harmonic balancer SBC

[MASTERBrian]

So, I'm going back through and putting a 350 I built 20yrs ago for a project that never came to be. I've been looking things over and turns out my harmonic balancer has some questionable wear on it.

Since what I seem to read says replace if in doubt, I need to get a new one. The motor is was built to be a nice running street motor, so it has a 270/280 Mega Hydr Cam, bored with 60 over flat tops, valve job, 4 barrel carb and I had the crank polished and balanced. I seem to recall taking the harmonic balancer in for the balance, but I see no signs of any drill marks on it.

Am I correct, that if he didn't alter the balancer, I can just replace it or should I have him rebalance the crank? I plan to pull the crank loose tonight to relube the bearings and I was hoping to then button up the lower end, so I can get this thing running soon.

With the above motor, is it necessary to go with a higher end balancer or is a nice 'factory' style ok? I priced two at O'reilly, one was $50 and the other $84. I've also priced elsewhere but obviously the prices are all over the place. I do like having a scale and the $84 one has that. Jegs has a Professional Products one that appears to be $150. Is that necessary on a motor that is developed more for street and low end torque than racing?

....I realize racers probably spend way more!

[MASTERBrian]

I should also point out. My block is a '74 350 block. The balancer measures 6" across, but everything lists 6-3/4" or 8", but I'm assuming that's the pulley size!

[Marv D]

The harmonic damper is a neutral balance on all SBC's except the externally balanced 400. They don't 'balance' it, they put it on the end o th ecrank in case it is some minuscule bit out, it will be compensated for in the crank balancing. Same with the flex plate / flywheel. USE the one the crank was balanced with. IF the elastomer is visibly dried and cracked then worry. But otherwise verify it is TDC when the pointer says "0" and don't sweat it.

[MASTERBrian]

Originally Posted by Marv D

The harmonic damper is a neutral balance on all SBC's except the externally balanced 400. They don't 'balance' it, they put it on the end o th ecrank in case it is some minuscule bit out, it will be compensated for in the crank balancing. Same with the flex plate / flywheel. USE the one the crank was balanced with. IF the elastomer is visibly dried and cracked then worry. But otherwise verify it is TDC when the pointer says "0" and don't sweat it.

That the thing, the elastomer looks cracked on the back and like an o-ring that is oblonged on the front. I'm now 'worried'!

BUT, if the crank isn't balanced with it, is there really reason to worry, other than the $$ outlay?

[Wrenchbender Ret]

You need to replace it. I like to use the 8 in on 350 engines. The new one does not need to be balanced with the crank.

[MASTERBrian]

Originally Posted by Wrenchbender Ret

You need to replace it. I like to use the 8 in on 350 engines. The new one does not need to be balanced with the crank.

My understanding was that if it came with a 6, it's needs to stay with a 6. Is that not true? What difference does it make? Also, what difference will it make on the balance of the crank if I were to go with an 8in?

[geezer#99]

Why replace it. Run a line of white paint from the center bolt out to the outer edge and check to see if it's moving.
Do you have a pic of the balancer?

[MASTERBrian]

Here's a few pics.

[geezer#99]

IIRC 6 inch balancers came on some 283's and 327's.
THe 6 3/4 and 8 inch came on 350's.

Are you sure you have a 350?
What's the casting number?

[MASTERBrian]

You tell me....those casting numbers are also listed for 327. Here's the catch, the original block was cracked do the machinist sold me this one. From the E304 code, my understanding is its a May 30 1974 block which would be a 350 block from flint Michigan from June 11 1974. 350 145hp 2 bolt tur hydro trans. The last part from the V0611CMR.

I bought a truck with motor from a friend, understanding was always that it was a 350. Since I don't have original block, anything else is out the window. It was in a 79 short wide pickup.

The machinist was and still is a reputable machinist in area, BUT there could be question if he lied about block being cracked because he needed 327. I'd doubt that, but possible. Then there's the question of whether the balancer on it was bad and someone not knowing grabbed a used one, being the wrong one.

As of now I have a 350,'bored 60 over. Crank was polished and balanced, what do I do?

[geezer#99]

Mark it and check it to see if it moves or buy another 6 inch one.
Rockauto lists some for a 327 if you want a 6 inch.
Could be you're right, someone used it because it was handy.
http://www.rockauto.com/

[cadillac_al]

It does have a weird imperfection in the 2nd pic around the 10:00 position. I would replace it.

[chevy_mike]

Without question, replace it. Even if it doesn't come apart while running, it is very likely the outer ring will spin and make your timing marks off. I have had to deal with 2 different engines that this happened to.

