Rebuild 1978 L48

[1978L48jafo]

Hi all,
Based on comments from this forum I went ahead with my complete rebuild. The original issues was rough idle and low compression on number three. I found the problem, the cam lobe is wiped for this cylinder along with the lifter. Question: this car sat in a barn for about five years and only has about 50k on it now any thoughts on what might be the cause? I tend to think dry start after sitting for so many years or a stuck valve.

Other issue. Cam was unrestrained, should there be a thrust plate to restrict in and out movement? I see no bolt holes to indicate something is missing. Please don't tell me it just floats in the cam bearings..
John:

hb

 

[Stingray6974]

That's right! The cam floats in the block. Actually all the lobes on the cam are ground at an angle to keep the lifters rotating to reduce wear. This angle forces the cam rearward into the block using the cam gear as a stop.
As for the flat cam lobe, chevy had a problem with flat cams and worn valve guides. Most common reason was reduced nickel content in the iron since 1978. As the edge of the lobe begins to wear the lifter stops rotating and the lobe wears very fast. This is why correct cam lube and break-in proceedure{sp} is so important in a fresh engine.

Mike

 

[1978L48jafo]

Mike,
Thanks for the response, do you think it is unusual that only one lobe is worn away? I would think if the issue was soft metal that I would see wear all over. The damage is on one lobe on just one cylinder.
John

 

[Stingray6974]

During the past 20 years I've replaced many cams with only one lobe gone. However it has always been an exhaust lobe on one of the four center cylinders. And on several engines the rocker arm stud was partially pulled out on the flat lobe.

Mike

 

[1978L48jafo]

Cam clearance on 1978 L48

Thanks Mike,
My concern of course was not missing a problem during my rebuild. Low mileage engine so even after honing all my cylinders are in tolerance.

I am putting in a crane high energizer cam 100052 with .454/.454 lift and the cam calls for 5:1 rocker arms. Given that my block and heads are stock height do you think there will be clearance issues? Do I need to bolt together with clay in a cylinder to check clearances?
thanks
John
:confused

 

[Stingray6974]

My favorite street cam! No you won't have any clearance problems. I recommend you buy the whole kit: cam, lifters and valvesprings. Install the cam straight up and use a good timing chain and gears, not the $25 set. Since this is a single pattern cam it will respond well to any exhaust modifications. Have you decided on what pistons you are going to use?

Mike

 

[1978L48jafo]

Have new flat top pistons from northern, hypereutectic,I am told they will increase my compression from 8.5 to 10.5. I am going with chrome molly rings included in northern's HP 350 kit. I already have a double roller chain, cam, lifters, and am in the process of ordering the matched springs and retainers. Exhaust is via stock manifolds and stainless steel side (chambered) pipes. The cam instructions recommend 5:1 rockers do you know if stock height push rods will work?

I am open to opinions on the intake and distributer. I am torn between keeping the stock look of the engine or going with the performance of an after market intake. As a minimum I am order one of the improved electronic modules assuming I reuse the stock distributer.

I am getting the pistons changed over Monday, I don't own a press.

I am also stripping my firewalls and repainting the underhood and frame while things are apart. this car leaked all over. My garage floor will never be the same......

Thanks again
John

 

[MoeJr]

Sounds like a good build but 10.5:1 with iron heads is gonna almost always bring detonation. Even with 93 octane gas I don't think you'll be able to time it for max power. rule of thumb is 1 point of CR for every 10 octane ie: 93 octane=9.3:1. U can get away with more CR with aluminum heads as aluminum dissipates heat better. Just my .02

 

[1978L48jafo]

Rule of thumb or formula for compression

Moejr,
Do you know the formula for compression? The northern rep computed this 10.5:1 figure so I hate to change my plans without verifing. My goal is to be completaly streetable without looking for special gas or octane boost. I am switching out L48 dish pistons with a set of flattops. the block height and heads are standard. Assuming an L48 is normally 8.5:1 ?
Thanks
:confused

 

[Stingray6974]

John,
With the stock 76cc heads you're comp ratio will be 9.1 to 9.3 depending on valve reliefs and deck clearance. The stock length pushrods will work and the rockers I think you mean 1.5:1 ratio.
So far the best HEI ign module I have found is............ACDelco. Along with the cap, rotor, and coil.

Mike

 

[1978L48jafo]

Mike thanks for the correction 1.5:1 rockers is what I have ordered. I am using the stock 76cc heads.

Your comments on the acdelco ignition, are you referring to the stock original or a GM remanufacture? I had heard good things amount the new modules but I don't know anyone who actually tried them.
John

 

[MoeJr]

Stingray is correct about your CR. I inputed these numbers into my engine analyzer and came up with 9.1:1. They were: 76 CC Heads,0 for the valve reliefs on flattops,.020 for deck height and .039 for crushed gasket. At 9.1:1 with 93 octane you should be a ok just make sure the carb is in tip top shape. I would use an aluminum Edelbrock performer intake with the Stock QJet. The QJet Carb is a great street/performance carb when set up right. Just my .02

Moe

 

[1978L48jafo]

After Market Intake Manifold

Thanks Moe,
I am really having a ball on this rebuild, I almost went with a crate engine.

On the manifold: I have seen in several places on the forum where vet buyers frown on aftermarket parts being used. Do you or others for that matter believe it to be an issue? I realize that L48's are not particularly desirable but the only visible deviation from stock I have taken to date is my stainless side pipes (& correct color leather seats).
Appreciate the feed back.
Jafo:duh

 

[MoeJr]

I am of a differnet thinking. U really cannot see an intake manifold unless the hood is up so it really doesn't show up much. As long as you keep your original intake oyu can always turn it back to stock fairly easy. I would rather have an aluminum intake that can't be seen rather than the side pipes but that is just my opinion I have seen some later C3's with em and can't get used to them on the later cars. I think 68-69 were the only C3's to get side pipes as a factory option.

 

[1978L48jafo]

SIDE PIPES

Moe,
Understand your comments, I thought about the pipes for several years before making the decision to purchase. Exhaust is a pretty easy swap out as changes go so I gave in to my urges and bought the side pipes. You are probably right and I will get tired of them eventually but not yet. Thanks for the input on the intake.

Jafo