LA 360 - 0.030" Undersize Main Bearing Clearance Questions

[d4rt]

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

Thanks for the response, Tommy. You're right, most of its time will be spent on the street, but it will also see the track. For the street, it seems like the current clearances are probably fine. You're also right that I probably shouldn't definitively say that it doesn't have enough clearance for something that is going to see the track. Based on most of the other feedback I've gotten, it's a gamble though. I mean, it might be fine. All of the major bearing manufacturers seem to recommend 0.001" for every inch of shaft diameter. That means I should be somewhere in the 0.0028" neighborhood. I'm no where close to that. Then again, the 318 that is getting replaced had a stock short block that probably has similarly tight clearances. I shifted that thing at 6000 RPM and never had an issue, but it was only at the track a handful of times. Just trying to make sure this thing gets done "right", I guess.

You're also right about new crankshafts not being perfect either. Idk, there is risk no matter which direction I go. Seems like a different crank has the highest probability of success. I'm also working with limited time. I need this thing ready to go by the first week in October.

I still haven't circled back up with my machinist. Having a hard time getting a hold of anyone over there today.

 

[340six]

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's pretend car has high standards

 

[Desoto291hemi]

D4rt ,

Thank you for the cordial response,,,,,I appreciate it .

Almost 3 clearance sounds pretty loose to me,,,,unless it’s a serious race engine,,,,even then 2.8 sounds fairly open to me. .

I try to keep my mains to around 2 ,,,big block or small block .
It helps the oil stay where it’s supposed to be,,,,,and the pressure too .
Have you done a complete study of all your clearance on each journal ,,,,at several different positions ?
If the crank is not egged shaped,,,,I think you should be good .
I have seen some cranks even polished a little different on each journal to make up for other issues .

I have seen cranks that were true even down to the tenth of a thousandth,,,,,now that’s close !
But,,,it takes an expert craftsman,,,willing to do several belt changes,,,,,and a good touch with the pressure .

It sounds like you are trying to do it right and I believe you should have a great engine when you get done .

Tommy

 

[d4rt]

D4rt ,

Thank you for the cordial response,,,,,I appreciate it .

Almost 3 clearance sounds pretty loose to me,,,,unless it’s a serious race engine,,,,even then 2.8 sounds fairly open to me. .

I try to keep my mains to around 2 ,,,big block or small block .
It helps the oil stay where it’s supposed to be,,,,,and the pressure too .
Have you done a complete study of all your clearance on each journal ,,,,at several different positions ?
If the crank is not egged shaped,,,,I think you should be good .
I have seen some cranks even polished a little different on each journal to make up for other issues .

I have seen cranks that were true even down to the tenth of a thousandth,,,,,now that’s close !
But,,,it takes an expert craftsman,,,willing to do several belt changes,,,,,and a good touch with the pressure .

It sounds like you are trying to do it right and I believe you should have a great engine when you get done .

Tommy

Yep, I checked both the main and rod journals in multiple spots looking for taper and out of round (egg) with a 2-3 in. outside micrometer. Everything looks pretty good in that regard. Not perfect, but within spec based on what I've read. Main journals 1-3 all have 0.0002 in. egg, zero egg for main #4 and 0.0003 in. for main #5. Zero taper on the main journals with the exception of main #5. That has 0.0003" of taper. The rod journals aren't quite as clean, but still pretty good. Egg varies from 0.0001" - 0.0004". Taper is all within spec on the rod journals too. The shaft diameter for the rod journals are within spec too.

Finally got my machinist on the phone. I'm going to bring the rods, pistons, crank and block back in to the machine shop on Monday. He's going to check my work and then we'll go from there. I might swing out to the salvage yard tomorrow and see if I can pickup a cheap crankshaft. There's a dozen Rams with 5.9 Magnums between the two yards near me. I'll have to pull it myself, but with the sale going on, I should be able to get a crankshaft for ~$30 out the door. From what I've read, the cranks in the magnums will interchange as long as I use an LA rotating assembly, balancer and flex plate, which is what I have. Kind of a PITA to pull an engine just for the crank without knowing whether the engine has been messed with or not.

