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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
So limit this discussion to GM small and big blocks, any year. And the words flexplate/flywheel are interchangeable since the same starter will be used on any particular application, manual or auto transmission.
I've done some limited research, just need to confirm. Since the GenI SBC till now, is it a fact that 153 tooth flexplates are 12.75" measured tooth to tooth? And 168 tooth flexplates are measured 14" tooth to tooth?
Thanks sofa, so is it a fact that the 168 tooth flexplate is meant for a BBC and the 153 tooth is for the SBC?
No, it's only two piece seal and one piece seal. You can put a 168 tooth on a SBC and a 153 on a BBC as long as you use the correct starter. This does not account for the weight on the flexplate or FW though.
It has NOTHING to do with BB vs SB, or 2-pc vs 1-pc. ALL V8s got the 14" wheel until the late 70s. BB and SB both. The 12.8" wasn't introduced until around 77 or 78. That's why the starter bolt holes for the late-model small wheel have to be drilled in earlier blocks. Trucks, BB & SB both, continued to use the 14" until … well, probably the present... I'm pretty sure the 5.7 Vortec did as recently as 2000, and the 8.1 still does.
It has NOTHING to do with BB vs SB, or 2-pc vs 1-pc. ALL V8s got the 14" wheel until the late 70s. BB and SB both. The 12.8" wasn't introduced until around 77 or 78. That's why the starter bolt holes for the late-model small wheel have to be drilled in earlier blocks. Trucks, BB & SB both, continued to use the 14" until … well, probably the present... I'm pretty sure the 5.7 Vortec did as recently as 2000, and the 8.1 still does.
Yeah, and regarding the bolt pattern for a starter meant for 168 flexplate, they have the offset pattern. And the bolt pattern for the 153 tooth flexplate starter is inline....
Whats funny is, I was shipped a 14" flexplate with a certain forged bottom end package, which is balanced internally in the front and externally balanced in the rear by the flexplate. But they sent a 14" flexplate and I counted 153 teeth.
Whats funny is, I was shipped a 14" flexplate with a certain forged bottom end package, which is balanced internally in the front and externally balanced in the rear by the flexplate. But they sent a 14" flexplate and I counted 153 teeth.
I hope that company measured the internal engine parts better than the flexplate. At least their screw-up was in your favor. 153 tooth is what you want, but you said EXTERNALLY balanced rear, which I read as that flexplate should have a weight on it.
Ok, my mistake, the last time I counted the teeth was a couple years ago. I recounted now and it is indeed a 14" 168 tooth flexplate. And it does have a large weight and 3 drill holes. But I do need a 12.8" flexplate. What do I do at this point? Call my machine shop?
It will depend on whether that 14" flexplate will fit inside the transmission AND if your block is drilled with the holes to accommodate a starter to work with it.
Since the block is already at the machine shop, have the 3rd hole drilled and tapped if it is not there already. It will save you tons of grief later.
Sofa can provide a nice diagram of what must be done.
internal balance everything and get a neutral balance 153 tooth flexplate. This is how any modern engine should be done and L98’s and LT1’s had 153 tooth so keep it simple and do the same
internal balance everything and get a neutral balance 153 tooth flexplate. This is how any modern engine should be done and L98’s and LT1’s had 153 tooth so keep it simple and do the same
I'm guessing this is for a 383. Yes, INTERNALLY balancing everything avoids these kinds of problems.
Well, I hope all this info is helping someone else, because I'm already 90% done the build and this was yet another snag. It's my first and last build, so it has to be done right.
I called 2 folks today to confirm my next step. Called Scat Enterprises, who made the rotating assembly I use and they said just get the 153 tooth 12.75" flexplate meant for external balance. Then I called my machine shop and they agreed. So I'm pretty confident going forward that's all I need to do....
I am sorta tempted to see if the machine shop can balance the 12.75" flexplate exact if I give them only the 14" flexplate. They did recheck the balance when I had it there, and there's 3 drill spots where they removed a slight amount of metal. Probably just my OCD, but it can't hurt to ask... I might call tomorrow.
You're lucky. When I built my 334 (stroked 305), no one made a 153 tooth 12.75" flexplate meant for external balance. I had to use a add-on counter-balance plate.
