s130LS2

Hey everybody, looking for some more information/measurements on grinding the Lq4 "long" crankshaft down to take a t56. Hears the deal. I have the rotating assembly into the machine shop to get balanced, going forged H beams and Wiseco pistons, (hopefully) keeping the stock crankshaft. The motor came out of a 99 HD truck with the 4L80e and has the "long" style crank that we all love. I decided to reuse the stock crank since it just needed a polish, but I want to run a six speed out back. So I figured I would have my machinist grind the crankshaft hub down the .400" to be able to do it.
My machinist has a core laying around with the "short" hub on it and he want's to measure from the thrust surface to the hub face, to take measurements but the thrust surface is wiped on that core. Anybody have that measurement they could pass on to me or do we just grind .400" off of my crank hub face, match up the pilot bushing snout and drill the flywheel bolts all the way through? I pm'd one of the other members here that mentioned he had ground one down and he said that it had been a while but that was the way he remembered doing it on the crank grinder.
Any more help or experience in the matter would be appreciated, Thanks.

S10xGN

iTrader: (11)

I'd think you'd want to turn it in a lathe just short of the final dimension, then grind it. Grinding 0.400" is a lot of bother. For the dim, just have him measure the difference in flange thickness?

Gutless

Just bolt an LT1 T56 to it. Thats what I did. Just need a nv4500 flywheel. Stock LS1 clutch bolts right to it. Retain stock LT1 input shaft, bellhousing and front plate.

Just cut the bottom 1/3rd out of the bellhousing, which doesn't exist on a th400 anyways.

s130LS2

I already have the Ls1 t56 set up Gutless. This is going in a 82 280zx and due to the steering rack the pan has to be modified and the bell housing is going to hang below the oil pan about an 1". Honestly what I'm shooting for is to get this long crank shortening stuffed into one thread, from start to finish. I just keep finding dead ends where somebody starts to cut one down and then the thread stops with no mention of the material removed or the final product, typical internet stuff.

S10xgen, I should clarify. My guy has my long crank cut (not ground) down to .910" but is getting hesitant to grind it down to the final .855" . The thrust surface on the short crank is toast and the only place he has to measure from is the reluctor wheel, which I'm pretty sure is a 58t. Which brings us to the measurements and the conundrum...
If he cuts another .055" off my long crank to match the hub diameter with the short crank it drops the total length from reluctor wheel to hub face down to 1.850" which is .025" under the total on the short crank.
Both the reluctor wheels are the same width and fall within .010" to the outer crankshaft surface. So would that thrust surface make up the other .015" or does that throw out bearing suck it up?

I was hoping somebody could measure from the 24t reluctor wheel to crank shaft hub surface on a short crank, and throw the measurement up just to compare. I kinda think he is waaayyyy over thinking it, but now he has me sucked down the rabbit hole, lol. I'm getting ready to move cross country in a couple months so will be assembling the motor this fall. He just doesn't want me to put this thing together and I'm .025" under when I assemble and have to do it all over again.

truckdoug

iTrader: (25)

i'd split the difference between the two measurements .0125" is only two or three red **** hairs

s130LS2

My machinist wanted to leave it at .025" but I still feel that its a little far out. I was hoping we could hit the nail on the head so I don't have to shim anything, just don't know if it will make a lick of difference with a hydraulic clutch. Any body have an actual measurement or just split the difference and live dangerously.

S10xGN

iTrader: (11)

I'm unsure of your need for that particular measurement. There's any number of places on a crank/block you could get a reference from. Why not use a dial caliper to compare the two flange thicknesses? Heck, you could prolly get close enough just making the flange flush with the rear cover.

s130LS2

Ok, I'm looking for that measurement because the thrust surface is shot on the short crank we are referencing. Essentially we are getting two different measurements between my long crank and the toasted short crank.
Check out my drawing at the top, for a reference. This is a cluster **** so bear with me, I'll try and explain it.

Measured with the wide depth mic;
My long crank flange is at 1.905" total depth from the reluctor wheel to the flange face.
Short fubar crank is at 1.880" total depth from the reluctor wheel to the flange face.
1.905"-1.880" = .025" difference between the two from reluctor wheel to flange face.

Measured with the dial calipers;
My long crank flange is sitting at .910" flange thickness right now.
Short fubar crank is sitting at .855" flange thickness.
.910"-.855" = .055" difference between the two.

So if we take that .055" that we need to cut off my long crank flange and subtract it from the total depth of the same crank, 1.905"-.055" = a total depth from reluctor wheel to crank flange surface of 1.850"

So the only base line we have is the fubar crank at 1.880" total depth. Using that we subtract my long crank total depth. 1.880"-1.850" = .030" puts us in the hole.

Confused yet? I am lol.
That's why I was hoping someone had a good crank lying around to measure so I could get some sort of a baseline number over to my machinist. the thrust surface is toast on the short crank we are referencing or my guy would just measure from there. Or should I just do like truckdoug says and split the difference. At this point my head really hurts. Just don't get why were getting two different measurements from these cranks. Thanks for entertaining me guys, I feel like I'm losing it. I had to have my machinist explain it to me three or four times.

S10xGN

iTrader: (11)

Sounds like your over-complicating things here, I'd be happy with a dial caliper dimension of the rear flange thickness. There's plenty of "wiggle room" in the clutch stack up...

s130LS2

Alright, sounds good S10xGN. That was really what my guy was concerned about was the clutch stack up. I swung by there yesterday and chatted about what y'all have told me so far. He's going to drop it back in the block, put the rear cover on and see where it's at with the fly wheel and trim accordingly. He has never turned one down either so he was a little nervous. I'll check back in when he gets it situated and throw some numbers down where we land with it. Thanks for the help!

CattleAc

iTrader: (7)

I didn't see anyone mention this, but...maybe just get a "short crank" and be done with it...???

By the time you get the machining work in yours, you maybe could have replaced it with a later crank??

(The reason I responded to this thread, is, I'm in the same boat. I built a forged 370 using the long crank because the original plan was to go 4l80e.
Now I have a t56...)

s130LS2

I see the "get a short crank" response in a lot of the other posts as well. I wanted to go this route because the rotating assembly is already out and getting balanced and machinist said he would do it on the cheap. Besides, I know other people have done it, it's just not documented. All the weird measurement s*$@ was unexpected, I figured it was a cut it and done thing. By the time I pick up a short crank, pay for the shipping and possibly a grind/polish I could reallocate that money into springs or a trunion kit. Did you just end up getting the short crank to run the t56 CattleAc?

CattleAc

iTrader: (7)

I still haven't discussed this with my machinist yet...I'm sure I'll probably just use a "short" crank. (I have several of these laying around).

Right now I'm running a 5.3L in front of my t56...