My question is, I have four new aluminum pistons to install but two of the four rod pins, seem a little tight. Once the rod is connected, the rod will move the pin back and forth but the rod will not move on itís own. Is the pin to tight to place in my Model T engine
Photo shows all four pistons and how two of the rods do not fall over to the side, as do the other two.
That is a problem with modern pistons - it's very common they need to be honed in the piston pin bore to get them loose enough to use. If put in an engine stiff like the two of yours is a certain cause for trouble later on - they won't loosen up by themselves unfortunately, there'll rather be piston galling to the cylinder walls..
Timesaver can loosen up the bore with lots of elbow grease, an easier way is to use a Sunnen hone machine.
I had the same problem on the motor I built last winter. Like Roger said, I used Timesaver. I made a mandrel to hold the pin and turned it slowly with a drill. Worked good and got a nice fit. But if you have access to a Sunnen hone, that's best..
A proper piston pin hone is far and away the right and best way to fix this. However, many of us in "make do" land don't have access to such fine pieces of machinery. If, since, and because, you only need about .001 more clearance, and SUPPOSEDLY the piston had been machined more or less properly (Check this! How shortly.) and only needs that final fitting adjustment, it can be done using a much more common (and much less costly) brake cylinder hone. It MUST be done carefully.
First, make certain the pin holes are in proper alignment. The piston pin can tell you this. Push in to one side of the piston. Is the pin too tight in only one hole? Check both sides of the piston individually. IF (the big IF again!) the pins are too tight in each hole individually, and roughly about the same too tight in both holes together (pin now pushed through both), then the holes are in good alignment. IF (big IF again) the pin is fairly loose in each hole individually, however becomes too tight when pushed into both holes together, then the holes are NOT properly aligned, and better steps need to be taken.
IF the holes are aligned well enough. A good brake cylinder hone can be used to take that .001 inch out. A drill press (on its slowest speed) is best to turn the hone, although a slow hand held drill can work. Handle with care. Hold the piston and hone as straight as humanly possible when running the hone. Any twist, turn, lean, or other deviation from straight will result in a pin bore that has high and low areas. Lubricate with your preferred light oil (I like 50/50 kerosene and 30 wt). Work for several seconds only, and recheck fit. Repeat as necessary. Only after you get a "feel" for how quickly it cuts, go longer periods of time. DO NOT run hone too long at any one time! You cannot easily put back material once the hone has removed it. If all you need is .001 to .002 refitting, the hone will follow the existing hole (as long as you run it very straight). If you need any more than that? Better get it done RIGHT!
Generally speaking, if the pin will push in in the first place. The difference between too tight and too loose isn't much more than .001 to begin with.
While running, move the hone back and forth in the hole so that the same spots on the stones do not run always on the same spots in the pin holes. This helps to hone a straighter hole in the piston, and evens the wear on the stones so that it continues to do a better job later. When making this motion, be careful to maintain straight and centered with the hone. The old brake cylinder hone I have has a long enough shaft that I assemble it through one side of the piston to hone the hole on the other side. That helps to see that it is centered and straight.
Another point about hones in general. Fresh sharp new stones can leave a rough cut, not smooth enough. If you go out and buy a new brake cylinder hone? It may be a good idea to run it in on something. A piece of pipe might work provided it does not have a welded seam inside, which most pipes do. The seam can chip and damage the hone stones. And of course, well used stones may not be worn straight enough. Use good judgement.
Definitely don't risk putting it together with tight pins. I know from personal experience what can happen. Mine seized up hard, at idle from two of the pins welding themselves right to the pistons.
Drill an oil hole mid way on each piston boss as well.
Here is an excellent video from Mike Bender.
Explains a lot and very well done.
Since the machine shop needs the piston to accurately bore the block I just have them fit the pins with a Sunnen hone, it is the only real accurate way to do it since the alignment of the holes is critical.
My 1912 engine just returned from a rebuild. #2 rod froze at the pin after a couple months of successful driving, piston totally scored, installed by a previous owner. Couldn't figure out why the pin froze, now know!
Pins should have .0005/.0007" clearance. Much more than that is too much. If you hold the rod and piston with the rod horizonal and the pin parallel to the ground, the rod should fall to the bottom by its own weight.
FWIW, my 1954 Sunnen pin fit booklet calls out a .0003/.0005 clearence for a pin clamped on the rod and floating in an unbushed aluminum piston.
For the same configuration with a cast iron piston, the Sunnen recommended clearance is .0006/.0008.
I agree with all of the above, basically...
However, aluminum piston to pins are normally tighter than cast pistons.
Aluminum does expand quicker than cast, and as long as the pins aren't super tight, they should loosen up when hot. Too loose and they rattle.
Mine were snug when my engine was apart for rings and such.
They probably have 50K on them over 35-40 years. I ran them...
Dan's method is spot on for judging adequate clearance! Don't try your luck. Most all new ones now require some honing.
I should have mentioned that when the pin is clamped in the rod, the pin can distort slightly because of the often times poor finish in the rod eye. It does not take much to distort a pin a few tenths.
Both my engines suffered wrist pin seizure after several thousand miles, despite being free moving on assembly. One engine seized completely but turned freely when cold next morning. The other kept running but with clatter from the piston. In both cases it was nos 1 & 2. Presumably they get less splash lubrication. Only damage was slight piston galling which was easily dressed with a file.
I am reassembling the first engine. I have drilled oil holes, used a brake hone and final lapped with time-saver, all as mentioned above. Following Dan's comment I will also clean up the rod eyes. Fingers crossed!
PS when I said free moving on assembly, I meant they passed the 'floppy rod' test on the bench.