lars

Rebuilding a Corvette L79 327 350hp Engine
A Photo Essay
by Lars Grimsrud


Received this ’66 L79 327/350 4-speed car with a suspected flat camshaft for repair from a Forum Member on the other side of the country:


A quick engine check showed that not only was the cam flat, but cylinder leakdown rates were between 25% and 72%, indicating that a complete rebuild was in order.

So here is the process:

Pulled the engine out. I left the tranny/bellhousing in the car, and didn’t pull the radiator or the fan shroud (yes, you can get the engine out easily without removing radiator or shroud):


Got it on an engine stand:


Unbolted the easy stuff:




Used the right tools to get things apart. Note the wrong diameter balancer previously installed and the incorrect timing tab


Finished tearing it down, took the heads off, and got the pistons and crank out:




Organized the parts:


Measured things to see how bad it was. This block was bored .060 over, and the work had been poorly done, with cylinders having been bored at 4.0645. This block will need to be bored .070 over for cleanup. “Sleeving” a 327 on all 8 cylinders is a risky ordeal, and will often result in at least one cylinder cracking between the head bolt hole in the block and the water jacket. This destroys the block. So I opted for a .070” overbore, which is still safe:


While the block and heads were being machined, I cleaned up and fixed all the other parts. Rusty exhaust manifolds were sandblasted and coated with the Eastwood Stainless Steel exhaust coating. Corroded aluminum components were bead blasted with a fine grit glass bead, and then rubbed with fine steel wool to bring back the natural sheen of the parts without the artificial “bead blasted” appearance:


With the block back from machining and a torque plate hone, I cleaned it up and prep’ed it for assembly. Block work, machining, and balancing was done by the nationally renowned “Block Shop” in Denver:


Crankshaft had been incorrectly ground, with .015” differences between cylinder strokes and position. Crank was offset index ground and polished to correct all the bad workmanship, and ended up at .030/.030. The snout was drilled and tapped for a balancer bolt. Crank grinding work was done by the famous Dave Olson of Mile High Crankshafts – “crank-man” for many of the top national race teams and engine builders:


Although not my top preference in a piston, Keith Black makes an off-the-shelf Hypereutectic .070 oversized piston with a slight dome, resulting in compression ratio at a street-friendly 9.98:1. Rods were re-sized and fitted with nice ARP bolts. If ultimate performance had been the goal, I would have had some custom, forged, light-weight JE pistons made. But for this build and the intent of the car, the cost penalty was not justified:


Crank installed and bearing clearances verified:


Pistons/rods installed and torqued:


Cam installed with chain and gears in preparation for degree’ing and checking:


Accurately determining Top Dead Center (TDC) – an essential operation before degree’ing the cam:


TDC nailed down, and the degree wheel locked in place. The timing tab has been accurately located on the timing cover and welded into the correct, accurate location. The “pointer” being used for the degree operation is actually over on the left side of the photo:


Working with “the numbers” obtained from the degree process (I like to degree the cam using both the “intake centerline” method and the “Open/Close @.006” method, and I compare the numbers to see if they are consistent), the numbers showed that this engine was running the cam 2 degrees retarded. So everything was disassembled, the cam was advanced, and the entire process was performed one more time to verify correct cam installation. The numbers after advancing the cam came in right on the cam card specs (good reason to check this stuff – a cam running 2 degrees retarded would have given up a lot of performance in the usable rpm mid-range):


The 2.02 “Camel Hump Fuelie” heads were given a nice 3-angle valve job, but were not ported or altered. Just a nice, precision machine job. Head work was done by noted cylinder head machinist and Bonneville Salt Flats Record Holder Dave Sarno of Sarno Racing Heads in Arvada Colorado:


The existing valve guides had been “knurled,” and I don’t like that. I had some nice bronze guides installed (visible through the new valve springs):


Heads installed, and timing chain/gears installed in the advanced position to correct the retard error. Note that the timing dots are installed “straight up” to put the engine at TDC with cylinder #1 on compression stroke in the firing position:


