My flex plate fiasco

[RodnRudy]

I got my 68 C10 together and driving last July. Ground up chassis and drive train rebuild, GM crate 350, 350 auto. From the get go there was a spot on the flex plate that the starter didn't want to engage. I suffered through the season with intentions of replacing the flex plate over the winter. I replaced the plate with a B&M heavy duty one, new ARP bolts and all. When I went to bolt the converter to the plate it wouldn't seat against the plate. I backed off the converter and cranked the engine over and found the plate had a terrible wobble in it. I figured it was warped so I removed it and went to NAPA and got an OEM replacement. Back home and new plate installed and it also had a wobble but not as much. While looking at the end of the crank shaft I found that there was excess flashing around where the flex plate bolts to it causing the plate to distort when I torqued it to the crank. This is a brand new crate engine mind you, seems they missed a step machining the rear flange. I went to my NAPA that has a machine shop also and made a template of a correctly machined crank. Back home I used the template and "relieved" the excess material with a burr bit on the die grinder and then put every thing back together. The converter fit, the flex plate has no wobble now and the starter engages as it should. It was a hair pulling experience for sure but as they say, "You live and learn."

[truckster]

I have to wonder how that crankshaft could have been balanced with the extra material on it.

[Shinysideup]

Amazing how much trouble something like that can cause. Glad to hear you found it.

[RodnRudy]

Truckster, The machinist at NAPA said no worrys on the end of the crank, I wouldn't be removing that much metal any way. Engine is still smooth running.

[truckster]

Originally Posted by RodnRudy

Truckster, The machinist at NAPA said no worrys on the end of the crank, I wouldn't be removing that much metal any way. Engine is still smooth running.

Cool. I just wonder how that got by a machinist at the factory during the balancing process.

[Gromit]

Wait, didn't you just need to drive that bronze bushing in a few mm to make clearance for the torque converter nose?

That is only there for non- automatics - you could actually remove it altogether if you have an auto.. but easier to drive it in a bit...

I'm no expert - anyone please correct me if I'm wrong.

[Gromit]

Found my photo of when I did mine.. please see attached jpg

(the extra schmoo is high temp threadlocker..not grease..)..

[James the III]

How new is this crate engine..
As g.m. sold off all the tooling to the gen1 sbc in 2013-14 and g.m. does not make them now.. someone else is..

[El Dorado Jim]

why is there a pilot bushing in the crank? and I just got a new crate engine, I will be checking the crank, thanks!

[saxart]

Originally Posted by El Dorado Jim

why is there a pilot bushing in the crank? and I just got a new crate engine, I will be checking the crank, thanks!

I was thinking the same two thoughts!

[RodnRudy]

I'll try to explain a little better. The pilot bushing is deep enough to not interfere withe the converter snout. The problem area was where the crank face is machined for the flex plate to seat. The flex plate bolt surface is 5" in diameter. Then the plate is embossed to the crank side, see Grommit's pic. My crank did not have a relief machined on the rear lug, the area should've been cut back to allow clearance for that embossed area of the flex plate. If you'll look at my pic with the masking tape you'll see where the excess area was that needed to be taken off. That allows the flex plate to seat flat on the mounting surface. I wish I had taken a pic before I relieved that area, it would have been easier to understand. Since the crank mounting flange was over 5" in dia. it caused the flex plate to distort or warp when it was torqued.
I bought the engine from Summit in either late 2015 or early '16. It's the 260HP version pre 85. Hope this helps to clarify your questions.
One more thing, the card board template in my first pic is the one I made from the crank at the NAPA machine shop. They use it to set up their balancer.

[James the III]

Originally Posted by RodnRudy

I'll try to explain a little better. The pilot bushing is deep enough to not interfere withe the converter snout. The problem area was where the crank face is machined for the flex plate to seat. The flex plate bolt surface is 5" in diameter. Then the plate is embossed to the crank side, see Grommit's pic. My crank did not have a relief machined on the rear lug, the area should've been cut back to allow clearance for that embossed area of the flex plate. If you'll look at my pic with the masking tape you'll see where the excess area was that needed to be taken off. That allows the flex plate to seat flat on the mounting surface. I wish I had taken a pic before I relieved that area, it would have been easier to understand. Since the crank mounting flange was over 5" in dia. it caused the flex plate to distort or warp when it was torqued.
I bought the engine from Summit in either late 2015 or early '16. It's the 260HP version pre 85. Hope this helps to clarify your questions.
One more thing, the card board template in my first pic is the one I made from the crank at the NAPA machine shop. They use it to set up their balancer.

I wonder if that was a returned engine as they don't come with a manual trans pilot bushing in the crank..
did the part you ground down look welded on..
As even a cast crank before finishing doesn't have that much extra material ..

[RodnRudy]

Only GM crate engine I've ever bought so not sure about the bushing. I do know there was too much material left on the end of the crank. The parting line was probably 1/4" wide. This engine came from Mexico, I don't know how much of the casting or machining process is done there.

