350 CHANGE OUT FROM 305

garagenc · #1 06-06-2007, 11:12 PM

Hey Guys, I haven't been on much, between the Navy Yard and my landscaping business they are running me ragged, But I need info so I'm asking:

Maybe some of you will remember that I'm changing out my 1991 305 for a 1991 350 because of a bad block.

Here's my question??

I'm planning on using my 305 flywheel and harmonic balancer on the 350, does anyone know know if this won't work? They will fit on the 350 crank. I had a auto parts store look up the part #'s for each and they were different. I've asked a chevy guy and another marine mechanic they both said that since I won't be turning over 4500 rpm's this won't bother the engine.
Does anyone know?

garagenc · #2 06-06-2007, 11:12 PM

Hey Guys, I haven't been on much, between the Navy Yard and my landscaping business they are running me ragged, But I need info so I'm asking:

Maybe some of you will remember that I'm changing out my 1991 305 for a 1991 350 because of a bad block.

Here's my question??

I'm planning on using my 305 flywheel and harmonic balancer on the 350, does anyone know know if this won't work? They will fit on the 350 crank. I had a auto parts store look up the part #'s for each and they were different. I've asked a chevy guy and another marine mechanic they both said that since I won't be turning over 4500 rpm's this won't bother the engine.
Does anyone know?

spareparts · #3 06-06-2007, 11:23 PM

check the bolt patern for the flywheel, all small blocks( except the 400) use internally balanced cranks, all the flywheels should inter change as long as it has the correct bolt pattern, they changed the bolt patern when they went from two piece rear main seal to to one piece(85?). There may have been some total weight changes for the flywheel , but they should all( ex. 400) interchange as far as balance, just make sure you use the right starter with the corrisponding flywheel.

spareparts · #4 06-06-2007, 11:23 PM

check the bolt patern for the flywheel, all small blocks( except the 400) use internally balanced cranks, all the flywheels should inter change as long as it has the correct bolt pattern, they changed the bolt patern when they went from two piece rear main seal to to one piece(85?). There may have been some total weight changes for the flywheel , but they should all( ex. 400) interchange as far as balance, just make sure you use the right starter with the corrisponding flywheel.

76GMC1500 · #5 06-06-2007, 11:23 PM

They should fit. Both motors are internally balanced. If you see any counterweighting on the flywheel or damper, it is for an external balanced motor and won't fit. The 305 and 350 flywheels may have different numbers of teeth, 153 and 168 are common sizes. 168 was older 350s. 153 covered both the 305 and some newer 350's. Both will work, but the starters have different mounts depending on the flywheel. As long as you use the starer that came off the 305, you should be fine.

76GMC1500 · #6 06-06-2007, 11:23 PM

They should fit. Both motors are internally balanced. If you see any counterweighting on the flywheel or damper, it is for an external balanced motor and won't fit. The 305 and 350 flywheels may have different numbers of teeth, 153 and 168 are common sizes. 168 was older 350s. 153 covered both the 305 and some newer 350's. Both will work, but the starters have different mounts depending on the flywheel. As long as you use the starer that came off the 305, you should be fine.

THEFERMANATOR · #7 06-06-2007, 11:33 PM

87+ small block chevy's are internally/externally balanced. The balancer should interchange, but the flywheel may not. 87+ 305/350 were neutral balance on the balancer for standard production engines(LT and LS series engines are a whole nother deamon), but the flywheel/flexplate has a counter weight on it for all of the 87+ small blocks. The counter weights were different weights depending on wether or not it was a perfomance engine or not.

I'll dig out my interchange book here in a little while and do some more checking. Do you know the casting number on flywheel?

THEFERMANATOR · #8 06-06-2007, 11:33 PM

87+ small block chevy's are internally/externally balanced. The balancer should interchange, but the flywheel may not. 87+ 305/350 were neutral balance on the balancer for standard production engines(LT and LS series engines are a whole nother deamon), but the flywheel/flexplate has a counter weight on it for all of the 87+ small blocks. The counter weights were different weights depending on wether or not it was a perfomance engine or not.

I'll dig out my interchange book here in a little while and do some more checking. Do you know the casting number on flywheel?

THEFERMANATOR · #9 06-06-2007, 11:49 PM

I went and checked and the regular production(truck style) engines from 87+ use the same bobweight for the counterweight for both a 305 and 350. So you can use your old flywheel from your 305 to a 350. GM PERFORMANCE parts and MERCRUISER both list the same flywheel/flexplate for all of the 1986-2000 5.0L/5.7L gen1 engines.

THEFERMANATOR · #10 06-06-2007, 11:49 PM

I went and checked and the regular production(truck style) engines from 87+ use the same bobweight for the counterweight for both a 305 and 350. So you can use your old flywheel from your 305 to a 350. GM PERFORMANCE parts and MERCRUISER both list the same flywheel/flexplate for all of the 1986-2000 5.0L/5.7L gen1 engines.