LA 360 - 0.030" Undersize Main Bearing Clearance Questions

[d4rt]

Hey there FABO, I've gotten myself into a bit of a pickle and I'm looking for some feedback.

I have a 360 that I acquired with a crankshaft that requires 0.030 in. undersize bearings. This is going in a 1970 Dart. The car is mostly street but I will also be racing it a bit too. I don't plan on spinning this engine past 5900-6000 RPM, maybe not even that high. I checked the main journals with a 2-3 in. outside micrometer and they measured between 2.7813 - 2.7816 in. Based on guidance from Mahle/Clevite, this is 0.0008 - 0.0011 in. out of spec (2.7795 - 2.7805 in. is the target range) for a 0.030 in. bearing. Using the specific measurement for each journal, I zeroed my dial bore gauge and checked bearing clearances. They're all tighter than I'd like by quite a bit. See below for a list of measurements:

• Main #1: 3.0055" Main Bore Diameter, 2.7814" (Minor) - 2.7816" (Major) Journal Diameter, 0.0016" - 0.0018" Bearing Clearance, 0.0002" Egg, 0.0000" Taper
• Main #2: 3.0054" Main Bore Diameter, 2.7813" (Minor) - 2.7815" (Major) Journal Diameter, 0.0017" - 0.0019" Bearing Clearance, 0.0002" Egg, 0.0000" Taper
• Main #3: 3.0054" Main Bore Diameter, 2.7813" (Minor) - 2.7815" (Major) Journal Diameter, 0.0017" - 0.0019" Bearing Clearance, 0.0002" Egg, 0.0000" Taper
• Main #4: 3.0053" Main Bore Diameter, 2.7813" (Minor) - 2.7813" (Major) Journal Diameter, 0.0019" - 0.0019" Bearing Clearance, 0.0000" Egg, 0.0000" Taper
• Main #5: 3.0050" Main Bore Diameter, 2.7813" (Minor) - 2.7816" (Major) Journal Diameter, 0.0009" - 0.0012" Bearing Clearance, 0.0003" Egg, 0.0000" Taper

As shown above, main bearing clearance ranges from 0.0009 - 0.0019. Main #5 is a bit of an outlier, which is kind of interesting. Someone more knowledgable than I might be able to explain that. The main bearings I have are full groove Clevite 77 P-Series (P/N MS1266P-030). I chatted with my machinist about this and he immediately started talking about getting different bearings. My thoughts there is that I'm unlikely to find a 0.031 bearing. I had a hard enough time finding any 0.030 undersize bearings. My current opinion is that I have the following options available:

1. Grind the crank to get the additional clearance. I've read that it is extremely difficult to grind 0.001 of a crank and keep everything true. My machinist didn't sound very excited about this proposition.
2. Polish the crank to get the additional clearance. This apparently can be done but it's hard to do without adding a bunch of egg and taper.
3. Get a different crank that hasn't been cut/cut less. Seems like a reman "crank kit" is the ticket here.
4. Run it and pray to the Mopar gods that I don't spin a main bearing ~1500 miles from my house

Option #3 is probably the best choice ugh. Not looking forward to another $400 - $500 sunk into this build. Option #1 was my initial thought, however that might cost nearly as much as just getting a crank kit and then I still have a 0.030 in. crankshaft. It sounds like a PITA to setup a crank grinder to take off only a 0.001 - 0.002. Plus, based on what I've read, it'll require tooling and talent that might not be present in a standard machine shop. Not a fan of option #2, although I guess some egg and taper, as long as it's within a reasonable spec, is a better reality than super tight bearing clearances.

What does everyone else think?

 

[d4rt]

Seeing a decent amount of views with no responses. In an attempt to provide as much info as possible, I might have accidentally provided too much info and made it a PITA for anyone to read/respond. Main post revised just in case.

