Motor Swap/Install sorry its long winded.

[joedoozer]

Harmonic balancer from a late Gen 305 to Gen 1 block 350........ Here is how it all started.

I bought my 72 LWB about a year ago. It had a newer (center bolt valve cover) 305 in it, and a 700R4 tranny. The original 350 was in the back on an old tire, complete from pan to carb. I decided to rebuild the 350.......8 months later and I am ready to bolt her in.

I got the the 305 out, and on the ground and I start pulling parts and swapping things. Sending units and fittings and what not. I notice the balancer is shorter and fatter than the one off the 350. It had a triple pulley on the crank, and the inside groove is for the alt, and the outside was the power steering pump (non-a/c). Obviously if I try and bolt the pulleys to the taller thinner balancer they won't line up with the alt or the pump.

Here is what I know of balancers. All SBC (except 400's i think) are internally balanced, so the balancer isn't there to "balance" the engine. If it were, you wouldn't be able to buy them from a catalog. It is in place to absorb harmonic vibrations that occur in the engine at certain RPM's. I know this is extremely important on racecars (short track and drag cars). The engines are screaming, and running in the upper end of the RPM range most of its life.

For a daily driver/cruiser it will never have the abuse a drag engine or a circle track car will get, or run over 4000 for lengthy periods of time. Can I use that balancer off the 305 for the 350? It fits the crank, it is the correct depth for the crank bolt, and the correct diameter for the front seal. I also have an add-on timing plate, so I can use different size balancers. Or should I start walking the junk yards for the correct pulleys for the crank (to get the correct spacing)? And yes I know the correct thing to do is buy a new balancer......but I am trying to avoid that. And if it does have any kind of a shake, I will fork out the money for a new balancer. I don't want to fatigue the crank at all.

Both balancers are in excellent shape. The rubber is in perfect shape, no dry-rot or cracks. So I would like to use one of them.

Sorry this dragged on, I kept going back and writing more stuff.

[monte0185]

actually if you stand the balancers up on the part that goes into the timing cover youll see that they are the same height. which will allow you to use the pulleys you want on either balancer. Now that being said use the correct balancer that goes with the engine. It Does make a difference believe me. Most people think 305 and 350 cranks are the same but when you get into balancing them they are completely different critters.

[joedoozer]

On a bench they are are not the same. So you are saying when it is installed it is? Once I seen they were physically different, I figured that was a good stopping point for the night. Plus I still have a broken motor mount, starter/flywheel issue to figure out. I will mount the brackets tomorrow and put the correct damper on, and see how it lines up. Thanks

[monte0185]

Can you send me some pictures. Those always help. If you lay them flat on the bench with the portion that goes into the timing cover face down to where you are looking at the bolt holes they should be the same height. Now the pulley's vary in height and depth. But the balancer should be the same. I have a 307 and a 305 and a 350 balancer at home and they are all the same height just different in the part that actually does the balancing. Ill take a pic or two tonight as well. Regardless you will need to use the correct dampener cause it does make a difference.

[joedoozer]

Balancer problem solved. If I would have just took the 5 minutes to bolt it on, along with the alternator. I would have seen it all lines up.

Next problem is the broken motor mount. And no junk yard around has one.

Which I will have to post pictures from. Because the one in the LMC catalog looks nothing like what was in the truck.

[joedoozer]

First pic is the side view as it would sit in the truck.


View from the face that bolts to the motor.


Last pic is the under side of the mount that bolts to the motor. The center of it is threaded.


Any idea where I can get these? Are the later model year mounts interchangeable?

I appreciate all the info you guys provide. I will be buying some people some beer at the Turkey Rod Run haha.

[71tahoe]

Which piece do you actually need. Pic 3 is the motor mount and 1 & 2 are mount and tower.

NAPA, Autozone, Advance Auto, O'reilly's, etc carry the mount. Check the threads when you get it. O'reilly's sold me one with metric. They were more than happy to sell me a bolt too. I got my money back and now I shop elsewhere for stuff that actually needs to fit correctly.

If you need one of the towers, someone on the board is probably parting a truck.

[joedoozer]

I am way to impatient haha. I need to take 10 minutes and do more research . The tower is good, and I took a pic of the good mount I had. The passenger side (engine mount), not the tower is destroyed. I found some at brothers, but I will check my Napa guy in about 20 minutes. I will post my findings.....for future impatient people that are looking for these .

Thanks all.

[joedoozer]

I found the mounts on Brothers, for $16 each and they have a standard bolt hole in the rubber. Napa had both mounts on the shelf, for $10 each....unfortunately they have a metric bolt in the center. The big "made in India sticker" was a dead give away. As much as I don't want a metric bolt on my truck, I need the mount today. These mounts are used on I6 and SBC up to 72, excluding the 283 in 1967. The "U" shaped engine mount with the through bolt is used on SBC 1973-1987.

I hope this thread helps someone in need in the future.

[joedoozer]

Double post....so I edited it .

[71tahoe]

The last set I bought at Autozone had SAE threads if that helps any.

[monte0185]

I just bought a set at advance that were sae thread.