what the *^&$(#@*&$&%(#*@&$%*!!!!!!!!!! Help?

[Tom]

Ok so as we all know, I have a 99 vortec 350 in my 79 pickup. It used to be backed by a th350. I went to the junkyard and bought a used 1pc rear main flaxplate when I get the engine. Ran it with the th350 for a while, till I got massive knocking. Thinking it was the th350, and since I wanted a new tranny anyways, I replaced the th350 with a 2004R. While the th350 was out, I found my problem. A MASSIVE, 360* crack in the flexplate. So I went and bought a brand new 1pc rear main flexplate. Had this going for about 3 months or so now, and its starting to make the kncoking noise like its cracking again. Ill check somtime this week, but Im almost 100% posative its another f'ed flexplate.

So my questions are, what the heck is causing these plates to crack? They dont do this normally, so somthing is wrong. What do I need to check? Is there a stronger flexplate avalible to purchase? Thanks.

[87 STEPPER]

Assuming it's another flex plate the only thing i can think of is, Did you torque it in the proper sequance and value's?

Or might the torque converter be putting stress on it in some negitive way?

[SCOTI]

Did you reuse the same converter? If you narrow the possibilities down to whatever contacts the flexplate, the converter seems like the most probable choice.

[Tom]

No it is a different convertor when I switched from a th350 to the 2004R. The only things touching the flexplate that were re-used are the flexplate bolts and the crankshaft.

[Mike76251]

Man, that is strange one......
Is your engine external balance?
If so....is your damper and your flexplate external balance too?

[Tom]

Im pretty posative all 350's are internal balance. The engine runs smooth as silk. I re-used the old balancer up front without problems. Im so confused

[Mike76251]

I read somewhere that Chevy went to external balance in their small blocks lately............Hmmmmmmm
I know the new 383s from Chevy are external.
That doesn't sound like your problem if it runs smooth.
You mix up external and internal parts on one and it will shake itself right out of the car.

I know there is no such thing as this but it sounds like too much torque then.
Try a Hayes or anything of the .080" thicker high performance type flexplates.

I just re read your post and have another idea.....
You say you got a 1-piece flexplate. Check to see if it has a weight welded on the flexplate near the outer edge.
Some of them do 'cause I have three small block flexplates that have it.
If you do then that is your problem.
Let us know please........
Mike

[swervin ervin]

Only thing external balanced is the flexplate. The harmonic dampeners are the same as always. The reason it has to be external balanced with one piece seals is because there isn't enough material left on the rear of the crank to balance it internal. The size of the seal housing takes this away.

I talked to a guy once about a 4.3 V6 that done something similar to this. It was also a one piece seal engine. I can't remember what he told me though. All I can remember him saying is he had the wrong flexplate on his and it caused vibrations.

If I were guessing, I would say it's the flexplate causing it.

Tom,

did you buy a flexplate for a Vortec engine. I'm don't think they are any different than any other one piece seal, but it may be worth a shot.

[Tom]

Mike76251- yes the flexplate[s] have the piece of metal welded on near the edge.

Other mike []- no I bought flexplates for a 1pc rear main 350. I too thought they were the same. I called the GM dealership and they have em for $120 a piece
I think Ill try and find a used one in the junkyard.

[Tom]

well, just got off the phone with the dealership, the flexplates are all the same for 1pc rear main small blocks. I guess its aftermarket time.

[Mike76251]

Originally posted by Tom
well, just got off the phone with the dealership, the flexplates are all the same for 1pc rear main small blocks. I guess its aftermarket time.

My small block takes a external balance damper and a external balance flex plate.
So does General's new 383. That guy at the dealership should know this.
The external balance damper's part # is 12498008.
The external balance flexplate's part # is 14088761
Look in a new GM Peformance Parts book and they are both listed.
All one piece cranks use a counter-weighted flexplate according to GM.
This makes all one-piece seal engines external balance.
As for which damper to use in this engine it all depends on the crank's part number.
A good way to check this would be to call that guy at the dealership and ask for a damper for the car or truck that engine came out of.
Go look at it (they should have it in stock) and see if the one you have matches it.
If it doesn't.....problem solved.

