I've used every technique from the many sources on the subject to get the proper clearance on my #3 connecting rod cap. The babbit looks new as does the other 3. The rattle is fairly loud at a fast idle or when not under load. The noise goes away when I short out #3 plug. I just completed another attempt to adjust and I can say the clearance is now perfect. Unfortunately, I find the blasted rattle is still there. Is there something else wrong that could give the same symptoms? HELP!!
just an idea.
Is your rod straight??
Did you look if one of the rod bolts do not touch the camshaft??
loose rods or mains usually produce a KNOCK. Interesting your "rattle" stops when you short out#3--maybe a wrist-pin? there are many places for a rattle on a Model T
Does the rod move front to back on the crank journal? I've found some that have a 0.035" clearance. They rattle...and it may also have a bend rod mentioned by Andre.
How much front to back play is there in the rod? If there is very much, take a flashlight and look at the position of both ends of the rod when the piston is at the top, then turn the crankshaft half a turn and check the position of the ends of the rod. The "rattle" you hear could be front to back noise caused by a bent rod which would cause it to move back to front as the engine turns. Although this type knock will probably not cause the engine to blow up, it will not be removed until the rod is straightened.
Another thing you can do is to use some prussian blue on bearing surfaces and tighten things up, rotate the crankshaft and then check the surfaces. The areas of contact will be wiped and those which are loose will still be dark blue. Look especially at the rod portion of the bearing. If you find an uneven pattern, a little "time saver" and a few cranks around might improve the bearing surfaces. You will also need to re-check the clearance after using time saver.
Other possible causes of knock are loose wrist pin or loose piston. However loose piston is usually more noticeable under acceleration.
Check the side clearance of your piston. That can cause a lot of noise. If you have alumn. pistons, that clearance should be less than ten thousands.
I'd check the center main particularly if the rattle gets better if you were to short out #2. Easy to get to, too.
Thank you all for your great suggestions. I can rule out all the above except the possibility of the rod not being true or the wrist pin. If I were to assume either of these two possibilities to be my issue, what harm can come to my engine if I continue to drive it?
am curious how you rule out center main bearing...did you actually check it?
John,did the knock develop, or was it always there?Did it start after a rebuild?
Check the crank journal towards the front and rear of the engine every 30 degrees with a micrometer and record your results.
Scott Conger - gotta' be careful here! My thought was the possibility of the center main too. However, if the center main is the cause of the "rattle", that's a real problem. In my humble opinion, tightening up ONLY the center main can lead to a broken crankshaft. The reason is that there can be wear on the upper or engine block half of the center main, instead of in the center main cap. This is partly because of the weight of the flywheel, clutch, etc. causes a very slight but constant, ever so slight "bending" of the crankshaft, which causes pressure (and subsequent wear) on the engine block half, that is to say, the UPPER half of the center main. Consequently, tightening up the center main by removing a shim or filing the cap, actually forces the crankshaft center journal UPWARDS, which causes the crankshaft to actually bend a bit with every crankshaft revolution, And frankly, the Model T crankshaft will tolerate that for just so long and then, the eventual broken crankshaft.
In other words, the only correct way to tighten up a worn center main is align boring all three mains. Not what anybody wants to hear, I know, but FWIW, there it is,.... in my humble opinion,.....harold
Jim Eviston, Thank you so much for your input.
I've owned it for just a year and don't know the history since I purchased it from the widow of the man who had it restored. I'ts had a regular percussion section from #3 in concert with the 3 others. I've been able to quite all but this one. I might add every thing looking up from the inspection plate looks brand spankin' new.
Don't laugh until you try this. Before you pull the engine it is best to know what the trouble is, very likely a wrist pin on #3 if the #2 spark plug doesn't change the noise. Drop the inspection cover, move crank pin between top center and bottom center, pull the cap, push up the rod and over to the other side, pull the rod down, remove the bolt holding the wrist pin to the rod, know the secret is to pull the rod down to expose the wrist pin and push it out you will need to rotate the piston so the pin will be allowed to slide free of the piston, with this accomplished push the piston up half way up into the cylinder, it will stay do to the pressure of the rings against the cylinder wall. Reinstall the inspection cover and start it up and run it just long enough to see if the noise is gone. If not pull the engine and re babitt if noise is gone pull head and replace piston and inspect rod. The trick when doing this is to not pull the piston down to far and pop out a ring below the cylinder while removing the piston pin, their a bugger to reinstall the oil ring. This is how it was done in the old days and I have changed rods along the road before. Good luck!
If you decide to do what Steve says, be sure you have aluminum pistons with all 3 rings above the wrist pin. The older iron pistons had one ring below the wrist pin and if that comes out,it would be a bugger to get the piston back up in the cylinder.
Thats a nifty trick Steve