SB 400 Crank

Are you building a 400?

Are the pistons you have for a 400(4.126" bore not counting any oversize) with 5.7 rods?

Are you planning on using 400 rod(2.1" not counting any undersizing) and main(2.65" not counting any undersize) journal sizes?

If you answered yes to these questions then you will be fine as long as the rod and main journals aren't undersized more than .020" and the cylinders aren't oversized more than .020". If you can swing the $$$ for a new crank, DO IT! As long as it is a quality crank! Go for Clevite bearings, moly rings, TOP quality gasket set, top quality oil(fossil for break in if you are plan on running synthetic), a low-mid range cam(roller if you can swing the $$$), a low-mid range intake with a 600-650 CFM carb, 1 5/8" primary tube headers with a 3" single exhaust system(2 1/4" duals with H pipe if you don't like single exhaust), a 180deg thermostat, HD fan clutch(or dual electrics as big as you can fit), and a minimum 3-core radiator or equivalent.

Got all that?

Have fun!

And remember all HD fan clutches are not created equal. The correct one should be square shouldered, finned, about 2 inches thick, 8-10 inches in diameter, and have a bi-metal coiled thermostat on it. They have some weight to them. Bi-metal means made of two metals that expand and contract at different temperatures. Seven blade fan. NO Flex fans.

While on this subject, warm weather is fast approaching. Fan clutches loose 100 rpm for every 10,000 miles on the odometer (on average) measured at 2,000 rpm. When's the last time yours was replaced? Whitelightning

All good points...but the 100RPM loss per 10K is a new one on me... They aint cheap, but ALLOT cheaper than a set of new heads and engine rebuild!

Sounds like new crank time, huh?

Idle at 2 grand? What speed you going? The fan gave up a long time ago.

-- Regards Gordie

-------------------------------------------------- Let's see.Mine has 253,000 miles on it so that means it's lost 2530 rpm measured at 2000 rpm.Does this mean it's now going BACKWARDS 530 rpm?

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Century Performance

Generally, fan clutch output under normal operating conditions will decrease by about 200 RPM per year. So, a three-year-old fan clutch is possibly due for replacement, or at least more periodic inspections. A four-year-old fan could very well be running partially disengaged and should be replaced.

Larry Carley, editor, Counterman magazine:

(bio:

for those notfamiliar with the man) There are still a lot of vehicles on the road (mostly trucks) that have a belt-driven cooling fan, and many of these fans have a viscous clutch to reduce noise and drag on the engine. There are two types: non-thermal and thermal. The non-thermal variety is designed to slip a predetermined amount so the fan speed peaks out around 2,200 to 2,400 rpm. The thermal variety contains a bimetal thermostat that increases or decreases the amount of slippage depending on how much heat the radiator is giving off.

The performance of a fan clutch will degrade over time by about 200 rpm a year. Eventually the fan clutch reaches the point where effective cooling is no longer possible and overheating results.

Radiator Info, from UnderHood Service magazine

Defective fan clutches are a common and often overlooked cause of overheating. The shear characteristics of the clutch fluid gradually deteriorates over time, with an average loss in drive efficiency of about

200 rpm per year. Eventually slippage reaches the point where effective cooling is no longer possible and overheating results. (On average, the life of a fan clutch is about the same as a water pump. If one needs to be replaced, the other usually does too.)

The 100 rpm per 10,000 mile figure I follow is from Glens service manuals. Mitchell service manuals have similar advice.

Fan clutches spin at engine rpm untill 2,200-2.600 rpm when slippage occurs. Or in layman's terms the fluids ability to keep the fan spinning at engine rpm is overcome by the air resistance. Thermal Fan clutches use valveing that is opened and closed by the bimetal spring or on some models a bimetal strip to control when slippage occurs. These can allow slippage at lower rpms when engine temperature allows it, there by improving gas mileage.

So you can laugh and scorn at my advise, but its industry standard. I have a feeling you wouldn't go four blocks down here in hot muggy west central Florida, you might get away with it in your neck of the woods in California. What's funny is I thought you were driving an 86 toyota cressida, that you put an engine in last year.

Whitelightning

Whitelightening,as usual a very informative and useful post. I was just goshing about the -253 rpm.Was intended to be mildly humourous.My appologies if I was not clear about this. I have a fleet of old jalopies,one of which is an 86 Cressida. Best.....Brian O.

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Good to know. And now I think I know why ol' mule is running a little hotter at idle and just above...

Snuffy