In the case of the 86-up wheel, I would STRONGLY recommend that you TOTALLY AVOID the terms "internal" and "external" balance.
The 305 and 350 are ALL "internally" balanced. The only stock SBC that's "externally" balanced is the 400. Of course, since the 383 uses the 400 stroke, it might well be "externally" balanced as well; but with proper attention to detail, it can be made to have the STOCK "internal" balance.
The problem is, the rearmost INTERNAL balance weight for the INTERNALLY BALANCED 86-up 305 and 350, is mounted on the flywheel, and to the untrained eye, LOOKS "external". It is NOT. It is merely the same thing as the funky-shaped flange on the crank in the earlier 3.48" stroke motors w 2-pc rear main seal, except that since that flange now has to be round, they moved that last little bit of weight to the wheel. Here's a photo of the counterweight.
"Internal" and "external" do NOT refer to which side of the seal the weight is on, or which side of the split between the crank flange and wheel. However even the manufacturers of cranks and other pieces have somewhat given up on the correct use of the terminology since it is so completely misunderstood and as a result gets butchered so bad in the world at large.
I recommend that you use the word "STOCK" instead of "internal or "external" whenever discussing the balance of a 383 rotating assy. Depending on the rods and pistons that are used, specifically if the rods are allowed to be longer than the stock 5.565" (for 400) and the piston pin to be up higher in the piston than the stock 1.425" pin height, it is usually possible to drill a hole in the rod journals of the crank, and thereby remove enough weight from the rod throws to allow the INTERNAL counterweights to fit inside the engine, which would then allow a STOCK flywheel to be used. This would avoid having to use the "pork chop" counterweight that NE84 shows. That counterweight will be necessary in a 383 w 5.565" rods (stock 400 length) in virtually all cases and even some w 5.7", unless $$$ Mallory metal $$$ is used to weight the crank. Which is SO $$$$$ that it will almost certainly cost MORE THAN a whole assy consisting of INTERNALLY balanced crank, long rods, and non-stock-configuration pistons.
Remember, purge "internal" and "external" from your discussion about balance, and replace with STOCK. That way, all the supplier has to tell you is, yes you can / no you can't just bolt your STOCK wheel onto your new motor. Avoid ANY supplier that can't tell you STOCK or NOT STOCK, and if possible, any that don't allow STOCK. This is a sourcing decision that MUST be made BEFORE you turn the first bolt. It's not something that can easily be changed after you already have the rotating assy in your hands. It's almost entirely a property of rod length.
Eh to me if the crank can not be balanced to the rotating bobweights by either shaping the counterweights, drilling them, or adding metal to crank to “balance” it then its not internally balanced. I get what you said but a flexplate that has a weight on it to aid in crank balance is still externally added in my opinion of the terms and becomes a type of external balance by definition.
They sell neutral balanced flexplates. Neutral balanced dampers. Theres no reason a machine shop cant balance a typical sbc crank to the typical bobweights and not need anything else to do it. My big 555” is “internal” balanced. Crank counterweight mods alone is enough to balance it for my system weights. Balancer and flexplate are neutral, meaning they dont aid in any balance effect of the internal crank/rods etc.
semantics maybe, just the way i viewed things and always referred to balancing terms
"Internal" balance means that there's enough room under the bottom of the pistons when they're at BDC, to fit a counterweight that completely counterbalances the setup. 305 and 350 ALL allow this. "External" balance means that there is NOT enough room to fit such a counterweight; the bottom of the piston would hit the CW before the CW could be made large enough to INTERNALLY balance the motor. If you look at a 400 or 454 crank, you'll notice that the counterweights aren't completely circular like they are on a 350 or 396 crank; rather, they're "flat cut". THAT is what "external" balance means: the weight can't be mounted "internally", that is, in the proper location for ideal dynamic balance, which means, directly opposite (in between, aka internal to) the rod journals that it's counterbalancing.
Here's a wonderful photo of a 400 crank counterweight that shows EXACTLY what the problem is, ganked shamelessly from that infinite source of photos of virtually anything that can be bought and sold. You can see clearly how the counterweight is "flat"; not all the way circular. This lack of metal means that it can't completely offset the weight of the rods that it's between. NO machine shop can fix this without somehow making that counterweight heavier; hence the use of $$$$ Mallory metal $$$$ plugs in the counterweights, which is MUCH denser than iron, by a factor of almost 2, to add more weight than the iron alloy that's drilled out to make room for it. If it could have been done, then the factory would never have done otherwise in the first place.
