another swap question/flywheels

[midwestls]

my motor is a 73 or 74 350, I'm putting it in my 87 LS that origanally had a 4.3 and I'm useing the stock 200r4. Will the origanal 350 flywheel bolt up to my torque convertor??? If not, will the 4.3 flywheel bolt up to the 350? Does anyone know how many teeth these two flywheels had and what starter I should be useing, the 350's or the 4.3's??? Any help would be appreciated

 

[85 Cutlass Brougham]

It depends on the transmission. The newer SBC's and 90degree V6's (after 1980, or engines with the passenger's side dipstick. Earlier engines have it on the driver's side) used a 153 tooth flywheel or flexplate, while earlier cars use a 168 tooth. Some newer transmissions have bells too small for the older 168 tooth flywheel, so I would just go with a flexplate from a 1980-85 305 to be safe. All SBC's use the same neutral balance on the flywheel except for the 400, so it is safe to interchange them. I used a 1985 305 flexplate on my 1977 350, for example, and took the starter from the same donor vehicle. It is important to use the starter from a vehicle with the same tooth count as the flywheel/flexplate you are using. It is also important to get one from a 2 piece rear seal engine, and not the newer one piece engines, as they will not interchange. This is why I specified 1980-85 as the year range, as they will have the 2 piece seal and 153 tooth flywheel.

Also, I am not sure what the unbalance weight (if any) is on a 4.3 V6, so it may also work in lieu of the 305 part. If it lacks any balancing weights, it should work fine.

 

[midwestls]

according to summit racing, my 87 4.3 is internally balanced with 168 teeth and also interchanges with 5.0/5.7 and whatever sfi 29.1 means (4.3???) if this is the case the flexplate on the motor (74 350)should work either way 168 or 153 right? (if it has the same holes as the torque converter)


now jegs, replacement, is for 86 and up V8 and 90 degree V6, ok, they say one piece rear seal and say it's a 153 tooth

somebody is probably wrong, does anyone know what is right? I dont quite have my 4.3 out yet and am trying to figure out if I need to order anything else. Again I've got a 200r4 in an 87 monte I'm trying to hook to a 73ish 350. Thanks for any help

 

[85 Cutlass Brougham]

Well, I just realized that it will not fit no matter what. This is because you have an 87 engine which would have a one piece seal, and you need a 2 piece seal flywheel. However, I think it would be a 153 tooth, not a 168. Either way, you need to match your starter and flywheel combo since the spacing of the drive pinion differs due to different diameters.

SFI is a certification standard for racing as certain parts need SFI certs to be legal in some classes for safety reasons. It is irrelevant to this discussion.

 

[midwestls]

alright. I figured mine is probably a 153 because last year I put an older 350 in a 87 Caprice with a 200r4 and ran into the same problem...flywheel too big. The car origanally had a 305. So did the older 350's come with both flexplates? Or just the bigger (168) ones???

 

[megaladon6]

older 350's could use either flexplate. 1 have a 383 using a 168 tooth plate for a 400ci, mated to a 200r4. just make sure that you have the right starter.
if you had the engine rebuilt and the main caps align honed, get the "race" starter with the solid mounting block. otherwise the gears will never engage right. i found that out the hard way.

 

[85 Cutlass Brougham]

There is a cutoff year when GM switched over, I believe it is 1980 or 81. However, you can use either on a 350 as they do bolt up. However, GM changed the crank flange in 1986 to go with the one piece rear main seal, and those will not interchange backwards to the earlier engines. Your only difference that you need to be careful about is the transmission bellhousing and the starter. This is why I would always run a 153 on a car with a transmission that came out after the switchover year. I ran into this with a 1970 Chevy 400 in a 1984 Camaro with a T-5 years ago, and it would not fit. We had to get a 153 tooth flywheel and have it match balanced to the 168 tooth that was done with the engine. This is not an issue in any SBC without a 400 crank, as the rest use neutral balance flywheels, and have their external balance weights in the crank flange instead.

 

[midwestls]

alrighty, I'm gonna finish pulling my 4.3 and match that one to the one on my 350 just to see the size difference (if any) and go from there. Thanks for all your help guys