LT 4 Heads

[3 Deuce]

In a history of the LT 4, two sets of heads are mentioned. An early and a late...Does anyone (Adminstrator or anyone else) know what the difference between them is and what was the VIN # break between the sets?

;help

 

[wx briefer]

News to me, please elaborate.

 

[3 Deuce]

If I had all the info I wouldn't have posted the thread. I've also sent an e-mail to Chevrolet through their owners center. I think it's mentioned in the the C 4 specific book put out by the guy who wrote the Corvette Black Book, but without the specifics I hope someone knows

 

[wx briefer]

I am not convinced you have ANY information, sounds like rumor to me or perhaps you are confusing LT1 and LT4.

 

[3 Deuce]

"CORVETTE SPECS "by Mike Antonick author of "Corvette Black Book", page237, under '96 Engine data, "Head: 10239902 (LT 4, manual, early) 12555690 (LT 4, manual)"

Is that good enough for you? I'm asking for VIN info from someone who might know, not comments without thought. :duh

 

[wx briefer]

Like I said, you still have no information.....

 

[CKA_Racing]

Have you checked any of the web sites like LT4.com?

I've heard of two different sets of heads for the 96 LT1 but not the LT4.
check this site also.
http://www.automotiverebuilder.com/ar/ar99928.htm

BTW - Not sure what kind of computer user you are, but I'm finding the above info by just using search engines and typing in key words like "LT4 late heads".

 

[3 Deuce]

First place I checked was LT 4.com...no info...the serial #s tell the story, I just want to know what VIN# it changes on and what they changed on the heads..changes aren't always for the better

 

[3 Deuce]

From a major source:The early 96 LT4 cylinder heads, had a recall from GM. There was a problem with the early rocker arms breaking. They recalled all the earlier cars for this problem. Not sure what the Vin # break, would be, but you should be able to contact your local Chevy dealer, and ask them for all the bulletins on 96 Corvettes. They should still have records of that, and that will indicate the Vin #'s that were recalled. They installed different rocker arms, in the cylinder heads, therefore requiring a different part # change to 12555690. As far as I know this is no longer a valid #, and has either been changed by GM again, or is a discontinued part. The new # or replacement part that is available from GM is a 12557773.
Hope this helps, or answers any questions.
Thanks,
Mike Patterson
mikep@corvettemike.com

 

[CKA_Racing]

If I'm understanding the info you have provided correctly, this has to do with the rocker arms and not the heads themselves.

This is the famous LT4 rocker arm recall. Your post as they are written does not even hint to this but are more like saying there is an issue with the heads. You want to know what vehicle vin #'s were affected?

Look here. This is what i found when i typed "LT4 rocker arm recall" in a search engine. There is more info out there. Use a search engine like Yahoo.com, google.com, msn.com or any of the others available.
http://www.hashmarks.com/techtips/rockerarmrecall.htm

You can also call any GM dealership and have them punch in your VIN # to see if the recall has been done already.

Hope this helps.

 

[lt4 gs]

Ya' know I thought this might be be where this was headed......and this is from our very own Knowledge base:

1996 LT4: Campaign: Rocker Arm Attaching Pin Not Fully Seated
Model Year: 1996 Corvettes With LT4 Engine
Subject: INADEQUATE RETAINING LOAD HOLDING ROCKER ARM ROLLER PIN IN PLACE
Source: Chevrolet Product Campaign
Number: 96-C-07A

TO: ALL CHEVROLET DEALERS

General Motors has decided that CERTAIN 1996 Chevrolet Corvettes equipped with 5.7L engines (RPO LT4 - VIN Code "5") may have been built with rocker arms that have inadequate retaining load to hold roller attaching pins in the rollers. When there is inadequate retaining load, the pin may back out, with a resultant engine failure likely to occur.

To correct this condition, dealers are to replace the rocker arms.

NOTICE: Previously received rocker arms P/N 12551311 must not be used. The rocker arms previously received should have been returned to GMSPO (reference GMSPO Information Bulletin #96-128). Any vehicles previously repaired with P/N 12551311 rocker arms as a result of the canceled Campaign No. 96-C-07 must have new rocker arms installed.

VEHICLES INVOLVED

Involved are certain 1996 Chevrolet Corvettes equipped with 5.7L (RPO LT4) engines built within the following VIN breakpoints:

YEAR MODEL PLANT CODE FROM THROUGH
1996 Y-Car Bowling Green "5" T5100052 T5111116
1996 Y-Car Bowling Green "5" T5600012 T5600363


Involved vehicles have been identified by Vehicle Identification Number Computer Listings. Computer listings contain the complete Vehicle Identification Number, owner name and address data, and are furnished to involved dealers with the campaign bulletin. Owner name and address data furnished will enable dealers to follow-up with owners involved in this campaign.

These listings may contain owner names and addresses obtained from State Motor Vehicle Registration Records. The use of such motor vehicle registration data for any other purpose is a violation of law in several states. Accordingly, you are urged to limit the use of this listing to the follow-up necessary to complete this campaign. Any dealer not receiving a computer listing with the campaign bulletin has no involved vehicles currently assigned.

