The Beginners Guide to Performing A Basic Rebuild on the Buick 3.8L Turbo Engine
|"This information is a result of some time and research by the author. I am not a machinist, nor a subject matter expert. Be aware that anytime you increase the performance of your car you run the risk of damage. Be smart about modifications. -editor"|
|Purpose and Scope|
|The purpose of this article is to help the guy that is concerned about having his 84-87 3.8L turbo engine overhauled correctly because of it "uniqueness". This article also focuses on a basic stock rebuild that is strong, street-able, and will last 100K miles, on a budget. This article does not cover stage blocks, girdles, or anything that is for track only or other specialty things (get my drift?). This is not a complete article, as it is meant to get you started, point you in the right direction to get the information you need, and help fill in any holes that manuals, articles and other resources may leave out.|
|Do your homework! There are excellent sources of information available online. If the answer you need isn't on this page, review the archives, browse the gnttype.org tech pages. Odds are you will come across the answer. I can't emphasize this point enough! There are articles on everything from how to remove the engine to setting sensors and tune-ups.
You should print out the Parts List, it lists several miscellaneous items that you may need.
Make all of your decisions before the work begins. Deciding you want different pistons after the shop ordered what you first told him to won't go over well.
I also highly recommend buying the Buick Power Source Manual. Some of the information is outdated, but most of it is very good reading, with good pictures and explanations. You can call Tuar Corp at (810) 239-5552 and order it over the phone with a credit card, should arrive in about four days. Cost was about 6 or 7 bucks.
|Dealing with the Machinist|
|Contrary to what you may think, any well-qualified and competent machinist can perform the machine work on the Buick 3.8 turbo engine. If you cannot get a good referral from a friend, just talk to some of the shops, ask questions, and see how well you get along with them. Pick one you can be comfortable with and communicate with. Beware of know-it-alls, and others that seem to treat you as unimportant. While most machinists have probably "overhauled 100's of those V6's" and act as if yours is not special, he is half right! Hopefully you can find a guy that will be open-minded to your desires and willing to deal with the less knowledgeable. There is little difference in the basic machine work, just a few extra considerations that will be discussed later in this article. Also, DO NOT LIE to the machinist. If you overheated the block, or let it run low on oil, admit it! He will respect you more for it. He will know what happened when he sees the engine anyway, because he will have all the evidence right in front of him!
The shop would also appreciate if you buy most of the hardware/parts from him (excluding some specialty items like a roller cam kit, or front cover, etc.). He has a set rate for labor, so his only other form of "profit" is by selling you parts. It will also make it easier if there is a problem with the parts ordered, one person to deal with instead of five.
If you don't like a machinist after talking to him, don't use him. You are not obligated to him just because you walked through his door.
You should also ask about warranty ..... find out what is and isn't covered. Get it in writing. They may even require a radiator inspection (which is a good idea anyway)
With a good machinist, you may expect turnaround times of about a month. You are not his only customer, so be patient! If he's a good machinist, you can bet he's busy.
|The shop would really appreciate it if you print out the Engine Specifications Page for him. That would leave out any question on what the requirements are.
The Power Source Manual has a very good description for chamfering oil passages and enlarging them (if needed). All good things to do if you have the time. Make sure the block is tanked and cleaned after any of this work is done.
Most machine shops should have a torque plate for the motor, since it's the same one for any 3.8-V6. A torque plate is used when honing the cylinders to re-create the stresses that a head bolted to the block would create. This improves ring seal. Practically a must.
Visit the Buick V6 Photo Guide for differences in the blocks available.
|Read the Head Sealing Tips article for differences in head gaskets. When the shop orders the gasket kit you can specify which head gasket you want included. The Fel-Pro 86-87 3.8-7 gasket kit comes with the Fel-Pro 9441-PT's (formerly the 9441-B) head gaskets which are factory replacements.
The cylinder heads are casting number 8445 that can be found on nearly any RWD 3.8L engine. Check out the Cylinder Head Photo Guide.
Quote from the power source manual - "Seat width is not critical to flow or horsepower. Width determines how long the valve job will last - the old saying 'the longer the race, the wider the seat' still holds true." The manual recommends an intake seat of 0.060-0.090-in. and exhaust seat of 0.090-0.110-inch. The manual also describes port and polishing the chambers and ports very well and includes templates. If you have the time you should at least polish the combustion chambers and remove casting imperfections from the runners.
