The Stovebolt Site Forums The Shop Area Engine Shop Shimming the mains on a 54-55 261 ????

Finally got the block bored (+.80) and decked and back from the machinist.
I got a shim kit to shim the crank, and am a bit puzzled by it. There are four different envelopes and 3 different shaped shims. I have that figured out.
The thing is they are all the same thickness.
So before I start working through the plasti gauge and do anything dumb, I'd really like to hear what experience has to offer.
If I assemble this with the shims provided and measure the plasti gauge do I then make my own shims from shim stock to get the proper .02 tolerance? That makes sense, and I can do that. I just want to make sure that's the way.
Thanks!

Jeremy

How thick are the shims you have?

Kurt

It has been many years since I rebuilt a 1954 235, but I recall that there would be shims for the crankshaft main bearings and for the rod bearings (the Shop manual confirms this).

Can you post link(s) to photo(s) of the different shims?

The whole purpose of shimming the main bearings is to establish the right oil clearance. If the clearance is right without shims, no problem. My Federal-Mogul master bearing catalog lists the allowable main bearing clearance on all four bearings in the 1953-55 engine series as .0005" to .0031". I like to set the clearance at about .0015" unless very lightweight oil like 10W-30 will be used exclusively. Then you might go a little tighter. These engines were designed for straight 30 weight oil, so the larger clearances like .002" or more were acceptable with the heavier oils.

If you're going to shim the main bearings, be sure the shims slip all the way over the ends of the bearing shells. If only the bearing caps are shimmed, the bearings will try to rock back and forth in the block and they will eventually spin, ruining the bearing and the crankshaft. The shim stock should be sandwiched tightly between the top and bottom bearing shells so nothing is able to move. Instead of using Plastigage, I like to cut a small sliver of shim stock, maybe 1/4" wide by 1" long, and place it between the lower bearing shell and the crankshaft. If .002" is the desired clearance, use that size shim stock. Torque the cap bolts and try to turn the crankshaft by hand. Don't try full turns, just rock the crank back and forth a little. If it's tight, add a thin piece of shim between the cap and the block and try again. When the crank can be turned with just a slight amount of drag, the shim pack is right on that bearing. Remove the checking shim, torque the cap bolts, and proceed to adjust the next bearing. Go to the next one and do the same thing. Continue until all the bearings are shimmed to the correct oil clearance.

The shim thicknesses listed in the F-M catalog for Chevrolet 6-cylinders appear to be far too thick to be of much use. The shim set #FSM-124S lists shims of .0102" to .0085", and the FSM 105S shim pack has .006" to .0085" shims in it. I'm accustomed to making my own shims from brass stock in the .0015" to .003" thickness range.
Jerry

Jerry -
I'm going to head over to the shop and take photos...
The shims I have are clearly designed to go under the caps with the bolts going through them. They will reach teh edge of the bearings but wouldn't keep the shells from rocking back and forth. I thought the pins in the bearing caps would keep that from happening.
Pins might be too fine a point.. they are more like small locating dowels...

Jeremy

If you read the 54 service manual (pre plasigage I assume) they tell you to read the current draw of the starter motor turning over the engine and shim the caps for clearance until the current draw is within range. Sounds pretty primitive to me but it was a whole different world in 54.

The 54 GMC service manual recommends Plastigage for bearing clearance which means it was around then. I remember seeing it in the early 50's. However, GMC were machined to fit while Chev was shim to fit.

I'm just a little spooky about allowing any clearance between the bearing shells. Yes, the dowels might keep the bearings from spinning, but with clearance at the parting line, nothing is going to hold the bearing shell firmly against the bore in the block and cap. That will interfere with heat transfer and possibly oil clearance. Then again, I might just be a picky old man! After 50+ years of tinkering with the innards of engines, I don't leave anything to chance.
Jerry

According To Egge,engines after around '47 or so (the 216 anyway)don't use shims. They did use shims from the factory, but there again I have a suspicion that was momentum from the past as well. But whatever the case if you order a bearing kit for an engine after '47 ('49?) or so, they don't provide shims. (at least for a 216) I didn't use shims in my engine,('52 216) but then again since I was getting the crank ground anyway, I just had them grind it to fit the bearings. Also there is nothing wrong with being a picky old man Jerry, my specialty is heavy industrial machinery, and I am one picky ***** but I have very few failures. Which I feel is a good thing when you are working on a multi million dollar piece of equipment.

I think the design of the shim is such that it will extend over/between the shells. Therefore no gap at the parting line.

Kurt

photos are here

http://www.flickr.com/photos/jeremy_vaughan/sets/72157627094707079/

Looks like I got the wrong bearings... so now I have to wait for some new ones to show up.
The block numbers say its an early block... but the block and caps are of the later design, ie one dowel instead of the earlier 2 dowels... yes the shims can be placed so that they will sit between the shells that is the way I think they should go too.
Jerry- 50 years of doing this is helpful info and I can always use information!
Man can I just get this engine done???!!!!

Jeremy

You clearly have a block designed for a 1954 truck, but cast in 1957, by looking at date code.
You will need late 1955-62 bearings for your engine.

Thanks! Is that weird? Why is it designed for a 54 truck?

The block is machined for the high-mount water pump. A 216/early 235 water pump would be needed to complete the buildup. Later engines had one big hole for the pump impeller to fit into, just above the timing gear cover.
Jerry

Shims were used on all 216s, and 1954 and later engines, if needed (check the Shop Manuals). I have rebuilt 1954&1960 235&261 engines that needed no shims (using reground crankshafts for over-sized bearings).

That 1957 date code on a 1954/55-1st-style truck block would have (obviously?) been on a replacement block for the higher-water-pump, higher-pressure engine, as suggested above (a 1954/55-1st engine). This is the first time that I recall someone posting this information but it is certainly a logical possibility.