 

[Ted265]

Myself as soon as I saw that the crankshaft was cut down that far I would have trashed it.

Why is that Dan? Nothing wrong with a crank being ground 0.030" undersize, the crank in my hemi 6 is ground 30 thou under and has been beaten on for 10 years and sees 7000rpm regularly with no issues. I dont belive it weakens the crank by any significant amount. Do you also throw away your blocks once they need more than a +0.020 over bore?

 

[Dan the man]

Why is that Dan? Nothing wrong with a crank being ground 0.030" undersize, the crank in my hemi 6 is ground 30 thou under and has been beaten on for 10 years and sees 7000rpm regularly with no issues. I dont belive it weakens the crank by any significant amount. Do you also throw away your blocks once they need more than a +0.020 over bore?

Back when I was doing more engines, the machine shops that we used wouldn't turn down a crankshaft more than 0.020", all I remember is that they talked about weakens the crankshaft, I don't know this as a fact. 0.040" is the most I'll bore a block

 

[340six]

Back when I was doing more engines, the machine shops that we used wouldn't turn down a crankshaft more than 0.020", all I remember is that they talked about weakens the crankshaft, I don't know this as a fact. 0.040" is the most I'll bore a block

You need a better machinist. And a car.
And as Newbomb said opinions are just that does not make it right. And I use gasket on oil pump. In fact I use copper ones.

 

[oldkimmer]

Ok, guys. This is a little know fact. The smaller the crank journal is the slower the bearing speed is. This is a win win. As far as his clearance is at .0018 and .0019 that’s .0001 ten thou of an inch. Just send it and it will be happy. The OP is making a mountain out of a mole hill. I’ve had factory big block cranks turned .060 many times years ago. They turned 7000 no problem. Kim

 

[Dan the man]

You need a better machinist. And a car.
And as Newbomb said opinions are just that does not make it right. And I use gasket on oil pump. In fact I use copper ones.

I use a gasket for the oil pump as well. Where could I get the copper ones?

 

[340six]

I use a gasket for the oil pump as well. Where could I get the copper

Carshopinc or eBay under same seller. EBay also has cars if ya need one to go with it.
Go to Google type in copper oil pump gasket or eBay. It will come up. They have lots of stuff at Carshopinc

 

[junkyardhero]

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, you did know that cars rolled off the assembly line with factory produced engines that were 10 on the crank, or 20 over on the cylinder, right? you think there wasn't ones rolling out that weren't 20 or 30?

yes, before the advent of cheap and/or available stroker kits cutting the journals for chevy rods was a common practice, as was offset grinding mains for more stroke. and that's offset grinding cast cranks.

 

[nckennyb]

Try some plastigage and see what it says about your clearances?

 

[65TerrorCuda]

It's easy to obsess over "this has got to be perfect" and then have a project become yard art and rust into the ground. The smell of varnish will remind you how long it's been.

I would never want to play poker with Dan, pretty sure I'd get smoked.

 

[replicaracer43]

Hey, @d4rt another thing not mentioned, is the line bore diameter in the block itself. You or your machinist need to torque the main caps down with NO bearing shell, and see if the tunnel is on size. There is right at .001 tolerance from smallest to largest allowable diameter, so if you happen to be on the low side, a quick few passes with the line hone could open your clearance up. Something else to consider.

 

[Dan the man]

dan, you did know that cars rolled off the assembly line with factory produced engines that were 10 on the crank, or 20 over on the cylinder, right? you think there wasn't ones rolling out that weren't 20 or 30?

yes, before the advent of cheap and/or available stroker kits cutting the journals for chevy rods was a common practice, as was offset grinding mains for more stroke. and that's offset grinding cast cranks.