The interesting part to me is my main housing bore diameter vs the desired spec and the the main journal diameter vs the desired spec. It was difficult to actually find the OEM spec for a main housing bore for a 360. Mahle references a range of 3.0025 in. - 3.0030 in. in their parts catalog. I found the same specs on page 60 of my "How to Rebuild Small Block Mopar Engines" book (the early edition that is LA specific):

I searched my FSM PDF and couldn't find this documented anywhere in there. The thing I find interesting about my bearing clearances is that my block measured 0.0020 in. - 0.0025 in. above the main housing bore spec. I don't do this stuff professionally, so I could be wrong, but even with the main shaft diameter of my crank being 0.0008 in. - 0.0011 in. larger than the upper end of the spec, I would expect a bit looser bearing clearances. Below is a table of the differences in main housing bore diameter and the major shaft diameter for each main for my 360:

When compared to the loose end of the acceptable specs listed by Mahle (3.0030 in. main housing bore diameter - 2.7795 in. shaft diameter = 0.2235 in. delta), mains 1-4 for my 360 all have a larger delta and main #5 is just slightly (0.0001) smaller. Shouldn't that result in a larger bearing clearance? What am I missing here?

 

[missing linc]

I'm no expert, but if you have doubts, and it sounds like you have lots of doubt, I would probably go with option #2 for both peace of mind and to prevent significant additional costs if it decides to take a dump on you in short order, plus what better time to go with a stroker crank for some extra cubes? If your machinist is confident that it can be ground and correct bearings can be sourced, ok.

For me, I don't want to do it twice and can't afford to anyway.

 

[RustyRatRod]

Option 2, whether stock stroke or not.

 

[d4rt]

Thanks guys! That's where I'm leaning too after thinking about it, as much as I hate to admit it. I'll have to stick with stock stroke since I already have new pistons. I really fell into a rat's nest with this build. It went from "let's find a good 360 short block that I can clean up and run" to "everything is wrong and needs to be replaced". Such is life, I guess.

For anyone else that stumbles into this post, I pulled a fast one on missing linc and RRR and updated my options list in the original post. Option #2 was originally "get a new crank":

1. Grind the crank
2. Get a different crank that hasn't been cut
3. Run it and pray to the Mopar gods that I don't spin a main bearing ~1500 miles from my house

Just wanted to make that clear.

 

[kick]

I’m assuming that you are using a quality micrometer and it came with a standard to check its calibration. You then also checked the calibration of your dial bore gage with that micrometer?
If your measuring instruments check good. Measure the inside diameter of each main bore with the bearings installed and reference those numbers to each journal on the crankshaft that you checked. Then you’ll know what actual clearance is of your bearings.

 

[d4rt]

I’m assuming that you are using a quality micrometer and it came with a standard to check its calibration. You then also checked the calibration of your dial bore gage with that micrometer?
If your measuring instruments check good. Measure the inside diameter of each main bore with the bearings installed and reference those numbers to each journal on the crankshaft that you checked. Then you’ll know what actual clearance is of your bearings.

The micrometers are mid/hobbyist level (Fowler), but both the 2-3 and 3-4 mics that I used for this were calibrated with a gauge block directly prior to taking any measurements. But yes, I did exactly what you stated here to get the bearing clearances I have listed in the initial post.

Main #1: 0.0016" - 0.0018"
Main #2: 0.0017" - 0.0019"
Main #3: 0.0017" - 0.0019"
Main #4: 0.0019"
Main #5: 0.0009" - 0.0012"

The variance represents the small amount of out-of-round for each main journal.

 

[d4rt]

Seeing a decent amount of views with no responses. In an attempt to provide as much info as possible, I might have accidentally provided too much info and made it a PITA for anyone to read/respond. Main post revised just in case.

