I am going to pick up an 89 350 block and build a 355. I also am putting a th350 trans behind it. I was wondering if the flywheels are the same or if I need to get a new one? I am a manual kind of guy but I cannot pass the deal on it.

Are there any things I need to know about what things do and dont combine? Does the 700R4 crossmember fit the th350 or does that need to be replaced? I believe the stock driveshaft works, correct?

Also was wondering if the 89 350 would have a steel crank since it is coming out of a 1500 Silverado? what are the chances?

what are the chances a 350 out of a 1/2 ton '77 van would have a steel crank? I know it would help to have casting numbers but I dont have them yet. Just wanted an idea of which may have what.

Thanks

 

The flex plate you have will directly fit a 89 block, but not fit a 77 block. You'll need one for an early block with 2-piece rear main seal (85-back).

Probably not a steel crank in either motor.

The drive shaft situation depends on which tailshaft length T-350 it is. IIRC a 9" one will use the same DS as a 700, but I've never done that exact swap myself so I don't know for sure. It's a trivial thing to get a drive shaft made of the right length though.

The crossmember will not work as it is, but it can be easily modified by adding a plate. The 700 mount is about 4" or so behind where a 350 or 400 one was.

 

every V8 chevy truck I've seen has had 4 bolt mains and about 3/4 of them have had steel cranks. just my .02

 

are the cranks that different that I could not take the flexplate from the 77 and use it on the 89 to connect to the th350?

Is there any way for me to find out if either has a steel crank without pulling the pan? will the engine casting # tell me? Or are there any RPO codes that would?

RB, why do you think neither of them would have a steel crank? I cant say for sure 84z is correct but I have heard of many trucks coming with steel cranks. Is there a theory of probability on this?

 

The 77 crank is the 2-piece rear main seal design, the 89 is the one-piece. The flange that the flex plate bolts to is completely different.

However, the bolt pattern on the flex plate for a 700 converter is the same as the one for either a 350 or a 400, I forget which; so if you get the usual replacement flex plate that has both converter patterns, it will bolt up to the trans.

Many trucks come with steel cranks; but light duty street trucks like Silverado 1500s with TBI motors are a pretty minimal load on a crank, so alot of those didn't get steel ones. For example I had a 87 K-5 Blazer motor (350 TBI) sitting in my garage for quite some time before somebody finally came and hauled it off, it had a cast crank.

I'd almost bet money that a 170 HP 77 smog van motor would have come with a cast one.

But who cares what I have to say about it, or anybody else; the motor has what it has, and all the conjecture and BS won't change it. Just look.