SCAT stroker cranks, Always like this?

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mini

mini

Small Bore Long Stroke
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So I finally get all of my parts from cnc-motorsports. Everything to finish my 318/390 stroker. And I plastigage the main bearings and every clearance is at .0015. Is this like all scat cranks? Where you need extra clearance bearings? Big piss off really. Especially when I bought the trimetal $200 jobbies
 
According to the service manual .0015" is a good clearance for main bearings. What is the problem?
 
That's actually a perfect clearance! were you expecting something different?
 
Im assuming he is building a runner vs stock. .002-.003 is good for most street/strip stuff.

And OP, is this out of the box or as machined by the machine shop? did you tell them .002-.003? if not im not surprised thats what you got...
 
(1) .0015 is OK for a stocker but not OK for a runner (2) I would assume a 408 SB stroker LA engine is a runner not a grocery getter (3) Plastigauge ain't accurate enough for a performance build. The rod journals/bearings are the most critical area with the rotating/reciprocating weights/forces/loading/unloading and is the end of the line in the oil path. Get some quality mikes and some snap gauges & see what you really have there. EDIT You did say 318/390 not 360/408 (which I'm building)
 
IIRC, I got the same clearances on main bearing for my 4" Scat out of the box crank.

IIRC, the rods were more.
 
Street/strip. I will definitely mic it but the machine shop only did the full balance and never touched the mains. It was tight when torqued down but this is the first new crank Ive installed. I will try this weekend with the new bearings and grab a good mic tomorrow. I was told for a street/strip its ideal around .0025, was I mislead?
 
I missed that you building a stroker some how. But .0015 is not bad. Did you have everything cleaned down? Did you have all the caps installed and measured one at a time?
 
mini said:
Street/strip. I will definitely mic it but the machine shop only did the full balance and never touched the mains. It was tight when torqued down but this is the first new crank Ive installed. I will try this weekend with the new bearings and grab a good mic tomorrow. I was told for a street/strip its ideal around .0025, was I mislead?
Click to expand...


Per 68 Plymouth service manual:

Diametral Clearance Desired: .0005' - .0015"

Diametral Clearance Allowed: .0025"


I like to follow the service manual whenever possible.
 
mini said:
Street/strip. I will definitely mic it but the machine shop only did the full balance and never touched the mains. It was tight when torqued down but this is the first new crank Ive installed. I will try this weekend with the new bearings and grab a good mic tomorrow. I was told for a street/strip its ideal around .0025, was I mislead?
Click to expand...

Did you have the line bore of your engine checked?
 
My 408 /cast crank Scat 4.0 went 2.3-2.5 rods ,2-6-2.8 mains. On uncoated Federal-Mogul race bearings. Bearing decision,has a factor here.
 
Yah, mine were a bit tight too with the SCAT and crank kit from Hughes; .0015" mains and .0017" rods.

I Think it was Smokey Yunick that said the minimum clearance to form a proper oil wedge required to float the bearings on the crank correctly took a minimum of .0022" to .0025. I guess it's going to have good oil pressure.

Once I warm it up the first or second time, I will still spin it until it runs out of breath, until I take my foot out of it or I hit the next gear. I figure it will "break-in" ok.
 
I'd be more concerned with taper than .0015 clearance. Plastigage will not indicate that, a mic will.
 
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