Factory Engine Specifications
Brian Sowle - gnfast@together.net
Introduction
This document contains all the dimensions, clearances, and spring pressures for the VIN 7 87 Turbo motor. These are directly from the GM manuals not Chilton's. Now I know that certain engine builders use looser or tighter clearances so don't start a huge thread on how this or that clearance is wrong. Like I said these are from the GM manual. If I were doing a rebuild I would stick with the Factory clearances. How many 140,000 mile cars do we have currently running???
Notes

Engine Dimensions and Fits

General

Piston Clearance Limits

 .
Top Land
.046 in. - .056 in
Skirt Top
.0008 in. - .0020 in
Skirt Bottom
.0013 in. - .0035 in

Ring Groove Depth

 .
#1 - Compression Ring
.185 in. - .194 in
#2 - Compression Ring
.186 in. - .194 in
#3 - Oil Ring
.188 in. - .196 in

Ring Width

 .
#1 - Compression Ring
.077 in. - .078 in
#2 - Compression Ring
.077 in. - .078 in
#3 - Oil Ring
183 in. - .189 in

Ring Gap

 .
#1 - Compression Ring
.010 in. - .020 in
#2 - Compression Ring
.010 in. - .020 in
#3 - Oil Ring
.015 in. - .055 in

Piston Pin Length
2.900 in

Diameter of Pin
.9391 in. - .9394 in

Pin Clearance in Piston
.0004 in. - .0007 in

Pin Press Fit in Rod
.0007 in. - .0017 in

Pin Direction and Amount Offset in Piston
.040 in
Major Thrust Side

Connecting Rod Specifications
Bearing Length
.654 in
Bearing Clearance (Limits)
.0005 in. - .0026 in
End Play
.003 in. - .015 in

Crankshaft Specifications
End Play at Thrust Bearing
.003 in. - .011 in
Main Bearing Journal Diameter
2.4995 in
Crankpin Journal Diameter
2.2487 in.
- 2.2495 in
Main Bearing Overall Length .
#1
.864 in
#2
1.057 in
#3
.864 in
#4
.864 in
Main Bearing to Journal Clearance
.0003 in. - .0018 in

Camshaft Specifications
Bearing Journal Diameter
1.785 in. - 1.786 in
Journal Clearance in Bearings .
#1
 .0005 in. - .0025 in
#2,3,4
 .0005 in. - .0035 in

Valve System Specifications
Rocker Arm Ratio
1.55 to 1
Valve Lifter Diameter
8420 in. - .8427 in
Valve Lifter Clearance in Crankcase
.0008 in. - .0025 in
Minimum Valve Margin
.025 in
Intake Valve .
Head Diameter
1.715 in. - 1.705 in
Seat Angle
45 degrees
Stem Diameter
.3412 in. - .3401 in
Clearance in Guide
.0015 in. - .0035 in
Exhaust Valve .
Head Diameter
1.505 in. - 1.495 in
Seat Angle
45 degrees
Stem Diameter
.3412 in. - .3405 in
Clearance in Guide
.0015 in. - .0032 in
Valve Spring .
Valve Closed
90 lbs
+or- 4 @ 1.727 in
Valve Open
245 lbs
+or- 10 @ 1.340 in


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