I just experianced the same thing as Crab with my truck, and for what reason I don't know why. Rebuilt rocker shafts, all new NAPA pushrods, and been driving the truck about 2-3 days a week with a lot of new fuel going trough it. I go and recheck all the valves for adjustment and their all where I set them when I did them last. There is no fuel problem since I fill it about every other week. The last time this happened I was driving back from our new house we bought, ( about a 90 miles round trip)  backed off on it coming up to a stop sign, and when I took off it started missing a little, but was better at speed. I took the valve cover off and two pushrods were not under the rocker, one exhaust and one intake on different cylinders, just doesn't make any sense to me. I've probably got 1200 miles on a new motor now.

                                                               Michael

Michael

Sandy Valley, NV

Same thing happened again tonight, same valve and I saw it stuck down. When I came back from the phone it was up, so I replaced the pushrod and it started normal. Took the car out and drove to the gas station for a fillup, and ran it hard on the freeway for about 6 miles. Car sounds and runs great, hoping the fresh 15 gallons of fuel will clear things up. Either way, we need to just run this thing a while I think and hopefully things will settle down. I got to admit, that little 312 with 3.56 gears  gets up and goes real good, 60-80 don't take long at all.

I would get rid of every drop of the old gas. In fact I buy repop gas tanks for all my old jalopies. It doesn't take much stale gas to cause an intake valve to hang open. You can add a stabilizer to gas when it is fresh and prolong the life of the gas, but once it is stale, it is nothing but trouble.

Kenneth

Fredricksburg, Texas

Thanks Ted, I had previously drained all the old fuel from the tank, about 10 gallons sat in there for 15 years. We have been adding a bit here and there to get it running, so I suppose its possible that could  be partly the cause. I did put 4 gallons in yesterday before starting it, and we plan to fill it when we get near a station.

You didn’t mention how long your car was down for repairs so I’ll touch on fuel age as being a possible culprit.  Old fuel can allow the vehicle to crank up okay but a varnish build up occurs in the intake guides on that first intial drive.  As long as the engine is heated, a problem usually doesn't surface.  Once the engine cools, this buildup will allow the valve to drag extremely hard in its guide and bent pushrods are the first indication of something going on.  This is something that will be seen on the intake valves and not the exhausts and it’s only when the engine has cooled and is restarted cold that this particular problem comes to the forefront.  But from experience, the fuel typically smells old (turpintiney) at the exhaust when it's old enough to do this.

Lorena, Texas (South of Waco)

Just for the record, the head I sent crab was a rebuilt 113 with new cast guides, hard steel ex seats and good used (refaced, so they were checked for run-out) intake valves. The exhaust valves were left out so crab could install new ones of his own.

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias

Same shafts, I did clean and inspect them however and they looked good. This is a new top end on an engine with 81K miles, it may have just been a bad pushrod or something but we drove the car the day before and it ran great.

To add, I put another pushrod in right away, started it up and everything sounds normal. Think I will go thru and check all of them one more time just to be on the safe side.

It sounds like you have a cam timing error, based on the statement "some seemed looser at a different spot on the cam" There are two classic Y block timing errors: following Eichman's Ford Y Block book instructions or doing it like a Chev ie putting the marks on the timing gears together instead of 12 pins apart.  I doubt the a the engine would run with either of these errors but it would bend pushrods because the valves will hit the pistons.

Doug T

The Highlands, Louisville, Ky.

If it stuck a valve in the guide you would see the spring is a little lower than the rest. You did get new guides and I hone and brush each one to make sure no debree is left behind. And I do hit each valve to make sure the locks are seated. Put another pushrod in, adjust the valves and do a quick compression check to see if the valve stuck the piston.

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias