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Owner of a broken cart
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421 Posts
Discussion Starter · #1 ·
Found this engine on FB market place.
(from the ad)
Lunati Cam: 261/267 with 112 separation part# 10120701.
Block casting: 14010207.
Head casting: 10239906:
1996 350ci, Vortec 5700, L31,
64cc chambers, 170cc intake ports, 1.94/1.50-inch valves
Came out of chevy square body. Has knock but runs.
Going with big block instead.


Picked it up cheap.
I bought it off Person A, who bought the truck from Person B on fb who had the motor built, but said it was knocking. We tried finding the guy, but he has since deleted that ad (since it sold ofcourse). Person A said only ran it long enough to back it off the trailer. Beyond that we are guessing theres only 40min on the motor.?
Anyways, im just trying to guess what went wrong with it. Also, id like to determine the compression ratio also.
Its 0.040+, had Felpro 1094 head gaskets, (piston type in pic). crank#3932442

Pics to follow
 

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Owner of a broken cart
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421 Posts
Discussion Starter · #2 ·
....
 

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Owner of a broken cart
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421 Posts
Discussion Starter · #4 ·
Other than the rear main, i didnt find any bearings that looked to be 'knocking'. I havent pulled the crank yet to look at those upper bearings.
 

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True Hotrodder
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1,668 Posts
i think you can say it has more than 40 minutes on it. It's going to be a connecting rod bearing if it's knocking. Clearance on one of them is wrong so the only way to really know is to mike the rod throws and bearings to see what you have.
 

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3,846 Posts
the knock was probably a Piston trying to seize in the bore.
looks like massive detonation problem.
Pistons are scrap.
Crank might need OK.
 

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I can resuse these pistons? :oops:
What caused all the damage to the skirts?
Was that scoring on the skirts? I thought it was just oil.... i might havr jumped the gun a bit. But if the crank journals check out i would resize rod ends and replace rod bolts. Basically do a basic rebuild and keep the cost down low
 

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Cars, Trucks, Boats, Motorcycl
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7,480 Posts
That's not skirt (lower part of piston) damage, that's 'ring land' damage likely caused by detonation/engine 'knocking', overheating, or some metal got into the cylinder... Too much ignition advance... Vortec heads with fast burn chambers tend to prefer 28 - 34 degrees max advance for max power... not the 36 - 40 degrees of total advance of older 'bathtub chamber' heads...
Dished pistons plus 64cc chamber Vortec heads is 8.5:1 compression ratio... maybe a tad less depending on head gasket thickness... less C.R. if these are 'rebuilder' pistons that sit low in the cylinders... can also increase chance of detonation by ruining 'engine quench' effects... If the 4 x 4 truck had loud exhaust, may not have heard the engine damaging 'pinging' noises...
Thick 'rebuilders gasket set' head gasket may have contributed to detonation:
 

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Not a Vortec block, all L31 blocks are roller crammed, this doesn’t even have complete provisions for a roller cam.

The engine has been run very hard under detonation. You can see that in the piston ring land deformation. And it’s been run very hot, perhaps without sufficient oil, as seen by the skirt wipeout on nearly every piston, which scored the walls.

The block might be recoverable if it isn’t cracked or warped and the bores will clean with not more than .040 over.

Be aware that GM uses the term Vortec across a lot of different engines, so people can call engines “Vortec” while they are not what we hotrodders refer to when we say “Vortec”. When we say “Vortec” we mean the 1996 through perhaps 2002, 350 cum 5.7, L31 engine. These only came with factory roller blocks and the highly desired L31, Vortec cylinder head. Even putting L31 heads on a non L31 block does not build an L31 engine though with earlier blocks (1987 through 1995) that have all the provisions finished or a factory block with the provisions that you finish can make a damn good copy of a real L31, it still isn’t the real McCoy. These in-betweenies of 1987 through 95 are Swirl Port LO5, 350’s that almost always used a flat tappet cam but often had roller provisions at least cast if not finished) And L31 head’s can be put onto even earlier flat tappet blocks which certainly do not make the complete assembled engine an L31 Vortec. Plus there were from 87 on to the end of Gen I engines in passenger cars including Corvette and Camero roller blocks with roller cams, but these are not L31 Vortecs either, probably the most interesting of these to the hotrodder is the L98.