"External" DOES NOT mean that the weight is mounted "externally" to the engine in some way, although, in most but not all TRULY "externally" balanced motors, it does happen to be. The missing weight that won't fit inside the rotating assembly is mounted on the damper on the front and on the flywheel in the rear.
Saying that just because the weight "looks" "external" to the naked eye, it's "externally" balanced, is EXACTLY the confusion in the marketplace. Note that this confusion DID NOT exist before the introduction of the 1-pc RMS: it never caused trouble with the older motors. Although, I seem to recall a few older "externally" balanced motors, where the weight was put on the crank flange, and therefore, to the typical street stroke, it would "look" "internal" (since the flywheel was neutral).
So yeah, you hit the head right on the nail in a way, "semantics" is EXACTLY the problem here. The problem being, what those words REALLY mean, as opposed to what the uninformed and uneducated THINK they mean. If they are given their TRUE meaning, which is, the "flat cut" counterweight situation and other similar approaches to the problem that various mfrs have used, then ALL 305s and 350s are "internally" balanced. That is the REALITY. But since the mutilation of those meanings resulting from the 1-pc RMS design has become popular among those who don't understand the TRUE meaning as described above, then confusion is the result.
Which is why it's best to AVOID those words ALTOGETHER when talking about 86-up SBCs, and instead, use the word STOCK. Then, there is no confusion between the REAL definition and the STREET STROKE "definition" of those technical terms. I would also avoid forcing a 1-pc motor to require a neutral wheel, since that is NOT stock, and additionally, is not possible in all parts combos without the expense of $$$$ Mallory metal $$$; doing that just causes more difficulty later, whenever any of the parts has to be changed. STOCK is the operative concept to stick with here. That way, everything in the world bolts right up without any "special" effort or expense or risk or confusion. You go to the store, you buy what's on the shelf, you bolt it up, you're DONE.
Last edited by sofakingdom; Jul 31, 2019 at 11:03 AM.
External" DOES NOT mean that the weight is mounted "externally" to the engine in some way, although, in most but not allTRULY "externally" balanced motors, it does happen to be. The missing weight that won't fit inside the rotating assembly is mounted on the damper on the front and on the flywheel in the rear.
lol so weight is mounted on the external of the engine so it is external balanced.
If it could have been done, then the factory would never have done otherwise in the first place.
Gm messed up. They used trex arm rods and big pistons, using a 5.85”-6” rod and shorter piston could have made it possible.
You can buy internal balance 400 cranks. My 2 pc rear aftermarket 400 was internal balanced with 6” rods. No reason gm couldnt have done it too.
Mallory makes alot possible but is money so not recommended. To me its pretty simple. Counterweight balance alone is internal balance. Any weight on the outside on flexplate or damper/balancer is external.
weight is mounted on the external of the engine so it is external balanced
No. I explained it above.
Counterweight balance alone is internal balance
Yes: but IF AND ONLY IF that is taken to mean, that the INTERNAL counterweights (the ones BETWEEN the journals) can be made large enough to COMPLETELY counterbalance the rods etc. that they are between, UNLIKE the 400 or 454 crank (EXTERNAL balance) that DOESN'T allow enough INTERNAL counterweight.
Any weight on the outside on flexplate or damper/balancer is external
No. The 305 & 350 are still INTERNALLY balanced, even with the little batwing on the wheel. The rearmost bit of INTERNAL counterweight, the part that used to be provided by the funky flange in the other photo I posted, is moved to the wheel. That DOES NOT make it "external".
Gm messed up. They used trex arm rods and big pistons, using a 5.85”-6” rod and shorter piston could have made it possible.
That is arguable. At the time, GM evidently felt that the ring package (keeping in mind, this was with the technology available and which would have had to be at zero cost to them back over 50 yrs ago) was more important than the balance technique. They were not willing to do what we feel MUCH more comfortable with TODAY, which is, narrower rings and narrower piston lands between them. That's different from "messed up".
You can buy internal balance 400 cranks. My 2 pc rear aftermarket 400 was internal balanced with 6” rods.
