crankshaft

[westsidek20]

Rookie questions,
Im thinking about doing a build to turn the 350 in my K20 78 into a 383, ive been looking at some kits that Jegs sell. I have some questions about the crankshaft, whats the diference between the two or one piece main rear seal? and internal or external balance?

[DustyRusty]

I haven't looked at the Jeg's kits so I can't say for certain as to quality and price.  I think your engine requires a two-piece rear main seal if it's the original engine.  IIRC, all the 383 stroker kits are external balance.  Normally, for ~$200 they can balance it for you so you don't have to take it to a shop when you take delivery.

You might want to do a little more searching on the 'net.  I've seen 383 stroker kits as cheap as $700 - $800 (includes balancing) complete w/ pistons, rings, bearings, cam, lifters, oil pump, timing set, etc.  Check out http://www.northernautoparts.com, http://larrysperformance.recycler.com/services.html, and https://shop.enginekits.com/osb/specials.cfm

Hope this helps a little.

Rusty

[Lt.Del]

you have a two piece rear main.










my 383 www.delbridge.net/install

[1979C20]

Del, if you loosen 4 and 3 mains, the upper seal comes out easier.

[Grim 82]

For the stroker conversion you would be using a 400 crankshaft, which typically was externally balanced meaning you needed a weighted flexplate/flywheel and balancer. Other small block chevy motors pre-87 are internally balanced and use a neutral balance flexplate/flywheel and balancer. Aftermarket companies make internally balanced 400 cranks, but aside from being able to use your original 350 flywheel and balancer I'm not sure if one has an advantage over the other. Your 350 block would require the 2 piece seal as stated.

[westsidek20]

So the kit I've been looking at is "eagle" don't know if its quality stuff or not (would appreciate any comments, its not going to be a racing engine, just street and light offroad fun)
They have different kits, they offer one piece or two piece main seal, so ill get the two piece kit. Now they also offer internal and external balance, what should i get? its the original 350.

[westsidek20]

Any help anyone? please...

[Grim 82]

Like I said, I don't know that there is really an advantage one way or the other, and I have never used Eagle products so I can't attest to their quality. Keep in mind the machining that your block will require for the conversion. Google 383 stroker build and see what you find, or search it on this site. Let us know what you choose.

[ohio hab]

I used a Scat rotating balanced assembly from Skip White Performance, bought many, great company to deal with. I use Scat because their Rods are better, much higher H.P. rating, and have had no problem. The kit also has forged piston's. Everything is in the kit, easy to do it your self, after block has been machined. I clearance my own block's very little is needed.

[The dream]

Thanks for all the info guys, I'm nervous this is my first build, maybe thats why i ask so many stupid questions.

 i will look up on scats kit, although I'm not aiming at Big HP gains, ill stick to the 400 pony range. Now Ive disassembled the engine and it looks like its going to need a 4.060 bore, what do you guys think? is it worth working with this block?

[1979C20]

That'll be a 388. I know a few people with them.

[jaredts]

Nothing wrong with .06" oversize.  People have gone beyond that and had problems.

[1979C20]

Someone on the forum said they saw blocks vome back from GM bored .090!

[The dream]

Thats great news. Its just that theres many people out there that don't want to work with anything more then a .030 bore and i was starting to worry, like i said before my first build. 

[DustyRusty]

If you're worried about too much overbore, have your machine shop sonic check the cylinders.  That will tell you how much you can safely bore them out to.

Rusty