Magnum 5.9 Timing Chain Noise?

You have a brain scratcher for sure.

The cause of the mystery noise has revealed itself, or at least I am 99% sure it has.

My connecting rod bearings arrived yesterday, the weather was nice, but I had work commitments. I really had work commitments today as well, but the weather was supposed to be good in the morning and start to rain again in the afternoon, so I blew it off and played hooky again.

I checked the first new bearing for size. I measured it at about 0.004” clearance, but in all fairness, because it is difficult to torque the cap off the journal to the correct torque there may be a crush factor here. Anyway partly because I didn’t have a lot of time to spend on it today, I decided to take the slight gamble that all bearings were the same and installed them all, torqued them down and buttoned things up.

If you recall, I mentioned that I saw something that would probably explain the noise when I did the bearing inspection.

As I was working myself along the inspection, I just happened to notice that #8 had some vertical scuffmarks on the cylinder, right down to the bottom. It didn’t look like it was scored, just scuffed. None of the others had that. On further investigation, when the piston was at or near BDC, I could see scuff marks on the piston skirt. “Aha!” sez I to me. “I’ll bet I have a collapse piston skirt on #8”. Then I decided to see if I could move it from side to side at all. Shor ‘nuff. Couldn’t get any noticeable movement on any of the others.

So, now I have a new timing set, a new set of bearings, and a fresh change of oil, even went heavier (20W50) to see if that might quiet the piston down a bit, or at least help preserve it’s life somewhat.

I fired the old boy up, and as expected, no noticeable change in noise. I let it warm up to operating temperature, and it might have gotten a bit better, but not much. The noise is worse at idle but by about 2000 RPM no load, it is all but gone. It changes a bit on accel and decel, which kind of makes sense to me for excessive skirt clearance.

A collapse piston skirt was one of the first things I suspected, but discounted any piston or rod noise early on because the noise didn’t change when I pulled the plug wire on that cylinder. So, I’ve learned something new.

I retrospect, the plug on #8 was quite oily, none of the others were. Compression on that cylinder was only 100 PSI, but compression for the engine was all over the map anyway. The low compression would be consistent with excessive piston to wall clearance or ring damage. I just didn’t make the connection between noise and an oily plug or the low compression.

Other than take it easy on the engine, I’m not going to do anything about it as the engine and transmission are scheduled for change out within the next 6 months or so anyway.

Years ago I had an early 60’s Ford cab over 5 ton truck. It had a British 6 cyl Daganham diesel engine. It had a collapsed piston skirt when I bought it, and it had had that same collapsed piston skirt for many years service before. It sounded like something was going to come through the side of the block, and not just diesel noise either. I transplanted the engine and transmission into a Boyerton step van I was using for work. When I finally had to tear it down because I was getting antifreeze in the crank case (just liner O rings) I had a good look at the offending piston. Yup, it was scuffed all right, as was the liner, but not scored at all. I installed a new piston and liner and got several more years service out of it before the rust bugs did a number on my poor old van.

So, that is the story. I’m curious to see if the engine dies because of this piston, or it will just carry on, rattling merrily away.