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Old 03-03-2010, 11:12 AM
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First time crankshaft replacment

Hello,


My name is Terry. I have a 78 Corvette I am restoring. I accidentally put a floor jack on my harmonic balancer for just a stroke and bent my crankshaft on my 78 Vette. I know WAY stupid thing to do. I found out as soon as I started up the engine and heard a funny sound. I wonder if you might be able to help me to determine what replacement crankshaft to get to put in my 78 Corvette. It's an L82 350. I looked in online catalogs and found listings with the specs for a 350 crank described in stroke distance like 3.480 in. or 3.750 Stroke, for a Chevy 350.
My question is this; whats the difference between a 3.480 in. and a 3.750 Stroke? (Piston travel?) And what are my options and where can I find which crankshaft will fit?

Terry

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Old 03-03-2010, 11:20 AM
richard stewart 3rd's Avatar
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Hi,
The 3.480 is the stock stroke, the 3.750 (400ci crank/stroke) is for stroking the 350ci to 383ci.
Rich
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Old 03-03-2010, 11:47 AM
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Hello Terry, for improving yours and other's education a bit, I'll expand on this subject. Small Block Chevy motors were built with 3 different crankshaft journal sizes through their production run. Refer to the following (which I copied from the Mortec site). From 1955 up through 1967, the Gen I small journal sizes were used. 1968-up small blocks up through the 350 size motor used the medium journals. When the 400 small block was introduced, it used the large journal size for its entire production run. Your crankshaft would be the medium journal size, with a stroke of 3.48".

These crankshafts can be had in either cast or forged configuration. Cast is cheaper to buy and will perform admirably in a street/strip type motor where the motor is run at limited rpm's. Forged is more money and generally used in a dedicated competition-type motor, although there are fellows who build street motors who insist on using a forged crank.

The reciprocating assembly (crankshaft, rods and pistons) in your motor is balanced internally. There are other small block Chevy motors, like the 400, which are balanced externally with the use of eccentric weights on the harmonic damper/balancer and the automatic transmission flexplate/standard transmission flywheel. Also, your cylinder block uses a 2-piece type rear main bearing seal. Later small blocks used a 1-piece rear seal arrangement to help prevent oil leaks at the rear of the motor.

Here's an example of a replacement crankshaft manufactured by Scat that would work well for you.....
http://www.summitracing.com/parts/SCA-910442/

Gen.I, "Small Journal"
265...Mains-2.30"-Rods-2.00"
283...Mains-2.30"-Rods-2.00"
302...Mains-2.30"-Rods-2.00"
327...Mains-2.30"-Rods-2.00"

Gen.I, "Medium Journal", includes "Vortec" 305 and 350 thru '98
262...Mains-2.45"-Rods-2.10"
267...Mains-2.45"-Rods-2.10"
302...Mains-2.45"-Rods-2.10"
305...Mains-2.45"-Rods-2.10"
307...Mains-2.45"-Rods-2.10"
327...Mains-2.45"-Rods-2.10"
350...Mains-2.45"-Rods-2.10"

Gen.I, "Large Journal"
400...Mains-2.65"-rods-2.10"
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Old 03-03-2010, 02:19 PM
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Thanks Guys!!

Thanks for the quick response. Man that was fast. So if I wanted to change my 350 to a 383 all I need to do is change the crankshaft? Not that I plan on it, but what about the rest of the internals? And the heads? Is there a kit that includes pistons, rods the crankshaft and bearings and higher compression heads?
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Old 03-03-2010, 02:37 PM
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Hi,
There are stroker kits, crank, rods, pistons, block needs to be clearance checked for the crank & ground accordantly, the cam
clearance needs to be checked also, & bored to make it 383ci
Heads you'll want a set that will complement the rest of the build along with the cam, if you click on the search button at the top of the page & type 383 stroker you'll get a lot of info on this subject.
Rich
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Old 03-03-2010, 03:32 PM
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Thanks Rich, for general educational purpose I'll do that. I mainly just wanted to be sure and get the right crankshaft to replace the stock 3.480 that I messed up. And while I'm at it replace the piston rod bearings and main bearings and engine mounts while I have the engine out of the car. I will also clean up and restore the engine compartment. Do you know if it's neccessary to remove the radiator for clearance to remove the engine?



