VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Rod bearing shims

I pulled the caps on my connecting rods today. One cap had no shims, 4 caps had one shim on only one side and one cap had one shim on each side.

Now the good news, the bearings and the crank looked to be in great shape. I have one rod that taps for the first 10 seconds after start up.

I guess with no or so few shims I'm at the end of the line so to speak.

So if there are no shims and the bearing is still a little loose I guess I'm ready for a rebabit ??

Thanks, Larry.

It was common to file the caps when the rods got to this point. All may not agree but they did this in the dealerships years ago and had good results. The caps file easier than you think and if too much material is emoved shims can be added.
Rods will not make noise at the start-up usually but the noise will come in after the oil gets hot and thins out. A main bearing will thump for a few seconds until the oil gets to it and there again MAY be heard when hot. Piston slap is worse for the first 5 minutes or so. A wrist pin can be heard at start with the engine at a slow idle. Racing the engine will get oil up to the pins and they will be qiet at idle with the noise slowly coming back.

I actually thought about filling the caps but was afraid to mention it.

I did not think a main would knock at idle but I do see it only has 3 mains. I don't know how hard it is going to be to tell if a main is loose.
Back in the day my dad used something like Plastigage. Do they still sell that stuff???

It does not knock under load when hot.

I'll drop the mains and take a look.

Thanks, Larry.

Technically you are correct, with no shims the rods are as small as they can be without a re-pour job. However; there are A LOT OF OLD CHEVYs running around that have had the rod caps filed. You can get some more mileage out of the rods but at a price. I did it when I was working my way through college and just didn't have the money to buy new rods. The trick is to take exactly the same amount off both surfaces and evenly across. Now I will tell you that it impossible unless you have very sophisticated machining equipment. The way I did it was to get a sheet of medium grit emery paper. Place it on a known FLAT smooth surface. A saw table works, I also used a plate glass mirror laid on the bench with the emery paper lying on top. I put a bit of oil on the clamping surfaces and attempted to apply even pressure while moving the rod cap in a circular motion. Don't try to take it all off at one time. I looked at the surfaces and noted machining marks. I then ground the cap until the machine marks kind of faded to near nothing, then tried it on the rod. BE SURE TO CLEAN IT VERY CAREFULLY. The grit from the paper and the grinding dust will ruin the Babbitt in seconds if you don't have it perfectly clean. You can use plasti-gage, but that isn't very accurate as your crankshaft is likely somewhat flat. Best bet is to use the hand crank and after removing all the spark plugs, turn it over by hand noting any drag or binding. The most likely place to feel binding is when the piston is exactly half way down the bore, or at 90 degrees turn of the crank. If it is still loose, grind a bit more. If it is too tight, simply slip in a 0.001 shim on one side and check it again. If it turns free you are all set, if not, add another shim on the other side and test again, repeating until you have a good fit.

Now, loosen that rod cap before checking the next one so that you don't feel the first rod as you are working on the next one. Finally after each rod has been fit, I tighten the front rod and test turn the crank. Then rod 2 and test, repeating until all six are torqued to 35 Foot Pounds. That way you can feel the accumulated drag and if one is still a bit tight, you will feel the one that caused it and address it.

Don't forget to install the dippers and be absolutely sure they are facing the right direction. The open side of the dipper should be facing the camshaft side of the engine.

If you cannot start the engine with the 6 volt starter, you have them too tight.

Probably more than you wanted to know, but that is how I got several thousand more miles out of my '37 Chevy in 1956.

Now for the price; if you want to have your rods re-poured at some later date, you will have to have a machine shop surface the rod cap so that it is perfectly flat and square to the rod, or find another set of rods. I believe most places that pour rods can do this and likely check for it before pouring the Babbitt as the practice of filing rod caps is not unknown!

Yeah i used platigage to double check mine when i did it

can get it online or at most ANY parts store

Checking rear main bearing

The center main will definitely knock at idle and will quiet down in a few seconds when the cold oil hits the bearing. The center main has a feed directly from the oil pump, so it will quiet down fairly quickly.

Ron

The BIG PROBLEM with plasti-gage on main bearings while the engine is in the car is that the weight of the crankshaft, and related equipment is always pressing down, so the plastic will be reading the weight of the crankshaft, and not the clearance. One way to correct for that is to place a jack under the crankshaft and raise it enough so that the crank is actually pressing up against the top of the bearings. All in all, I have better luck with feeling how it feels on the hand crank.

Ron

Thanks to everyone for all the great tips and the link.

A lot of good information there.

I'm now "armed and dangerous"

Thanks, Larry.

Plastigage is OK for the mains. Just support the weight of the crankshaft so the weight is not pressing down on the Plastigage.The maIns can be set looser than the rods.tHEY CAN BE .002 TO .003".
I would not recommend Plastigage for the rods. Use the method described in the shop manual for your year engine. That is the tapping the rod back and forth on the journal with a small hammmer. I have seen so many that used Plastigege for the rods leaving too much clearence and having rod noise. It is difficult to get right down to the required .001' CLEARENCE ON THE RODS WITH pLASTIGAGE.

I have used the method posted by Ron Eyres on several engines. That is after trying plasigage several times without long term success. Interpreting the crush is very difficult given the inconsistency of the crankshaft surface, bearing surface and the fact that holding the parts completely still (particularly rods) is difficult. I even tried several small pieces located around the bearing surface. Got mixed results as the crush was not consistent around the bearing. Then had to guess which one(s) were accurate. The "resistance" method better compensates for all those problems. I have also found that a "tad" too tight is far better than too loose.

I have had mains knock at .003".

When I did mine, I used the Feeling method with the Hand Crank. But I did use Plastigage to get it right about .0015" - .002".

Double Checked it all when I went back in the bottom half last month. Still Looking GREAT !!

I don't have a problem using plastigage to get bearing gaps in the ballpark. I do it frequently. My caution is double edged. Make 100% sure to remove all remnants of the plastigage. Don't rely on the reading to set the final adjustment.

I THOROUGHLY CLEAN BOTH SURFACES !!!