[jetmechvf24]

Just bought my first Pontiac, (67 GTO). Got her home and attempted to tune the engine and see if I could get it running better (had a miss and rough idle). Put the vacuum gage on it and the needle was jumping like crazy. Pulled a valve cover and found 1 broken pushrod and the cam lobes flat on #7 and #8. (Not a good day)

Engine- 76 400 block, 6x-8 heads, edelbrock rpm intake, holley 750, headers. (not sure on the rest)

I am a Chevy guy, have done several cams and would like to know if there are any suggestions before I proceed? Being it has 4 lobes flat, I assume some of the metal made it through the engine and caused some serious wear on the bearings. The engine still had 50psi oil press cold and 20psi at a warm idle, increasing pressure with rpm.

Decision time - Pull the motor and go through it, (clean, inspect, bearings) or put a $120 Summit cam in it so I can make next weeks car show and a finish the rest of the year.

I also have to find a repair manual for the cam change or rebuild. (any suggestions on a good repair manual?) chilton, haynes,?

[74Grandville]

6x-8 will give you pretty low compression on a 400. make sure not to go to big on the new cam. i'd look at a summit 2801 type as max size.

you'll want to buy Rocky Rotella's book. "How to Rebuild Pontiac V-8s"

[screamingchief]

I would just throw another cam in there and run it till I found a better 400 block to build as that '76 400 block is the weaker 557 casting,and you really dont wanna invest much more time,effort,or $$$ into that engine.

And plan on finding a better set of heads for the next build too.

That or plan on using the L2279F domed forgings with the 6X-8 heads.

Eitehr way I would consider the current engine expendable due to the 557 cast block alone.

Also agree dont go crazy for the temporary cam either,keep it pretty mild.

Bret P.

[Tim Corcoran]

Before you put a new cam in it check your valve spring pressure. There is a reason why the cam went flat you don't want to repeat history. You know about using oil with ZDDP in it for flat tappet cams right?

[chiphead]

Cut the oil filter open and look for metal. Tiny splinters is the cam lobes. Bigger chips/slivers would be bearing inserts or journals. With good oil pressure and no knocks, you wouldn't be risking much to throw a cam in it.

Agreed, if it is the 557 block, throw the summit 2800 or 2801 cam in there and drive it like you stole it. Even if you totally destroy the engine, you'd be out about $400. 6X-8 head cores are worth about $150 to the right person, the 557 weak block is worth about 100 bucks, the crank is worth $75 and the sheetmetal is worth another 100 or so. The pistons & rods are about worthless.

Keep the revvs below 5200 and it'll stay together.

[lust4speed]

I just tore down an engine and found a flat cam. Owner was in dis-belief since the engine ran good. Cam had just reached the point where the crown of the lobe was flat and the lifters were just starting to have a slight concave center instead of a nice even convex bottom. There was no sign of metal anywhere in the engine, and the cam and lifters were caught at a perfect time.

I've also torn down engines with massive concave lifter bottoms and really worn cam lobes and there was metal everywhere including behind the piston rings. Every case is different, but if you can't see metal sparkles in the nooks and pockets inside the engine, I'd throw a new cam in and drive it.

[Squidward]

Do the cam and have fun. Hopefully the filter grabbed most of the cam lobe sparkles.

The 2800 is a good mild street cam, but will probably leave you wanting more. I am currently running one in a 350. Try the 2801.

[2002Z4CSS]

Originally Posted by Squidward

Do the cam and have fun. Hopefully the filter grabbed most of the cam lobe sparkles.

The 2800 is a good mild street cam, but will probably leave you wanting more. I am currently running one in a 350. Try the 2801.

I have the Melling cam that is the Summit 2801 equal. I have a 1975 low compression 400 and this engine loves that cam.
Click here on this link to rear what my cam sounds line in my low compression 400 with Pypes Street Pro stainless steel exhause system. This junker will burn the tire at will from 30-40 mph on dry cement after the cam and exhauste was done

[Pontirag]

the 76 400 is not worth a rebuild, maybe a minor freshening up but thats it. as for the cam, replace it the timing set, a new oil pump, and call it good, avoid anything but a stock cam, a tired old 76 400 will die if you pump it up even a little bit. I dont think you will find any cam debris in the oil filter unluss its been on there for 30 k miles. be carefull not to get stoopit on oil selection, stay away from heavy wt oils, better to use 30 wt and a good pump rather than an old pump and 50 wt. I have a 74 400 with over 225k miles on it, new freeze plugs,timing set oil pump and an HEI, and I have put almost 30K more miles on it and it runs beautifully, no noise, no oil burning, nothing. I dont beat it though,

[Lee]

Originally Posted by Tim Corcoran

Before you put a new cam in it check your valve spring pressure. There is a reason why the cam went flat you don't want to repeat history. You know about using oil with ZDDP in it for flat tappet cams right?

Also, they may have tried to install a higher lift cam with the stock springs. Personally, I'd pull the cylinder heads and have them freshened up AND have the shop install a set of properly measured (for coil bind, retainer-to-seal clearance, installed height, seat pressure and open pressure) to match whatever cam you will be using.

[gtofreek]

I will warn you that in most cases when a cam goes flat, the debris gets into the piston pin bores and pinches up on the wrist pin.

What this does is make the piston tight on the pin, so when the engine runs, the pistons "pop" as they pivot back and forth. This can cause a funny noise when running. It will also lead to piston and pin failure after some time. Because the pins are tight in the pistons, the piston skirts will also be jammed into the cylinder wall harder, causing excess friction and loading of the piston skirt. Pistons won't be long for this world.