

Dutchman
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Re: Diagnosing damage

Post by Dutchman » Wed Mar 18, 2020 8:47 pm

Dutchman wrote:
Wed Mar 18, 2020 8:42 pm
The mains are definitely showing crank flex regardless,un loading and staying in it would be my guess.
Other than chassis tuning and driver improvements to keep it in power without unloading.not much will help that crank.
What oil system and clearance.
Top alcohol motors will rattle if you shake them dry.
The no 1 cam bearing may be caused by the crank flexing pulling on the chain.

Racing68
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Re: Diagnosing damage

Post by Racing68 » Wed Mar 18, 2020 10:30 pm

Wet sump, Moroso 20485 double kickout pan, melling anti-cavitation pump. .0032 mains .0028 rods. It holds steady oil pressure 80-82 psi on the dyno all the way to redline during a 200 rpm/sec pull about 14-15 sec total time for the pull. I did one pull like that to see if it had any pressure loss over what would be a run down the track, less than 2 psi fluctuation over entire pull. On the cam bearing that pic is of the top, the whole bearing looks like that, i guess it could be whipping the cam with loading and unloading of the chain. Not sure what the deal is on the pistons all but 1 and 7 look perfect.

Racer71
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Re: Diagnosing damage

Post by Racer71 » Wed Mar 18, 2020 10:45 pm

Could the crank flex be what’s causing the piston scuffs? Since its opposite ends of same bank maybe it’s rocking the pistons?

dannobee
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Re: Diagnosing damage

Post by dannobee » Thu Mar 19, 2020 12:52 am

You mentioned dyno pulls. Something caused the piston scuffing and overheating. Were the egt's close? Did plug readings reveal anything? What oil is he running? What's the cooling system like? Does it overheat on or after a pull? Does the backside of the piston have burnt oil residue?

Racing68
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Re: Diagnosing damage

Post by Racing68 » Thu Mar 19, 2020 9:54 am

No egt's just a pair of wide bands 12.5-12.8, plugs looked good no speckles and fuel ring looked good. Running Brad Penn 20-50 this past season and using a pan heater. Mezzere elecrtic pump and small radiator with fan starts pull at about 150-160 and ends around 195-200. No burnt oil on any pistons not even a discoloration on the #7.

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Re: Diagnosing damage

Post by dannobee » Thu Mar 19, 2020 11:26 am

How were the rings gaps? Did any of the ends show evidence of touching? Scuffing will usually be either overheating or ring gaps butting and wiping all of the oil off of the bore, usually right before it rips the top of the piston off. And it could have been the second ring, not just the top.

What about cooling system and head gaskets? Plenty of coolant flow around #7 cylinder?

Piston to wall clearance was within spec when assembled? Was it different when you performed the autopsy?

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Re: Diagnosing damage

Post by piston guy » Thu Mar 19, 2020 11:30 am

If it's only on the "plug side" , "I" would think fuel wash ( down side of the cylinder) was the problem . IF it is scuffed on both sides of the piston , clearance "went away" for some reason. Not crank flex. Others may have different opinions.

Racing68
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Re: Diagnosing damage

Post by Racing68 » Thu Mar 19, 2020 12:04 pm

Nothing to indicate any butting of the rings top or second. I have not checked the gaskets yet but it's a felpro mls gasket i will check that later today for water port alignment. Clearance was set at spec plus .0012 extra i'll check what it is now also

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