PARTS INFORMATION

Notice: -------

A pre-shipment of part numbers 12557779 (Rocker Arms) and 10108625 (Rocker Cover Gaskets) will be sent to involved dealers of record the week of May 6, 1996. Pre-shipment will equal parts for approximately 40% of the number of assigned vehicles to be repaired. Pre-shipment parts will be charged to the dealers open parts account.

Parts are to be obtained from General Motors Service Parts Operations (GMSPO). Please refer to your "Involved Vehicle Listing" prior to ordering requirements. Normal orders should be placed on a DRO = Daily Replenishment Order. An emergency requirement should be ordered on a CSO = Customer Special Order.

Quantity/ Part Number Description Vehicle ----------- ----------- ---------

12557779 Rocker Arm Assembly 16

10108625 Gasket, Rocker Cover 2

OWNER NOTIFICATION

Owners will be notified of this campaign on their vehicles by Chevrolet Motor Division (see copy of owner letter included with this bulletin).

DEALER CAMPAIGN RESPONSIBILITY

All unsold new vehicles in dealers, possession and subject to this campaign must be held and inspected/repaired per the service procedure of this campaign bulletin before owners take possession of these vehicles.

Dealers are to service all vehicles subject to this campaign at no charge to owners, regardless of mileage, age of vehicle, or ownership, from this time forward.

Owners of vehicles recently sold from your new vehicle inventory with no owner information indicated on the dealer listing, are to be contacted by the dealer, and arrangements made to make the required correction according to the instructions contained in this bulletin. This could be done by mailing to such owners a copy of the owners letter accompanying this bulletin. Campaign follow-up cards should not be used for this purpose, since the owner may not as yet have received the notification letter.

In summary, whenever a vehicle subject to this campaign enters your vehicle inventory, or is in your dealership for service in the future, please take the steps necessary to be sure the campaign correction has been made before selling or releasing the vehicle.

SERVICE PROCEDURE

ROCKER COVER REMOVAL

LH SIDE

1. Note setting of all electrical devices and then disconnect battery.

2. Remove fuel rail beauty cover.

3. Remove booster vacuum hose from intake manifold.

4. Remove distributor vent hose from intake manifold.

5. Remove fuel rail cover attaching studs.

6. Remove hoses (2) from A.I.R. check valve.

7. Loosen A.I.R. check valve tube at exhaust manifold and pivot away from rocker cover.

8. Remove air cleaner assembly.

9. Remove accessory drive belt.

10. Remove generator bolts and rear bracket and lay generator aside.

11. Remove rocker cover bolts (4) and cover. Both rocker cover gaskets should replaced with new gasket P/N 10108625.

RH SIDE

1. Remove fuel line beauty cover.

2. Remove PCV fresh air hose.

3. Remove rocker cover bolts (4) and cover.

ROCKER ARM REMOVAL AND REPLACE

1. Rotate engine clock wise to TDC number 1 cylinder firing position. This can be done by watching number 1 cylinder valves as crankshaft balancer hub arrow approaches the 12 o'clock position. If a valve moves as arrow moves to the 12 o'clock position, the engine assembly is in the number 6 cylinder firing position. Crankshaft must then be turned one more revolution to reach number 1 cylinder firing position.

2. In this #1 firing position the following rocker arms should be replaced with new rocker arms P/N 12557779:

Exhaust 1,3,4,8 Intake 1,2,5,7

3. Loosen rocker arm nut and lift rocker arms from stud.

4. Install new rocker arms P/N 12557779. Be sure push rod is properly seated in the lifter and rocker arm.

5. Install nuts and torque to 25 Nm (18 lb. ft.).

6. Rotate engine clock wise one more revolution until hub arrow is again at 12 o'clock position. This is a number 6 cylinder firing position.

7. In this #6 firing position the following rocker arms should be replaced with new rocker arms P/N 12557779:

Exhaust 2,5,6,7 Intake 3,4,6,8

8. Repeat steps 3 through 6.

9. After rocker arm installation be sure that the roller tip of the rocker arm is squarely seated on top of valve stem. (Refer to 1996 Corvette Preliminary Service Manual Section 6AlB-l3, Figure 14).

ROCKER COVER INSTALLATION

RH SIDE

1. Install rocker cover and bolts (4). Torque bolts to 12 Nm (106 lb. in). New rocker cover gaskets P/N 10108625 should be used.

2. Install PCV fresh air hose.

3. Install fuel line beauty cover.

LH SIDE

1. Install rocker cover and bolts (4). Torque bolts to 12 Nm (106 lb. in). New rocker cover gaskets P/N 10108625 should be used.

2. Install generator, generator bolts, and rear bracket. Torque front generator bolts and bolt with nut to 50 Nm (3 7 lb. f t) Torque rear bolts and bracket bolt to 47 Nm (35 lb. ft).

