Exhaust - Puff of Tailpipe Smoke on Startup
90chevy29Number: 90-300-6A
Section: 6A
Date: July 1990
Corp. Bulletin No.: 066102
Subject: TAILPIPE SMOKE ON STARTUP
Model and Year: 1987-90 C/K, RN, G AND P TRUCKS WITH 5.0L OR 5.7L ENGINES
TO: ALL CHEVROLET DEALERS
Some vehicles may exhibit a puff of tailpipe smoke on startup which is difficult to diagnose. Some suggestions for diagnosis and recommended corrective actions are listed below:
THROTTLE BODY INJECTION (TBI) VEHICLES (1987-88 MODEL YEARS ONLY)
If the smoke is white or bluish white, and occurs only at startup, and no unusual oil consumption is noted, then the joint between the intake manifold and the cylinder head may be suspect. The intake manifold bolt torques should be checked. The intake manifold bolts (particularly the two bolts nearest each corner) should be removed and the inside of the bolt holes in the manifold should be inspected for signs of threading (grooves cut in the manifold by the bolts). If several of the intake manifold bolts have very low torque (10 ft.lbs. or less) and/or the manifold bolt holes show signs of threading, the intake manifold should be replaced with service manifold listed below.
ENGINE INTAKE MANIFOLD P/N
All (5.0L and 5.7L) TBI 14102183
ALL V-8 ENGINES (1987-90 MODEL YEAR CARBURETED AND TBI)
If the smoke is blue or bluish-white and occurs at startup, the recommended corrective action should be installing valve seal kit P/N 10132715. This kit incorporates an umbrella seal for the exhaust valve stem. See Section 6A4 of Applicable Shop Manual for assembly sequence.
ALL FLINT MANUFACTURED V-8 ENGINES (1987-89 MODEL YEAR) RATED BELOW 8500 G V W R
If the above procedure is not totally effective, and the smoke is blue or bluish-white and occurs only at startup, it is recommended that the clearance between the exhaust valve
stem and the cylinder head valve guide be checked following the procedure and specifications outlined in Section 6A of the applicable unit repair manual. If the valve stem to cylinder head valve guide clearance is found to be excessive, it may be due to an incorrect machining of the exhaust valve stem. Some production exhaust valve stems in Flint manufactured engines with a G V W R of less than 8500, have been found to have a rougher finish than normal. This rougher finish has a tendency to cause premature wear on the cylinder head valve guides, resulting in excessive clearance. The following information should be used to identify a Flint manufactured engine prior to checking valve stem clearance.
Figure No. 1:
Engine manufacturing and build dates codes are stamped on a pad at the block to passenger side cylinder head parting line (see Figure 1). The following example depicts a Flint manufactured engine code.
IMPORTANT: Flint manufactured engines with a GVWR above 8500 use valves supplied by a different manufacturer and should not require checking.
V1202ABC V = Flint
12 = Twelfth Month (December) 02 = Second Day Of The Month ABC = Broadcast Code (Engine Usage)
The first letter indicates the plant where the engine was manufactured, the next four numbers indicate the date of manufacture, and the last three digits are the broadcast code. All engines that were manufactured at the St. Catharines Plant, which have an engine code beginning with the letter "K," have valves supplied by a different manufacturer and generally do not exhibit this excessive valve stem clearance condition. The following example depicts a St. Catharines manufactured engine code.
K1202ABC K = St. Catharines
12 = Twelfth Month (December)
02 = Second Day Of The Month
ABC = Broadcast Code (Engine Usage)
If the exhaust valve stem clearance is found to be excessive, then one of the following procedures should be performed.
PROCEDURE 1
Following the procedure and specifications found in section 6A of the appropriate unit repair manual, ream the exhaust valve guide(s) and install new exhaust valve(s) with an oversized stem. Install new valve seals contained in kit P/N 10132715 on all valve stems.
PROCEDURE 2
If the valve guide hole(s) are out of round and cannot be corrected by reaming, replace the cylinder head(s). It will be necessary to install all new service exhaust valve(s) in the
replacement head(s). The service exhaust valves have the correct stem finish. Transfer all remaining valve train components from the original head(s) to the service replacement head(s). Check for correct valve stem to valve guide clearance and for proper valve seating on all intake and exhaust valves during installation. Install new valve seals contained in kit P/N 10132715 on all valve stems.
Parts are currently available from GMSPO.
WARRANTY INFORMATION
For vehicles repaired under warranty use:
Labor Operation Number Description
J0200 Replace intake manifold and gasket
J0547 Install valve stem seals only
J0510 Replace right cylinder head
J0511 Replace left cylinder head
J0517 Replace both cylinder heads
J0520 Ream valve guide/replace valve in right cylinder head
J0521 Ream valve guide/replace valve in left cylinder head
J0527 Ream valve guide/replace valve in both cylinder head
Obtain time allowances from appropriate Labor Time Guide.