| BALANCE SHAFT & CRANKSHAFT COMBINATIONS |
Balancer Assembly and Crankshaft Combinations On
GM 2.5L (VIN U) Engines
General Motors has provided the remanufacturing industry with another challenge when it comes to assembling GM 2.5L engines with balancer assemblies.
The balancer assembly first appeared in 1987 GM N body vehicles equipped with manual transmissions, such as the Pontiac Grand Am and Buick Somerset. This engine uses a crankshaft with the casting number 10044390. This crankshaft gear features 82 teeth while the driven balancer gears have 41 teeth.
Some OE parts books may list 625 as the casting number for the 1987 model year crankshaft. To-date AERA members have been unable to find crankshafts with this casting number.
Vehicles with VIN Code U engines may also use a crankshaft with the casting number 10044406. Unfortunately, there are two versions of this crankshaft. One version has a 78-tooth gear, which mates with 39 tooth balancer gears. The other version still uses 82 teeth and requires a 41-tooth balancer assembly.
Vehicles with VIN Code U engines manufactured for 1988 model year vehicles should only use casting number 1000406 crankshafts with 78 teeth.
Using the wrong combination of crankshaft and balancer assembly has caused complaints ranging from significant noise in the lower end of the engine, to premature engine failure. AERA members have reported 2.5L truck engines equipped with crankshafts that have a balancer drive gear although a balancer assembly is not used in this application.
For additional information see AERA Technical Bulletins: TB 778. 720, 690R & 511.
The AERA Technical Committee |
| LOW OIL PRESSURE ON 1987-90 'N' BODY ENGINES |
Low Oil Pressure On
1987-90 GM 2.5L (151 CID) N Body Engines
AERA members have reported low oil pressure conditions on 1988-90 GM 2.5L (151 CID) engines used in N body vehicles such as the Pontiac Grand Am and the Buick Somerset.
These engines are equipped with a combination balancer/oil pump assembly located in the crankcase to reduce high rpm engine imbalances. Furthermore, the oil filter cartridge is housed behind the filter access plug in the oil pan.
If the oil pan has been distorted by overtightening the filter access plug or drain plug it is possible for oil to leak back into the pan at the discharge side of the filter. This can results in extremely low or even no oil pressure.
This situation can be avoided through careful inspection of the oil pan area that houses the filter cartridge. Warped or otherwise damaged oil pans should be replaced.
For additional information see AERA Bulletin SB 157.
The AERA Technical Committee |
| CYLINDER HEAD IDENTIFICATION FOR 1985-87 2.5L ENG |
Cylinder Head Identification For
1985-87 General Motors 2.5L (151 CID) Engines
AERA members have reported confusion over replacing cylinder heads for 1985-87 2.5L (151 CID) engines even when using cylinder heads with the same casting number. The source for this confusion lies with General Motors using two differently machined configurations of a head carrying the same casting number for both the standard engine as well as the shortened version used in N body vehicles, such as the Pontiac Grand AM, Buick Somerset, etc. In 1985-86 this head carried the casting number 10027767. In 1987 it was replaced by casting number 10038808.
GM uses a shorter version of the 2.5L engine for the N body FWD cars, VIN code U, than for the cars that have VIN code R or 2. Although some components will interchange, the key pieces such as the block, head, crankshaft and camshaft will not. By measuring the center-to-center dimension of the rear holes of the cylinder head parallel to the flywheel, you can easily distinguish between the two applications. If the measurement is 3.670 it is the shortened version for the N body cars (VIN code U). If it is 3.980, it is the longer head for all other
vehicles (VIN codes R and 2). GM cast these bolt hole pads in an elliptical shape to allow for both versions.
The AERA Technical Committee |
| MAIN BEARING KNOCK |
Main Bearing Knock On
GM 3.3 & 3.8L (Buick 3300 & 3800) Engines
AERA members report knocking noises coming from the front of GM 3300 & 3800 Buick engines. The noise is most noticeable when the engine has reached operating temperature. One possible cause for this knocking noise may be from excessive oil clearance at the front main bearing location.
Diagnosing excessive main bearing clearance is easily done by removing the accessory drive belt from the engine after it has reached operating temperature. If the noise diminishes when the engine is started again, front main bearing clearance may be more than .0012 (.030mm). The clearance may be reduced by installing .001 (.025 mm) undersize main bearings. GM permits the use of only one bearing shell half in the cap, but warns not to reduce
clearance below .0008 (.020 mm).
GM specifies the main bearing clearance as .0008-.0022 (.020- .055 mm). AERA suggests machining the crankshaft main bearing journals and the main bearing housing bore so that the minimum allowable clearance is maintained, avoiding the possibility of main bearing knock.
The AERA Technical Committee |
| HARMONIC BALANCER BOLT |
Problem On Replacing Harmonic Balancer Bolt On Some
Buick Built 3.8L (231 CID) V6 Engines
When the crankshaft in the subject engine is replaced, the original harmonic balancer bolt may not fit the crankshaft.
Some replacement crankshafts have been drilled and tapped for a 3/4 - 16 bolt instead of the original 5/8 - 18 bolt.
