I had a real bad knock in my 94 7.3 IDI Turbo with close to 400,000 kms on it. I cracked all the injectors with not much success. Glow plug tips were all present and accounted for. Then I opened up the oil filter and found some metal. I've got the engine upside down and found number 7 piston has some play in the cylinder when cranked back and forth in mid stroke. This play makes the same sound as the knock I heard except of course at a much lower level. I haven't been back to it with the holidays and all so I haven't pulled the head or checked any bottom end bearings. Oil pressure was always good though. I was wondering if anyone has had any experience with this? Has anyone done just one piston in these engines with any luck? This engine always ran well and started good. I put a rebuilt IP and Injectors in about 75k ago because it was getting a bit lazy at cold weather starts. Before we yanked it, compression on 4 of the cylinders was 450 lbs +/-. I wish I had taken the time to check all of them. Number 7 wasn't checked as my adapter hose wouldn't fit under the turbo.
Thanks to all who read this long winded tirade,
73nut

 

If the piston slap was your noise, shorting that injector should have changed it. Is it always there or does it come in with the throttle as piston slap usually does?

If you are pretty sure that piston is really loose, I guess the next step would be to pull it out and see what is causing the condition. Is the piston cracked/collapsed or is the bore shot? Hope I gave you something to think about.

 

Thanks for the reply,
When I cracked the injector the knock was somewhat reduced but it was still there. It was present at all throttle positions. The piston was definately loose in the bore and will have to be pulled out. With the engine upside down you can see the piston skirt move against the cylinder wall as you swing the crank back and forth. It is pretty plain at mid stroke. There is also an audible "click" as this happens and this sound sure imitates the knock. I've heard that sometimes these engines develop piston problems and was just wondering that if the bore is OK (and the rest of the engine seems to be Ok), if anyone has gotten away with changing just the one piston. The cost of a reman seems to be around $7,000 or more plus my own labour. From what I can tell from some others on this forum, rebuilt engines seem to have mixed results. My thinking is that if I'm going to have an engine that I keep wondering about it might as well be one I've spent a few hundred dollars on instead of several thousand and then start arguing with a builder about warrantee. Does that make sense? Hopefully I can get back to it before too long, I have to sneak away from the keeper of the cookie jar.
Thanks again,

 

Due to the fact you have 250K miles on that engine, I would say think about total rebuild. #7 is one of the most prevelent cavitation cylinders and would at the least require sleeving, my thing is if you do one do all....... If you have an engine with that mileage and no head repairs to date you are probably due for them. Piston slap from info I've seen can wear one side of the cylinder wall only, but not necessarily wear the other side. Have you been using SCA's religously throughout the life of the engine.

One other point I would when ready pull all injectors number them and see if one is toast ie #7 a weak injector can induce a knock like a rod bearing. Due to the fact it fires early and then so does the cylinder fire before TDC.

 

This should open a can of worms, no I haven't been using SCA's. The first I've read about them is on this forum. I see that you guys are pretty adamant about them. I've been running a few 7.3's since about 1994. All of them were used when I bought them. One of them has over 500,000 km on it. No problems so far knock on wood. I even had a 6.9 that I bought brand new in '86. It had 400k on it. The only reason its gone is that the body rotted off it. How long can an engine last w/o SCA's? I guess you can tell by my red face that I'll be putting some stuff in my rads real soon.