[Gromit]

Thanks for posting this. Now I see it; the part that was proud of the mating surface was darkened and I didn't understand what I was seeing.

I wonder if there are other motors with the missing machining step on Summit's shelves? Might even be able to inspect for the condition through the crate slats; though the plastic bag wrap would make it difficult to see - maybe poke a hole in the wrap and use a USB borescope - sounds like a lot but cheaper than round trip shipping. That must have been difficult work with the die grinder.

I found another photo of mine (please see attached) that I took when removing the packing. Mine came with that bronze bushing too of course.

The manual says a pilot must be installed and they recommend a roller type; maybe the one it comes with is something GM used for the crank machining process?

Here is a cut-and-paste from the manual re the pilot:

"Pilot Bearing:
You must install a pilot bearing in the rear of the crankshaft if the engine will be used with a manual transmission. The pilot
bearing aligns the transmission input shaft with the crankshaft centerline. A worn or misaligned pilot bearing can cause shifting
problems and rapid clutch wear. A roller pilot bearing P/N 10125896 is recommended for this engine. This heavy-duty bearing
adds an extra margin of reliability to a high performance drivetrain."

[RodnRudy]

Thanks for posting that picture Gromit. In it you can see the rough part of the casting and the parting line. It is directly out from the dowel pin hole on the flange surface. On my flex plate it measured 1 1/4" out from the edge of the center hole to the embossed area. The face of the crank flange mounting surface was more like 1 3/8" from the hub edge to the edge of that machined surface right at that parting line. On the crank I looked at at NAPA that whole area where you see the rough casting in your picture was machined down about 3/16". The pictures I've posted show the template I used to relieve my crank. I made this pattern off of the NAPA crank. I used my old flex plate to show where the embossed area was laying on that flange (black arrow showing embossed area)

[garyd1961]

Originally Posted by James the III

How new is this crate engine..
As g.m. sold off all the tooling to the gen1 sbc in 2013-14 and g.m. does not make them now.. someone else is..

How is it then that GM still sells new 350 crate engines?

[El Dorado Jim]

Originally Posted by garyd1961

How is it then that GM still sells new 350 crate engines?

I just bought a 350 gm crate engine,they are all made in mexico....

[James the III]

Originally Posted by garyd1961

How is it then that GM still sells new 350 crate engines?

Sold the tooling.. does not mean they won't sell the units..

The bbc crate engines are not built by g.m. but are built for them..
after the sbc tooling being sold I'm willing to bet this is the case also, after g.m. dealer network and warehouses run out of stock..

my 454 ho bought in 2004 was not built by g.m. it was built for g.m.

A company outside g.m. bought the tooling..

G.m. sells new cars with parts not made by g.m. and you buy at the parts dept those parts not made by g.m. but g.m. sells and stocks them..

Why you think crate engines and small block parts be any different..
Just because the label on the box says g.m. doesn't mean g.m. produced it.

[El Dorado Jim]

I checked my new crate engine, looks fine, it even has the bronze pilot bushing installed already too ! thanks for the heads up on looking at the crank...

[LockDoc]

Originally Posted by James the III

I wonder if that was a returned engine as they don't come with a manual trans pilot bushing in the crank..
did the part you ground down look welded on..
As even a cast crank before finishing doesn't have that much extra material ..

I can't say all of them do but many GM crate engines come with the pilot bushing installed. I have bought two of them and both came with a pilot bushing installed. I posted about it back in 2015. Many others have mentioned it too.

LockDoc

[James the III]

Originally Posted by LockDoc

I can't say all of them do but many GM crate engines come with the pilot bushing installed. I have bought two of them and both came with a pilot bushing installed. I posted about it back in 2015. Many others have mentioned it too.

LockDoc

I haven't bought a crate with 2 piece seal in years.. all the one piece rear main seal, and none of them had one installed..
And looking at the base 190+260 crates. there isn't a part # listed in the included parts included list.. But that don't mean much ,I guess.

[saxart]

Originally Posted by El Dorado Jim

I checked my new crate engine, looks fine, it even has the bronze pilot bushing installed already too ! thanks for the heads up on looking at the crank...

Yes, I checked mine this weekend, and it too has the bushing, but based on what Gromit says above, it should be replaced with a bearing? (I have a manual transmission)

[LockDoc]

Originally Posted by saxart

Yes, I checked mine this weekend, and it too has the bushing, but based on what Gromit says above, it should be replaced with a bearing? (I have a manual transmission)

I don't know why, the bushing will work fine as long as it is the correct size for the trans you will be using.....

LockDoc

[saxart]

Originally Posted by LockDoc

I don't know why, the bushing will work fine as long as it is the correct size for the trans you will be using.....

LockDoc

Yeah, that's what was in my old engine.

[El Dorado Jim]

Originally Posted by saxart

Yes, I checked mine this weekend, and it too has the bushing, but based on what Gromit says above, it should be replaced with a bearing? (I have a manual transmission)

I have never ran the bearing in any of my vehicles, the bushing works fine, and I checked , it is the right size for my sm 465