The interesting part to me is my main housing bore diameter vs the desired spec and the the main journal diameter vs the desired spec. It was difficult to actually find the OEM spec for a main housing bore for a 360. Mahle references a range of 3.0025 in. - 3.0030 in. in their parts catalog. I found the same specs on page 60 of my "How to Rebuild Small Block Mopar Engines" book (the early edition that is LA specific):

View attachment 1716283921

View attachment 1716283922

I searched my FSM PDF and couldn't find this documented anywhere in there. The thing I find interesting about my bearing clearances is that my block measured 0.0020 in. - 0.0025 in. above the main housing bore spec. I don't do this stuff professionally, so I could be wrong, but even with the main shaft diameter of my crank being 0.0008 in. - 0.0011 in. larger than the upper end of the spec, I would expect a bit looser bearing clearances. Below is a table of the differences in main housing bore diameter and the major shaft diameter for each main for my 360:

View attachment 1716283923

When compared to the loose end of the acceptable specs listed by Mahle (3.0030 in. main housing bore diameter - 2.7795 in. shaft diameter = 0.2235 in. delta), mains 1-4 for my 360 all have a larger delta and main #5 is just slightly (0.0001) smaller. Shouldn't that result in a larger bearing clearance? What am I missing here?

The measurements I took on the main housing bore diameter didn't sit well with me after reading up on that a bit. A main housing bore that is 0.0020 in. - 0.0025 in. out of spec would likely impact bearing crush/fitment. This probably would have been immediately obvious to someone more experienced.

Well....it turns out I screwed up. When I went to setup my 3-4 mic to get that measurement, I set the mic to 3.0300 instead of 3.0030. I took a new measurement this morning with my mic set correctly and it came out as follows:

Main #1: 3.0030
Main #2: 3.0029
Main #3: 3.0029
Main #4: 3.0028
Main #5: 3.0025

Given that the OD of the main journals on my crank range from 0.0008 in. to 0.0011 in. over the large end of the spec, it makes sense that clearances are as tight as they are. I'm still in the same situation as I was, but at least this makes more sense.

 

[toolmanmike]

I read online that no more than .0002 should be polished off the journals. THe article didn't say why. Those clearances are a bit tight. My 273 had 1 or 2 that were just under .001 but I ran it. It's been running for 14 years now without an issue.

 

[PRH]

FWIW, I like to set the bore gauge up to read the “clearance”.
I set the bore gauge to zero from the measured shaft diameter.
Install the bearings in the mains, TQ to spec, and check the ID with the bore gauge…….read the clearance.

If the crank measures big, there’s no reason to believe the clearance wouldn’t be small.

Personally, I have no problems running bearing clearances that are at the max clearance spec, or more.
But I’d never put something together for an application like you’re building with clearances tighter than .0020………and I wouldn’t feel all warm and fuzzy about that clearance either.

Imo, you’re looking for a crank, or someone who’s real good with a crank grinder.

If the clearance ended up at .0035-.0040”…..I wouldn’t even raise an eyebrow.

 

[d4rt]

I read no more than .0002 should be polished off the journals. THe article didn't say why. Those clearances are a bit tight. My 273 had 1 or 2 that were just under .001 but I ran it. It's been running for 14 years now without an issue.

My research indicates the same and the reason seems to be that there isn't a good way to do this without introducing egg (out-of-round) and taper into each journal. Since I'll be spending a fair amount of time at the track, I'm probably stuck with getting a new crank unfortunately. Just don't want to risk it.

 

[toolmanmike]

My research indicates the same and the reason seems to be that there isn't a good way to do this without introducing egg (out-of-round) and taper into each journal. Since I'll be spending a fair amount of time at the track, I'm probably stuck with getting a new crank unfortunately. Just don't want to risk it.

Yes, engines that see rpm and race duty are usually built on the loose side of spec. I have a couple of machine shops around. It would be interesting to see what they would do to get an extra .001

 

[d4rt]

FWIW, I like to set the bore gauge up to read the “clearance”.
I set the bore gauge to zero from the measured shaft diameter.
Install the bearings in the mains, TQ to spec, and check the ID with the bore gauge…….read the clearance.

If the crank measures big, there’s no reason to believe the clearance wouldn’t be small.

