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#1063432 - 09/04/19 01:16 AM Engine Knock  
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Keithss Offline
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Jackson,mi
Well I have to pull the engine on my 85 SS this week.
I bought a new 383 Stroker engine from the GM dealer in 2014, put it on the road the summer of 2015. About 1,800 miles on it now.
It developed a knocking sound several years ago, sounding like it was near the number 6 or 8 plug. As it warmed up it would go away. The sound got loader over time. It was really loud when cold and will quiete down as it warms up, but never go away. After having a number of people listen to it, and no positive idea what it was, I decided to pull the engine and have it torn down for inspection. My thought is a broken piston, but I will find out in the future.

Engine in the car before I had to remove it
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Engine on the dyno before I installed it in the car in 2015
[Linked Image]

New rear end this spring
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Front suspension
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Car at a car show this summer
[Linked Image]

Keith

#1063435 - 09/04/19 04:34 AM Re: Engine Knock [Re: Keithss]  
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Oil pressure good? Wonder if a rod bolt could've contacting oil pan rail? Let us know what you find,hope it's nothing too costly or serious.


Lance
1985 Monte Carlo SS Street Car
#1063437 - 09/04/19 03:11 PM Re: Engine Knock [Re: Keithss]  
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Keith, take a look at the inside of the valve cover as well. I had those same covers and I had a couple of rockers that would make contact.


85 - ZZ383, 6-speed, 8.5"
70 - Stock, 35k miles
#1063438 - 09/04/19 03:27 PM Re: Engine Knock [Re: Keithss]  
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mmc427ss Offline
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That engine probably has a GM roller cam and lifters. Once had a GM roller lifter that seized internally. Just a thought.
Good luck.
Bob

#1063446 - 09/05/19 02:05 AM Re: Engine Knock [Re: Keithss]  
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BadSS Offline
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Pearl, MS, 39208
Sounds like (without actually hearing it) a classic piston skirt flap noise to me. My guess is there's going to be a skirt that has collapsed on a piston and/or there is excessive wear on a piston or the cylinder wall. Could be any number of things though.


Original owner of 1985 SS black hardtop w/gray interior. Frame-on restoration - 406 sleeper w/ heavily ported FIRST TPI. However the 1.875" headers, 3.5" duals, TH400, Ford 9", notched frame, and 10-point cage w/swing-out bars might tip you off it's not a lil' ole 305 TPI. Other mods: 2" drop, 18" wheels, f/r disk brakes, and custom stereo system.
#1063449 - 09/05/19 04:03 AM Re: Engine Knock [Re: Keithss]  
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mmc427ss Offline
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The 4.3 in my 275K Astro has severe piston slap when cold. My own fault, should have replace the poppet injector setup way before I did, washed out one of the bores. When below 50 degrees the engine has to warm for several minutes before it dissipates. On a 75 degree day you really can't notice it at startup. Once the engine starts to get hot absolutely no noise, slap, engine runs great for it's age.

Cracked or broken skirt, could be. Piston slap in his engine not likely if it persists after pistons are hot.

At 1800 miles you hope it's something simple, not a shortblock teardown.
Bob

#1063482 - 09/07/19 12:35 AM Re: Engine Knock [Re: Keithss]  
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Keithss Offline
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Jackson,mi
This is what I know at this time.
Engine is torn down.
Remember there is only about 1,800 miles on the GM crate engine.
The crank is WAY out of balance, the rod bearing are showing ware.
The crank has 5, .978 holes drilled the the forward end an 3 in the rear end .
The pistons are too sloppy in the bore, calling for .002 have .005.
A 383 should have a bore of 4.030, my bore is 4.005. Rods should be 3,75 mine or 3.,800.
Going to rebalance the whole crank with damper , balance the flex plate to the engine.
Replace the piston with .020 over and hone the cylinders to match.
Not that this has any thing to do with the problem, but having a new valve seat profile machined while it is down, better flow.
This is not what I was expecting when I bought a crate engine.
Money down the tube, what's new.
Keith

