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I just finished rebuilding my 390 for my 73 F350. Did break in, cool down, and changed oil. Ran fine. Sat for about a week got into it started it up. Idle rough, I could get it timed at about 15° in the idle would smooth out, but once trying to drive it, there was a lot of hesitation it wouldn’t go anywhere. Anything off idle would cause a sputtering and a backfire through the carburetor. I thought it was the carburetor at first, so I had that rebuilt. Took off passenger side valve cover number three and number one intake valves not opening. The lifter was moving up and down, but it didn’t look like the lifter itself was pressurized. The cam looks fine. That’s not wiped out. I’m at a loss at what it is. Any help is appreciated.
Usually it means Original Poster...but in this context I think it means oil pressure. 390's are usually pretty good about having lots of oil pressure...so that's my .02.
Did you by chance use a good quality oil with lots of zinc or ZDDP to protect the cam and lifters during break in?
My take on OP
When discussing about an item someone else posted would be original poster
When discussing issues with engines, OP would be oil pressure.....
It sucks, but it is pretty common on new flat tappet cams. Must run good break in oil and follow break in instructions. I run a bottle of Lucas ZDDP additive in every oil change with my 460 since I have an aftermarket cam and heavier springs. Almost 20k miles on it with zero issues.
Just curious, what was the break in procedure you used? New cam blanks must be made of an alloy like iron & peanut butter .... seems as if I read a lot of failures.
Back in "the day", one only occasionally heard of it. We broke them in with stock springs after generously coating cam lobes with Crane cam lube with moly. We used a good oil like Kendall GT-1 and once started, kept rpm immediately and steady above 2,500 for 20 minutes, watching temps and standing there with garden hose in hand to spray the radiator if needed for cooling, and if available .... a large fan. Driving in traffic is not a good idea as one must stop, etc for traffic, but once broke in, taking a "road trip" to the next town was good. If one had special springs, they could be put in next week.
Occasionally a fellow got overanxious to let it idle just to hear it lope, and that's when they didn't do so good.
Ask your builder what clearance was set on valves to car or truck engine? Probably has nothing to do with the cam failure but did a 390 years ago and machine shop set guides at car setting and the engine was in a pickup. The owner came back from vacation with a hand full of bent pushrods. Said it would run fine all day and when shut down at night would seize a valve. We must have better cams and lifters in the day.
You can't polish a turd. With Johnson out of business there are no quality flat tappets anymore. roller cams are no longer an upgrade they're a requirement.
Back in 2007-8 I worked for a engine parts company, all they sold were engine parts.
No spark plugs, no oil, no air filters just hard engine parts.
We sold engine overhaul kits for everything domestic from an old Ford N4 tractors to Detroit diesel engine.
All of our cams came with break-in lube and SPECIFIC BREAK-IN DIRECTIONS!
If it was an over the counter sell we went over the instructions with every customer and we still had people came back and tell us that lobes were flattened during the break-in.
They'd get that deer in the headlight look on their face when we asked them if they used the tube break-in lube like the instructions showed.
I'll never understand why they got soo pissed when we wouldn't refund their money.
New cam blanks must be made of an alloy like iron & peanut butter .... seems as if I read a lot of failures.