[MASTERBrian]

I called the machinist and he said bring it by and he'd check it out. He said since he would have had it to balance the crank, if it had been bad he would have known....of course 20yrs of setting could cause damage as well, I'm sure. That said, he seemed to be of the opinion that some older 350's used a smaller balancer and thus it could have been original.

My understanding is the crank is internally balanced, he said he would have spun it balanced it, then stuck on the balancer and flywheel and balanced them separately if needed and thus he'd just have to balance a new one, but going bigger would also affect my timing cover's timing pointer, so I'll just take all of that in to see where we are.

[Rickysnickers]

FYI I had to replace the balancer on my 350. I have a 6.75" balancer on mine. I bought one of these, http://www.oreillyauto.com/site/c/de...316P&ppt=C0332 Works great.

[MASTERBrian]

Just ordered one from machinist, he didn't like looks of mine. My timing pointer is set for an 8", so that's what we went with. He'll balance it and have it ready Monday/Tuesday..

Thanks for all of the replies

[MASTERBrian]

I'm back here on this....

I got the replacement in last week and yesterday I finally got a chance to install it. I rented the install tool and everything seemed to be going ok. I was making progress, then it got to the point, it just seemed to stop moving. I stopped, checked everything and it seems good. There is about 1/8" from edge of pointer to edge of balancer and that is what I recall there being. I seem to have just shy of 3/4" from back of balancer to front of timing cover. It wasn't like it hit something and stopped, it just got tougher to turn and if I keep going something feels like it might give and break, so I think it's on.

The issue is I held up the old water pump and pulley, lightly put pulley on front of balancer and they don't align.

I'll try to post pics from my phone in a few, but what do I do? Pull it back off and measure? Should have thought of that before, but i didn't. Am I missing something else?

The old balancer was a 6" balancer, the new one is an 8". I've swapped pulley's from what was on this motor, as those had the extra notch for the A/C belt and for now I'm not running A/C and the ones on the motor in the Suburban had the one less pulley, so I'm going to run them. The dimensions all seem the same, except for having the extra pulley. The balancer on the 350 in the burb is a 6-1/2"? I haven't measured the thickness of the balancers....maybe that is the issue.

Anyone know??

[MASTERBrian]

Pics.

The Orange water pump and Orange balancer ate on the engine in the suburban, which I read comparing to. They aren't the one in question with pulleys not lining up.

[MASTERBrian]

Went back out and looked again. The pulleys appear off by about 1/8-1/4". I'm guessing maybe the key moved on me. I'll pull it back off and check again unless I hear something before hand.

Holding old balancer for comparison. I am guessing they are the same size at the length of shaft, but no clue.

[GASoline71]

Originally Posted by MASTERBrian

Pics.

The Orange water pump and Orange balancer ate on the engine in the suburban, which I read comparing to. They aren't the one in question with pulleys not lining up.

The 2nd pic shows the balancer not installed all the way on to the crank snout if you ask me. Looks like the timing tab was pried away from the cover a bit to make the marks work.

Gary

[MASTERBrian]

Originally Posted by GASoline71

The 2nd pic shows the balancer not installed all the way on to the crank snout if you ask me. Looks like the timing tab was pried away from the cover a bit to make the marks work.

Gary

I thought maybe that tab is slightly bent, I might pick a new one up and replace it. I just threw it on because I was putting the timing cover on and didn't have a washer besides the pointer. I also can't believe how bad that cover looks in the pics. I had considered replacing it, but got tired of trying to find a replacement that would definitely work with a double roller chain that was horribly expensive! Luckily in person the bit of marring isn't too bad and it's not like the cover is a highly visible piece...

I'll pull the balancer later and re-check it and get some measurements to know for certain. Thanks!!

[MASTERBrian]

Snuck out and pulled the balancer off. It appears to be 1.3" from crank gear to front of oil seal. Both balancers have a shaft length of about 2.4". The woodruff key was questionable looking in the rear section of it do i pulled it and will pick up a replacement.

One question I have is, the crank gear woodruff key sticks out a bit. Will the balancer slide over that as well? I don't see what would stop the balancer hub other than the crank gear.

[garyd1961]

Your old balancer looks like a 307 balancer to me but the machinist should have known if it was.

[MASTERBrian]

That old balancer was small, he said run it until he saw it closely, then he ordered a replacement.Both ate same hub size.

[GRX]

Good that you got a new key. Check & deburr the keyway in the crank snout too. Hope the seal in the timing cover is in good shape. Don't go dry. Use brake fluid as lube when pressing on the dampener.

As to your question why this part is needed ... to start, the name "balancer" is a misnomer as we are working with a harmonic dampener. The rubber and weighted outer ring are there to dampen and absorb torsional vibrations. Otherwise they would build to the point of extreme shaking at certain speeds.