The OEM replacement bolt (3/4 - 16) and washer are:
Bolt No. 271629
Washer No. 1199944
The AERA Technical Committee |
| ENGINE VIBRATION & FLYWHEEL MOUNTING PROCEDURE |
Engine Vibration And Flywheel Mounting Procedure
On Buick 6.6L & 7.0L (401 & 425 CID) Engines
Buick 6.6L and 7.0L (401 & 425 CID) engines are balanced to very close limits. The replacement of any part within the engine or drive line can result in a vibration condition. In replacing the engine or crankshaft the following instructions should be followed.
1. Mark drive shaft before disconnecting so that installation can be in original position.
2. If automatic transmission unit, mark position of converter to flex plate.
3. Remove engine. Check all motor mounts and replace if broken or damaged.
4. Install engine. Use extreme care to see that flywheel, or flex plate bolted to converter are installed in original position.
5. Align flex plate or flywheel to crankshaft, aligning hole in crankshaft flange. See (A)
Following the above procedure, if a vibration is experienced, it will then be necessary to purchase balance weight part #1178109 from a Buick dealer and install it under head of two converter pump bolts, then start engine to check vibration. The weight may have to be rotated to a different location until vibration is corrected. Use tachometer and note critical speeds.
Balancing should be included in the labor charge of installing
the engine or crankshaft.
(insert illustrations)
Align hole (A) in crankshaft flange to (B) alignment hole in flywheel or converter drive plate. Converter drain plug (C) must be installed in notch (D) in drive plate to allow removal of drain plug.
The AERA Technical Committee
##END## |
| VALVE TRAIN NOISE ON V6 ENGINES |
Valve Train Noise In 1978-84 Buick V6 Engines
180 (3.0L), 231 (3.8L) & 252 (4.1L) CIDS
Valve train noise is a common complaint on the Buick built V6 engines after rebuilding the heads, the short block or complete engine. The noise is almost always attributed to inadequate lifter preload. Checking the valve tip to rocker arm tip clearance and insuring proper lifter preload will eliminate this
problem.
Inadequate lifter preload is compounded by replacing the stock steel shim type head gaskets with thicker composition type head gaskets. The difference in thickness is only about .015, but when combined with the rocker arm ratio of 1.55, nearly .025 of lifter preload is lost by making this change.
In addition, some members report that they are finding pushrods of varying length (standard, plus .030 and plus .060) in these engines. It is recommended that AERA members check and sort these pushrods according to length.
The correct lifter preload for these engines is .080 to .180. By using pushrods of varying lengths these figures are achievable. Some members report using the intake pushrod for 348-409 CID Chevrolet engines as a standard practice on the Buick built V6. This pushrod is about .060 longer than the standard length Buick V6 pushrod. The AERA Technical Committee recommends checking valve lash on each valve and selectively fitting each with the correct length pushrod to give adequate lifter preload.
The AERA Technical Committee |
| PISTON KNOCK ON V6 ENGINES |
Piston Knock In
Some 1978 Buick Built V6 Engines
It has been reported that some Buick built V6 engines, which may be found also in vehicles of other GM divisions, may have a faint knocking noise particularly during warm up. The noise may be caused by the number 6 piston contacting the counterweight on the crankshaft.
A scuff mark on the skirt of the number 6 piston indicatesk the piston has been striking the crankshaft counterweight. To correct the problem, it is recommended that .010 be carefully filed or ground off the area of the scuffk mark.
The AERA Technical Committee |
| DETERMINING CORRECT CAMSHAFT - ODD & EVEN FIRE ENG |
Please Destroy Original TB 241 Dated Jan., 1982
Determining The Correct Camshaft On
1975-77 GM (Buick) Odd And Even Firing 3.8L (231 CID) Engines
Members are cautioned that there are two different types of
camshafts for the odd firing General Motors (Buick) 3.8L (231
CID) engine:
Type 1 has a non-integral distributor drive gear, a
removable drive gear on the end of the camshaft.
Type 2 has an integral distributor drive gear on the end of
the camshaft, permanently attached.
To identify an even or odd firing engine, check the V.I.N.
number. The fifth digit from the left denotes the type. A
letter C indicates an ODD firing engine. All other codes
indicate an even firing engine.
1975 through early 1977 General Motors (Buick) 3.8L (231 CID)
engines used odd firing. Later in 1977, even firing engines were
used.
The AERA Technical Committee
April 1982 - TB 241
##END## |
| V6 TIMING CHAIN NOISE |
Timing Chain Noise On Some General Motors (Buick-Built) 1975-78 Engines
Timing chain noise has been experienced on some of the subject engines. This can occur on 1975-77 odd-firing and some 1978 even-firing V6 engines. The noise is a result of the timing chain damper spring hitting the inside of the timing cover.
After removing the timing cover, check for a worn or shiny spot inside the timing cover in the area of the damper spring pilot. If this condition is found, provide additional clearance by carefully grinding at the worn spot, but be careful not to
machine through the timing cover casting.
The AERA Technical Committee |
