It will be too tight. Go on the loose side of your measurements in the first post and you'll be in the ballpark. Ring gap will need to be 19/24 as well.

Aaron

 

Shigley's "Mechanical Engineering Design" has a 60 page section on journal bearing design. It would be interesting to work through it and figure out what would be the ideal bearing clearances.

I've always heard to keep the main bearing clearances tighter then the rods to avoid pressure loss to the rod bearings?

Last 4G63 I built I used 0.002" on the mains and 0.0025" on the rods. It ran to 9000 RPM often and handled 500-550 HP daily for a couple years.

With regards to ring gaps, there is an SAE paper floating around that's pretty interesting. They did a ton of testing and even 0.065" gap didn't lead to excess blow-by. Blow-by is all about ring tension and gas venting to the back of the ring. Old rings with large gaps don't have excessive blow-by because of large ring gaps. They have blow-by because the loss of ring tension to provide initial sealing before the gas behind the ring can seal things up. Also carbon deposits on the ring lands preventing the gas from getting to the back of the ring is a big problem with old motors.

Going smaller on the second ring then the first lead to ALL KINDS of problems though at any gap level.

 

I stated .002" in my earlier post and honestly you should be fine with those clearances.

Personally I run clearances looser than .002" on a high Hp high RPM build.

 

Good info here

 

Keep it simple. Even if you are aiming for 800hp. Use the ptw the piston mfg recommends. If you are super concerned have them hone an extra .0005, but I doub that is needed especially if you are not doing road course or standing mile etc.

Oil clearance. Its just not infinitely adjustable really. If you have main and rod bearing housings that are with in spec for out of round and taper and also for diameter, you dont want to go cutting caps and honing the block or rods to adjust oil clearance. Same applies for the crank all though its easier and safer to play with clearance on the crank size but if you have a virgin crank leave it be. So really the main method of adjusting clearance is the bearings and you only have 2 options other than standard. So dont fret if your oil clearances dont fall neatly at some round number such as .002". Most likely unless your block is damaged the main bearing housing size is going to be somewhere in the middle of an .0008" window factory spec and they are probably not all going to be the same down to a tenth of a thou and that is perfectly fine. New rods purchased are usually perfectly on the tight side of the factory spec. (at least with Turbo Tuffs off the top of my head). So basically buy the extra clearance bearings and use oil that gets you the oil psi you want. One other thing. Plasti Gauge isnt very helpful. Neither are $300 dial bore gauges. Check it with a nice Sunnen or equivalent. Id have the machine shop show you with their gauge since a good dial bore gauge and setting fixture will cost the same as your shorty block lol

 

why do ppl say plastiguage isnt helpful yet it is the method the service manual uses to identify if the clearance is in spec? plastiguage isnt spot on accurate but it identifies if the crank is within the wid range of the spectrum of its tolerance. isnt the degree of error in plastiguage method small enough to measure if a crank is within spec in relation to bearing clearance?

just curious.

 

never hurts to plastigage, but i agree it shouldn't be used only.. unless of course you trust your machine shop that much. (which you should, or you shouldn't be using them)

i did both.. used mitutoyo micrometers, dial bore gauge, calipers, etc, to find the data myself then used plastigage as well just to confirm everything again.

the most important piece to the puzzle when building an engine is the machine shop and how good they are..

personally engines i build i blueprint them all to make sure the machine shop did nothing wrong.. never hurts. is it 100% necessary? no.

plastigage is pretty accurate though when used right and using a decent brand.

bunch of things said in here i dont agree with.. someone said a dial bore gauge is not useful.. i used it quite a bit to check for clearances myself & to check the machine shops cyl bore work, etc. other then a telescoping snap gauge.. cant use nothing else in the actual cyl down mid section and so forth.

if you want to build it right you should invest in similar tools i did .. it helps know everythings done right and no short cuts are taken.. pic of my tools:



they add up quick, but honestly even for non engine builds you will find yourself using them off and on. i find myself using the digital caliper/mic the most out of them all.

 

Vinny Ten - Oh hell yeah. You're making me think of the 90s drag scene.

 

Thanks for e tip Ted. Any tips on where online I can shop for mitsuyo equipment that ships to barbAdos?

Also here the machine shop only maybe bore your blocks or maybe. Repair or mill your head. Any clearances or building is up to the engine builder.

 

Because its not practical for a dealership or mechanic shop to have an accurate dial bore gauge. Our set up is close to $3k for the gauge and the setting fixture. Your average mechanic is not going to have that.

I think plasti gauge can give you an idea, but not the full picture. Also it has a shelf life and is temperature sensitive. You dont know how long it has been sitting in a warehouse etc. Or how else it has been mis-handled. Of course im not an expert. I was 8 years old when I first stood on a milk crate and sand blasted some valves in an engine machine shop. 24 years later I run my own and I have never used or seen plasti gauge used but one time in class in around 2000 hahah. So maybe im not the best person to speak on it lol

 

Can you define to me what "blueprinting" an engine is in terms of how you percieve it?

Not trying to start crap or anything, but I am one **** SOB when it comes to building an engine, and I even CMM'ed my engine block to verify the measurements which is much more accurate than any hand tool, and I still wouldn't tell anyone I "blue printed" my engine..

Blueprinting an engine is much much more than actually just measuring an engines clearances and what not...

 

At 800HP you are making a lot of heat, and things tend to expand. I'd run very loose clearances if it were my motor, especially if it was intended for extended play time. If the motor was a street deal that needs to run a 1/4 or dyno once every month then you'd have to make compromises that a dedicated race motor wouldn't have to. Since your build is for a track car I'd go ahead and run a good amount of clearance.

I've heard people say to run less crank clearance than rod to promote oil flow and I think that's crap. Less clearance means less flow. Same goes for ring gap. I've read tons of arguments for tighter top than 2nd or tighter 2nd than top. I've tried both and never noticed a difference.

Goodluck with the build

 

my name is Tom, but no problem. I got most of my mic's from ebay. otherwise you're going to pay a fortune. I was very careful though when i got the parts used. they still had the caps on the mic ends yet the kit is 20 yrs old or so. everything works perfect though still and calibrated right on.

piston diameter
piston to wall clearance
cylinder bore
main bearing clearance
rod bearing clearance
-
bearing thickness
id of crank mains
od of crank mains
id of connecting rods

(basics to selecting your proper bearing size etc)


etc etc etc..

ok then lets just say i measure things as any builder does..

the tools i posted a pic of are what i use. i used the wrong wording sorry.

 

Tom, Ted its all the same, there both 3 letter names, they both start with t

 

"Blue Printing" has to do with location and alignment more so then clearances. Are the bores perpendicular and centered over the crankshaft as well as correctly spaced? Is the head surface parallel to the main bores and at the correct height? Are the crank throws at 180 degrees to each other, the right offset and is the keyway at the correct location. "Blue printing" literally means machining the engine to match the original design specifications (blue prints) and targeting the actual values and not just being ok with the allowed manufacturer’s production tolerances.