View Full Version : FWD LS4 Crank in a 5.3 Truck block?


Keith Johnson
08-04-2012, 08:52 AM
My son got a long block last year with LS4 internals in a 5.3 truck block. He has been saving his money up slowly to build it up for his air bagged '77 dually. He is having problems with the LS4 crank. We had a friend machine a spacer for the TCI flywheel but now it seems he has a problem with trying to put a 5.3 truck pulley on the front. I Just read on here that the Ls4 crank is 13mm shorter overall. 3mm in the rear (already solved), and 10mm in the front. It seems the front of the crank .010 larger diameter than the truck pulley. This is my first dealing with the Ls motor and my 18 year old is ready to throw in the towel. Any ideas other than replacing the crank. Keith Thanks.

TyCZ28
08-05-2012, 11:36 PM
Honestly your putting too much effort and thought into it... Just get either an LS1, Lq4, LQ9, lm7 etc. crank thats the right size. i picked one up a few months ago for 40 bucks and paid 20 to have it polished... they are cheap and easy to find.

bww3588
08-07-2012, 04:08 AM
It seems at this point the engine is already together and half the equation is solved. Tearing the engine down to replace the crank would be a last resort in my opinion.

I would have the truck balancer machined down 13mm and have the inside opened up to fit the larger snout.

Be very very cautious to get the measurments exactly correct as the balancer is a press fit.

Or....you could possibly use an entire front drive accessory system.

bww3588
08-07-2012, 04:09 AM
If you chose to have the truck balancer machined, I suggest spending a few extra bucks on a crank pinning kit. Just for extra insurance.

TyCZ28
08-07-2012, 12:23 PM
It seems at this point the engine is already together and half the equation is solved. Tearing the engine down to replace the crank would be a last resort in my opinion.

I would have the truck balancer machined down 13mm and have the inside opened up to fit the larger snout.


Read better... 10mm SHORTER.. he needs to make a spacer for that much which is not safe and wont balance out properly...

he already made a spacer for the flex-plate.

bww3588
08-07-2012, 04:47 PM
Sorry...

Machine the pulley 10mm and not 13.

No spacer is needed as that would only compound the problem.

TyCZ28
08-07-2012, 08:50 PM
i fail to see how machining 10mm off of the pulley will solve the fact that the LS4 crank is 10mm shorter in the front than it needs to be...

if the crank is 10mm shorter and he machines 10mm off the pulley now hes 20mm short...

or am i missing some sort of LSx voodoo here

bww3588
08-07-2012, 09:38 PM
I think both of us are over thinking it.

The more I think about it, as long as the flange the pulley sits against (timing gear) is in the same location, the pulley should fit just fine, there will just be an extra 10mm between the bolt surface of the pulley and the end of the crank. I honestly don't see this being a problem as long as there is enough surface area for the pulley to have enough press fit to stay put.

Keith Johnson
08-16-2012, 08:43 PM
Thanks for the replies. We got the pulley on with the installation tool that he bought. We got the engine and trans dropped in Friday night. We are now trying to start with his Fast EZ EFI Master Kit. We finally got the fuel rails on the Fast RT intake just to realize we have to take them back off to take the intake apart to drill for the map sensor. He dishearted some, but he will try to find out some answers tomorrow at work at Comp Cams. He will have to talk to the fast engineers to try to figure it out. Lots of wires!!!! Keith

TyCZ28
08-16-2012, 08:57 PM
Could have gone Carb's and used the MSD box to control the ignition. would have only been a few wires and gave it the LS power and the old school look.

codyvette
08-20-2012, 03:21 PM
If they already have the parts to go FI, go for it. Tuning is a lot of fun and in the end yields better power band than a carb. At least overall. Learning FI also allows you to make some money back to help pay for that bad ass Fast system.