Chrankshaft Water Pump/Balance Shaft Sprocket. Why 2 pc and adjustable?
 

I am doing a build and purchased a short block with new liners, new forged pistons and new forged rods.

My plan is a balance shaft delete, TVS blower, larger injectors, LS1 throttle body and MEFI4B to control the unit. This is going into a 1986 Lotus Esprit.

I took the short block apart to clean and paint the block. When I did this, I noticed that the crankshaft sprocket the turns the water pump and balance shafts had a crack at the key. I also saw that this was a two piece unit that looked to be adjustable (GM 55557168). I looked on line and these go for >$100.

I had pieces from another LSJ engine and went into that pile to find a replacement sprocket. All I found was a one piece sprocket GM 90537301. This obviously was not adjustable and it had a smaller hub thickness (.413" vs the .741" thickness on the GM 55557168 sprocket). This made me think that maybe the GM 90537391 was from the parts pin of a 2.2 L I had and that it got mixed into the parts bin of the LSJ.

A couple of questions:

1) why the 2 pcs design of the GM 55557168? It looks like it can advance and retard about 5 degrees. Why would they need this for just the water pump and balance shafts?

2) Since I am doing the balance shaft delete, my thought is to use the GM 90537391 and just make a spacer hub to shim out the sprocket and accommodate the different overall thickness between the GM 90537391 and GM 55557168). This would be simple to make as it would be .328 thick with a key slot (.741- .431).

here is a pic of the two sprockets

In for answer on adjustable WP/BS sprocket. This is the first I have seen these and I have no idea what the adjustment would be needed for. You are deleting your BS so timing won't matter at all. I would just use a standard fixed sprocket. Where did you get your short block from? If the timing chain and BS chain/components are used I would replace those with the OEM Cloyes timing chain kit from Crate Engine Dept. with the upgaded ARP bolts for the guides.

I already have new chains and guides, as well as the ARP upgraded bolts. Just did not mention it in the listing.

10-4, well I wouldn't mess with that adjustable gear at all especially with BS delete. As it is cracked and due to it's construction it looks like a liability.

No, I will not use the adjustable one because it is cracked

I cannot understand why the GM 55557168 is adjustable. What was it intended to do?

On the other hand, I do not know if the GM 55557168 is standard with the LSJ. Do you know what is?

I know that on CED they list the timing chain kit as L61/LSJ which I bought for my L61. I know for a fact that the WB/BS sprocket is fixed std. sprocket and not adjustable. I'm curious as to the reason for the adjustable sprocket as well. Hopefully someone here knows and will chime in.

I called the local chevy parts department. They show that the current number for the crankshaft waterpump/balance shaft sprocket is 12642713. The old number was the 55557168. So for some reason they made this sprocket adjustable for the lsj

A new one is $145...yikes

Since I am deleting the balance shafts, why not take the 90537301 and make a hub shim to get it to the same thickness (note: I would only need to do this shim on the crank side to get the same plane in the engine as the GM 55557168)? It would be no cost to do.
thoughts?

actually the accessory gear is spring loaded and I would assume its to absorb the shock load of going wot just replace the gear with a new unit of the same yours is the only one I have ever heard of or seen cracking some advice for ya you should extend the crank keyway also the stock key bends rather easy

only the lsj and the lnf use that gear
the only difference from the l61/lsj timing set is the accessory gear

Mr Belvedere

thanks, that makes sense on why it is adjustable.

I already had the crank milled to take a full key

its not an adjustable gear

This helped me in my search so I might as well return the favor
I got for my SAAB (GM parts basket :) ) a replacement balance chain kit with the plain sprocket wheel. But originally installed was the "adjustable" one.
After getting to SAAB WIS I found this about the balance system, I'd say this is the reason for the complex 12642713 / 55557168 part

the spring loaded gear is used on lsj and lnf cobalts and hhr only and neither one comes with a dual mass flywheel except the solstice/sky with lnf i wonder if when used in a saab manual car that they use dual mass flywheel and gm just went with it

I have no knowledge about Cobalts, but for SAAB it is quite a mess with flywheels, there is like 20 entries just for the 9-3 2.0 Ecotec (per power, ethanol compatibility, year range, gearbox, xwd) https://webautocats.com/epc/saab/sbd/02-25531/0900/
It seems there was a single mass flywheel for - B207E/L (lower power versions 150/175hp) in years 2004-2006 only if with 5 speed and not ethanol (BioPower) :D
Also in that year range the EPC lists a solid sprocket gear 12789018, but ... it is NLS and replaced with spring loaded 55557168 in 2005.
This means that in 2006 there might have been SAABs out of factory still with SMF and but already with the spring loaded gear.
The B207R rated at 209hp seems to have DMF all the time (I have it on both mine - 2005 5speed and 2010 6speed xwd both non ethanol).
If there was some technical reason why some versions had DMF and some SMF or it was money issue, I can just guess.