Last week my truck was running really bad going to work, pinging, and popping when you tried to accelerate under load. It would gradually speed up if you did not press the accelerator too far down. Thinking maybe points, I decided to drive it home and work on it over the week end. Here is what I did, first tried checking points, and found the distributor was loose, so I checked timing, and with out a gun got it as close as I could, even then no matter what direction you turn distributor the popping continued. So next guess was carb, totally rebuilt it, cleaned out fuel filter, and still popping. But I can also here a noise that to me sounds like a lifter thru the pipes, like someone tapping inside the combustion chamber. Now for some history on the motor, it is a 302, with a new set of heads, crank kit, timing chain, oil pump. the only used parts internally is the cam, and lifters. My question is any idea what it could be, I plan on tearing it down this weekend, but would like a second opinion, I have read similar post that point to different things. I think the new springs in the heads may have been too much for used lifters causing them to collapse, the popping sounds to me like valves are not opening when a large load is applied, such as acceleration. It reminds me of a bad accelerator pump on a holley carb. Anybody have a magic answer before I go buying parts?

 

quite often popping is open intake valves and indicates a timing problem or a wiring problem (wrong firing order) but if this just happened while driving I would think timing , check your rockers maybe a stud/bolt broke off this will cause what you alude to.

 

took off the intake today, everything looks good so far, rockers fine, pushrods look fine. Haven't checked lifters yet, I wonder if maybe cracked intake valve, nothing is stuck open.

 

Found my problem,
Number four intake lobe on cam was gone, totally round keeping intake closed. Also had a sunk lifter on same cylinder, but exhaust valve, so new cam and lifters is going in. Decided on the Crane 260 degree cam. Suppose to be amild cam, but also giving good low end torque. This was best priced cam I found for a stock motor, and am thinking going any bigger would not be worth it. Looked at rockers to see if maybe something was wrong with them to cause the cam failure, but all looks okay, so I am going to clean them up real good, and put some cam lube under them.

 

So you havn't determined what it was that caused the cam to do that? Hopefully the fix is in the parts you replaced, otherwise you'll just have the same problem happen again further down the road.

 

It has new heads, maybe the new springs were too much for it. The cam was original, could also see pits thru out the lobes. so I am thinking just parts failure. Everything else okay, gonna take a pipe cleaner to the lifter channels to be sure thay are not clogged, and did find one pushrod that was clogged, that may have been the problem, not sure, but by looking over everything else, I can only think problem solved. Someone said that 302's do this sometimes, I don't have any experience with them, so maybe this will be my only time. If it doesn't work, then I will replace the whole motor next time. In the last month it has had new crank kit, heads, oil pump, timing chain, carb, not much left.

 

I tried a 260H cam and found the power band too high for my truck , very little low end , it didn't start to go until about 2500 rpm. Took it out and put in a 252H , big difference moved the power lower in rpm band to about 1800 where you can feel it come on, much happier as with the o/d trans I'm running between 1800 and 2400 a lot.

 

I may try that, lowest I saw from crane was the 260, may have to try another brand, I was only looking at the crane due to price. I did find where the rocker arm for the intake that lost the lobe was intalled backwards, by that I mean the rocker was correct, but theflange that it rides on was backwards, this is the pedestal non adjustable type, inside the rocker it have a raised v-groove, and the flange has a recessed v-groove, I could see where there whas a second groove reversed, like someone reinstalled it backwards, maybe it was causing the rocker to hang up, I am going to clean it up, and make sure that all the rest are facing the right direction this time.

With the 3-speed trans, do you think the 252 cam would be good, I may post a new topic on this so I don't buy the wrong cam, not too interested in doing this again anytime soon.lol

 

sorry that 252H is a Comp cams as was the 260H