Main bearing crush

[Daran Summerton]

Guys I am once again working on my 455 Olds stocker. Question is about the main bearings from different manufactures. On a 3" main, has anyone ever taken a measurement of the bearing above the bore once the bearing is snapped in. Is there a min. number (Thousandths) and still maintain sufficient crush. I am beginning to think excessive crush maybe pinching along with the CN crank flex from the heavy rotating assembly. I have wiped #4 main 5 times on 5 different motors. Can I adjust the measurement using 1000 grit on a piece of glass? Thanks

[Alan Roehrich]

Darren, that's a common Olds 455 problem. The block is weak there, and that main saddle moves. The way to solve it is to have the align bore finished at the minimum spec, put the bearings in (the ones you want to use) measure the ID of the bearing with the cap torqued. Then subtract 0.0035", and that is the diameter you want the crank journal. I know some guys are running 0.004" on the mains.

I've been talking to King about making some better rod main bearings, and I'm told the project is being considered.

[Daran Summerton]

Thanks Alan, have you ever taken a measurement? I know each manufacture will have different dimensions. I have heard good things about king. I hope to address the block movement with fill, studs, steel caps and halo but the crank will flex so will need additional clearance to compensate. Appears to me the oil holes are catching the parting line if that makes any sense?

[Alan Roehrich]

Darren, no I have not taken a measurement. If the oil holes are properly chamfered, they really cannot catch on the parting line, as the bearing would have to move a ton in order to grab. Several of us have looked at this for years, and the best we can tell, the main saddle moves, and when it does, the bearing pinches the crank at the parting line. Usually, when it happens, it gets bad enough, fast enough, that it gives you false ideas about why it happens.

So long as your bearing bore is round, and the correct size, the crush is correct with the bearing at stock length, that is what gives the bearing proper eccentricity, while holding the bearing in place. If you shorten the bearing the way you are thinking, the bearing will lose crush, which will take away eccentricity, which in turn will do the opposite of what you are trying to do, instead of getting more clearance at the parting line, you'll have less. That problem will be compounded by a lack of crush to located the bearing, so it will try to move more.

At this point, I'd suggest you get a set of Federal Mogul 108M race bearings, finish the block (align hone) to minimum size, install the bearings, torque the caps (and any added hardware, girdle, etc) measure the bores, grind the crank to yield a minimum of 0.0035", and a maximum of 0.004" vertical oil clearance. I'd send the bearings, mains and rods (Clevite is fine for the rods), off to HM Elliott, and have them coat the bearings.

Also, I'd suggest you find someone that will let you sort through oil pumps. You need to find one with the least amount of clearance between the sides of the gears and the housing as possible, 0.003" would be ideal, but I'd bet you'll have a hard time getting under 0.005". When you get your pump picked out, then use either a machinist's stone, or a piece of sand paper on a piece of glass, to sand the housing so that with the gasket in place, you have about 0.002" end clearance in the pump. If you use a standard volume pump, with a stamped steel cover, get a second cover from an old pump, and install it as a support for the cover that came with the pump, you'll need to get correct length bolts.

[Daran Summerton]

Thanks Alan I will not reduce the crush. I would like to know which bearings have the most clearance at the parting line. Guess the only way is to mic different brands. Good info on pumps, this is not my current issue because every other bearing looks like right out of the box. Just #4

[Alan Roehrich]

Darren, you'll have to measure the bearings, as they are installed in the block, and you'll need a really good dial bore gauge, such as a Sunnen, Starrett, or Mitutoyo, in order to do so. You can't just use a micrometer to measure the bearings to see how thick they are. The only thing that matters is their shape and size in the as installed position and condition.

The Federal Mogul is a fairly hard alloy bearing, and it is a 1/2 groove bearing set, as opposed to the full grooves in the Clevite bearings. I think the lack of the groove in the lower bearing shell may help to build a better film of oil, and hydrodynamic wedge, which may help keep the crank off of the bearings.

[Dan Lattimore]

Daran----What Alan said.-----After proper prep and clearances your old motor is running 10.90s in a Cutlass GT stocker with over 200 passes.------Danny

[Daran Summerton]

Thanks Guys!

[Bill Edgeworth]

Have any of you Olds guys tried one of the J&S main girdles to see if it will solve the problem? Seems girdle use is gaining popularity on some types of engines.

[Daran Summerton]

I intend to. The weight of that rotating assembly along with a 4.250 stroke is the challenge for me as well as thousands of others. Buicks seem to respond to the support as well.