The Stovebolt Site Forums The Shop Area Engine Shop Rod Bearing Shim Question

Hi everyone,

I am looking for opinions on how difficult it is for a novice with basic tools and the sevice manual to remove some shims from a noisy rod bearing. 1951 216 engine. Thinking about making this a winter project but I am really nervous as I have never done anything like this before.

Thanks for your thoughts!

Chris

I think the main thing to remember is cranks do not wear round. When setting the rods make sure you can shake them side to side in all positions of the crank when done.
Also, if the journal is to far out of round you may not improve the knock.

Just a thought ,every one here had to build there first engine,it's not that hard to do,get the shop manual for you're truck and engine and it will go step by step on the rebuilding.Also take you're time ask questions of us at stovebolt and maybe a engine shop in you're area.If you buy you're parts from a engine shop they will be more likly to help with questions.
One thing I do when I'm building one is I bring the crank and block to the engine shop and have them look them over I don't have the tools to measure the clyinders plus they do it for a living then after that I have them clean the block and have them do the machining then I take it all home and put it together.I buy whatever bearings and rings and pistons from them also.


Pete

If adjusting clearance on poured-bearing rods was as difficult as we've been led to believe, none of the stovebolt engines would have survived long enough for any of us to have the opportunity to work on them. Just about anybody with more than three brain cells to rub together can do an acceptable job of adjusting rods- - - -he just has to pay attention to detail and be willing to invest some serious time on a creeper or under a lift.

The usual oil clearance range on babbit-pounder rods is from .001" to .003". The closer you get to minimum, the less often you'll have to go back in and readjust things. Yes, it helps if the crankshaft journal is reasonably round and smooth. Nothing chews up Babbit quicker than a rough, out-of-round connecting rod journal. Lots of rod journals have been smoothed out with a piece of cloth-backed fine-grit sandpaper and some "shoeshine" motion, however. It's possible to get a pretty good idea if the shaft is round enough to proceed by taking some measurements with a dial caliper, and most folks who don't do machine work routinely have better luck getting an accurate reading with one of those tools than with a micrometer. No, it's not as accurate, but it will be close enough to get a ballpark figure whether the shaft is round enough to proceed. A reasonably accurate dial caliper can be has for less than 40 dollars online or from a place like Harbor Freight or Northern Tool. Most of the wear on a rod journal happens from top to bottom as the piston/rod assembly reaches its upper or lower limit of travel and changes direction. I believe the maximum "out of-round" allowable is in the neighborhood of .002", but the closer to perfectly round it is, the better. Ditto on "smooth"- - -a mirror-polish would be nice, but I've run many miles with crankshafts that had some noticeable pits. High spots are another matter altogether, so smooth them out as much as possible.

Once the shaft is determined to be reasonably round and smooth, and the surface of the soft metal in the rod isn't badly deteriorated, remove a shim or two until the crankshaft has a noticeable drag when the rod bolts are tightened and the flywheel is turned by hand. Reinstall shims until the drag is barely noticeable. I like to put a small piece of .0015" brass shim stock between the rod cap and the crankshaft, and remove shims until I get a firm drag, then remove the spacer and reassemble and torque the rod. I've had better results using this method than I do with Plastigauge.

My Motor manual says it's possible to compensate for up to .004" of bearing and/or crankshaft wear by removing shims. Just use a little common sense and don't get the rods too tight. I'd rather run with rods that have .0025" of clearance and rattle a little, than with .001" clearance and too much drag.
Jerry

I have rebuilt quite a few old John Deere two cylinder tractor engines which have shim adjusted babbited mains and rods. These engines turn about 1100 RPM and the babbit is very robust. Oil clearance spec is .003. They are full pressure lubricated engines.

I got some very good advice from the folks at Paul's Rod and Bearing about how to adjust these bearings, and I believe the same principles will apply here. Paul's specialize in rebabbiting all makes of rod and main bearings.

I also got the same advice from an old master machinist who put the crank in my 235 about 30 years ago.

It is important to polish your journals with strips of 220 grit and then 400 grit emory cloth. Go finer if you like. Scratches or pits are not going to hurt you. High spots are your problem.

The babbit can be smoothed up with double ought (00) steel wool.

Install the caps with shims and torque it up. make sure you can turn it over with no drag. Unbolt cap and remove a shim from each side. Torque it up and see if it drags. If it does, add a shim back. If it doesn't, repeat and take out another shim.

Because your crank is probably eggshaped from wear, it may only drag in two places 180 degrees apart, so be sure to rotate the engine all the way around.

The thickness of the shim you put back in after it drags is going to be pretty close to your oil clearance.

I agree that this is actually a more accurate way to adjust the bearings than using plastigage on an engine where you haven't turned the crank.

Kurt

kurt_51carryall you know a elderly fellow that i know said to do exactly the same thing . i find it funny he can make just about anything run. if i try it will most likly grenade. but thanks for posting it very usefull !!!!