I'm not saying that cars didn't roll off the assembly line bored 0.020", and I'm sure that you have done more engines than I have but one thing that's for sure is that all of the engines that I have worked on all where a standard bore and I know this because of two reasons, first my dad always miked the bores and there was never any markings on the pistons. The only one that I was ever told that was bored by the factory was when GM supposedly bored the 396 to a 402. We used well known machine shops for all of the machine work that we needed done, now this was back in the mid '70's through the early '80's and none of them even turned a crankshaft 0.020" that I know of, at least they never did on any crankshafts that they did for us. Boring blocks 0.060" over, I have direct personal experience with that and it wasn't nothing but a over heating night mare.

 

[340six]

I'm not saying that cars didn't roll off the assembly line bored 0.020", and I'm sure that you have done more engines than I have but one thing that's for sure is that all of the engines that I have worked on all where a standard bore and I know this because of two reasons, first my dad always miked the bores and there was never any markings on the pistons. The only one that I was ever told that was bored by the factory was when GM supposedly bored the 396 to a 402. We used well known machine shops for all of the machine work that we needed done, now this was back in the mid '70's through the early '80's and none of them even turned a crankshaft 0.020" that I know of, at least they never did on any crankshafts that they did for us. Boring blocks 0.060" over, I have direct personal experience with that and it wasn't nothing but a over heating night mare.

You know NOTHING but always give advise.
Also no one mikes

 

[Dan the man]

You know NOTHING but always give advise.
Also no one mikes

So you know first hand that new cars came with engines that were already bored and turned crankshaft BS. I caught my mistake on spelling. If you notice several others have agreed on off setting of the rear seal.

 

[Scody21]

Try some plastigage and see what it says about your clearances?

Using a mic is better than the smash test.

 

[340six]

So you know first hand that new cars came with engines that were already bored and turned crankshaft BS. I caught my mistake on spelling. If you notice several others have agreed on off setting of the rear seal.

Yes and blocks were clearly marked showing an over bore. Common knowledge, codes are stamped on block's
In 1973 tons of 340 were 20 over. I have pulled many 1973 factory 340 at yards that were 20.

 

[junkyardhero]

Yes and blocks were clearly marked showing an over bore. Common knowledge, codes are stamped on block's
In 1973 tons of 340 were 20 over. I have pulled many 1973 factory 340 at yards that were 20.

mister minivan over here acting like you gotta be some part of secret society and have a decoder ring to suss out the mysteries of mopar engines. anybody that's been around these things for longer than a cup of coffee knows that the factory did us a solid and marked the blocks and then even gave us the legend key in the FSM!

i guess mazda mpv's and ford aerostars don't come factory trick or whatever.

 

[Dan the man]

Yes and blocks were clearly marked showing an over bore. Common knowledge, codes are stamped on block's
In 1973 tons of 340 were 20 over. I have pulled many 1973 factory 340 at yards that were 20.

Like I said earlier just because I never seen any didn't mean that it didn't happen.

 

[340six]

Like I said earlier just because I never seen any didn't mean that it didn't happen.

The fact that you know so much (according to you) but don't know basic things that are common shows how much you really know. Scary you give advise out.

 

[340six]

mister minivan over here acting like you gotta be some part of secret society and have a decoder ring to suss out the mysteries of mopar engines. anybody that's been around these things for longer than a cup of coffee knows that the factory did us a solid and marked the blocks and then even gave us the legend key in the FSM!

i guess mazda mpv's and ford aerostars don't come factory trick or whatever.

Great now ya tell me. You could have told me it was in the FSM before I learned the secret hand shake, and bought a decoder ring, and special glasses for the invisible ink.

 

[Newbomb Turk]

Yes and blocks were clearly marked showing an over bore. Common knowledge, codes are stamped on block's
In 1973 tons of 340 were 20 over. I have pulled many 1973 factory 340 at yards that were 20.

Chrysler didn’t throw anything away. They used everything.

 

[Dan the man]

The fact that you know so much (according to you) but don't know basic things that are common shows how much you really know. Scary you give advise out.

I probably know more than you realize or want to admit. I think that your one of those guys who can't stand it when it's possible that someone knows as much or more than they do. Maybe one day you'll learn how to comprehend what you read. I'm not going to explain that to you