3. Tighten A.I.R. check valve tube at exhaust manifold and torque to 55 Nm (41 lb. ft).

4. Install hoses (2) from A.I.R. check valve.

5. Install booster vacuum hose to intake manifold.

6. Install distributor vent hose to intake manifold.

7. Install fuel rail cover attaching studs. Torque studs to 12 Nm (106 lb. in.).

8. Install fuel rail beauty cover.

9. Install accessory drive belt.

10. Install air cleaner assembly.

11. Connect battery and reset all electrical devices as noted in Step 1.

12. Install Campaign Identification Label.

CAMPAIGN IDENTIFICATION LABEL

Each vehicle corrected in accordance with the instructions outlined in this Product Campaign Bulletin will require a "Campaign Identification Label". Each label provides a space to include the campaign number and the five (5) digit dealer code of the dealer performing the campaign service. This information may be inserted with a typewriter or a ball point pen.

Each "Campaign Identification Label" is to be located on the radiator core support in an area which will be visible when the vehicle is brought in for periodic servicing by the owner. When installing the new Campaign Identification Label, be sure to install the clear protective covering. Additional Campaign Identification Labels can be obtained from VISPAC Incorporated by calling 1-800-269-5100 (Monday-Friday, 8:00 a.m. to 4:30 p.m. EST). Ask for Item Number S-1015 when ordering.

Apply "Campaign Identification Label" only on a clean, dry surface.

CLAIM INFORMATION

Submit a Product Campaign Claim with the information indicated below:

PART FAILED PARTS LABOR LABOR REPAIR PERFORMED COUNT PART NO. ALLOW CC-FC OP HOURS ---------------- ----- ------- ------ ----- ----- ------

Rocker Arm 18 12557779 ** MA-96 V9790 1.1* Replacement

* For Campaign Administrative Allowance, add 0.1 hours to the "Labor Hours".

** The "Parts Allowance" should be the sum total of the current GMSPO Dealer Net price plus 40'6 for the rocker arms and rocker cover gaskets needed to complete the repair.

Refer to the General Motors Corporation Claims Processing Manual for details on Product Campaign Claim Submission.

May, 1996

Dear Chevrolet Corvette Customer:

This notice is sent to inform you that Chevrolet Motor Division is conducting a recall campaign that includes your vehicle.

REASON FOR THIS RECALL

General Motors has determined that certain 1996 Chevrolet Corvettes equipped with 5.7L (RPO LT4) engines may have been built with rocker arms that have inadequate retaining load to hold roller attaching pins in the rollers. When there is inadequate retaining load, the pin may back but, with a resultant engine failure likely to occur.

WHAT WE WILL DO

To correct this condition, dealers are to install new rocker arms in your engine. This service will be performed for you at no charge.

WHAT YOU SHOULD DO

Please contact your Chevrolet dealer as soon as possible to arrange a service date and so the dealer may order the necessary parts for the repair. Instructions for performing this service have been sent to your dealer and parts are available. Please contact your dealer to arrange a service date as soon as possible. You may ask your dealer if you wish to know how much time will be needed to schedule and process your vehicle.

The enclosed owner reply card identifies your vehicle. Presentation of this card to your dealer will assist in making the necessary correction in the shortest possible time. If you have sold or traded your vehicle, please let us know by completing the postage paid reply card and returning it to us.

We are sorry to cause you this inconvenience; however, we have taken this action in the interest of your continued satisfaction with our products.

Chevrolet Motor Division GENERAL MOTORS CORPORATION


General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.



© Copyright General Motors Corporation. All Rights Reserved.

http://corvetteactioncenter.com/kb/question.php?qstId=191

 

[lt4 gs]

Sorry Bob, now it needs to be here.......

 

[CKA_Racing]

"Ya' know I thought this might be be where this was headed......and this is from our very own Knowledge base:"

True but it takes less clicks to open msn.com and search on LT4 rocker recall because i knew Hutchins web site had info on it. I thought it may be in the KB but was not sure.:L

 

[wx briefer]

3 Deuce?

 

[Vettelt193]

Sorry Bob, now it needs to be here.......

You don't have to tell me you are sorry... Now I am curious about the heads, since 3 Deuce posted two different part numbers, which is hard information that there were two sets. This is the first I have heard about it and want to learn more, and if the head swap was directly related to the rocker problem or if it was an entirely different reason all together.

 

[lt4 gs]

my guess is: that the recall cured the rocker/head probs that were out there, and the new head may have been an in line change.....I could bother my friends at bowling green....but it won't make a lot of difference. IMHO, of course.

 

[Vettelt193]

I am with you on that guess... but, my curious side is wondering if one set of heads is better than the other...

 

[lt4 gs]

Bob: Two heads are always better than one!!

 

[Vettelt193]

Bob: Two heads are always better than one!!

My day has not been that great, but this forum and lt4 gs has been putting a smile on my face all day!

 

[vets4-2]

You don't have to tell me you are sorry... Now I am curious about the heads, since 3 Deuce posted two different part numbers, which is hard information that there were two sets. This is the first I have heard about it and want to learn more, and if the head swap was directly related to the rocker problem or if it was an entirely different reason all together.

me no know but if there are two diff. # me want more info!