odd balance shaft question

[zedicus]

my balance shafts seized (yes, both) but the oil pump is still spinning correctly and building good oil pressure. what broke and where, to allow this to happen?

 

[19Eclipse90]

How did you verify that the shafts are seized? I'm very interested in the rear shaft considering it is driven by the oil pump. I find it very unlikely that it actually is seized if the oil pump still turns and you still have good oil pressure.

 

[zedicus]

i was changing the head due to another issue and had all the timing off and was trying to time the rear balance shaft. i had the bolt out of the balance shaft locate hole because i was not having any luck spinning the pump and feeling the shaft weight. i wedged a screwdriver in the ballance shaft locator hole and spun the tar out of the oil pump and verified the screwdriver and balance shaft were still wedged tight. then still in disbelief i got a long punch through the balance shaft locator hole and managed to beat the balance shaft around about 1/4th turn. again i verified that in so doing, the oil pump sprocket did not move.

i realize being this close to the front case it was not the best idea to go ahead and assemble it but i was pissed off and who knows how long it had been that way so what would it hurt if it stayed?

the car fires up nicely, builds oil pressure almost instantly. im going to do a oil change this weekend and stuff a magnet up the drain hole to see what is in the pan. the pistons and walls all looked beautiful, it doesnt rattle or anything when running. both front and rear balance shafts are locked tight though.

 

[pauleyman]

There is no way. The shaft is bolted to the oil pump. You need to stop driving it and pull that front case. If shaft is seized the oil pump cannot work. Its possible somebody cut the shaft and left its remains in place and you actually have a stub shaft. Thats the only logical explanation I see.

 

[19Eclipse90]

then still in disbelief i got a long punch through the balance shaft locator hole and managed to beat the balance shaft around about 1/4th turn. again i verified that in so doing, the oil pump sprocket did not move.

If you moved the shaft, it isn't seized. Being tight is different. Was the BS belt installed for the front?

The rear shaft is keyed the same way the front is where it attaches to the driver -- the oil pump gear in the case of the rear and the BS sprocket for the front. Could the gear have been modified to allow the shaft to spin inside of it? Sure, but I wouldn't assume something like that.

Not to say I don't have theories, but you probably won't know what is going on until you take a look.

 

[zedicus]

the motor came out of a bone stock wrecked car. when it originally went in this car the balance shafts spun (thats how i set the rear balance shaft timing the first time)

technically isnt the oil pump geared over to the balance shaft? its behind the castlenut, right? so if the shaft seized and the shaft side gear split, walla, seized shaft functional pump? in theory.


the front balance shaft belt was on, it 'seized' and ate the balance shaft belt. i did manage to get the front balance shaft to turn with a ratchet and rubber mallet. technically you are right, they are not siezed, but they are stiff enough they would eat a belt in seconds.

 

[19Eclipse90]

The shaft side gear is driven by the oil pump sprocket but it is the two internal gears together that pull oil from the pan and transfer it to the rest of the engine. If that gear split, the pump is on borrowed time.

I have a theory for the front shaft as well, but until the oil pump is checked, it's not worth mentioning. It shouldn't have seized if it was properly lubricated. The bearings may have gone out but that won't seize the shaft without making a terrible amount of noise first.

 

[zedicus]

there was no noise and honestly it has nothing to do with the reason i pulled the head. but in pulling the head i looked over cylinder walls and inspected things and found nothing concerning other than both balance shafts inoperable.

i will be doing some work on it this weekend and depending on what else i find i may pull the front case. expect updates in a few days.

the oil pump is a gear pump and not a veined shaft or anything? i have been in them but i have drank and slept since then and memory is a little fuzzy on the inards of the dsm oil pump.

 

[19Eclipse90]

Yes, it's a gear pump. Do let us know what you find.