1986 Chry. LeBaron T&C Wagon - What are these 'balance shafts'?

Putting in main bearings into a 1986 Chrysler LeBaron Town & Country Wagon
(before they assigned Town & Country to the minivans). Big ol' cast iron
unit that is chain driven with two counter-rotating shafts. Only
information I can find is that they are 'balance shafts'? What is the
purpose of this unit, and does it have to be timed? (person already removed
it from car).

Marc (remove the NOSPAM letters from email address if replying by email.
Thanks)

 

Four cylinder engines above a given displacement ten to shake
themselves right out of the chassis, the balance shafts counter
act this tendancy.

You betcha they have to be timed.

 

Thanks for the reply. I see the balance shafts themselves are timed to
themselves... but do these have to be timed to the engine somehow? No
timing marks or anything on it. Chilton's book is useless as it doesn't
even mention these balance shafts.

Marc

 

There should be marks on the outside (end) face of each gear*,
they should be pointing at each other (3 o'clock, 9 o'clock) if
not there or obscured, position the keyways both to 12 o'clock,
at this position they get timed to the crankshaft with cylinder
number 1 being at Top Dead Center.

(* if you only have the oil pan off, you're probably not in deep
enough to see these marks)

IOWs, correct timing equals both balance shaft -keyways- being at
12 o'clock when the crankshaft keyway is at 12 o'clock (TDC#1)
or
The gear -marks- are 3 o'clock-9 o'clock with cyl #1 at TDC

Not surprising, but have you looked in the section that pertains
to "engine oiling?"