91 RS Drop Top

This is a question that came up in a previous thread on a related topic. I keep seeing conflicting opinions.

Do a 305 TBI and a GM 350 truck motor use the same balancer?

My 91 RS has 350 truck motor and someone told me it has a 305 balancer on it. I don't know anyhting about balancers.

The car does have some vibration, and at idle sometimes I get a loud low hum that seems to reverberate through the entire car. I think I saw somebody refer to a similar hum on here once. Said it was common in 3 rd gens.

Anyway, whats the no sh-- story on balancers? Are they different for the truck motors? Even if they aren't, could a worn balancer be causing the hum?

SpitotRs305

there are 2 sizes of balancers 6in. and 8in. and they are interchangeable for the 305/350 the only difference is timing tab location... one is at 12oclock and the other is more of a 2oclock posistion...

now this can also be much more complicated depending on the type of balance that was done on the rotating assy. as sometimes elcheapo rebuilders will include the harmonic balancer and flywheel in the actual balance... making it a pain to swap balancers

91 RS Drop Top

Ok. That actually leaves me a little more confused, at least as to what to do.

Here's how I found out my RS didn't have the original 305 in it: I was trying to set the timing and it was way off. The timing cover has the timing tab at 2 o'clock. Cou;dn't get teh car ro run. We figured out that it was the 350, and eyeballed the timing to 12 o'clock. Car is running good no. So which was correct for a GM truck 350? The timing cover with the tab at 2, or the balancer that needed the tab at 12?

I need to change one or the other so I can time it precisely.

Then of course I have the vibration, so I thought maybe it was hte balancer that is wrong

89IROKCONVERT

as long as the balancer matches the tab i dont think it would matter but to be sure i would go with which ever one goes with the motor in this case the large balancer out of the truck

91 RS Drop Top

so the truck motor should have the 8 in balancer? is that the one that gets timed at 12 o clock?

89IROKCONVERT

i just know that the one for the truck is larger in diameter and thinner at least thats the way it looks i once bought one from a junk yard and it was from a truck and wouldn't fit my car thats how i learned the difference.

06andersen

i have a 1986 camaro it has a 305 in it and it has bad bad head gaskets so i pulled the motor.. i dont like thr 305 cuz its....slow lol. i have a 327 with camel hump heads that i want to throw in it. i dont have a harmonic balancer for it tho....i know the crank dont have the bolt hole but i want to use the balancer is it possible? i mean also i could drill and tap a hole if i had to????? help please

five7kid

iTrader: (14)

From the factory, 305's had thin small dampers, thick small dampers, thin large dampers, thick large dampers, 2 o'clock dampers, or 12 o'clock dampers.

From the factory, 350's had thin small dampers, thick small dampers, thin large dampers, thick large dampers, 2 o'clock dampers, or 12 o'clock dampers.

From the factory, cars had thin small dampers, thick small dampers, thin large dampers, thick large dampers, 2 o'clock dampers, or 12 o'clock dampers.

From the factory, trucks had thin small dampers, thick small dampers, thin large dampers, thick large dampers, 2 o'clock dampers, or 12 o'clock dampers.

In short, you can't tell by the damper whether it's 305 or 350, or what type of vehicle it came from.

And, I don't care who you hear call it a "balancer", it's a harmonic damper, not a "balancer".

Regardless of the engine it came from, it will be balanced neutral. Unless it's a factory 400 type damper, or needs one and doesn't have one, it's not the cause of your vibration (unless it's defective, of course).

06andersen

so then i guess that still never answered my question can i use the damper from my 86 on my 66?

five7kid

iTrader: (14)

No. The 305 is bolt-on, the 327 is press fit. (I didn't answer that part because you weren't the original poster.)

06andersen

yah i know that its bolt on... i could dril and tap it and make it bolt on

91 RS Drop Top

Thanks five7kid. So the bottom line is I don't need to devote anymore thought or effort to the harmonic damper, regardless of which type it is. Right?

BASSETT IROC 85

iTrader: (2)

327 small journal is a press fit a large journal has a bolt.

06andersen

you can convery it to a larg jurnal right?? or convert it or put a different one in like one our of a 350 or maybe one that has a bolt hole

BASSETT IROC 85

iTrader: (2)

You can't swap a large journal crank into a small journal block.

06andersen

whats better small jurnel or larg ones

five7kid

iTrader: (14)

It doesn't matter. You're stuck with what you've got.

No bolt means a steel small journal crank.

06andersen

yah i know im stuck with it..ijust didnt know if one was better. i know small journals are uncomon

five7kid

iTrader: (14)

Small journal 327's were made from 1962 to 1967. The 327 was the bread & butter engine during those years. Steel crank.

Large journal 327's were made from 1968 to 1969. The 350 came out during that time, and the 327 became a lo-po 2bbl base V8 engine. Cast crank.

Other than limited choices with regard to harmonic dampers, the small journal would otherwise be considered the superior and more common crank.

06andersen

i was told that i could put the 350 crank in it? i guess i prolly could as long as it was the small journel. i have a few more questions if ur up for it?

five7kid

iTrader: (14)

There was no small journal 350 crank. So, you'd either have to have a large journal block, or cut the 350 main journals down to small journal size. Which would probably cost you more than a used 350 shortblock.

(If we keep this off-topic discussion up, I'm going to have to move your posts with the responses to them to a new thread.)

06andersen

yah i know i just went out and bought a 4 bolt main 350 so ill prolly just work with that if i have problems with the 327 that i have. for some reason the pistons turn hard i havent gotten the starter in yet but i hope it turns it over. thanks for the help man

ninetyone

iTrader: (2)

ok, I have a question. My car was a 305 tbi, now it's a 350 tpi. I know it has the 305 starter, flywheel and 700r4 trans. Now, my problem is when i go to time it. Timing tab is pretty visible on the timing cover. Timing tab appears to be at 1:30. I found TDC with a piston stop. so i remarked the balancer ,but it turns out the new mark i made is right on with the mark originally on the balancer. So, do i have the wrong timing cover? Tdc is coming out to more like 2 o'clock, which is way lower than the timing tab itself! The balancer is a real small one, probably like 6 inches in diameter.