Unsure what to do with 0.0020" Main Clearance

[jdperform]

Way back sometimes we would have to sand the backs of bearings on Indy car engines NO bull. All 3 cars finished Indy 500, best was 3rd. Hokie? Yes it is. Did it work? Yes it did. One could look at it as, just get to where you want it. It matters not how.

[vortecpro]

This easily fixed.........you sand the back of the bearing counting sand strokes. You want to sand the bottom 1/3 of the radius, so as too increase the vertical clearance. This is done all the time. Of course you want to CK clearance with a Sunnen bore gauge. You can easily get 4 tenths......easy.

That is easy.

I caught one of my engine builders doing that one time. I fired him on the spot.

I fired Probe the first time I inspected one of your pistons. The reality is its done by serious engine builders ALL the time to fine tune bearing clearance, you just don't know. We can grind .0005 off your crank no problem in my shop, that is if we ground it the first time, of course that doesn't help you now.

[vortecpro]

Way back sometimes we would have to sand the backs of bearings on Indy car engines NO bull. All 3 cars finished Indy 500, best was 3rd. Hokie? Yes it is. Did it work? Yes it did. One could look at it as, just get to where you want it. It matters not how.

Of course you did as did many real engine builders in this business, internet experts...........

[houser45]

Vortecpro . is right on the money on this one, you can’t polish off the crank what you want accurately the journals Will end up cupped, I would take and brush the main bores in the line hone way before I would try grinding anything off the Crank. The first thing I try is a different brand of bearings, If I couldn’t get what I wanted then I would sand on the backs of the bearings with 180 wet sandpaper by hand and granite plate with the 180 the parting line in the bearing to get the .0005 clearance you need. Hand fitting bearings the way Vortech Pro. recommended is done all the time

[houser45]

Way back sometimes we would have to sand the backs of bearings on Indy car engines NO bull. All 3 cars finished Indy 500, best was 3rd. Hokie? Yes it is. Did it work? Yes it did. One could look at it as, just get to where you want it. It matters not how.

I was taught this by one of the best sprint car engine builders in the country when I worked for him.

[Mark O'Neal]

This easily fixed.........you sand the back of the bearing counting sand strokes. You want to sand the bottom 1/3 of the radius, so as too increase the vertical clearance. This is done all the time. Of course you want to CK clearance with a Sunnen bore gauge. You can easily get 4 tenths......easy.

That is easy.

I caught one of my engine builders doing that one time. I fired him on the spot.

I fired Probe the first time I inspected one of your pistons. The reality is its done by serious engine builders ALL the time to fine tune bearing clearance, you just don't know. We can grind .0005 off your crank no problem in my shop, that is if we ground it the first time, of course that doesn't help you now.

You da man!

[Mark O'Neal]

Vortecpro . is right on the money on this one, you can’t polish off the crank what you want accurately the journals Will end up cupped, I would take and brush the main bores in the line hone way before I would try grinding anything off the Crank. The first thing I try is a different brand of bearings, If I couldn’t get what I wanted then I would sand on the backs of the bearings with 180 wet sandpaper by hand and granite plate with the 180 the parting line in the bearing to get the .0005 clearance you need. Hand fitting bearings the way Vortech Pro. recommended is done all the time

I was being facetious.

[gmrocket]

First, you should make sure your blocks main saddle diameter is at the max recommended diameter which is 2.442”

Have you done that? If not, open it up to the max.

If it’s already there, I wouldn’t hesitate to touch the main bore housing with the hone to give you the .0005” to .001” extra you want.

Then cut a strip of shim stock, the same thickness you went over max dimension, to use between the one side of where the bearing halves meet,,it will be pinched and stay.

[rebelrouser]

So I want to learn from the experts, so tolerate my question. The old .003 clearance I thought was for old muscle car type engines, because the crank and block wiggled a little because we were taking a block and crank designed for 300HP and making 600HP with it, so it was operating over its design limit. On aftermarket blocks that are stiff, and a good straight performance crank, I would say .002 is about right, the block and crank should not wiggle much. When I assemble a short block I rotate it and check the amount of torque in inch lbs. it takes to rotate, do any of you guys mess with that? If I missed something on the bearings or measurements, it is kind of a failsafe, if it gets a little hard to turn, I have found where I need to look for a problem.