[1FaastC10]

Mike, you and i seem to be disagreeing alot lately... i worked a GM Parts counter for over a year, and i have a Vortec 350. when i first bought it i looked into the internal/external balance thing. the flexplate is counterweighted, and the balancer is not. there is enough meat in the front of the crankshaft to internally balance it, but as Mike said earlier the rear seal adapter neccesitates a counter balanced flexplate.

[Mike76251]

Originally posted by 1FaastC10
Mike, you and i seem to be disagreeing alot lately... i worked a GM Parts counter for over a year, and i have a Vortec 350. when i first bought it i looked into the internal/external balance thing. the flexplate is counterweighted, and the balancer is not. there is enough meat in the front of the crankshaft to internally balance it, but as Mike said earlier the rear seal adapter neccesitates a counter balanced flexplate.

In a hundred years, no one will care...........

I did not mean to make you feel that way....sorry.

Now...with that aside let's disagree again!!LOLOL
I understand that if you use a rear-seal adapter to put a two- piece crank in a one-piece block that you then need a non-counter weighted flexplate 'cause the crank mass determines counter weight/no counterweight.
The only (?) small block crank that is two piece and needs a counterweight is a 400.
Is that mess close?

[swervin ervin]

As I said, the only production small block that is fully externally balanced is the 400. This is why the 383 is, it uses a 400 (3.75" stroke) crank. If you have ever noticed, the ZZ4 engines use the same balancer as the 1971 LT1 or L82 350's did. I know for a fact they weren't externally balanced. Oh, and ZZ4's are one piece rear main seal engines.

I guess you can call it externally balanced if you want to, because it is in a way, but not the balancer. Balancers are the same.

[1FaastC10]

the 383 crate motor that GM sells is an entirely different animal than the 2 piece 383 that most guys put together. it retains a 4.00" bore, and uses a 3.8" stroke crank. it also uses the same counterweighted flywheel as the 86+ 5.7s, i'm really not sure about the balancer though, so it could be a full external balanced engine.

[Mike76251]

Originally posted by swervin ervin
As I said, the only production small block that is fully externally balanced is the 400. This is why the 383 is, it uses a 400 (3.75" stroke) crank. If you have ever noticed, the ZZ4 engines use the same balancer as the 1971 LT1 or L82 350's did. I know for a fact they weren't externally balanced. Oh, and ZZ4's are one piece rear main seal engines.

I guess you can call it externally balanced if you want to, because it is in a way, but not the balancer. Balancers are the same.

GM needs to revise this book. It is the current one.

[swervin ervin]

They have it correct.

All small block and V6/90* cranks which use a one-piece seal require a counterweighted flywheel for proper engine balance.

They never say anything about the balancer, or as it's real name, harmonic dampener. In all the info I have read, never, ever, have I seen it say the balancers are different for one piece seal engines. Only the flywheels/flexplates are counter weighted.

[PHOENIX]

[79BIG10]

Just another thought but what about your starter? Could it be giving too much torque on the flexplate and cracking it?

[79GMC454C35]

79Big10 might have something. Is the starter too close to the ring gear? Does the starter need to be shimmed as to not put a load on the ring gear? I know Harleys destroy starters & ring gears when the starter jack shaft pinion gear is too close to the ring gear. The pinion gear puts a side load on the ring gear as it comes out & the two mesh. Something to consider.

[Tom]

I think you guys are on to somting too. I re-used the starter from the old motor [79 model]. Is this starter a 153 or 168 tooth starter? Also, how many teeth is the new style flexplate? Ill check and see if I need to shim the starter tonight. Thanks for the help so far guys!

[1FaastC10]

Tom, i believe they are both 168 tooth. i do know that a starter for a 168 tooth, will not engage the smaller 153 flexplate.

[79BIG10]

Tom is should be 168 on both flex plate and starter. I used my old starter as well on my ZZ4. I'm thinking they used the same flex plate on the Vortec as well but not for sure.

[Tom]

Well, I just orderd a 168tooth TCI SFI approved, thicker then stock flexplate. And Im getting some new ARP bolts to use. This dam thing is not breaking anymore!!!

[swervin ervin]

Make sure to use locktite on the bolt threads too.