Curious about this. Particularly when pertaining to a sbc 350. My understanding is prior to 1985, these were mainly internally balanced through the crank, after 1986, they were balanced by adding weight to the flywheel/flex plate and the crank? I also see talk regarding zero balance, etc.... Here's my confusion, my sbc 350 was machined 20 years ago and I had it balanced. The motor was assembled, never ran as I changed directions....fast forward I tore it down and went back through, replaced gaskets, etc. During the recent rebuild I noticed the harmonic balancer needed replaced due to separation. I had/have been back in contact with original machinist as he's still in business. Even I started going back through engine I took all my old receipts to him and we discussed what he had done, etc. When I realized the balancer was bad, I took in my old, which was 6", not a common balancer on 350, he said go back to 8", especially since my point was for 8". He ordered one and said it needed balanced since engine was balanced....I thought he said externally balanced. May have mis-understood. But he did take material out of the balancer. Fast forward 500 miles on motor and I'm having starter issues and my flex plate has a few teeth getting messed up. Actually 2nd starter in the 500 miles. I can explain that if need be, but for now I'll stay with balancing question. Because I don't want issues and because I'm questioning a flex plate with a few bad teeth, I called machinist and asked about balancing a new flex plate. He questioned this a little and I explained that the motor was balanced and when he ordered me a new balancer he balanced that as well....He then said ok, I understand and said yes I needed flex plate balanced. Next day he called had flex plate ready and I went to pick it up. He didn't add weights, he took material away via drilling and he might have mentioned neutral balance or something like that. In any case my block is a 1974, two piece rear main and thus from my reading on this today due to discussion elsewhere about balancing it seems my motor should be internally balanced. What gives here? This machinist is very well known in area and from my understanding used to build awesome motors, so I have no reason to doubt him. My motor feels very smooth....so if something isn't right I haven't felt it. Externally balancing parts for an internally balanced motor seems like would be rookie mistake, so I doubt that's the case. Is it normal to take material from flex plate and balancer on internally balanced motor? I'm sure he said it was externally balanced originally....so is that possible? I understand only 400's were externally balanced and he knows mines a 350. What happens if an engine is internally balanced and a flex plate or balancer goes out? Is the balancing gone or do you do what he's doing? Seems like you'd still want those parts balanced to mesh with everything. Can someone make sense of this for me?
Internal balanced are considered neutral balance. Some builders balance the damper and flywheel as well to make sure they are neutral. An external balanced motor relies on counterweights on the damper and flywheel to offset the imbalance of the rotating assembly. Sent from my Moto G Play using The H.A.M.B. mobile app
The crank should have been balanced to neutral balance, and he hopefully just balanced the damper and flexplate to neutral balance also. You'd have to ask him what he did, we can only guess.
Eating the teeth off the flywheel is't a balanced/unbalanced thing, just starter positioning. Assume you are using starter bolts, not just regular bolts? And then there's shimming the starter if needed.
I very much recall places on crank where material was taken from it, so he must just be neutral balancing the flex plate and the damper. Makes more sense now. It threw me when he said that about the dampner this go around but if memory is correct he had flex plate and damper when he machined engine 20yrs ago. I would also wonder how someone could balance a motor but not take these things into consideration. I was starting to wonder if the flex plate was a balance thing. I did shim both starters and I'll shim the new one if needed. Crazy thing is both previous ones were fine shimmed, then not. First one failed completely after 100 miles, ended with faulty battery terminal connection. A screw fell out of 2nd one when I pulled it out. To back and got money back and ordered mini torque powermaster from speedway.
I only had one rebuild balanced in my life,I recall the shop wanting me to bring in my fly wheel, I don't recall if they wanted the balancer too. I ask the guy "so if you balance my flywheel to the engine, and I need to change it, doesn't that mean I have to pull the bottom end out too?" "yes" he said. I thought that was a pain, so I just had the FW and PP balance separately.....probably didn't really need that anyways.
they are all balanced from the factory. The starter shimming thing...do you measure the clearance before deciding whether to add shims or not? should be 1/8" between the starter shaft and the outside of the ring gear teeth. Use a 1/8" allen wrench, if it fits in there, but you can't twist it, it's perfect. Too tight, add a full shim, try again. Too loose, add the outer half of a shim (cut it in half first), and try again.
SBC engines have three (3) different timing pointer locations:- Pre '69 engines, TDC mark is 2° to the left of the keyway centre line; '69 and later, TDC mark is 10° to the left of the keyway centre line; and 1984 -'95 engines, TDC is at 12 o'clock position on the damper. I went the opposite way from an externally balanced 1990 350 and went to an internally balanced assembly. A smaller and lighter balancer allows the engine to rev quicker.
That is the main reason that I liked to have each piece balanced. If, for some reason, the damper, flywheel or clutch has to be changed you only need to have the new component balanced.
Not being there to see the damage. I wonder if the starting motors aren't quality units. We had to change re-builder/supplier to cure an issue like this a few years ago (was an old small block as well). Might check to make sure the crank did not get bent at some point.
I definitely think it's an issue with lack of quality on part of starters, which is why I am now going another route. Why would the crank get bent? ....surely you aren't suggesting the starter issues could been bend the crank! This motor only has 500 miles on it, even though it was built 20 years ago. I did go back through it and relube internals and change seals and gaskets, but per machinist recommendation I did not pull crank back out.
Don't believe a starter would bend a crank or flex plate, however, you would be surprised what would during storage. We usually see it on the front end due to jacking the engine by the balancer. I wasn't implying that it was probably bent, just that we have seen it on rare occasion and that it is easy to rule out.
Got you. The entire time it was stored it was assembled and on an engine stand. Cannot recall ever putting any pressure on the old balancer.
I hate to admit this, but it is true. I replaced 3 " bad starters", ( all warrantied) before I accidentally discovered that one of my mounting bolts was bent! Bought two new OEM bolts and problem disappeared. I did find out that my auto supply store carried 3 different priced starters for SBC though. Two were reman's and one was new. Cheapest reman was pretty sketchy quality wise. Long reply just to say, make sure you are using correct starter bolts.
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