Valvetrain installed. The hydraulic flat tappet L79 “Nostalgia” cam (Comp P/N 12-671-4 Advertised duration @ .006 276/283°, Duration @ .050” 229/236° Lift .468”/.462” 108° Intake Centerline) was given a liberal coating of moly cam lube on all lobes:


Corvette oil pump pickup screen is different from the standard Chevy pickup screen. The screen was installed and verified to be ½” off the bottom of the oil pan using a wad of tin foil:


Bottom end buttoned up (after removal of the tin foil check wad):


Masked off and ready for paint:


Primed with catalyzed epoxy primer:


Topcoated with actual Chevy Orange mixing formula in catalyzed urethane:


Final assembly complete with a custom built stainless hard fuel line to accommodate the Speed Demon 750 carb:




Flywheel and starter installed, and engine ready for installation on the engine run stand:


Engine installed on the run stand with partial exhaust system with mufflers and wideband Air/Fuel probe up the tailpipe:


Oil system being primed. Note use of an old distributor housing to correctly complete the internal oil passages and assure proper oiling and pressure:


Nice oil pressure at 60 psi:


Setting the valves. Valves were set at ½ turn. Note oil has been pushed up into the rockers:


Oil verified to be coming from all 16 rockers:


Distributor re-installed, and static timing set to assure that the engine will fire on the first hit of the starter. Engine ready to start for cam break-in:


Carb bowl filled with fuel to assure instant start:


First click of the starter resulted in instant startup. Engine brought up to 2400 rpm to assure proper cam break-in:


Instruments monitored. Oil pressure 60 psi, and manifold vacuum rock steady at 17.5 inches:


At the elevated rpm during cam break-in, total timing was checked and verified at 36 degrees total. Vacuum advance was hooked up and verified. Engine checked for leaks. Cam break-in duration was limited to 15 minutes. Coolant temp stabilized at 190. Rpm was then dropped down to 950, which is about right for a cam of this size. At 950 rpm, manifold vacuum ended up at 12 inches, which is pretty good for this cam. Oil pressure eventually dropped to 40 psi at 190-degree hot idle:


Carb idle mixtures were right on the numbers at 14.7:1. No leaks, no problems, and the engine test was deemed successful:


Bolted up the new clutch and pressure plate to the engine with a new pilot bearing in the crank:


Lowered the new engine assembly into the chassis (note that fuel pump and starter are removed to clear the frame rails):


Engaged with the tranny and bolted into the chassis:


Hooked up everything, fired it right up and drove it outside:


Hooked up a wideband to monitor carb performance on the first test drive. Mixtures were right on the numbers:


Put the hood on:


Engine complete:


Car and job complete:

leif.anderson93

Very comprehensive write-up along with terrific pictures. Would expect nothing less from you Lars. Thanks for sharing the build on this L79.

warrenmj

Excellent writeup! Can you do my L79 next?

lars

Thanks for the kind words, Leif - glad you liked the story..

Mark - Looks like you're just "down the street" from me. If you're serious about doing some work, we can talk, but my schedule fills up pretty tight with carb builds and car builds - I stay pretty busy...

65tripleblack

Thanks for the writeup.

The bores on a 1965 "461" intake won't accept a 750 cfm carb. Didn't think the "490" would either....................unless that's a dual inlet 650?

Did you sonic test the bores, especially on the thrust sides, for adequate wall thickness?

Nostalgia plus camshafts are dandy...............but better use boutique oil like Brad Pitt with them. Fast flanks need more phosphorous than flaccid OEM flat tappet camshafts.

DansYellow66

Man - you made that look easy-peasy - which I know for most of us it wouldn't be. Great job and documentary.

Tampa Jerry

Lars: Great as usual. Are .70 over pistons common? Do you know how many miles the engine had on the last rebuild? Lastly, have you ever thought about either retiring here in central Florida or at least becoming a snow bird . Jerry

Flatironsjim

Mike Geary

I loved this! Rebuilding the 327 was by far the most enjoyable part of the resto's I've done. Least enjoyable? Stripping paint & undercoat (on my back)!

