Post Number: 7
|Posted on Saturday, October 24, 2015 - 06:12 pm: ||
I'm putting an old T&M small marine engine back together, and have a little slop in the rod I'd like to fix.
The rod is brass, and has a hinged cap with only one bolt to tighten it to the crank.
Babbitt is poured on the upper side, but the hinged cap has evidently been run on bare brass.
Is that configuration common in the old T&M's, or is the Babbitt just an old fix to tighten the rod up from years ago?
Post Number: 825
|Posted on Saturday, October 24, 2015 - 06:47 pm: ||
Since the pressure in a 2 cycle engine is always downward, the babbitt is only needed in the upper part of the con rod.
A little ( and patient) work with a file on the cap will make it OK. I assume that you'll be running at shows only - not in a boat, under load.
Post Number: 8
|Posted on Saturday, October 24, 2015 - 10:53 pm: ||
Miro, thanks for the information.
That had never occurred to me, but you're exactly right.
After reading what you wrote, I went to the garage and used a small hone to round out the cap a little, and am within a few thousandths of the size I need to eliminate any slop in the rod. (I Think) The brass hinged cap was out of round, but now measures a whole lot better.
It was also shimmed pretty far out to compensate, but now I think that I'll only need one thick shim, or 2-3 thin ones.
The way the hinge on the cap works I don't think I could get away with no shimming at all without some major machining-and I'm definitely no machinist. The hinged end sort of slides over the rod end on a taper when it's closed, so to keep the crank hole round I'll still need to shim a little.
I'll find out in the next few days if I have any problems with it -hope not!
The crank mics at 1.110-1.108", and my rod end bolted almost completely closed is at about 1.085-1.089" diameter.
I figure a real machinist might laugh at those numbers and keep on going, but for a shade tree like me it's pretty good and think I'll quit. (unless I hear a pretty good knock on startup).
Thanks again for the help,
Post Number: 552
|Posted on Sunday, October 25, 2015 - 10:41 am: ||
I have never had a T&M apart but I know some of the Caille marine engines had babbit in the upper part of the con rod and the lower was bronze. See photo's below. Designed this away because the babbit would wear easier then the bronze. When you got slop in the con rod you would simply take out a shim and continue on. Once the babbit would wear down even with the bronze then it was time to re-pour the babbit bearing and add the shims back and resize the bearing.