Personally, I have no problems running bearing clearances that are at the max clearance spec, or more.
But I’d never put something together for an application like you’re building with clearances tighter than .0020………and I wouldn’t feel all warm and fuzzy about that clearance either.

Imo, you’re looking for a crank, or someone who’s real good with a crank grinder.

If the clearance ended up at .0035-.0040”…..I wouldn’t even raise an eyebrow.

Yep, this is how I did it when coming up with the bearing clearances I posted. I agree 100% too. This is basically exactly where I'm at. I'd rather it be way on the loose end than tight. Going to have another chat with my machinist today.

 

[d4rt]

Just to plan ahead, I started looking around for 0.001 undersize bearings this morning. Options are extremely limited for main bearings. I basically only found 3 options, all of which are sold out pretty much everywhere:

• Clevite MS1266HGX
• King MB 517XP STDX
• Sealed Power MA Series 4999MA1

There are also 0.001 in. undersize bearings for 0.010 in. main journals. Same availability issues though:

• Clevite MS1266HG9
• King MB 517XP 010X

This makes me wonder what racers are doing these days to get the desired clearances. I guess you either need your own personal stock pile of main bearings or more cranks are getting ground to a target clearance.

It's also kind of interesting that the same availability issues don't seem to exist for rod bearings. Summit has plenty of options for rod bearings that give 0.001" of extra clearance. Heck, even Summit themselves makes a rod bearing for SB Mopar:

Summit Racing Race Series Rod Bearing Set - SUM-481HXS

I wonder what the thought process is there. You'd think if there is enough demand to offer rod bearings that the same demand would exist for main bearings. I guess maybe it comes down to the 360 having a different main journal diameter than the 273/318/340.

 

[Dan the man]

I'd probably get a new crankshaft, you can get one for $400. You already stated that you had trouble with finding 0.030" bearing as it is. I think that your going through a whole lot of un needed hassle. I'm sure that you had your machine shop check out the main bore alignment. Myself as soon as I saw that the crankshaft was cut down that far I would have trashed it.

 

[Newbomb Turk]

I'd probably get a new crankshaft, you can get one for $400. You already stated that you had trouble with finding 0.030" bearing as it is. I think that your going through a whole lot of un needed hassle. I'm sure that you had your machine shop check out the main bore alignment. Myself as soon as I saw that the crankshaft was cut down that far I would have trashed it.

Nothing wrong with a .030 under bearing as long as the clearance is correct.

You’d throw **** away real engine builders would use.

You do realize some guys turn Chrysler rod throws down from a hefty and stupid 2.75 journal (unless you are burning fuel) to 2.200 don’t you?

That’s a .175 UNDERSIZE.

 

[Dan the man]

Nothing wrong with a .030 under bearing as long as the clearance is correct.

You’d throw **** away real engine builders would use.

You do realize some guys turn Chrysler rod throws down from a hefty and stupid 2.75 journal (unless you are burning fuel) to 2.200 don’t you?

That’s a .550 UNDERSIZE.

I've heard of it, but why do it? If cross drilling a crankshaft makes it weak, I wonder what turning it down that far does for it. I personally don't know of anyone who has or had a crankshaft turned more than 0.010". And a block that's been bored 0.060" can't be bored again without being sleeved. I think that I heard that they turn down the journals that far so they can use chevy rods.

 

[Dan the man]

Nothing wrong with a .030 under bearing as long as the clearance is correct.

You’d throw **** away real engine builders would use.

You do realize some guys turn Chrysler rod throws down from a hefty and stupid 2.75 journal (unless you are burning fuel) to 2.200 don’t you?

That’s a .175 UNDERSIZE.

I know a lot of guys who have built a lot of engines and I can't remember any of them using a crankshaft that was turned 0.020". Myself, I wouldn't use a 0.030" under crankshaft, but that's just me. The OP said that he had a hard time even finding bearings for it.