The head bolts from the factory are called TTY (torque to yield) and are a one-time-use bolt, which means they cannot be re-used. Again, I refer you to the Head Sealing Tips article for more information about fasteners. I believe the common practice is to use the ARP Head Bolt Kit (P/N 123-4003). These can be re-used. Also, beware of the head stud kit, as this would prevent the removal of the heads without removing the engine first (due to the heater box).
|If your crank is bad and can't be turned, then it's time for a new one. The original GN crank (P/N 12350247) is no longer available, but you might get lucky and find a Turbo T/A (P/N 25535742) crank hiding in a warehouse or dealer somewhere. It's the same but has cross-drilled main journals (which is better for journal oiling). Vist the Crankshaft Photo Guide for a description of our cranks.
If all else fails and you need to purchase a re-manufactured crank, be very picky! You may get one that has rolled fillets on all but one or two journals that were repaired. The machine shop may prefer that you get the part yourself through an automotive parts place, so that he doesn't upset his suppliers by returning what is deemed a good serviceable part (which may have to be done more than once). Ideally, get one that has been turned no more than 0.010" and has not had any rebuilt journals.
If you're feeling adventureous, search the archives for references to which motors the crank was used in and search the junkyards!
|If any of the rotating pieces have been replaced (highly likely), have the motor balanced! Balancing of the rotating assembly is a common machinist's task. A balanced assembly simply runs more smoothly (i.e. less vibration). You should be encouraged to stick with the stock balancing specs (which are listed in the Power Source Manual). On the subject of vibration, with the motor removed is a good time to inspect/replace stock motor mounts. There are poly-mounts available for higher HP use, but for a street driven car you will have to make the choice if you want to put up with the added vibration.|
|For a description of the different kinds of bearings available visit Clevite
List consensus is to go with the following bearings:
Bearing part number example: MS-960-10-P. MS=main set, 960 is the part number, 10 is the journal undersize, and P is the type of bearing.
|Pistons, Rings, and Connecting Rods|
|None of the GM pistons are available any more, so you have a few choices for stock replacement: Check the Piston Photo Guide for comparisons. The best piston for street use may be the forged TRW L2481F.
(info on rings here)
For the connecting rods, stock is the best you can get for the street. If you need to replace any of them, a reconditioned stock rod is fine. Make you sure get the right part number. Check the Connecting Rod Photo Guide to help with identification of the correct part.
|There has been a lot of discussion of cam failures on the list. One reason was quoted as being the number 3-exhaust lifter bore being slightly off-center from the factory causing premature lobe wear of aftermarket flat-tappet hydraulic lifters. Also stay away from cast budget rollers kits, as the only thing to use on roller lifters is billet steel. This is another item that you may want to get yourself and not go through the machine shop. Talk with any good TR vendor and they should recommend a good cam to use. I bought a billet roller kit which included the cam, roller lifters, double-roller timing chain and gears, valve-springs, and thrust button. This kit required no modification of the block! My machinist was very impressed with the kit.
This motor does not have adjustable rockers, so exact measurements and clearances will have to be made in regards to push rod length. It will be different from motor to motor, depending on cam, head gaskets, how much the head was surface or milled, etc. Don't skimp on this part. Review the Lifter Preload Article for more information.
For street use, the stock shaft and rockers are more than adequate, supposedly down into the 10-second range. But visually check your used one well for wear before you re-use it, and replace it if necessary.
|Aftermarket front covers are available from most TR vendors with externally replaceable front seals (stock cover uses a rope oil seal, which is included in the gasket kit). Some will even deburr the cover inards for you. If the small hole for the oil pump drive shaft (the cam sensor shaft) on your original front cover is wallowed out...the whole thing is junk. There are also high volume oil pump kits available if you can't afford a new cover.|
|There isn't much I can add here that isn't already in a Chilton manual. I would like to say that if you are going to assemble your own engine, you should do a few test mockup assemblies to make sure all of the parts fit togethor correctly, nothing binds or interferes, etc. Also refer the Torque Specification page for proper bolt torque values. There is a host of chemicals that are needed. Acetone for cleaning, engine assembly grease, various RTV sealants, Anti-sieze compound and Loctite first come to mind. A Tap & Die kit can be a life saver!|
|I would also suggest replacing the water pump at this time, it's cheap and easy with the engine removed. Seams like every engine I overhaul, I end up replacing the water pump anyway in the first 500 miles, so get it over with :).
If you use measurements from your micrometers or any other measurement equipment, compare your gauges to the machinist. They check theirs, we generally do not. If you say turn to 3.008 and he does, if yours was off the problem really was yours and not the machinist.
|The above information was obtained from several sources, including:
www.gnttype.org website articles, mailing list, and archives
The Buick Power Source Manual
I can't take all the credit for this article. Editing, error corrections and suggestions have been provided by: