Pontiac’s 389ci Engine

Pontiac Overhaul Time

Updating Pontiac’s venerable 389

Story and photography by Jim McGowan

Every time I get involved with an engine project I swear it will be the last one – ever! It’s hard work, both mentally and physically, particularly if you choose to do it yourself. Regardless of what engine you’re building, lots of research and financial decisions need to be made before you start, or trouble will be knocking on your toolbox lid.

Once it’s established that you need/want to rebuild that chunk of iron, you must then decide how you want to build it, how much you can spend, what parts will you use, what shop will do the machine work, etc. The list goes on and on.

The article featured on this page is from the May 2010 issue of Pontiac Enthusiast Magazine.

This ’65 GTO engine was an untouched original until the decision was made to freshen it up. It ran relatively well, had an average compression of around 175 (with a low of 165), but was suffering from blow by, front and rear main seal leaks, a few valley pan and other miscellaneous drippers, plus over four decades of use. Environmental issues were also at play here. It needed a complete going through (there was also a lot more wrong, as you will see). The time had come to clean it up and bring it into the 21st century. I wanted to use a combination of original and contemporary internal parts, but keep the external appearance stock. I did my research (for several weeks) as to what parts vendors I wanted to use, found a highly-recommended local machine shop and the rest is documented here.

I am going to include as much info as possible, but since space is a consideration, and pounding in piston after piston is boring, I must abbreviate the step-by-step assembly project. However, I will include part numbers (when available) and suppliers for your reference. We are starting with a stock-bore 389 cid block, but the basic machining and rebuild process will hold true for any Pontiac (or other V-8).

While gas prices have continually fluctuated, the octane rating here in California has dropped. We are down to 91-octane premium, and it looks like another point drop is eminent. This Pontiac will be street driven about a 1,000 miles a year, so I am lowering the compression from 10.75:1 to 10.25:1 and bumping the cam and valve train up to Ram Air IV specs. The 10.25:1 compression is still a bit high; 9.5 would be better, but for casual pleasure driving it has proven to be OK and the engine sounds healthy. Hardened exhaust valve seats and stainless steel valves will also help with the octane drop. Cast pistons and rings are fine for my driving purposes, as is the bulletproof original Pontiac Arma Steel crank. After careful measuring, it was determined that the cylinders would clean up at .030 over and the crank would be turned .010 under. The block would also be align-honed and the original connecting rods resized and ARP rod bolts installed.

During the tear down we had a few surprises. Two of the pistons had broken rings (the blow by), most of the connecting rod and main bearings were showing lots of copper and the block was clogged with sludge. Probably the reason it was running hot! It’s what you don’t know that grenades your engine. Luckily, the broken rings hadn’t scored the cylinder walls and we had no spun bearings. Timing of the rebuild was accidentally perfect.

Be sure to use a good ZDDP additive in your oil before initial fire up, as most of today’s over-the-counter oils have had this critical lubricant removed by the EPA. Two bottles for safety and then the ZDDP content in the oil should be sufficient, but it’s all chancy now. I used two bottles of Justice Brothers Engine Treatment, which worked well and the cam survived the run in without any problems. We didn’t dyno the engine, but estimate the horsepower to be slightly over 400, with the torque slightly more than exciting!

The photo captions will tell the rest of the tale. My strongest advice on rebuilding your engine is spend the cash on the best parts and machining. You only want to do it once, so do it right!

Machining:

• Block: cleaned, Magnafluxed, align-honed; bored .030-inch over

• Heads: cleaned; Magnafluxed; bronze guides and hardened exhaust valve seats installed; three-angle valve job; stainless valves

• Crank: turned .010-inch; polished

• Rods: rebuilt; ARP bolts installed, pistons fitted

• Reciprocating assembly:balanced

1 After much agonizing, I made the decision to rebuild my original ’65 GTO engine. Except for machining, etc. that can’t be done personally, the R&R, strip down and re-assembly will be done at home with the help of a few friends. This is the first time the engine block has been removed from the car.

2 The original Arma Steel crank (#9773383), rods and pistons were intact. The bearings were showing lots of copper and a few were ready to take a spin. The timing on this project was perfect, even thought I didn’t realize it at the time. Two of the pistons had broken rings, but luckily there was no cylinder wall damage.

3 The factory cast 10.75:1 pistons were in good shape, as were the cylinder bores. The bore diameter was checked and we determined that a 30-thousands (.030-inch) cut was all that was needed. Next step: remove the pistons.

4 Before removing the crank, we mic’d all the journals and found that turning them 10-thousands (.010-in.) would bring them back to perfection. The term 10-under refers to removing material from the journal surface, making it 10-thousands under size from stock.

5 Early Pontiac engines came with an almost bulletproof Arma Steel crank, which are popular with Pontiac engine builders. The ID is plainly visible on this part.

6 The factory rods were cleaned and resized to perfectly round and new Clevite 77 bearings and ARP rod bolts installed. Unless you’ve had a catastrophic engine failure or are building a race engine, there is normally no need to buy new rods.

7 After careful measuring, the block is installed on the boring machine and the cylinders machined. Boring makes the holes slightly larger, hence the term 30-over(size). The block was completely stripped and cleaned prior to starting the machining process.