Yes, absolutely. This principle applies to any SBC with strokes much above 3.48". It is precisely what I advise, because the use of the longer rod allow enough INTERNAL counterweight to be present to INTERNALLY balance the motor. An ideal 1-pc RMS 383 build, for example, would have long rods of this sort, not necessarily 6.0" but certainly longer than 5.7", which would then allow INTERNAL balance, together with a STOCK flywheel with the rearmost bit of INTERNAL balance weight mounted on it. Such a configuration allows total interchangeability with all STOCK configuration, off-the-shelf, flywheels.
As said, this is exactly the semantic problem with using the words "internal" and "external". Those words DO NOT mean, "whatever I think they mean". They DO NOT mean, "mounted somewhere other than integral to the crank". They DO NOT mean, "what it looks like to me". They have a specific meaning, just the same as you wouldn't call a blue thing red and realistically expect everybody else to go along with you. Only people who are uneducated think that. As said, it is possible to have INTERNAL balance with weight mounted elsewhere, and EXTERNAL balance with the full static-balance weight on the crank.
Using the word STOCK for the 1-pc RMS SBC dodges the whole confusion. As said, STOCK in relation to the 1-pc RMS SBC means, INTERNAL balance, with the rearmost bit of INTERNAL balance weight mounted on the wheel. EXTERNAL balance would be required if a 3.75" stroke and 5.565" rods is used, and in some cases depending on the weight of the big end of the rods, 5.7" rods; since in those cases, it would not be possible to fit the required counterweight size INTERNALLY, i.e. between the rod journals, because the CWs would interfere with the bottom of the pistons at BDC. NEUTRAL balance in that type of motor is also NOT STOCK, and therefore is to be avoided. The word to concentrate on is STOCK.
There IS NO OTHER correct definition of these terms. They have been around FAR longer than 1-pc RMS SBCs, or for that matter, SBCs, or even V8s. Confusing the mounting location of the rearmost weight with basic internal engine dimensions is ONLY done by people who don't understand the REAL definition of those terms, and is common in the marketplace, causing endless grief to inexperienced or uneducated people building motors and choosing the wrong parts because they don't know the definitions of them. This "discussion" we're having here is a good example of the problem; you have someone that knows the REAL definition of the words and is showing it in photos, and someone using the "layman" mis-definition. Only one is right. The other is wrong.
Agree to disagree on this lol. Anyone can internet search what manufacturers are using. Scat, Eagle, fluidampr, and other major companies have definitions laid out on their sites or in articles which coincides with what i said. I suggest a refresher might be in order
Seems like a healthy debate, which I'm going to avoid... Not to pick sides, because I respect a point of view from someone that's been in the business probably well before I even started turning wrenches in the early '90's, but as Orr said above...
Here's the Harmonic Balancer, 'Balanced' rotating assembly and Flexplate I'm using. Just keep in mind when I originally ordered the bottom end, I didn't specify which size flexplate I needed (I received the 14" as mentioned), hence my issue after I found a starter which cleared my headers.
Um, okay. So for the $1,000,000.00 question - Is there a 383 rotating assembly available that uses BOTH a neutrally balanced harmonic balancer and 153 tooth (12.8") neutrally balanced flywheel/flexplate with all "balancing" done to the counterweights of the crankshaft? If so, who makes it? And what connecting rod length is used?
Not sure of any “kits” but a good machine shop can do that. I ran eagle before and the machine shop/builder balanced it. Neutral flexplate and balancer. 1 pc rear main block
carl at cnc blocks did my 400” turbo machine and balance. 2pc rear main however but no matter. Neutral flexplate although 168 tooth i believe for my th400. Neutral balancer. Modern cranks modern rod/piston sizes it can be done fine
same with my 4.25” stroke 555”. Neutral everything internal counterweight only, but has a extra center counterweight which helps. 6.635 rod but heavy piston. Still balanced fine
Not that I'm going to convince anyone of anything, but I would contend that the batwing on the flywheel exists to balance the ridiculous 1 piece flange and has nothing whatsoever to do with the internal vs external balance debate. If it weren't for the shape of the flange it wouldn't be needed in the first place.
At least their screw-up was in your favor. 153 tooth is what you want, but you said EXTERNALLY balanced rear, which I read as that flexplate should have a weight on it. 
