sreZ28

First, let me apologize for my ignorance. I have to admit I know very little about engine building.
I'm beginning my first build, and putting together a rotating assembly. I read a few books and decided I knew enough to get started. In my youthful ignorance I decided I would piece it together from craigslist parts.
So far I have:
-Wiseco forged flat tops (1.260 compression height, 369g)
-pins (106g)
-forged scat 6" rods (big end 430g, small end 176g).
I was planning on buying a forged 3.48" crank. However, what I have so far seems really light. With locks, bearings, and rings, will this still balance nicely? What are good choices for these things? I have an 880 roller block, should I get an internally balanced crank and get a conversion kit, or stick with the 1pc rms style? I have a nice 2pc rms neutral balance flywheel, will this work with both or only one? I care much more about it being sturdy and well built than fast.
Thanks

AlkyIROC

Internal/external balanced crank has nothing to do with the bob weight of all the components on the crank.

Externally balanced cranks are for the SBC 400. The use a special externally balanced dampener and flexplate/flywheel. All other SBC engines are internally balanced and the dampener, flexplate/flywheel are considered neutrally balanced.

Doesn't matter what parts you gather up to build the engine, they will all need to be balanced by a professional balancer. All the rods/rod bolts need to weigh the same. The rods need to weigh the same on both ends. The pistons with wrist pins all need to weigh the same. Once the total weight of pistons, rings, wrist pin, rods/bolts, rod bearing etc are all added up, a bob weight is then put on each crank throw and the crank is spun up to balance it for that weight.

It's up to the person doing the balancing to determine if weight needs to be removed or added to the crank to balance it out.

sreZ28

Ok, cool. Thanks for getting back to me so quickly and with such good information.
I thought that the newer blocks like I have are externally balanced, and need a special flywheel and harmonic balancer. Is that wrong?
I have been worried because I read an online article by Hotrodders magazine in which the author built a stroker ford engine from scratch and had a difficult time balancing it because the shop owner said it would look like Swiss cheese. I haven't been able to find a decent explanation anywhere else.
I am definitely planning on having the rotating assembly balanced by a reputable shop. In one of the books I read, it said the longer rods lessen thrust against the cylinder wall, and make it cheaper to balance the rotating assembly because it is lighter, and doesn't need mallory metal added. Is there any truth to that?
Some crankshaft companies list a target bobweight that they are supposed to be close to. Is there a point in buying a lightweight crank if you are closer to that? Is a light rotating assembly a good thing or a bad thing, or neither? I'm not looking to drop an extra $300 if it's not worth anything.
Are there any rings, bearings or pin locks that are particularly solid? I heard Clevite 77 or Vandervell Bearings, and total seal rings were really good, but I'm quickly learning how little I know.
Thanks again. I really don't want to mess this up.

Night rider327

iTrader: (13)

What are you looking to do with this engine? That should be the 1st question. All else then falls into place.

Yes light cranks/rotating assemblies are great, but not really needed or noticeable to 75% of us here on the board. If you plan to spin 8,000 rpm it's a MAJOR thing.

Or if it's a max effort HP race engine it's a major thing.

But for most street/strip cars a $190 scat 9000 cast crank works great.

All but the 400 sbc is internal balance, the 400 is the only stock sbc thats external balanced.

86LG4Bird

iTrader: (1)

If by "newer", you're talking since early/mid 80's, then you could be referring to the weight on the flexplate that compensates for the material that had to be removed from the crank to make room for the "newer" 1-piece rear main seal. 1-pc RMS engines are still referred to as internally balanced.
So yes, there are "1-pc RMS" flexplates and flywheels and there "2-pc RMS" flexplates and flywheels. At the front, the damper is always neutral unless you're talking about the 400 ci engine.

sreZ28

Thanks everyone, this is all really good stuff. So 8000 RPM is a bit excessive for me. This is really just supposed to be a mild to medium daily driver. That said, I would like for it to last me a very long time. Is the forged crank really worth the money here? I don't think it will ever see the top side of 6,500 RPM, but if it adds dramatically to the longevity of the engine I'd prefer to pay for it now rather than later.

86LG4Bird

iTrader: (1)

You don't need a forged crank.
However, if at all possible, I'd advise reconditioning a stock crank rather than buying a junk aftermarket cast crank.
I'm spinning the factory cast crank to 7100 rpm for 5 years now in my LT1. I would never try that with a Scat or Eagle cast crank.
AFAIK, there are NO quality aftermarket cast cranks.

Night rider327

iTrader: (13)

I'm going on 10 years with a scat 9000 cast crank in mine. Many low 11 second passes and many street miles on it.

The scat 9000 cast crank is almost as strong as a GM forged crank, and lighter than a GM cast crank.

My 1st engine combo I shifted at 6400 rpm, and my last combo I'm shifting at 7200/7300 rpm.... Both with the same scat 9000 cast crank

MoJoe

iTrader: (5)

Are you sure about those pistons / height? With a 1.260" height, your crank (3.48 2) + 6.000" rod + 1.260" piston only adds up to 8.500". That is going to be 0.500" in the hole of a 9.000" "decked" block, or 0.525" in an uncut 9.025" stock block.

Considering these discussions revolve around 5ccs and 0.005" to 0.040" measurements, a full 1/2" will give you 6:1 compression.

sreZ28

I'm sorry, but I think you might want to check your calculations one more time.
3.48/2=1.74
1.74+1.26+6.00=9

So if I do grab a forged crank, it's not going to be so far out of balance that they tell me to get lost right? If I snag one of those scat 9000 cast cranks should I grab the lightweight one?

bbc632

Did what I do buy once and go ahead cry once then it's done. By the best you can and just do it .

couchmotors

Scat is a better product than eagle Chinese junk.Scat has a better hardness test than eagle.plus there nitrated eagle cast cranks are not only there forged ones are. I have a scat 9000 stroker in my 496 i called scat when i was building mine and talk to them. Plus every time i see a motor let go its always eagle interals. In my opinion scat makes a great product but you have to balance them before you build. I can get a rotating assy balanced for 125 in jax fl. But i weigh all my parts and make sure there within .o01 grams of each other. I have built hundreds of motors i always have the rotating assy balanced. You just get a better lasting motor plus the car dont shake. If your going to build your motor build it to last no matter if your a daily driver or all out drag racing it will pay off in the end

MoJoe

iTrader: (5)

Good for you for checking my math. I don't know where/how I lost an even 1/2 inch!