Guys I will also post this over at Team Chevelle. I have a new stock specification cam for my 1968 L78 motor and am planning to put it in before Spring and the new driving season. Never done this before but have a buddy who is a great mechanic and he will help me. The previous owner had put a hydraulic cam in the motor and I want to change it back to the original style with solid lifters. I bought the cam, lifters, valve springs, keepers etc from Summitt. What more should we do while we are at it? I want to keep the stock intent of the motor and want to freshen it up so it will run strong. Does it make sense to:

1.) Do a valve job while we are at it?
2.) Polish and port the heads?
3.) What else?

If we do polish and port the heads what HP should we expect out of the engine?

What else can we do to get the most performance and HP while not taking away the stockness (if that's a word) of the motor?

Thanks

Mark

Did the previous owner remove original springs? Are the heads "840" numbers. Are you going to check the valve guides? How much driving do you intend to do? What size push rods are on heads? Is car a manual trans? Miles on engine from previous owner's work done?

To the best of my knowledge:

Springs were changed whe the previous owner went from original solid to replacement hydraulic cam and lifters

Heads are original

We will check the valve guides

1000-3000 miles per season, probably a little less next year because of
the Chevelle getting done.

Don't know what size the push rods are yet. Will have to check them when we start the cam change

Trans is M22 correct date code and VIN

Don't know how many iles since work was done by previous owner. he said it had been a number of years and he drove the car regularly in the summer months.

Does this help?

We have no idea what condition the original heads are in and how many miles are on the engine but: if I were going to pull the heads I would pull the motor. Providing the bore is with in specs – do a hone and put in fresh rings and check bearing wear and clearances. A BBC loves new rings. But here Goes:

Changing the cam means you have to remove the:
Rad – Intake – all Bracket in front of engine - Fuel Pump – Water Pump and Timing Cover. Fortunately you can remove the timing cover on a BBC with out having to lower the Oil Pan.

1.) Do a valve job while we are at it? Involves: A trusted Machinist – Guides – Possible New Valves.

2.) Polish and port the heads? Absolutely NOT. DO NOT DESTROY the original L78 Castings that. If you want more performance buy Aftermarket or Experiment with another Set of Square Ports. Porting requires years of Experience. You can CC the Combustion Chambers and Smooth the Combustion Chamber Roof around the Entrance to the Valves to attain the CC goal and help eliminate detonation. The BBC has a specific “S” signature on the roof of the combustion chamber that must be strictly adhered too. This is not easy. You require an Old Set of Valves in the Seats to prevent from hitting the Seats with a Grinding Stone – Plexiglass and a Titration Burette.

3.) What else? New Timing Chain and Sprocket Set (Experience – lol)

If we do polish and port the heads what HP should we expect out of the engine? Virtually NONE if you are installing the Stock Cam.

What else can we do to get the most performance and HP while not taking away the stockness (if that's a word) of the motor? – reread the above.

Ron:

Thank you for the input. Your comments lead me to a couple of more questions/comments. I amnot second guessing you, just trying to provide more info and gain more knowledge from those much more experienced than I am:

I did a compression check and all cylinders are within 6% of each other at around 215-227 psi. Also the motor does not burn oil. Based on this would you still recommend honing the cylinders and replacing the rings? I was hoping to not get that far into the motor but will do it if necessary.

There is a very trusted machinist/engine builder in the area who would do a good job with the valve job. I've got this much $$ into the car, why not new valves and guides too?

I think with the info you provided , changing cam would be fine. You would like the difference and sound. I have the same cam and drive about 2000 miles a year. If previous guy did the changes correctly there probably isn't much wear on guides. 4 speed means you won't be worried about idle problems. With added pressure you should have the heavy duty push rods and guide plates thinking 7/16. I am thinking previous guy probably left along. Doing any type of home machining and porting i would not do. You look at the factory performance and i think it is enough. I think you should put a heat shield below the intake manifold before reassembly to keep hot oil off bottom of intake

Mark:

Compression looks excellent and no sign of oil burning is a BIG Plus. I would assume all you need to do is do a Cam Swap.

As Charlie mentioned, with a chisel, carefully pull the pins holding the Heat Shield under the intake and Clean it out.

You can buy a very handy Valve Spring Tool from Summit that screws onto the Rocker Studs to compress the Springs and Remove the Keeper and Retainers in order to replace the Springs. You can get a good idea on the condition of the Guides at this time by holding the Valve Stem with you fingers and slightly raise the Valve off the seat then rock the stem in the Guide. A Dial Indicator would be handy to measure the deflection or arc at the top of the valve Stem. You don't want any more then say .007" arc at the tip of the intake valve stem and no more then .010" for the Exhaust Valve. that would indicate acceptable Valve Guide Ware. Actually .003 for intake and .007 for exhaust would be right on spec on the edge of the Valve Cup but we can't get there with out removing the Heads.

I forget whether the L78 have Exhaust Valve Rotators but if it does clean them with gasoline or Varsol, blow them out with Air and lube with oil. Ensure they rotate nicely.

I would use a new set of Machined Keepers not the Cheapies and new Valve Stem Seals. Of course clean and inspect for galling of the Rocker Studs and Rockers. BBC love to do that. In that matter, always keep one set of Springs, Rocker, Keepers & Retainer and Rocker Stud in the Glove Box when running a BBC. You can replace a broken Bee Hive between lights and flush out the Bowls of the Holley at the same time - :o))

After assembly, trusting you have the Cam and Tappet bases heavily lubed with heavy ZDDP and cam degreed at specs, set the LASH Perfectly and I mean RIGHT ON even if you have to rotate the engine a dozen times by hand. Ensure the distributer is in proper position. The BBC like more advance then you would expect - Probably 18 to 21 Degrease, I run mine at 18. Fill the Crank with 40 weight SG API Oil and fire her Up.

I would run something like 10w40 or 20w50 DINO (Mineral) 4 Stroke MotorCycle Oil in the engine as it has the highest ZDDP Content with Best Shear and is SG API and better then either SL or CI-4. However, to break the cam in use something like a SAE 40 SG and change it out after an hour or 2 of running the engine. It would not hurt to put in some GM OES PN: 88862586 or that new product ZDDP Plus for the Break in.

Have FUN that's why we own them.

PS: If you want to spend some more money buy a set of Comp Cam Pro Magnum Roller Rockers and ARP Poly Locks - then you will save the guides and will not break the Bee Hive they should fit under that L78 Valve cover.

Mark, we have a large collection of L78 cars and these motors are great....but....there's always a but. The valves are the weak link...there are an awful lot of BB CE engines out there. The stock GM valve is really a 2 piece item....broken valves or valve train problems were the major cause of engine failure back in the day....if you are sure the valves are factory original then consider repalcing them and related hardware for peace of mind....if the engine still has the stock plastic timing chain set up(another weak link)...get rid of it!!! steel double roller is the way to go....3/8 pushrods are fine with the L78 cam...if you want....go with some aftermarket hardened ones...the stock rockers are fine also...the bottom end on these motors was bullet proof....within reason....make sure your heads have the right parts in them and you should be good to go....you can still get a lifter valley shield from GM that will fit under the 163 intake...good luck.


wilma

Guys:

Thanks again for all your input. The car is pretty original so I want to be true to that or at least make sure any changes from original are strictly bolt in. We will do the cam later in the winter, just before driving season. I will let y'all know how it comes out.

Mark