MTFCA Forum

I have noticed my engine has developed a knock at idle. I shorted out each plug one at a time to see if noise would subside but stayed the same. I pulled the crankcase cover and checked the connecting rod caps. Nothing looked out of place but all rods moved side to side easily. I could hit them against the crank journal with no effort. The engine has less than a thousand miles on it. Runs great except for this issue. I did assemble this engine and used plastic gage at the time for clearance. Is this movement acceptable? I am thinking this is the source of the noise. Tried posting video of rods but could not load it. Had to settle for a screen shot of it.

What plastigauge did you use? green @ .0015 reading? Sounds a bit loose on the side play. If @ .0015 Possibly a slightly bent rod is the cause. Rotate & see if the rod slides back to front while turning. If you have electric start, turn over listening.

Thanks SpeedyInc, I don’t recall the size plastic gage I used but had followed advice of rebuilder at the time. I tried moving all the rods up and down and found no discernible movement. But they do all clatter when moved side to side. Today I do not have anyone around to crank engine while I observe the rods but I will do that. Perhaps it is a bent rod that may oscillate sideways. Rods and caps were purchased from a Reputable Supplier so I just installed as is. They have X oil grooves and dippers. I am trying to avoid pulling caps at this point and get thoughts & advice from forum members. John

John

when checking for knocks and there is no discernable difference in knocking when each plug is shorted, always short #2 and #3 simultaneously as the last check.

If the knock ceases, it is a center main bearing. If that is the case, with such low mileage, I'd suspect a misaligned 4th main at the back of the transmission has caused the crank to be under stress and has worn the babbit some. Let's hope that's not the case, as simply tightening the cap is definitely not the correct solution.

Scott, I will have to try shorting 2 & 3 when I button her back up.
For what it’s worth the oil is very clean no sign of metallic fragments or flecks. Bad main bearing would definitely be a bummer! Thanks

Update, I pulled the rod caps and plastic gaged and got about .001”. Re Torqued caps and closed it up. Ran the heck out of her and then let it run at idle for a few minutes. No knocks detected at all just purred at idle. Now if I can get my steering squared away.

When you say side play, do you mean front to back or right to left? The right to left should be the same as up and down, however front to back should not cause a knock unless the rod is bent or the piston cocked.
From your story, it appears to me, that one or more of the bolts might not have been tightened all the way and now is.
Norm

Norman, The looseness seemed to be excessive to me front to back, you could really clack them back in forth by hand. When I torqued down with the plastic gage all seemed to spec. I think you were right in that the rod cap nuts weren’t tight enough. I also had put on those oil dippers. They are soft metal stamping and they may have relaxed a bit over time. They looked deformed from the lock nut. Assembly error … me