 

[Newbomb Turk]

I've heard of it, but why do it? If cross drilling a crankshaft makes it weak, I wonder what turning it down that far does for it. I personally don't know of anyone who has or had a crankshaft turned more than 0.010". And a block that's been bored 0.060" can't be bored again without being sleeved. I think that I heard that they turn down the journals that far so they can use chevy rods.

How many .030 under or cross drilled cranks have YOU PERSONALLY seen fail?

How many cross drilled cranks have YOU PERSONALLY seen fail?

How many Chrysler engine have YOU PERSONALLY seen fail due to full groove main bearing?

Answer that and then I’ll know how to answer your question.

 

[Dan the man]

How many .030 under or cross drilled cranks have YOU PERSONALLY seen fail?

How many cross drilled cranks have YOU PERSONALLY seen fail?

How many Chrysler engine have YOU PERSONALLY seen fail due to full groove main bearing?

Answer that and then I’ll know how to answer your question.

I don't know of any machine shops that w

 

[d4rt]

I personally wouldn't have a problem running this crank if the clearances checked out. The egg and taper are well within spec, the journals are in great shape, the old bearings looked good and the crank spins easy in the block. Before I bought this engine, it made 80 lbs of oil pressure at ~3000 RPM (tested it with a drill, priming rod and mechanical gauge). You're both right IMO. I think the crank is otherwise fine, it just doesn't have the oil clearances necessary for running it hard and grinding off a thousandth for the extra clearance is a difficult task. Sounds like it can be done, but that could also get screwed up and then I'm really in trouble. Seems like this would work fine in a milder, purely street build.

I think a new crankshaft is really the only option here for me. Now the question is, which is the best avenue to go about getting a "new" crank? What's everyone's opinion of a recently purchased Scat or Eagle cast cranks? How much machine work is generally required to get them in a usable state? I can have one of either shipped out from Summit today for $380-$390. I'd probably have it by Tuesday. There are also "crankshaft kits", however the ones I've found are all reman and cut at least 0.010 in. There's also no guarantee that you get a 0.010 in. undersize crank. I reached out to a couple of suppliers last night and they both said I could end up with a 0.020 in. or 0.030 in. crankshaft, which could put me right back in my current position depending on how good the machine work is. Seems like a gamble, which makes me lean back towards just getting a Scat or Eagle crank from Summit. The other possibility is that I could go hunting in the local salvage yards. Based on what I've read, a crank out of a newer 5.9 Magnum would work. Plenty of those in the salvage yards around here and I could probably fish a crankshaft out of there for ~$50. There's even a 50% off sale at the Mesa Pull-N-Save tomorrow....

 

[Newbomb Turk]

I don't know of any machine shops that w

Any machine shops that what Dan?

I know personally of an asshole that calls himself a machinist and an engine builder. He’s neither.

But like you, he has an unfounded fear of grinding a crank.

I was helping one of HIS machinists assemble some blown alcohol BBC for a boat.

He had THREE SETS of main bearings to try and get the clearance set.

It took forever to sort it out and it was still junk when we had it done.

I asked said asshole why he didn’t turn the crank .010 under and get the journals back to size and shape.

The asshole said “it’s a factory 427 crank, I want to keep it original”!

So I explained to him what an idiot he was (and still is) and told the guy I was helping to find another job as fast as he could. The moron signing your checks is headed for disaster.

Sadly, that fat drunk is still in business and still screwing people over even though he’s been bankrupt twice and he’s changed names at least three times.

And Dan, I didn’t ask what a shop you know of does.

I asked you specifically what your experience is.

You failed at that too Dan.

 

[Dan the man]

Any machine shops that what Dan?

I know personally of an asshole that calls himself a machinist and an engine builder. He’s neither.

But like you, he has an unfounded fear of grinding a crank.

I was helping one of HIS machinists assemble some blown alcohol BBC for a boat.

He had THREE SETS of main bearings to try and get the clearance set.

It took forever to sort it out and it was still junk when we had it done.

I asked said asshole why he didn’t turn the crank .010 under and get the journals back to size and shape.