Quote:
Originally Posted by richard stewart 3rd
Hi,
There are stroker kits, crank, rods, pistons, block needs to be clearance checked for the crank & ground accordantly, the cam
clearance needs to be checked also, & bored to make it 383ci
Heads you'll want a set that will complement the rest of the build along with the cam, if you click on the search button at the top of the page & type 383 stroker you'll get a lot of info on this subject.
Rich
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Old 03-03-2010, 03:55 PM
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Quote:
Originally Posted by torg57
Do you know if it's neccessary to remove the radiator for clearance to remove the engine?
You could probably get it out with the radiator in place, but you'll have to remove the shroud, fan and fan clutch anyway. It's only a matter of 4 more bolts to take the radiator out. What if the motor swings on the cable/chain and the water pump pulley takes a chunk out of the radiator while you're pulling the motor???? Ask me why I ask!!!
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Old 03-03-2010, 03:57 PM
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Hi,
The last corvette I changed engines in was a 67, SB out BB in the other one was a 68 BB out & it was wrecked, the one I have now is an 88, I removed the rad on the 67,& the 68, the one I have now looks as if it needs to be removed, but for your's I don't know, I would probably remove it & have it flow tested just because of Murphy's law.
Good luck,
Rich
PS You might try at corvette forms
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Old 03-03-2010, 04:34 PM
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What if the motor swings on the cable/chain and the water pump pulley takes a chunk out of the radiator while you're pulling the motor???? Ask me why I ask!!! [/QUOTE]


You are so right, why did I even ask. This is the first time I pull an engine. The most I've ever done was re-ring the pistons last year with the engine in the car. I will wind up removing everything I can get to while the engine is out and refurbishing or replacing it anyway.
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Old 03-03-2010, 04:39 PM
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the one I have now is an 88,


Thanks Rich. What a coincidence, I have an 88 too. A burgundy with the 4+3 manual shift in it.

Terry
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Old 03-03-2010, 04:57 PM
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Hi,
I'm looking to have mine painted, my sister
picked a color some kind of green, I've asked other
people how it (color) looked, told it's very nice I personally
have no idea I'm color blind, also mine is for the lazy people
700R4.
Rich
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Old 03-06-2010, 02:28 PM
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engine separation

Quote:
Originally Posted by techinspector1
You could probably get it out with the radiator in place, but you'll have to remove the shroud, fan and fan clutch anyway. It's only a matter of 4 more bolts to take the radiator out. What if the motor swings on the cable/chain and the water pump pulley takes a chunk out of the radiator while you're pulling the motor???? Ask me why I ask!!!

I have everything removed from the front of my engine and ready for extraction. I have an engine hoist and rigging and an engine stand. Can you direct me to instructions to show me how to remove the engine but not the transmission?
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Old 03-06-2010, 05:05 PM
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Quote:
Originally Posted by torg57
I have everything removed from the front of my engine and ready for extraction. I have an engine hoist and rigging and an engine stand. Can you direct me to instructions to show me how to remove the engine but not the transmission?
This response come late- but are you absolutely SURE the crankshaft is actually bent?

I can see how the damper could have been damaged- but to bend the crank by a one-hit w/the floor jack?

I'm doubting the hell out of it, personally. One stroke of a floor jack (unless you use a NASCAR-type jack) would barely compress the rubber of the damper- let alone well and truly bend the crank snout.
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Old 03-06-2010, 07:34 PM
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Quote:
Originally Posted by cobalt327
This response come late- but are you absolutely SURE the crankshaft is actually bent?

I can see how the damper could have been damaged- but to bend the crank by a one-hit w/the floor jack?

I'm doubting the hell out of it, personally. One stroke of a floor jack (unless you use a NASCAR-type jack) would barely compress the rubber of the damper- let alone well and truly bend the crank snout.

X2.......I was just wondering??!! Cranks bend THAT ez?!
6sally6
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Old 03-06-2010, 07:41 PM
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Quote:
Originally Posted by 6sally6
X2.......I was just wondering??!! Cranks bend THAT ez?!
6sally6
Darned sure don't in MY experience.

Shameful as I am to admit this, but I've jacked an entire SBC engine up off it's mounts- by the damper- long enough to wedge wood blocks to hold it up to remove the pan (pan was cast Al- I didn't want to crack IT lol).

Much younger, much more "hurried" than I am nowadays, but I did do it, just the same. :
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