The Stovebolt Site Forums The Shop Area Engine Shop Let's talk main bearings for a 261

Pulled the crank, believe it was first time the engine was
apart. Main and rod bearings all looked good, the crank
looks good, no scoring all journals are all within spec.
after polishing off the stains. There are no shims in this
engine. So the question is....What's with the shim packs
addressed in the shop manual and which are listed in the
parts books for the main bearings?
If the crank is on size and straight and within spec then
why would you need shims. The standard brg. shells should
fit without shims, no??

And while were at it here, any suggestions for sourcing the
standard mains, rods and std. ring sets? My FLAPS doesn't
seem to remember a '59, 261 ser. 60 truck engine nor does
Rock Auto, The Sealed Power catalog or any other site I've
searched this morning.

dg

Not used in your engine.

The shims were used in the earlier engines with dowel pins on the back sides of the main bearings. If yours has the anti-rotate tabs on the bearing shells at the parting line between the block and the main caps- - -no shims.

Here are the part numbers for the later model (1956-62) 261 engine main bearings:

TRW: MS1721P

Federal-Mogul: 960M

Mt Federal-Mogul shop master bearing catalog lists bearing sizes as STD, .001, .010, .020, .030, .040, .050, and .060" undersizes. Some of those are probably obsolete now, as the catalog I'm quoting was printed in 1991.

This catalog also lists main bearing bore sizes, if you're interested. Bore size has a direct relationship to whether or not the bearing is round and has the right oil clearance when the bearing is torqued into place. We never relied on Plastigauge on the race engines- - - -all the rod and main bearings were torqued up and the ID of the bearing was measured with a dial bore gauge, then compared to the crankshaft OD. We would try for an oil clearance tolerance of .0002" or less, even if several individual bearing shells had to be measured. It was not uncommon to go through 5 or 6 sets of bearings to achieve that tolerance, due to manufacturing variations.
Jerry

I checked EGGE and Kanter for part numbers and prices.

Kanter main bearings
Kanter rod bearings
Kanter rings

EGGE - 1959-1962 261 engine parts

If the crank and bearings look good, why not just mike the bearings. If they are within tolerance, run them. Thats what I do with my old GMC engines.

Well Jerry there taint now way I'm looking to get .0002" oil
clearance on a 3,000 rpm stovebolt bearing. I'm aware of the
earlier shims and thought the later ones were beyond that but
the shop manual and all the Sealed Power listings I've found
mention shim packs. Brian linked me to Summit's catalog which
lists the 960M brgs and 1950CP rod brgs.
Since the 235 & 261 crank and brgs are the same I would think
they would be available from many sources. Think I'll try
another NAPA store next week and see if I can avoid the $15
shipping add on.
Rings look like they might be a problem and I may end up
contacting EGGE next week also. I need to order a 240 grit
silicon carbide Flex Hone from Brush next week also, my little
three legged KD toy stones ain't up to the task of cross
hatching the cylinders.

For the cost of new bearings Ken, I might as well start out
with a new set.

Just did a quick total weight on the rods and found more
fluctuation from the factory there than I did with the
pistons. Again, don't know what the factory tolerance
was but I'm sure it wasn't supposed to be 3.2 grams.

dg

"Reading is fundamental"- - - -like we used to say in the public education system. We were shooting for a +/- .0002" VARIATION in oil clearance on the race engines. The actual clearance we were after was .0035" so the crankshaft would spin freely at 8K+ RPM, and we used 40 weight racing oil and a high volume Melling oil pump to keep the bearings well-supplied with oil at those speeds.

For rings, just get a set for a 265 V8 (same bore) and use 6 of the 8 ring sets. Those rings don't know what engine they're in, and they can't count how many cylinders it has.
Jerry

TOUCHÉ!!!! "tolerance of .0002" or less", must have just
skimmed that line, dyslexia you know.

Already have a set of Sealed Power 5412X rings coming for $45
. Have to keep that in mind next time Jerry. So the ring width
and radial wall thickness of the rings are the same in the V8
and 261?

That's the last of it for the short block cept for a gasket
set. Might be able to pickle the short block by turkey day
. Probably gonna be to cold to work on the head by then.
Have to wait till spring to finish it up.

dg

I once used half a set of 85 HP flathead Ford rings in a big-bore Volkswagen engine when J.C. Whitney refused to sell me a set of rings - - - -they wanted to sell another complete kit- - -cylinders, pistons and all. The bore size just happened to match the 3 1/16" + .040" Ford cylinder size. I did have to open up the compression ring grooves a few thousandths on a lathe so the rigs would fit the grooves. That same rebuild involved honing the wrist pin bushings and piston bores .015" to accept a set of Corvair wrist pins due to wear on the original pins.

That engine went another 50,000 full-throttle miles- - - -the only way to drive an air-cooled Volkswagen!
Jerry

Top compression ring and second intermediate ring for a 265 are
5/64" (.0781") as compared to the 261's top two rings, which are
3/32" (.0938").
Might have a bit of a problem spacing those two top rings from the
265 set to the .002" to .0035" ring groove clearance.
I think you'd end up throwing away more than two two sets of rings
from that 8-pack.
Think I'll stick with the Sealed Power 5412X rings made for the 261.

Now, back to the bearings. While I'm waiting for the ship to
come in with the new parts, just out of curiosity I think I
might fire up the wood stove, (it's 27°F out thar this morning)
and check the old mains as Ken mentioned. For sixty bucks
it's not worth using the old ones but it wouldn't hurt to
add those measurements to the autopsy simply to see how
much wear was actually on them. Wish I knew a little more
about the history of this engine. Some parts show very
little wear and others a lot.
Denny G

Yes, those compression rings would need some .015" shims above them to fit the wider groove, which would probably be harder to find than the 3/32" original-equipment rings. The advantage would be less drag, which is why we used 1/16" compression ring thickness on the race engines. Of course, they weren't expected to last more than a thousand miles or so between rebuilds.
Jerry

DG;

Rockauto has 261 parts listed. Just try model years 1960 - 1962 C40. For some reason they don't have parts listed for 1959.

SimS

None of the suppliers seem to list series 60 trucks
and....many don't have listings going back beyond 1960.

I'm all set on new parts, now all I have to do is scare up
some of the old parts that are missing, like oil pan,
inspection pan, rocker arm, pushrod, starter, generator,
carbinator, 261 oil filter, that will do for a start.
Don't cha just love putting puzzles together!!!!

dg

FWIW I just bought a set of Main and rod bearings for my 55 235 truck engine. The best price I found was from Summit Racing. Delivery took only a couple of days.

Denny,

I don't know if you saw these Rings on eBay...

http://www.ebay.com/itm/1954-1955-C...252142689644?&_trksid=p2056016.l4276

Mike B

Yes I did, thanks Mike.
dg