I apologize in advance for the long post, but I want to make sure I put in every detail I can think of to get the best response. I've been working on Ford V8s for over 20 years, but never had a problem like this. I think I'm looking at an engine with bent valves, but won't be sure until I yank the heads, which won't be for a few weeks due to funding.

Here we go:

I have been working on my neighbors F100 that has a 68 302 from a mustang in it. It's a crate motor that he got online from an engine rebuilder back east. It has a slightly bigger cam, but it's close to stock. It has 1.84/1.55 valves. He had a local garage put the engine in. First he had problems with the rocker arm on #3 cylinder coming loose every few days. I finally had to put a 2nd nut on the rocker arm to lock it down. The engine was leaking oil from everywhere so last week he dropped it off and I bead blasted his valve covers and intake and put it back together with new gaskets of course. Before I tore it apart, I carefully marked the distributor and where it was set so that I could drop it right back in and fire it up. I dropped it in and it wouldn't start. Thinking I was somehow off a tooth, I started moving the distributor around. I slid it to the right and it started up and ran pretty smooth. I put the light on it and it was way off the mark, and when I slid it back to the left into the correct range (10-16 BTC) it would die. Set it back to about 20 degrees BTC and it ran great. I pulled the distributor out many times to change what tooth it was set to. I eventually ended up setting it back to the same spot I originally dropped it in to and set it back to 20 degrees advance. It didn't start hard at all, so I took it for a test drive and it drove pretty well. My neighbor picked it up and we discussed the problem. He thought it came with a double roller timing chain, but we couldn't be sure until he found the build sheet. He drove it to work the next day (about 20 miles) He said on the way back it started running rough and makes a loud noise.....sounds like a diesel. He brought it back over and I thought maybe the timing chain had skipped again and that the exhaust valves were still open when the cylinders were firing, hence the noise. I also checked the rockers and they were still set properly and the pushrods aren't bent. I pulled the timing chain cover off and the dots were lined up. It was just a standard chain, so we don't know if it was from the original engine or if it was what came on the crate motor. It doesn't say Ford on it, but it says made in the USA. It looked loose, until a new double roller chain was installed, and they appear to have the same amount of slack. I could be wrong on that because I didn't measure them, just moved them with my finger. Anyways, I installed the new chain straight up, and put everything back together. Now it runs when timed, but it still sounds like a diesel. I took a compression test and all the cylinders are still only at about 100 pounds, but they are all the same. None are higher or lower than others. It was the same before the new chain, but that doesn't surprise me because the old chain was straight up when I tested it. To me it sounds like the exhaust valves are slightly bent, not seating properly, and that explains the noise and compression. That is just my guess at this point.....What do you think?

Also, what else can cause a timing chain to skip other than being hard on and off the throttle.

Thanks!

 

Update: So I talked to the guy that does my machine work, and he thinks that maybe the problem I had with the timing is the balancer slipping. He said he has seen it many times, and now that I'm thinking about it, I was driving a Corvette years ago when the rubber insulator dried out and the whole outer ring of the balancer slipped off. So when I got home I wiggled the outer ring of the balancer and it seems a little looser than the ones on my other engines. So maybe that explains my timing issue and why I thought the timing chain slipped. He doesn't think the timing chain moved at all.

New theory: Spun/bad bearings. So I'm on my way out to check. He told me to pull plug wires when it's running and if pulling a wire changes the sound of the banging, then it's bearings. I'll also be opening the oil filter to check for metal. I thought I would have seen it in the oil if the bearings were going out, but he says I won't, and to check the filter.

More to come........

 

Conclusion: Spun Bearing. Loudest one I've ever heard. I've heard rod knock before, but nothing like this. I did a youtube search to listen to other people with spun bearings that sounded the same. Right there I was pretty much convinced of a spun bearing. I tried the trick with the spark plug wires but it didn't seem to do anything. When I cut open the filter I found bits of copper and aluminum. Looks like he'll be needing his crank turned. I always assumed you would be able to see metal in the oil on the dipstick, but my machinist says no.
I also thought that a spun bearing would have less compression in that cylinder since the bearing is now thinner or missing, therefore the piston doesn't come up as high in the cyliner.....unless he wiped out all the bearings.

This is what poor maintenance gets you. The guy has had an oil leak out the back of the intake since he got it......on a new crate motor! The guy who installed the engine also installed the intake. The first time he brought the thing over the oil didn't even register on the dipstick. This was back in December. Since then he has checked the oil everyday (so he says) Reguardless, the damage was done back then, and it held out until now before letting go. It also doesn't help that even though I told him to drive slower, he drives up and down a long steep grade at 70+, even on hot days.

 

New update: I thought it had a spun bearing. I pulled the filter off, cut it open and there was lots of metal in there. Looked like copper too. I thought that confirmed it was a spun bearing. So we pulled the engine out the other night and yesterday got it drained and on a stand. Flipped it over and pulled the pan. Lots of metal in the bottom of the pan. I then went along checking for movement on the rods thinking it had a bad bearing. None of them moved so I started pulling rod caps. Went through all of them and they all looked brand new. So I pulled the mains.....same thing. Totally confused, I inspected further thinking well maybe his cam went flat so I started looking at the lobes. They were perfect too. Then I started checking the pistons and on the #2 but even more so on the #7 I could move the piston back and forth in the bore. Definetly a problem. Turns out this is called piston slap. I pulled the heads off to get the piston out. First thing I noticed was that the pistons were .060 which I thought wasn't a good idea. I thought rule of thumb was to not go past .030 especially when there are so many good rebuildable standard bore blocks around. So I thought when I pulled the piston out the rings would be damaged or missing. Not the case. All the rings looked just find, but the skirts on the pistons are beat up. I put a ring in at the top of the bore, squared it up and the gap measured .022 I pushed it farther down the bore and the gap increased to .042 I know not the most accurate way to measure bore diameter, but I think a .020 increase is the problem. Looks like it's time for a new short block.

 

That sounds like a terrible rebuild. I wouldn't be surprised if those two cylinders were outside spec for a 60 thou piston from the beginning... meaning the block should have never been used for a rebuild in the first place.

 

I"D be concerned with the copper in the pan, its gotta be a bearing. If the rods and mains are ok then I'd check the cam bearings

 

I'm going to finish tearing it down and check the cam bearings. That's actually what I was looking at when I reached in and grabbed the skirt of the piston and noticed it moved quite a bit. I agree with Conanski, that it probably shouldn't have been used in the first place. What do you expect for a $1200 long block. I spoke with my machinist and he said to finish tearing it down and bring it to him to check out. He said it's getting common to punch these out to .060 these days because all the old blocks have already been rebuilt once already. He says it's a problem with FE's too. Turns out this 302 is a 79 casting. I haven't checked the date code yet. Anyways, he said he can check the block and see how many cylinders are bad and sleeve it to get this guy back on the road. This is his daily driver. I'd prefer to find him a roller block, preferably once of the 351 variety. Unfortunately funding is really tight for this guy and he really just needs his truck running.

 

"He said it's getting common to punch these out to .060 these days because all the old blocks have already been rebuilt once already."

That's why I'm a fan of boring an engine to .020" for the first rebuild. Then you can go .040" and .060", and get three rebuilds instead of just two.