Roller provisions are three cast bosses over the main oil galley in line with the number 2, 3 and 4 cam and crank mains. This mounts the spider that rides on the dog bones that align the roller lifters to their cam lobes. The lifter bore bosses are raised compared to flat tappet blocks and finish machined across their tops. In the timing case there will be two ears each directly across the cam bore from each other in finish form they are drilled and tapped for the cam thrust plate. There most likely not be a provision for a mechanical fuel pump but there are some that do. These blocks can be fitted with flat tappet or roller cams again the roller requires the provisions be finished but you do see roller blocks that are finished with flat tappet cams in them. To run a flat tappet cam in a roller block only requires the cam and f/t lifters, the regular 7.8 inch push rods instead of the roller’s 7.2 inch, and the use of a standard flat tappet timing set. In this case the thrust plate is not used nor the spider or dog bones that are unique to the roller installation. The flat tappet and the roller timing sets do not interchange across the cam types.

This knowledge should armor you up when Gen I SBC hunting.

Bogie
 

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Owner of a broken cart
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421 Posts
Discussion Starter · #13 ·
Thanks for the info. ya, i determined it was an 85' block before i bought it. Wasnt worried about it being a true 'vortec'.

Is there a site/app i can use to calculate compression ratio? I used to have software for such a thing years ago, but its long gone. This had a 0.015 compressed thickness head gasket.

Ive found some replacement pistons. Hopefully i can match the weight of these. I'll gauge the bores for roundness and honeability.

I aint never seen this kinda damage before. o_O :oops:
 

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Cars, Trucks, Boats, Motorcycl
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7,480 Posts
Thanks for the info. ya, i determined it was an 85' block before i bought it. Wasnt worried about it being a true 'vortec'.

Is there a site/app i can use to calculate compression ratio? I used to have software for such a thing years ago, but its long gone. This had a 0.015 compressed thickness head gasket.

Ive found some replacement pistons. Hopefully i can match the weight of these. I'll gauge the bores for roundness and honeability.

I aint never seen this kinda damage before. o_O :oops:
That horse was worked hard and put away wet! LOL !
A search for Summit Compression Calculator will bring this right up:
Compression Calculator
Can you find the Compression Height of the old pistons or Deck Clearance?
Stock piston compression height is 1.560", but low priced 'rebuilder' pistons may be only 1.540" or 1.548"...
Those are for milled down block decks which is often standard done as part of rebuilding process to avoid scraping gasket residue off and/or assure a true flat deck surface... oftentimes the stock C.H. can be specified at the same low price...
Vortec heads are thin wall castings and prone to cracking... especially in an overheated engine...
Some hyper pistons like KBs may have 1.561" or 1.565" compression height to make sure you're getting max HP and good engine quench effects...
 

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The first thing you need to do is to measure the bore and see if it was overbored for the rebuild. Most likely it was. Then you need to decide if there is enough wall thickness left to bore and hone it further. Then look it over carefully for any obvious cracks. I didn't see any pictures of the cylinder walls, so its hard to tell how bad they might be. If you just hone them, you will increase piston to wall clearance. In the picture that shows a side view, is #1 rod in #2 cylinder or am I looking at it wrong?
 

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Owner of a broken cart
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Discussion Starter · #18 ·
The first thing you need to do is to measure the bore and see if it was overbored for the rebuild. Most likely it was. Then you need to decide if there is enough wall thickness left to bore and hone it further. Then look it over carefully for any obvious cracks. I didn't see any pictures of the cylinder walls, so its hard to tell how bad they might be. If you just hone them, you will increase piston to wall clearance. In the picture that shows a side view, is #1 rod in #2 cylinder or am I looking at it wrong?
Its 40 over.
The cylinder walls look great except where the piston damage occured. I will assess first thing.
It had less than 1hr on the build.
Oil was typical dirty but no water in it.
 

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Owner of a broken cart
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421 Posts
Discussion Starter · #20 ·
Less than 1 hour I would expect the oil to look clean and new...
Did you not see the destruction? All that had to go somewhere. The oil was dirty from damage. Not dirty from mileage.
 
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