#1063485 - 09/07/19 04:47 AM Re: Engine Knock [Re: Keithss]  
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Man Keith, I hate to hear that. but you have a good plan and platform to build on. Those 383 crate engines get to 383 cid (actually only 382) by using a standard 4" bore and slightly longer stroke of 3.8" as you indicated. The 3.8" stroke also allows them to use the typical "383" pistons used for a 3.75" stroke (1.425" compression height) to put the deck height at "0" with the typical 9.025" tall deck (3.8/2 = 1.9+5.7+1.425 = 9.025"). Typical 3.75" 383 with 5.7" rods and 1.425" compression height pistons will put the piston .025" down in the hole. Using the 3.8" is not a bad set up - keeps you from having to deck the block and can adjust your desired quench with the head gasket thickness.

With you going .020" over you'll end up with a 6.3 or 386 cubes. If you think you' might spray it the 4032 alloy are good for a small shot and the 2618 alloy pistons will handle a bigger shot. Biggest issue with the 2618 pistons is they do require a bit more piston to wall clearance (more noise at start up) than the 4032 and the 4032 needs a little more than hyper-u-tanked-it pistons.


Original owner of 1985 SS black hardtop w/gray interior. Frame-on restoration - 406 sleeper w/ heavily ported FIRST TPI. However the 1.875" headers, 3.5" duals, TH400, Ford 9", notched frame, and 10-point cage w/swing-out bars might tip you off it's not a lil' ole 305 TPI. Other mods: 2" drop, 18" wheels, f/r disk brakes, and custom stereo system.
#1063486 - 09/07/19 12:42 PM Re: Engine Knock [Re: Keithss]  
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My crate 383 is the same way, 4.0"bore, 3.8" stroke. I put 15,000 hard miles on mine before it developed low oil pressure from rod bearing wear. We reused the whole bottom end, just decked the block and a quick hone on the cylinders with new rings and bearings. Its had another 5,000 hard miles on it since with no issues.

Good luck with rebuild. Try not to make it harder than it should be though, that's a good base in there.


Lance
1985 Monte Carlo SS Street Car
#1063487 - 09/07/19 07:10 PM Re: Engine Knock [Re: Keithss]  
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mmc427ss Offline
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When we built the 350 for Tom's 67 Camaro 14 years ago a ZZ4 shortblock was bought. Spend a good bit of money fixing it. Crank was out by 10 grams, 3 rods needed resized, and we decked the block to get close to zero deck. Out of the crate engines are just that, mass produced, "can't see it from my house".

Later after he bent a few valves on the AFRs because of human error we had it back to the machine shop again, honed, check the rods and pistons and decked again to get that zero deck number.

Bob

#1063530 - 09/13/19 11:50 AM Re: Engine Knock [Re: Keithss]  
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Keithss Offline
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Jackson,mi
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The heads are done with a new valve angle job.
Now we are just waiting on the new pistons to arrive.
Once they are here, the crank will be balanced, hopefully internal balance.
Bore cylinders and re-assemble.
Then off to the dyno for testing and tuning.
Keith

#1063576 - 09/19/19 05:56 AM Re: Engine Knock [Re: Keithss]  
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mmc427ss Offline
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Good luck on the dyno, should make more power than the first time.

So piston slap was the culprit? No broken piston, ring land, wristpin, valve train problem? Rod knock?
Bob

#1063577 - 09/19/19 02:42 PM Re: Engine Knock [Re: Keithss]  
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I'm betting it was a rod bolt hitting the pan rail just slightly...been there, done that...


Lance
1985 Monte Carlo SS Street Car
#1063656 - 09/28/19 08:45 PM Re: Engine Knock [Re: Keithss]  
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Keithss Offline
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Jackson,mi
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I should be getting my engine back this coming week.
When I checked last Friday, the bottom was assembled the cam and timing chain were installed.
Needed Heads, lifters. adjust push rod and intake manifold.
As soon as I get in back, it is off to the dyno again.
Keith


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