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Old 12-06-2003, 09:30 PM
bcw bcw is offline
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305/350 crankshaft

I'm building a 350 for my 86 chevy p.u.. I got the engine from a
friend who had replaced the the wore orginal crank but never put
it back together. After inspection I thing the replacement may be
from a 305. The casting #(3932442) match the orginal and two
other cranks I'v compared too.

I found small differences in the counterweights on all four but
all casting # are the same.

I'v searched the old poasts and knowledge base and found only
one thred on the interchangeability of a 305/350 crank and one
reply said there could be a balancing problem.

I'm trying to find the exzact diffrence so I know for sure if the
replacement will work without blancing problems.

Thanks.

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Old 12-06-2003, 09:39 PM
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Ive heard that there is a balancing issue also...but Ive used a 305 crank in a 350 ,& ive also used a 350 crank in a 305 with no problems. maybe I got lucky...I dont know.. my machinist said he has seen it, but its not common
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Old 12-06-2003, 10:19 PM
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cast iron 442 cranks are the same 305 or 350, the only time you get into balance problems is when you try to swap different no. castings and lite weight GM rods and pistons, even then there is no problem on a street cruiser.
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Old 12-06-2003, 10:52 PM
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The thing I saw said on the 305 crank there are 5 machined places on the counterweights that you can lay a straight-edge across & it touches at all 5, whereas on the 350 version, the machining is different, so it won't touch at all 5 places. Haven't had two side-by-side so I can't say for sure. If this is true, the casting numbers for 305 & 350 cranks could be the same, but the part numbers would be different.
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Old 12-07-2003, 05:18 PM
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They are a little different. I`m not sure on balancing or weights.

I threw my 305 crank in the garbage.

When I put in my 350, I had to buy a new flywheel because my old 305 flywheel bolt pattern did not match up to the 350. So would the fly wheel or crank bolt pattern be different? Then we got that all together and I went to put on my starter from my 305 and that did NOT work with my new flywheel! Boy was I pissed.

The 350 came from an early 80`s truck and the 305 was in my 86 Trans Am. Close in years ....both had passenger side dip sticks but thats the differnces I found.

I hope that can help a little.

Good Luck
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Old 12-07-2003, 05:33 PM
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I don't see how your flywheel bolt pattern wouldn't match as ALL v-8 chevys use the same pattern unless you try to go from a onepiece rear seal motor to a two piece crank, but then the blocks are different too. I can see the flywheel o.d. difference,as there are two different sizes.
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Old 12-07-2003, 05:42 PM
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Hey Bob ...I do not remember if the 305 was a 1 piece or not. My 350 is a 2 piece.

If you can figure that out let me know!!

That stock 305 flywheel just did not fit on the 350.
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Old 12-07-2003, 06:01 PM
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t he bolt pattern issue is a 1 piece vs. 2 piece rear main issue, doesnt matter if its 305 or 350...same with the diameter
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Old 12-07-2003, 09:16 PM
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Quote:
t he bolt pattern issue is a 1 piece vs. 2 piece rear main issue, doesn't matter if its 305 or 350...same with the diameter
That's not entirely true. There's more to the story. 305/350 cranks have the same bolt pattern up till 86(with th exception of some late sixties trucks with 327's and some later model marine applications) when the one piece rear seal was used. Since 86, The 350 crank utilized a smaller bolt pattern for use in later model cars with smaller trans tunnels and the need to use the smaller clutch/flywheel package. The 305 however was predominately used in bigger vehicles( I know it doesn't make sense) and these cars had less of a clearance problem so GM continued to use the bigger pattern bolt flange. BOBCRman has it right. Same casting but different catalog numbers. You need to match the flywheel with the bolt flange and you will be okay. You used the pre 86 crank with a 2 piece seal and big bolt pattern. You will need to get a 350 big bolt pattern flywheel and staggered bolt pattern starter motor.
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Old 12-07-2003, 09:23 PM
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Their are two BIG differences between 2-piece and 1-piece rear main seal cranks. The 2 piece crank has a larger hole and is neutral balanced. The 1-piece seal crank has a smaller center hole and is externally balanced.

As far as the 305/350 issue, we have different bobweights made up for each (using stock piston, etc.) There definitely is a difference in balance between the ewo. If there is any question as to which crank we have, a quick spin on the balance machine answers it.
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