Connecting Rod Issues

[TEET]

Hi All,

I recently picked up a used K301 to drop into my 682, as the KT17 series 1 was fragmented.

I found a K301 fairly close to home that was removed from a 1250 with 250 hrs on a rebuild. I fit it in the 682 after fabbing some engine mounts, installing a 82 series ISO frame, and making a longer drive shaft. I performed the usual checks on the engine, and gave it a basic tuneup..points, plug, air filter, changed the oil, and she ran pefectly....for about half an hour. I was just driving it around making sure everything felt and sounded right, which it did...then....NOCK,NOCK,NOCK pretty dang loud. I shut it down immediately, and rolled it into the garage. I turned it over a few times with the plug out, and it still had great compression...so I assumed the rod was screwed up somehow.

I pulled the engine, and tore it down to the point I could check the rod, and I was quite surprised to see that one of the nuts had backed off the stud and dropped into the oil pan, the other was half backed out..... I tore it down some more and removed the piston and rod....I'm also very surprised...and happy that there is no scoring or wear on the crank whatsoever. I polished it up slightly and it miced at 1.5"...standard size. The cylinder was bored .30+ by the po and was in excellent shape, still showed very nice cross hatching from being honed.

I ordered a new Kohler std rod and gaskets so hopefully it will be going back together soon, but my question is....why would the nuts back off of the studs on the rod? Improper torque by the person rebuilding it previously? Ive never seen that happen before, but I don't really want it to happen again.

Thanks,

Jeff (teet)

[R Bedell]

Jeff:

I have come to learn (the hard way) that anytime I do a rebuild, I always put a new Connecting Rod on, even if the old one looks good.

Now, maybe the PO simply forgot to tighten up the bolts, torqued them to the wrong value, or ETC. For the cost of a new Rod, it is not worth tearing it back down again if your are luck that an implosion didn't occur.

[Amigatec]

Rod bolts due stretch over time and this may have been the case here.

I have only seen one other motor even do this and that was a cheaply rebuilt 366 Chevy.

[TEET]

Originally Posted by R Bedell

Jeff:

I have come to learn (the hard way) that anytime I do a rebuild, I always put a new Connecting Rod on, even if the old one looks good.

Now, maybe the PO simply forgot to tighten up the bolts, torqued them to the wrong value, or ETC. For the cost of a new Rod, it is not worth tearing it back down again if your are luck that an implosion didn't occur.

I think your right Roland. My guess is that the PO used the old rod on the rebuild. I didn't see any type of lock washers either, and I'm not sure if there should have been. Most of the other engines that I have rebuilt usually have bolts connecting the 2 halves of the rod, and this one has nuts and studs...if that makes a difference?

I will double and triple check the torques on the new rod once I install it...

I wish there was a way to see if they stretched Pat....They look like hardened studs, but anything is possible, especially when it was rebuilt by someone else.

Thanks,

Jeff (teet)

[Matt G.]

When a rod is re-used, I think it must be torqued more when reinstalling. And of course, some people don't have a torque wrench, and as a consequence, shouldn't be messing with the inside of an engine, but still...good thing you caught it.