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If you get new bearings, keep in mind that inexpensive bearings do wear over time. Datsun used triple alloy bearings which do not wear out, but only if the engine loses oil pressure they will be damaged, or if debris gets into the oil.
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Bearing Knock
If your engine is knocking, you may need new bearings:
- Rod knock: repetitive double-tapping sound that increases with RPM. May become quiet when delecelerating. Do not confuse it with a cracked exhaust manifold (use a hose to your ear to narrow down the location of the sound)
- Main bearing knock: A dull, heavy knock
Rule these out first:
- Cracked exhaust manifold cause a tapping sound very much like rod bearing knock
- Engine mount knock -- inspect the mounts
- Exhaust pipe knocking against chassis -- inpect system especially whiling tipping the throttle
Measuring Bearing Clearance
When installing new bearings, Measure Bearing Crush.
It is difficult to tell by visual inspection if bearings are worn. It is normal to have some pattern on them.
Direct measurement: The best way to check is to use plastic thread. Buy the Plastigaugeᵂ (just a couple of dollars) and put it back together. The amount the thread is squished tells how much actual clearance it has.
Indirect measurement: Measure the journals with a precision micrometer, then calculate the clearance.
It is suggested to measure clearance after fitting/refitting bearing shells to confirm actual clearance.
Datsun Factory Service Manual uses Plastiguage:
Measuring Main Bearing Clearance
Regarding rod bearings, it says "Measure connecting rod bearing clearance in the same manner".
Inspection
Scratched bearing indicates debris in the oil
Lightly scratched, but still in spec
Main bearings look OK, so measure clearance to be sure
Bad conrod bearing next to good one - Troubleshoot Bearing Problem
Problem: Bearing shows abnormal wear in center
Camshaft Bushes
Datsun recommends not replacing the bushings during a normal rebuild. Of course if they are damaged, they should be replaced. A hone is required after fitting new bushes. Certain kinds of 'hot tank' block cleaners also require the removal of the bearings.
Rockauto * ITM ENGINE COMPONENTS 5C4146STD * SEALED POWER 1592M Camshaft Bearing Set STD
Damaged
Connecting Rod Bearings
A12/A13/A14/A15 12111-20900 BEARING-CONNECTING ROD STD <> 12111-20900 12111-20901 BUSHING-CONNECTING ROD UNDERSIZE 8 12111-20902 BUSHING-CONNECTING ROD UNDERSIZE 12 12111-20903 BUSHING-CONNECTING ROD UNDERSIZE 25 (0.25 mm undersize) 12111-20904 BUSHING-CONNECTING ROD UNDERSIZE 50 (0.50 mm undersize) 12111-20905 BUSHING-CONNECTING ROD UNDERSIZE 75 (0.75 mm undersize) 12111-20906 BUSHING-CONNECTING ROD UNDERSIZE 100
B10 12111-18000 BUSHING-connecting rod (standard size) F500 (8) except coupe 12111-20900 BUSHING-connecting rod (standard size) F770 (8) coupe
F-770 is comprised of
(1) a topmost layer of babbitt
a nickel barrier layer
(2) a copper-lead matrix base layer (F77/F770}
(3) a steel backing layer
F-770 is tri-metal bearing. The lead-copper alloy has a higher load capacity than plain aluminum bearings and higher than alloy-tin (F820 or F500) bearings with better performance at extreme temperatures. First used by A12 (A10 did not have them).
Clevite 77 Vanderwall VP-R
F77 and F770 are identical except for the method of applying the copper lead to the steel: F77 is cast while F770 is sintered.
1984 Nissan Competition Catalog said: The -25720 ... bearing shell produces the most desirable bearing clearance for racing purposes when applied to a standard size crankshaft. The other shells exist in order to obtain proper clearance when compensating for the variations in the crankshaft or connecting rod journals.
8 each required:
* 12111-25720 .0590"
* 12111-25721 .0588"
* 12111-25722 .0585"
* 12111-25723 .0592"
* 12111-25724 .0583"
Main Bearings
Crankshaft bearings - thrust bearing has no hole is lower half -- for improved load bearing capacity. The other bearings use identical top & bottom halfs.
BEARING SET A12/A13/A14/A15 * 12207-H1001 SET-BEARING STD <> 12207-M7201 <> 12207-H1000 $71.58 * 12208-H1000 SET-BEARING 0.20MM * 12209-H1000 SET-BEARING 0.25MM * 12210-H1000 SET-BEARING 0.50MM * 12211-H1000 SET-BEARING 0.75MM * 12212-H1000 SET-BEARING 1.00MM
1984 Nissan Competition Catalog said: The ... -H2310 bearing shell produces the most desirable bearing clearance for racing purposes when applied to a standard size crankshaft. The other shells exist in order to obtain proper clearance when compensating for the variations in the crankshaft or connecting rod journals.
MAIN BEARING (#1/#5, SHELL THICKNESS) 4 each required
* 12215-H2310 .0720"
* 12215-H2311 .0718"
* 12215-H2312 .0715"
MAIN BEARING (#2/#4, SHELL THICKNESS) 4 each required
* 12231-H2310 .0720"
* 12231-H2311 .0718"
* 12231-12312 .0715"
MAIN BEARING (CENTER, SHELL THICKNESS) 2 required
* 12247-H2310 .0720"
* 12247-H2311 .0718"
* 12247-H2312 .0715"
12231-H1000 - inner main bearings (#2 & #4)
12233-H1000 - outer main bearings (#1 & #5)
12255-H1000 - center thrust bearing
Thrust Bearing
See: Thrust Clearance
Main Bearing Cradle
Although probably unnecessary, you can fabricate a main bearing cap girdle (ladder frame support) such as many modern engines have. The theory is that it stiffens the block for high HP applications. Also called a main cap girdle.
Garage Nakamura halo cradle
Specs
Bearing Clearance * Main: 0.020 to 0.062 mm * Rod: 0.020 to 0.050 mm
Main Bearing Journal diameter * 49.951 to 49.964 mm
Crankpin Journal diameter * 44.974 to 44.961 mm
Journal Taper and out of round * measure multiple spots * less than 0.03 mm
End-play * crank thrust: 0.05 to 0.15 mm
Bearing Crush * main: 0 to 0.03 mm * rod: 0.015 to 0.040 mm
Part Numbers
Tri-metal was used as original equipment. Very very durable bearings.
ROD BEARING Nissan 12111-20900 BEARING-CONNECTING ROD STD (8 required) Mahle/Clevite CB980P (pair) P-series (Tri-Metal) Mahle/Clevite CB980A4 (set) A-series (Aluminum) Sealed Power 467320CP
MAIN BEARING Nissan 12207-M7201 set STD Sealed Power 7135M