Does the location of the connecting rod in reference to the piston pin look like a problem?

I know some may consider this to be OCD (obsessive compulsive disorder), but I want to be sure that this isn't uncommon (I hope the picture is clear enough to see that there is an uneven amount of the piston pin showing on either side of the connectiong rod)-

The con rod is not rubbing the piston on the left side, but it is pretty close.....

Bob

It should center itself once installed in the block. If it doesn't,then you've got a problem.

Jack, what could the problem be? None of them are perfectly centered, but this one is way off.

Could the rods (all four) be sprung? What would be the odds?

Bob

What happends when you turn the crank? Does the gap stay the same or does it move? Where does the rod ride on the crank end?

Bob,

If one rod is way off from the others I would suspect a sprung rod. I don't think I have ever had an engine where I thought they were all perfectly centered.

Paul

The gap stays consistent when you turn the crank, and the rod seems to ride dead center on the crank pin.

I have a feeling it's the castings that hold the crank pin inside the pistons (they're probably not exactly the same length). I may try removing the piston and turning it around, just to see if there's any difference. Also, these pistons (IZUMI brand, wherever they might be from, next time I'll insist on Egge ones) have a mysterious blue dot (see above picture) on one of the wrist pin holders - I wonder if this means something. In the above photo, the blue dot is facing forward (#1 piston).

BTW, is there an accepted and standard way the pistons should be installed? I thought it was with the open side slot faces the camshaft, but I honestly don't see the difference.

Bob

Well, I turned the piston around, and the gap is identical to before. Maybe the rod is sprung? Tomorrow I will fit another rod (I have a spare) and see what happens.

I should clarify that the slot I was referring to above was the HORIZONTAL slot facing the camshaft, and the VERTICAL one facing away, but I admit I don't know enough to confirm this.

Bob

Bob,

I would turn the rod around and see if the gap moves to the other side. If it does you have a sprung rod.

Paul

I believe the open slot on the pistonbshould face away from the cam. If I've got my thinking correct, the cam side is the side that takes the thrust from the piston on the power stroke so it should have the solid side of the piston against this surface.

Art

You're correct Art. The "pressure" side fo the piston should be solid, i.e. no slot.

I'd only be concerned if the crank bearing bore and pistion pin are not parrallel. If they are O.K and you have some clearence on the closer side(you say you do) run it,If will be fine.The spacing is rarely even . The rod may have been bent and straightened once..Those commonly will shoe up like yours.

Paul, I turned the piston around, and the gap remained identical as before, in the same location, so it probably isn't a sprung rod.

Next, I replaced the rod with another one, and it lines up in the same place, too. I can only guess that the crank pins do not line up perfectly with the cylinder bores. Could this be a problem, or does this occur sometimes?

Bob

David, the piston pin and crank pin are most definitely parallel - With all bearings snugged up to .0015, I can turn this crank by hand (with some resistance, but not much). It's just that from front to rear, the two don't seem to be exactly in line with each other.

There is a wee gap on the one side, but it makes me nervous. Would it be OK to file off a little bit off the inside of the piston on that side, or am I just being obsessive over nothing?

Bob

I once had a wrist pin that was WAY off center regarding the slot for the wrist pin locking bolt but this had to be a rarity. As long as there is no contact between the con rod and the piston or the wrist pin and the cylinder wall you are probably okay.

Another posibility is that the cylinder was bored off center. Not sure what the exact spacing would be between cylinders but you could try measuring if someone can post the dimensions.

It seems odd for it to be so far off; I would be concerned, too. You might try measuring the distance between rods, in case the crank is funny.

The Model A crank is longer than the T crank, so the #1 and #4 rods are well offset from center of pin.

The Chevy crank is shorter than the T crank, so the #1 and #4 are offset also, but in the other direction. The wear on the pistons and cylinders has to be uneven, but I've never seen that to be identified as the source of a problem.

rdr

Warren,

Best I can tell, the bore spacing on the model T is 4 1/8" between 1&2 and 3&4 and 5 1/4" between 2&3.

My guess on Bob's issue here is that the rod is bent slightly, though the big end and small end bores are probably parallel since it was hopefully machined that way.

If it was mine, I believe I'd pull that rod out and inspect it to see if the small end is not centered over the big end.

Though it is probably of no consequence, if there was more than 0.030" difference on centers, I'd rather find a better rod if I was building my engine.

Seth

Seth,

I get the feeling that the rod is OK. I tried turning both the rod and the piston around tried a different rod, and the result was that they always lined up in exactly the same place. Remember, all four are off center some, but this one is way off center. The only logical conclusion I have is that the cylinder bore is off a little, which I'm afraid, is not probably not easily fixable (if at all).

At this point, I have too much time (and money) in this block to give it up now. There is some clearance there - I think I will grind a hair off the rod, and file a wee bit off the piston end. This will give me a little more breathing room, I hope.

Bob

Bob,

If the rod is straight then I certainly wouldn't worry about it. If the bore is in the wrong place or if the crank journal is in the wrong place, no biggie (IMO) in an engine like the T.

Seth

What's most important is where does the wrist pin come in relation to the bore? Let's say the piston was removed but the rod and wrist pin were still in place. Would the wrist pin be dangerously close to the bore?

It wouldn't hurt to dress a little off the piston to create more clearance if it bothers you. After some use you may get some crankshaft end play and your minimal clearance may get used up fast.

Jerry, the wrist pin has sufficient clearance in relation to the bore, but that is one factor that I forgot to inspect - thanks for the tip.

It's your second point that has me most concerned - as the crank wears, that little gap could easily disappear!

Bob

Well, here's what I've come up with - I don't know if you can tell by my picture, but I added about .125 gap on that tight side (I also knocked a bit off that wrist pin, just to be on the safe side). The shiny spoy on the left side of the con rod is the wrist pin clearance in question.....

I'm not really happy about this, but I don't see what else I could do. I'm hoping will be OK. I've heard T's are very forgiving.....

Bob

Bob,

0.125" is a MILE inside the engine. The clearance you had would have been fine even if the rear main were to wear severely. Since you tell me that you are going to run a magneto, you would never have developed enough axial play in the crank to have caused any problems.

Stop grinding on things and go back to assembling. I'm afflicted with OCD but I ain't worried, so I think I'm qualified to tell you to chill out!

Seth

If all the rods are off in the same way, and if the rods have moved toward the back, you most probably have crankshaft endplay. You can check, by taking a large screwdriver between the timing cover and the front pulley and prying forward, then put it between the front mount and pry backward. On one of mine, I have about 3/16th inch play. I was going to re pour the rods, but have decided to pull the engine and pour all the bearings, and turn the crankshaft, that is rebuild the lower part of the engine. That same condition could even cause a knock if the rods are continualy hitting the piston boss as the engine turns, and if worn enough the wrist pins could even score the cylinder walls.
Norm

Bob,

Have the cylinders been bored? What size are the pistons? T's are very forgiving and I would not worry about running your engine. My own OCD would now be worried about the engine being out of balance due to the metal removal. But I probably would get over it and run it.

Paul