will my pre86 chevy flexplate work with a post 86 block? - Honda Motorcycles - FireBlades.org
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post #1 of 11 Old 10-25-2005, 3:30 PM Thread Starter
 
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will my pre86 chevy flexplate work with a post 86 block?

I'm gonna swap the motor in my car (if it ever stops raining some weekend). I have an '85 so it has the 2 piece rear main seal and I'm dropping in a late 80s camaro engine so it has a 1 piece seal. Anyone know if I can still use the flexplate thats already in the car or do I have to buy one for the newer engine?
I'm thinking no I can't use it but wanted to check with someone who knows better.

if you can't convince them, confuse them.
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post #2 of 11 Old 10-25-2005, 3:34 PM
 
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Re: will my pre86 chevy flexplate work with a post 86 block?

Not a problem, Although I thought they got rid of those two piece seals in the 60's. The only thing you have to look at is the bolt pattern of the crank. The only other thing that could get in the way would be if it used to be mated to a stick transmission. Then all you have to check is that the TO bearing is removed.

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post #3 of 11 Old 10-25-2005, 3:45 PM Thread Starter
 
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Re: will my pre86 chevy flexplate work with a post 86 block?

looking at all the part catalogs and crap it says pre 86 had 2 piece rear main seals. but I'm sticking with the stock automatic 200-4r for now. putting the 5 speed in is gonna take more work and will be done eventually.

so as long as it matches the bolt pattern of the crank I'm fine?



so I guess I'll ask another question. I have almost all of the parts to do the 5 speed swap but at the time I got them I was sticking with original engine so I bought a flywheel that would go with the pre-85 block but now I'll have the post 86 block. is it basically the same thing, check the bolt pattern?

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post #4 of 11 Old 10-25-2005, 4:01 PM
 
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Re: will my pre86 chevy flexplate work with a post 86 block?

Oops. Flywheel changed, and also went to external balancing in 86. It will not work even if you manage to bolt it up.

You MUST use pre or post 86 stuff together.

www.s-series.org/htm/tech/GMPerfParts/076-081.pdf



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post #5 of 11 Old 10-25-2005, 5:31 PM Thread Starter
 
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Re: will my pre86 chevy flexplate work with a post 86 block?

Quote:
Originally Posted by luvtolean
Oops. Flywheel changed, and also went to external balancing in 86. It will not work even if you manage to bolt it up.

You MUST use pre or post 86 stuff together.

www.s-series.org/htm/tech/GMPerfParts/076-081.pdf
ok so the flywheel for the manual definetly won't work so I'll work that out when that time comes. But will the flexplate for the automatic still work (85 flexplate, post-86 engine block)?

I guess I should also cross check the crank thats in that new engine with whats in that pdf. I know its a crank from a 400 and I imagine its gotta be from a post 86 engine as the block that its in right now I know is post 86 (looked up the numbers that are stamped on it)

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post #6 of 11 Old 10-25-2005, 5:34 PM
 
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Re: will my pre86 chevy flexplate work with a post 86 block?

Yep, if it's a 400 crank it's (almost) definately externally balanced. This matters for the flexplate as well.

You can't put an early crank in a late block. The rear main seal is too different.

You need to cross check everything.



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Re: will my pre86 chevy flexplate work with a post 86 block?

So what do you do when your flex plate shatters and you need another one on an externally ballanced crank?

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post #8 of 11 Old 10-25-2005, 5:57 PM Thread Starter
 
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Re: will my pre86 chevy flexplate work with a post 86 block?

Quote:
Originally Posted by luvtolean
Yep, if it's a 400 crank it's (almost) definately externally balanced. This matters for the flexplate as well.

You can't put an early crank in a late block. The rear main seal is too different.

You need to cross check everything.
ok good I'm gonna check all that stuff. I bought the engine on ebay and just had to buy mostly small stuff for it. but I ended up buying a new intake also so I could use a Demon carb that I wanted. The guy who I bought it from ended up being an asshole and I probably got ripped off but its too late now (his ebay account was deleted a couple weeks after I got the engine).

So when it stops raining out I'll go and pull the rest of the numbers from everything. I just looked up the number I had pulled off the block a long time ago and now can't find anything on it, so now I'm not sure what year it is. I know exactly what the heads are though so maybe thats why I think its a post 86 block.

I'll probably have more questions later once I get all the numbers checked and ****. but I'll find out what I can in the next couple days.

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post #9 of 11 Old 10-25-2005, 6:07 PM
 
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Re: will my pre86 chevy flexplate work with a post 86 block?

Quote:
Originally Posted by nedro
So what do you do when your flex plate shatters and you need another one on an externally ballanced crank?
An Externally Balanced engine has a set imbalance in the crank assy, harmonic balancer and flywheel/flexplate. So you just buy a new one with the proper unbalance.

I don't know what a 400 SBC is, but I know the externally balanced Ford HO 302 is 28 in/oz unbalanced.

You can add mallory metal to an externally balanced crank and make it internally balanced, and this is desirable (and expensive) in performance applications. It will require a new neutral balanced flywheel and balancer as well.




Last edited by luvtolean; 10-25-2005 at 6:19 PM.
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post #10 of 11 Old 10-25-2005, 6:25 PM
 
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Re: will my pre86 chevy flexplate work with a post 86 block?

Quote:
Originally Posted by luvtolean
You can't put an early crank in a late block. The rear main seal is too different.
Technically I was wrong on this.

GM has an adapter on that page I linked. Part #10051118



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post #11 of 11 Old 10-26-2005, 2:57 PM Thread Starter
 
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Re: will my pre86 chevy flexplate work with a post 86 block?

couldn't find a number on the end of the crank but found the block number. Its an 80-85 block so I'm good to go with the flexplate from the automatic thats in the car right now and I'll be fine when eventually putting in the 5 speed.

The heads are from 86-91.

so all the parts I have are still good. and the weather looks good this weekend until sunday night so as long as my friend doesn't have anything else come up I think its still a go.

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