Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Photos of Main Bearings
View Single Post
  #23 (permalink)  
Old 12-11-2012, 08:13 PM
painted jester's Avatar
painted jester painted jester is offline

Last journal entry: Wifes 79 comeing together!
Last photo:
Join Date: Jan 2011
Location: Central Michigan
Age: 70
Posts: 2,510
Wiki Edits: 0

Thanks: 200
Thanked 671 Times in 519 Posts
QUOTE Hcompton:
"To jester: have your rods sized to the proper fit and you wont need to do crazy stuff to make your builds work. With the crank properly polished and the rods properly sized your bearings should be drop in if you buy quaility products. Use clevlite bearings and you can just drop them in place and check them with the plastiguage and they will be right over the life of the engine if they are replaced before the bearings fail and takeout the crank."

I couldn't post this earlier my post was sent by mistake

#1,2,3&4 are bellow the line! That pertain to these:

#1)You already stated you don't measure wall thickness because they are perfect! But some may be interested! and I don't say not to use plastigage! I have it and sometimes use it on final assembly! its a good tool I didn't mean it was only for a backyard mechanic (I re read it and it could be mistaken for that) I had no time to proof read!!!

#2) Some bearings need a little extra clearance then the books say! #3!! How do you set the additional clearance If your already at its max? or if you set it, it will be over max?? Or don't you set it you take it for granted (their perfect) and plastigage is too

#3 I also check bearing crush!! If you just drop em in How do you know? Have you ever seen a Bearing gauge block ????? But then again they are perfect out of the box!!!!

#4) The clearances I look for not in your repair manuals

#1) Measuring Wall Thickness of Main and Rod Bearings If any ones interested.

Although the best method to measure clearance between the crankshaft and crankshaft bearings is by using a bore gauge while the bearing is installed in the cylinder block or connecting rod, the question of measuring wall thickness of the bearings to calculate the clearances.To measure the wall thickness of a main or rod bearing correctly the location on the bearing that you measure and the tool you use will determine the level of accuracy of the measurement. A micrometer with a ball anvil must be used to fit the curvature of the bearing I.D.

Micrometers with pointed or blade anvils and dial calipers should not be used as they can give false readings and damage the bearing surface. Obviously using an accurate, recently calibrated micrometer is a must for reliable measurement.

Just as important as using the correct tool is the location on the bearing that is measured. Crankshaft bearings should be measured 90 to the parting line. By design most crankshaft bearings have an eccentric design, which means the wall thickness at the parting line is not equal to that at the 90 center line.

The purpose of the eccentric design is to compensate for casting distortion during operation, create a “wedge” affect that promotes the formation of oil film, and for slight tolerance differences of the jointing components. To determine the amount of eccentricity, measure the bearing at the centerline and then at approximately 3/8” above the parting line since some bearings may also have an additional “relief” near the parting ends.

The amount of eccentric dimension and the presence of a relief cut vary by engine make and/or model. The center line measurement determines the amount of clearance between the bearing and crankshaft and is the common dimension given when wall specifications are stated.

#2) OIL CLEARANCE - RESIZED BEARINGS Clevite 77 recomendations

Clevite T 77 Example:
"The oil clearance shown in this catalog are for the factory
manufactured precision sizes. When installing a resized
bearing, adjust the oil clearance shown as follows:
For babbitt and TM-77 copper-lead:
Add .0004” (.010mm) to both low and high limit
For TM-112 copper-lead:
Add .0008” (.020mm) to low limit and .0004”(.010 mm) to the high limit"

#3) Typical values of the crush height of 1.5-2.5” diameter bearings:

For passenger cars: 0.001-0.002” For high performance cars: 0.002-0.004”.

#4) Blue print oil clearance on a blue printed tight tolerances re machined engine!
Clearances I look for:
Grocery getter .001" High performance cars .0015 to .002 depending on
oil pump pressure the higher the pressure the more I can increase the oil clearances on a race or drag car !!
I cut and pasted this!

"Higher oil clearance causes an increase of the oil flow passing through the bearing and resulting in a lower oil temperature rise. However higher clearance produces less uniform distribution of the oil pressure - greater pick pressure, which increases the probability of the bearing material fatigue. Minimum oil film thickness decreases at higher pressure and may cause direct metal-to-metal contact between the mating surfaces. Too high clearance produces excessive vibration and noise. Lower oil clearance results in a more uniform oil film pressure distribution and a greater oil film thickness however too small clearance causes overheating the oil and a sharp drop of its viscosity. High performance bearings has an increased clearance providing more stable hydrodynamic lubrication under conditions of high loads and high rotation speeds." Typical values of oil clearance C :

Passenger cars:

Cmin = 0.0005*D Cmax = 0.001*D

High performance cars:

Cmin = 0.00075*D Cmax = 0.0015*D

where D - the journal diameter.


Last edited by painted jester; 12-11-2012 at 08:31 PM.
Reply With Quote