8 After the cylinders are bored, the top of each cylinder is given a slight chamfer to facilitate piston ring installation and to take the sharp edge off the cylinder left by the boring and honing.

9 We began assembly by installing the oil galley plugs. They were removed for the block cleaning, and if not replaced it will dump lots of oil on the garage floor at fire up. It would also mean pulling the engine again to install them. Next, the brass freeze plugs will be installed.

10 The rear galley holes are now plugged and the brass freeze plugs installed. It is important to follow a procedure when installing internal sealing parts and double-check each step. Oil or water leakage can mean having to remove the engine to access the problem areas.

11 Federal Mogul high-babbit cam bearings are now inserted using a special tool. This is something that you should leave to the machine shop if you don’t have the specialized tool necessary. They will install the bearing for a few more bucks. The installation starts at the back of the block and moves forward.

12 The main bearings are now installed. Here we see the thrust bearing being put into place. The oiling holes in the bearings match up to oil holes in the block. These holes keep the crank lubricated and spinning happily.

13 The Viton rear main seal from BOP Engineering is now installed following the supplied instructions. A little filing is required at the top edges to make the fit perfect. Here, we are determining the seal is level with the block surface. Viton has better wear and thermal characteristics than neoprene or the old style rope seal. The BOP rear seal is available in 3- and 3¼-inch diameters. They recommend using a silicone sealer with this seal.

14 The complete reciprocating assembly was balanced at the machine shop. Here we blow out all the crank oil passages before final installation. Notice the beautiful polish job on the rod and main journals.

15 With the crank in position, we used Plastigauge on each journal and torqued the main caps to 120 ft-lbs. The Plastigauge crushed to between .002 and .003-inch, which is perfect for the mains. We did the same for the rods to check their clearances. This is a little extra work, but worth every second for the life of your engine.

16 The two-bolt main caps were installed and permanently torqued down in stages, finally reaching the required 120 ft-lbs. The crank endplay was then measured and found to be a perfect .006-inch.

17 Prior to installing the pistons, the rings were installed in the cylinder bores and the ring gaps measured. They were ideal at between .016/.018-inch all around. We then installed the ring sets on the pistons.

18 There is a small notch in the side edge of each piston, which MUST face the front of the engine. Each bore was washed with transmission fluid and then wiped with a good coating of engine oil before the pistons were installed. Rubber hose was used on the rod bolts to prevent damage to the rod journals.

19 Crane Cams anti-pump up lifters (#99282-16), chromoly push rods (#28620-16), and 1.5 ratio-stamped steel rocker arms (#28800-16, now discontinued) were installed. We soaked the lifters in engine oil for several days to pre-lube them.

20 Liberal amounts of assembly lube were used when installing the cam and lifters. The Ram Air IV Blueprint Series Crane Cam (#969681) was installed followed by the lifters. This cam has a gross lift of .469-inch and provides 16 inches of vacuum at idle for the power brakes. Despite various rumors I’ve heard, the RA IV cam idles nicely at around 800/900 rpm and is very streetable.

21 Here’s the Crane Ram IV valve springs and retainer kit (#28308-1) and a valve spring installed height measuring tool from the PROFORM/Specialty Auto Parts line of engine building tools. Checking valve spring height will help prevent coil bind as the spring compresses when the engine is running.

22 Hardened exhaust valve seats and stainless steel valves are now almost required today, and will protect the combustion areas using today’s 91-octane (or less) premium fuel.

23 We’re using a Fel-Pro engine gasket kit from Ames Performance (Ames #N575). These are self-sealing head gaskets and are top quality.

24 The assembled heads are now installed. Small dowel pins on the block hold the head in place as you install the bolts, but it’s a good idea to screw one bolt down tightly to ensure the head doesn’t slip off. The head bolts will be progressively torqued to 95 ft-lbs.

25 With the heads secured, the valley pan can be installed. A cork gasket is used as a seal and the edges peened around the circumference for a tight fit to prevent oil leaks. Two bolts in the center of the pan pull it down tightly.

26 With any open holes covered with tape to prevent stuff from falling into the block, the engine was installed into the car. Now all the other parts needed to fire this beauty can be reinstalled.

27 With the engine secured and ready to fire, we can now set the valves. We’re using a Proform valve lashing tool (#66778) on the Crane Cams adjustable 3/8-inch Poly Locks (#99788-16). This early Pontiac engine has pressed-in 3/8-inch rocker studs, later models have 7/16-inch studs and can use roller tip rockers.

28 Before buttoning up the valve train we poured some oil into the rockers for pre-lubrication. Just a little will do the job until the high-volume oil pump from Ames Performance starts pumping. The oil filter was also filled with oil before we installed it. We added two bottles of Justice Brothers Engine Treatment that will assist during initial cam break in, and then filled the crankcase.

29 I added two bottles of Justice Brothers Engine Treatment to the initial fire up oil for the cam run in. This was added insurance due to the lack of ZDDP in today’s engine oils. Once the engine has a few hundred miles on it, I’ll change the break-in oil and filter.