Personaly I would consider Plasti-Gauge OK for a stocker type rebuild only, not a HI Perf or 383 engine.

I would much rather see you use a dial bore gauge than plasti-gauge. Probably 10x more accurate. Even if you get a reasonably priced one. And cheap considering what happens if you get the clearances wrong. A snap gauge is the worst thing you can use.

GM specs for SBC from my 72 Service Manual are shown below. 1.5 is way too tight. Stick to the middle as a minimum, or even on the loose side of the GM spec. That's where 427HotRod's and Jebbysan's specs come from, as well as their many years of experience building engines. Look at the 255HP 350 spec (LT-1) almost no where is 1.5 thou acceptable. Roughly 2.5 is much better. Too tight spins bearings. Way too loose, over spec, and you have low oil pressure. Worn SBCs can drop below 10 at idle. That's very low. (Probably 3.5 thou+) Should be 10-20 in a good build. 20 is great. Over 20 at idle is too tight. Std vol, Hi Press Z28 pump / spring is all you need in a SBC. If it is clearanced correctly. Unless you have a drag race only engine. That's where all the "tricks" you read about on the internet come into play, but none of them are needed on the street. Just a good solid build with good clearances.

This is THE #1 thing to get right on a SBC build.

Consider the source when you get recommendations from this forum or any other source. GM, Jebbysan, 427 Hotrod, are some of the best.





Do yourself a favor, just buy, or borrow, the right tool.

.

 

Leigh's posted sheet is a good reference but the numbers I use make for a better controlled leak.......a little less strain on the pump shaft and the pressure comes down quickly when the revs fall so there isn't a bunch of unneeded oil slinging around......but plenty of oil coming through to keep the oil cool......oil is cooler in an engine when it is moving......the faster it moves the more heat it can shed.....

We fired up the 406 Pontiac the other day and it has 60psi cold at idle 40 hot......but the crank was turned .020 and I had .002 on the mains with a .020 bearing......well, they don't make a "21x" so I had to run with it, no time to hold the crank hostage in a shop for a month taking .001 off of it.........it is fine, but I told them 10w30 only on this engine as the damn main journal on a 400 Pontiac is almost 3" in diameter! They have been out banging on it and it revs to 6200 all day.......about 540hp......with a 4 speed.....so .002 will fly but not optimal and they DO make a .011 and a .021 for small block chevrolet....so my Chevy build always get what is needed......
As I have mentioned before too....and you might think this is crazy......but .003 bearing clearances on the crank will let a lot of small particles just wash right through as opposed to .0015......which dam near won't let anything through......endurance racers know this.....it is just an extra insurance policy......the tight clearance will take a piece of debris and grinding it right into the babbit.....leaving those "streak marks" you see on some engine teardowns......the last checkpoint for the oil is the mains and rods......nothing else is that tight getting to the crank......the cam bearing journals are grooved....a piece of **** that gets through the filter somehow or through a bypass will make it all the way through the engine to the crank.......

Jebby

 

With that in mind , would you plug the bypass Jebby....anyone can throw in their 2 cents. I have a racer buddy that lives by that

 

You can.....but when you do you have to run a full flow oil filter like the Fram HP4.......the last 350 I built I left the bypass in.......
I have actually seen a Purolator blow on the dyno at 5000rpm because the bypass was plugged.....the Fram HP4 flow a lot more oil......the Wix racing and others are similar.....

Jebby

 

I’m still trying to get my hands on a dial bore gauge, but for grins I did the plastigauge again, this time having forest removed the crank and all surfaces dry. Pretty close to the previous measurements, maybe .00025 looser. So, regardless of what a dial gauge would show me, I’m kind of limited to what bearings are available anyway, right? So if I choose .001 under bearings then that should get me in that range, with center three at .002-.0025. 1&5 are already at .0025-.003, so I’d keep those. Wouldn’t that be my only option anyway?

 

that would be a good goal to get to

 

Yep...get the .001X bearings. Use them where you need them. You can even mix/match them to get .0005 added clearance as long as they are the same MFG and design in each set. I don't remember...is this a steel or cast crank?

JIM

 

I can't remember if you ever got your original question answered about too tight to turn?

Did you:

• Check to see the the crank spins freely in oil all by itself, without even the seals?
• Same with the camshaft?
• Gap all your piston rings? Measured or filed deburr edges?
• Rings installed in bores with lots of oil (can't see it)
• Who honed the block and what finish?
• Does the cross hatch feel smooth or does it catch your fingernail?
• What kind of rings thickness, low or high tension?

But yeah, if it's your first one, a new engine is surprisingly difficult to spin by hand. Who'd a thunk it?
It gets worse with valve springs
A lot of it is the rings. As they wear-in, the bores get smoother. They take off the high spots on the cross-hatch.

 

Yeah...that is why the preferred build order is:\
Crank
Cam/Timing Chain/Degree
Pistons/Rings/Rods

When doing in this order you can check if the crank and cam spin freely......then add each piston and spin one rotation, then add the next piston....it will get harder as you go but what you are feeling for here is bind......and when you get all eight in....you can turn it over with a bar and it should make a nice "metal wipe" sound, that's the fresh ring pack sliding over the fresh crosshatch......if it makes the sound and spins freely....you are good to go!
Then:
Oil Pump/Pickup/Pan
Lifters
Heads/Pushrods/Valvetrain
Intake/Distributor

Jebby

 

Here lately I've been doing cam first....as I've seen a few wonky cam bearings that aren't even close to the right size in packages. One was a Gen II Hemi and the other was an LS.

I've also had to straighten the last 3 new cams.

But you're right...you'll know the crank is good while you're setting all the clearances and for sure you'll give it a good spin just for fun when you're done!!

Break away TQ can be pretty high with stock rings. When doing something like a Super Stocker deal...you can literally "palm" the balancer and turn it by hand with all 8 pistons/rings in place!

JIM

 

I had a box of bad cam bearings last year. the number 1 was too small I believe.....such a hassle waiting on that one thing that someone else screwed up

 

I remember giving my oiled crank a good spin with no seal, and it just spun round and round a few times!

So how do they get the rotating friction down that low on the superstock motors?

Is it mostly about the rings and the hone job?

 

A lot of it is light tension rings.....super thin like LS....1.0mm top and second.....I think some run no oil ring at all......
The 385 I built earlier this year had the LS ring pack in it and it was super easy to spin over......like half the friction....sealed right up too......

Jebby

 

This comes from the school of hard knocks. All this info comes from mistakes i've made or from engine builders over the years. I got so disgusted with professional engine builders mistakes/excuses and BS that I wouldn't let them drill an ******* in a hobby horse. I found it's cheaper and easier to do it yourself. (aside from the machining work)
For clearances I like to use 0.0025" on the mains, 0.002" on the rods, and 0.004" of ring gap per inch of Cyl. bore (N/A application). And the camshaft fit is very very important, if it does not spin easily when first installed, you have a cocked bearing which will get wiped the minute you start the engine. Once that happens , say good bye to your oil pressure as the cam is fed first and then the mains. That's why it's so important to get the camshaft bearings in correctly. Went thru five sets of cam bearings once to get the proper install. But once fitted correctly, the engine had 60psi cold and 30 psi hot at 650rpm's was very pleased seeing that. Perfect for a street engine. And parasitic drag was 25lb-ft initial and 22lb-ft final. Took me two weeks to assemble this motor. Could not get the Intake center-line ICL / cam advance to my satisfaction so I had to broach a new key-ways in crank gear. Dead nuts on now @ 4° advanced with ICL of 108°.

 

Yep..rings and cylinder finish primarily. Thin and low-tension oil as well as compression rings. Pistons are made with shallow grooves and rings are back cut to relieve tension as well as using gas ports to get the seal better. Piston skirt design and rod angle will also come into play. And dead-on machine work where everything is straight as possible.

JIM

 

SCAT 9-350-3750-6000-L Series 9000 Cast Pro Comp Stroker Lightweight Crankshaft

 

• Check to see the the crank spins freely in oil all by itself, without even the seals?

yeah, pushed with single finger, spins about a bit more than a whole turn.

• Same with the camshaft?

No, not with just oil on the journals. I used the moly lube on the journals so it turns easily with finger and thumb but doesn’t spin

• Gap all your piston rings? Measured or filed deburr edges?

No, I measured ring one in cyls 1&2 and both were .020 then bumbled forward… will do all this time around.

• Rings installed in bores with lots of oil (can't see it)

I used WD40. Will use 30 weight this time and slather it on.

• Who honed the block and what finish?

MJM in Escondido, diamond bore, finished for moly rings

• Does the cross hatch feel smooth or does it catch your fingernail?

smooth from the machine shop

• What kind of rings thickness, low or high tension?

Don’t know that; came with the pistons (neighbor). Am open to buying new to ensure I get this right

 

Std moly rings are fine for what you're doing. I just coat the piston skirts with oil and a little on the rings. They don't need to be dunked in oil.

On cast cranks...I don't use the harder "race type" bearings like I do on steel cranks. In the Clevite line those are the "H" series. Not sure what King calls theirs off hand. Good regular bearings will be fine for it and provide some more "embeddability" for any trash that happens to go through it. I'm guessing that SCAT crank (they are good) might have a large radius on the mains...so make sure your bearings are chamfered around the edges to clear it.

JIM

 

Now that is good engine building advice.
It's all stuff I have heard many times at the race car machine shop.