Thanks Lars for taking the time to photodocument. And I learned something -- always thought that .060" over was max for safety margin.




Mike

Bluestripe67

Well done Lars. Like someone said, building an engine is very satisfying. Dennis

emdoller

MikeM

Whose old worn out plug was that engine out of?

Chummy85623

beautiful

65tripleblack

lars

The 750 mechanical secondary Speed Demon bolts right on. No problem. Runs nice with smooth transition into WOT.

I did not do sonic testing of the block. I've had 100% success going as much as .080 overbore on the 327s. If this were a competition engine seeing high rpm and high cylinder pressures, I would have opted for another block at .030 overbore. For a light street application, this is going to run nice and reliable. And it still has room to go to .080...

I've been running the XE-series quick-ramp flat tappet cams for many years in my builds, and they run reliably with standard oils once correct cam break-in has been achieved. Knock on wood, but I haven't had a flat cam in 40 years of building these engines...

No, the .070 over slugs are not common, which limits off-the-shelf availability. KB makes the 327 Hypereutectics in .070 and .080 + off the shelf. Otherwise, any of the piston manufacturers will custom make .070 pistons for a few hundred bucks more.

Yes, I have thought about that Florida snow bird thing... I don't like hurricanes, so you guys will just have to keep shipping the cars to Denver.

lars

The owner just stopped by with his flatbed trailer and picked up the car after going for a test drive and checkout of the new engine setup. Our conversation:

"It feels like a new car..!"
"It is.."

Hopefully the car will continue to deliver lots of smiles and fun - this thing really feels good on the throttle, and is a real kick to drive. Right now, car and trailer should be somewhere eastbound on I-70 headed back to Mississippi:

capevettes

Nice, comprehensive writeup Lars. I'm sure the owner will have many years of trouble free driving.
You did a Q-Jet for me years ago on a 69 I have since sold. Car ran like a scalded dog. If you ever get to Cape Cod, I have a room over my garage for you if you want to "play" with my cars.

ptjsk

Very cool write up Lars! Great pics too.

Thanks for taking the time to share.

Pat

Lotsacubes

Great story line for someone who's never done a complete tear down/rebuild. It's on my bucket list to someday do an engine that's not important if I screw it up.

Something you said I don't understand.... "the numbers showed that this engine was running the cam 2 degrees retarded. So everything was disassembled, the cam was advanced, and the entire process was performed one more time to verify correct cam installation."

Does this mean you installed the cam gear in the same timing position as the cam you removed initially? Meaning whoever installed the cam gear last time had it timed wrong? Also, since I've never installed a cam, how is cam timing changed? Is there like a slot that allows you to change the relation between cam and gear then just torque it down? Which implies just friction keeps the gear/cam timing once you set it (which seems strange for such a critical function of the engine).

Thanks Lars. Really enjoyed it.

lars

Exact cam timing is determined by a tolerance stack-up of all the parts that contribute to cam position. That means the position of the keyway goove in the crankshaft; the keyway grooves in the timing gears; and the machining process of the cam itself. The process of "degreeing" the cam identifies if all these tolerances are affecting the installed position of the camshaft. Every cam is supplied with a spec card that identifies its correct and intended installed position with relationship to the crankshaft position. If this relationship is not correct, it will have significant impact on the performance of the engine.

In this case, the "degree" process identified that the components parts, as used all together, was resulting in the cam running 2 degrees retarded. The brand name and quality of the cam and the timing gears leaves me to suspect that the crankshaft keyway had probably been machined incorrectly many years ago, and that this engine has always had the cam running several degrees retarded, with a corresponding adverse impact on performance. This is corrected by utilizing a timing chain and gear set offering multiple positions of the crankshaft keyway, allowing the engine builder (i.e., me) to either advance or retard the cam to correct these machining errors.

Lars