Main Bearing Clearance

-
Rodzilla

Rodzilla

Well-Known Member
Joined
Jan 6, 2011
Messages
1,152
Reaction score
67
Location
Red Deer, Alberta
I've only got a .001" clearance on main bearings. Whats my options to get clearance to .002-.003" ? Are there under size bearings of a couple thou? Or can I do anything with current bearing? Or turn down crank a couple thou? Ideas or suggestions? Thanks
 
Undersize main bearings
340/318/273
http://www.ebay.com/itm/CLEVITE-MS5...73-318-340-MOPAR-DODGE-PLYMOUTH-/250900537402

360
http://www.summitracing.com/parts/SLP-4999MA1/

If you mean the journals too big...then u do need oversize bearings
Here are the rods..
http://www.cnc-motorsports.com/engi...triarmor-coated-bearings-0-001-clearance.html

When the term undersized is used..it refers to the journal diameter being undersize, therefore the bearing would need to be bigger to take up the space...if the journal is too big...then u need a larger inner bearing diameter=oversize
 
That set on ebay doesn't say how "undersize" they are. Wouldn't that be kind of important info?

Never mind, I found the same part # on Summit, .001" undersized.
 
????? !!!!!! U-N-D-E-R-S-I-Z-E-D !!!! ????? Isn't that going the wrong direction?

What sort of situation do you have that you have "too little" clearance, is this a crank that's ground incorrectly?
 
NO! Youre thinking of an undersized crank after you grind it, which then requires oversized bearings.
I have the opposite issue, not enough clearance therefore I need bearing that are undersized. Meaning a bigger inside diameter.
 
............How r u checking the clearance?....r u torquing the caps, then measuring inside diameter, then measuring the crank, then calculating the difference......if ur using plastigauge @ .001 clearance , u have that top and bottom, therefore u have .002 thou clearance..........kim.......
 
oldkimmer said:
if ur using plastigauge @ .001 clearance , u have that top and bottom, therefore u have .002 thou clearance..........kim.......
Click to expand...

Ahhhh, doh, I'm dumb. Whats the verdict on .002" clearance, enough? Or get some .001" undersize bearing?
 
oldkimmer said:
............How r u checking the clearance?....r u torquing the caps, then measuring inside diameter, then measuring the crank, then calculating the difference......if ur using plastigauge @ .001 clearance , u have that top and bottom, therefore u have .002 thou clearance..........kim.......
Click to expand...

Nope. If the crank is laying on the bearing on the bottom, and you torque the cap, the space left is the clearance.
So if your plasitgage says ".001" because that's how wide it squished and that's what you matched up, you have .001 total clearance, or .0005 per side, and yes that is too tight. You need an undersize bearing for one that is too tight. And oversize bearing for one that is too lose.

If you are measuring you measure the bearing bore top to bottom with the cap torqued, and then the crank journal, and subtract the crank measurement from the bore measurement.

Please answer the question on how you're measuring and was the crank was just turned or used?
 
67Dart273 said:
Wild you need to step up here

A crank ground UNDERSIZE, as in .010, .020 uses UNDERSIZE bearings.

UNDERSIZE bearings give you LESS clearance, not more.
Click to expand...

I did..lol

look everyone..ha ha...if he has too lil clearance he needs either to have the crank polished/ground or a bearing with a larger Inner Diameter=oversized bearings.

undersize technically means the bearing will have a smaller inner diameter.

K? LOL
 
moper said:
You need an undersize bearing for one that is too tight. And oversize bearing for one that is too lose.
Click to expand...



And though the above sounds funny, technically you mean a bearing that has a larger inner diameter for a journal thats too large/tight, which means oversized bearings...and a bearing with a smaller ID for a journal that is too small/loose-undersize

the terms reference the ID between both bearing halves.
Click to expand...
 
Just set it up at zero and wear the clearance in it. heh
 
moper said:
You need an undersize bearing for one that is too tight. And oversize bearing for one that is too lose.
Click to expand...

Allow me to call a spade a spade

creative-office-bullshit.jpg
 
Umm,you may not need undersize bearings. How are the rest of the clearances? You may be able to swap bearings around ie; If there is one set a bit too loose or just looser,swap them in and put your tight one where the loose one was. This is bearing blueprinting 101...
 
LOL... You could have just said I was wrong...

I'll say I had that part of my post backwards, my bad.
 
i'd get the crank measured/ground/polished then buy the bearings that match...

the shop that does the work will tell you the right size bearings you need.

spending cash on .001 different bearings is probably a bad idea, unless you already had that crank polished
 
Just measure the journal diameter and have .001 polished off the thing.
 
needsaresto said:
Umm,you may not need undersize bearings. How are the rest of the clearances? You may be able to swap bearings around ie; If there is one set a bit too loose or just looser,swap them in and put your tight one where the loose one was. This is bearing blueprinting 101...
Click to expand...

You beat me to it! I was going to suggest the very same thing... You're right,,,, bearings 101!:banghead:
 
Crank is new,,,polished at machine shop. I'm not happy then that clearances suck.
How I measured; put top bearings in, added crank, added plastigauge, added caps with bottom bearings and torqued. 110 ft/lb first time around as per arp, then 90 ft/lbs second time. No diff for either torque.
I'm going to test that theory about how the crank is laying against the top bearing and my clearance gap is only at the bottom (cap side). Essentially if I put plastigauge in between top bearing and crank then it sure disappear because there is no clearance on that side,,,I call BS.
Actually I'm going to put it on both sides and check it.

Undersize bearings ARE when the bearing thickness becomes thinner to accomodate larger journals. Oversize bearing ARE when they become thicker to accomodate ground journals. End of that story.

But thanks to everyone for their input.
 
Rodzilla said:
Undersize bearings ARE when the bearing thickness becomes thinner to accomodate larger journals. Oversize bearing ARE when they become thicker to accomodate ground journals. End of that story.

But thanks to everyone for their input.
Click to expand...

N.E.G.A.T.I.V.E.

UNDERSIZE bearings are for use with UNDERSIZE crank journals.

UNDERSIZE shells DECREASE clearance

http://www.carcraft.com/techarticle...rmance_engines_bearing_clearance/viewall.html

I suggest you download and read these two Clevite Catalogs

From here:

http://www.mahle-aftermarket.com/C125790900540AC0/vwContentByKey/W28P2MXF358STULEN

Performance catalog:

http://www.mahle-aftermarket.com/C125790900540AC0/vwContentByUNID/97C716A640FD0B1AC12579AB0062923E/$FILE/EB-40-07.pdf

Master catalog:

http://www.mahle-aftermarket.com/C125790900540AC0/vwContentByUNID/58A5032D3003098AC12579AB00615520/$FILE/EB-10-07.pdf

A direct quote from the above master catalog, page 29:

14o87sx.jpg
 
I'll give it a read,,makes sense but for the last 20 yrs I've always related grinding a crank to needing oversized bearing (as in thicker not larger I.D.) and never had an issue talking about it that way before. Maybe people assumed they new what I was talking about and translated it into what I needed without correcting me.
I will post up later about what I findout as far as clearances go while running plastigauge under and over the main journals tonight.

Cheers
 
oldkimmer said:
............How r u checking the clearance?....r u torquing the caps, then measuring inside diameter, then measuring the crank, then calculating the difference......if ur using plastigauge @ .001 clearance , u have that top and bottom, therefore u have .002 thou clearance..........kim.......
Click to expand...
How do you get to that??? If it gauges out at .001 you have that all the way around!!!!:D
 
You must log in or register to reply here.
-

Back
Top