[n2omike]

I have ran .0018"-.0020" on SBF circle track engines with 302 main size and over 800HP with zero issues.

I did some more measuring, so a little more data.

I have a Mitutoyo dial bore gauge, so I decided to do some more measurements, and see what I came up with. I measured the clearances three different ways. All mics are nice older Mitutoyo Vernier style.

1. Plasti-gage: 0.0020"

2. Comparator. Measured the crank with an outside mic, locked it in place, then zero'd the dial bore gauge with it. I then placed in in the torqued bearing and came up with +0.0025". I have avoided using the dial bore gauge on bearings before, as it scratches them. These are the MS-590 HX without the flash layer, so they seem a bit harder on the surface, and don't scratch as easily... and it seemed to work just fine. Happy, but decided to try something else to make sure...

3. Used the dial bore to find the main saddle, then subtracted.

Main Saddle: 2.4415"
Top Bearing Half: 0.0953"
Bottom Bearing Half: 0.0953 (have a rounded anvil Mitutoyo 0-1 mic)
Main journals come out between 2.2488 - 2.2490

Subtracting... 2.4415 - 0.0953 - 0.0953 - 2.2489 = 0.0020"

So, plasti-gage gives 0.0020"
Comparator gives 0.0025"
Subtracting shows 0.0020"

Go Figure... lol

I'm not a machinist by trade, but am practiced well enough with the mics to get consistent readings.
Thoughts and ideas?

Thanks!

[My427stang]

Mike, just my opinion

1 - Plastigauge...like a moped, fun to ride, but that's about it, heck it's not even as good as a moped LOL. I don't even buy the crap anymore, and I used to use it all the time in the 80s and 90s. Here's a punch line, the least accurate it ever was, was on small block Fords too, no idea why

2 - Using the dial bore gauge against the mic..that's how I do all, and I trust it. However, you can tweak those numbers if you wrench on the mic, if it's a good mic, checks to the standards and you can repeat your numbers, I can that the best way. I will say though, each brand is different, FM seems to be the loosest, Clevite the tightest, but literally splitting hairs

3 - Fun with math...I also like it, but bearings aren't a constant shape, I much prefer using method #2 to also look for taper.

If you are worried about less than .001 per inch, can't you just hit it with a polish? or is that crank something that cannot be polished? You can't reshape it, but you can take a little edge off

[Mark O'Neal]

Mike, just my opinion

1 - Plastigauge...like a moped, fun to ride, but that's about it, heck it's not even as good as a moped LOL. I don't even buy the crap anymore, and I used to use it all the time in the 80s and 90s. Here's a punch line, the least accurate it ever was, was on small block Fords too, no idea why

2 - Using the dial bore gauge against the mic..that's how I do all, and I trust it. However, you can tweak those numbers if you wrench on the mic, if it's a good mic, checks to the standards and you can repeat your numbers, I can that the best way. I will say though, each brand is different, FM seems to be the loosest, Clevite the tightest, but literally splitting hairs

3 - Fun with math...I also like it, but bearings aren't a constant shape, I much prefer using method #2 to also look for taper.

If you are worried about less than .001 per inch, can't you just hit it with a polish? or is that crank something that cannot be polished? You can't reshape it, but you can take a little edge off

Which is why I refuse to sand them.

[n2omike]

3 - Fun with math...I also like it, but bearings aren't a constant shape, I much prefer using method #2 to also look for taper.

Thanks for all that.
As for "not a constant shape", with the round anvil mic, you can measure them at the center of the bearing... which is what I did. Still not sure why I'm coming up half a thou different between method #2 and #3.

Has anyone done both methods, and compared?

With people saying 0.0020" is good as long as the machine work is spot on... and my measurements giving me somewhere between 0.0020" and 0.0025"... I'll likely put it together.

What weight oils are you guys using with semi-tight clearances? My go-to has always been Mobil 1 15w50... which being synthetic, doesn't seem all that thick... at least in the summer.

Thanks!

[gmrocket]

Your main saddle is .0005” under max.

You can fix the problem you think you have by getting it to the 2.442”+

I like mine on the loose side as it never hurts.

[MELWAY]

I would just go back to the H std bearing instead of the HX. And find a good crank grinder to take off .0015” or what ever to achieve the clearance you want.