The asshole said “it’s a factory 427 crank, I want to keep it original”!

So I explained to him what an idiot he was (and still is) and told the guy I was helping to find another job as fast as he could. The moron signing your checks is headed for disaster.

Sadly, that fat drunk is still in business and still screwing people over even though he’s been bankrupt twice and he’s changed names at least three times.

And Dan, I didn’t ask what a shop you know of does.

I asked you specifically what your experience is.

You failed at that too Dan.

Me, personally have never had to have a crankshaft turned more than 0.010 ".

 

[Newbomb Turk]

Me, personally have never had to have a crankshaft turned more than 0.010 ".

So you don’t know if more than that has any adverse issues but you are SURE anyone doing it is wrong?

Got it.

This goes back to the rear main seal issue Dan.

Most of the time it’s pretty easy to verify something I say. A phone call to Felpro would have gotten you the exact same information I got in 1995.

Then you’d know.

Want to hear another wives tale? Some guys refuse to use a gasket under the oil pump. I say you ******* A better have a gasket in there. And the professional arguer’s come along say that’s bullshit.

So I took time out of MY day to sit through a webinar put on by PERA where a Melling engineer spoke about OEM type oil pumps.

So I asked the guy giving the webinar if it mattered if you use a gasket or not.

He said there is never a reason to NOT use a gasket between the pump and cap. EVER.

And yet and still there are guys on this very forum who will argue to the DEATH they don’t use them and won’t.

You need to rise above their ignorance and learn from people in the industry who take the time to go do webinars and **** like that so we don’t guess and do dumb **** continually.

In fact, I suggest you go to pera.org and look at all the webinars they have produced to educate people.

You can learn a lot watching them.

 

[Desoto291hemi]

I personally wouldn't have a problem running this crank if the clearances checked out. The egg and taper are well within spec, the journals are in great shape, the old bearings looked good and the crank spins easy in the block. Before I bought this engine, it made 80 lbs of oil pressure at ~3000 RPM (tested it with a drill, priming rod and mechanical gauge). You're both right IMO. I think the crank is otherwise fine, it just doesn't have the oil clearances necessary for running it hard and grinding off a thousandth for the extra clearance is a difficult task. Sounds like it can be done, but that could also get screwed up and then I'm really in trouble. Seems like this would work fine in a milder, purely street build.

I think a new crankshaft is really the only option here for me. Now the question is, which is the best avenue to go about getting a "new" crank? What's everyone's opinion of a recently purchased Scat or Eagle cast cranks? How much machine work is generally required to get them in a usable state? I can have one of either shipped out from Summit today for $380-$390. I'd probably have it by Tuesday. There are also "crankshaft kits", however the ones I've found are all reman and cut at least 0.010 in. There's also no guarantee that you get a 0.010 in. undersize crank. I reached out to a couple of suppliers last night and they both said I could end up with a 0.020 in. or 0.030 in. crankshaft, which could put me right back in my current position depending on how good the machine work is. Seems like a gamble, which makes me lean back towards just getting a Scat or Eagle crank from Summit. The other possibility is that I could go hunting in the local salvage yards. Based on what I've read, a crank out of a newer 5.9 Magnum would work. Plenty of those in the salvage yards around here and I could probably fish a crankshaft out of there for ~$50. There's even a 50% off sale at the Mesa Pull-N-Save tomorrow....

I’m confused a little .
Your first post stated it was basically a street engine,,,,,maybe an occasional drag race .
Would not see above 6000 RPM,,,,,but the crank doesn’t have the “ clearance necessary for running it hard ? “
If it’s a good crank,,,,,any professional guy that polishes crankshafts can take anywhere from .0003 to .001 off of it easily .
Yes,,,,,there are good crank men out there,,,,,not cheap,,,,,but the right operator with the velvet touch can get that done for you .

Or,,,,you can buy a new crank,,,,,but beware,,,,,all new cranks are not created equal .
I’ve seen many of them not perfect as well .

Good luck .

Tommy