Hello,
I've got a machined 68 350 block and want to check the main bores. The FSM says to torque mains 1-4 to one torque value, and main #5 to another.

1. Does the torque sequence matter? Aka, do I need 1-4 torqued completely before moving on to #5, or to do them all evenly in incremental steps together, etc?
2. I'll be using ARP studs for the mains. The torque value for the #5 main is 10 lb-ft different than what the FSM calls for. My inclination is to follow the ARP instructions...any thoughts to the contrary?

Thanks.

 

If you are going to use ARP studs you absolutely have to use their torque specs and their lube that they supplied with the studs. There really is not a sequence but I generally try to do them in three steps.

You might be one of the few that get lucky but you might as well figure on getting the block align honed with the studs,

I have found the best way to check main bores is with the block standing upright. You need to check them for out of round along with size and that is very hard to do with the block on an engine stand.

 

The sequence of the caps/studs doesn't matter - you can do #1 then #5 then #4 then #2 or whatever you want.

Bill was talking about the sequence when tightening a single stud. Don't go straight to 100+ ft-lbs. Do it in three steps, which should also be in the ARP instructions, working your way up to the final torque value.

One important hint - when installing the crank you have to get the #3 bearing seated correctly since it's the thrust bearing. I like to torque down #1 and #5, make certain the crank turns nicely, put in the #3 cap and snug it down to 40 or so ft lbs, when give the crank several good whacks on the nose and the rear flange with a dead blow hammer. Use a pry bar or large screw driver to wedge the crank forward while finishing the #3 fasteners to final torque. This little dance helps keep the back face of the thrust bearing, which takes all the forward load from the torque converter or clutch, square to the crank. Now you can use feeler gauges to double check that there's the right clearance and no tight spots between the back of the bearing and the face of the crank. The other side (front of the bearing) isn't as important. Note that you need to use a light lubricant like oil when checking clearances - not assembly lube. So final assembly usually means pulling it back apart, again, and using assembly lube along with the whole process.
Checking the thrust isn't strictly necessary, especially if nothing has been changed, but I have had a couple of blocks that had wonky caps and just did not seat squarely without a fight.

 

I have pretty much gone to just using oil period. Unless the engine is going to sit around for years before being started. I do put assembly lube on rockers and other high load stuff.

 

Thanks to both of you for the replies, I assumed as much but wanted to verify.

The machinist align honed the mains w/ the studs. I've had the block for a few months and just getting around to starting installation. My plan was to
1. Install the caps and check the bores w/ a bore gauge.
2. Remove the caps, install the bearings. Check the installed ID to compare to the crank journal measurements and verify clearance.

Then I stumbled across a discussion about not using a bore gauge on the main bearings due to damage, instead measuring the bearing shell thickness outside of the engine and figuring out a clearance that way.

Which way is "best practice"? I checked my rod bearing clearance w/ a bore gauge, is there something different about the main bearings that make them more susceptible to damage?

 

Nothing different about the mains. Some bore gauges put more pressure to the surfaces measured so they may mark the bearings heavily. If you used that bore gauge on the rod bearings with no damage, there should be no damage to the mains. I also agree with Bill K. about just using oil on the bearings unless the motor will be stored for a long period of time. Even then you will be priming the oil system prior to initial start up.

 

I'm an old guy but was taught to measure the shell of the bearing using a measured ball bearing then the diameter of the main journal and main bore

 

Correct, because even a properly calibrated dial bore can still dig into the bearing shell and result in an incorrect measurement.

 

Ask him how he torqued them, in three stages or whatever. Do it the same way he did.
But even though ARP tells you to do it that way, I never do it that way. I believe that last Torquing sequence, by only having to move it a few foot pounds, doesn’t give you an accurate reading. I go to 30 pounds then to the stated max torque value. That’s the way my machinist torques them for an align hone as well. Hasn’t failed us yet.

 

cutassefi and 1970supreme are correct, measure the bearing shells, the guy who built my engine years ago was very fussy about clearances, a well built short block is the foundation for a long running engine.

 

I make the last torque step fairly large - ~30 ft lbs - specifically so it's a decent turn and not just a pop of a few degrees.

**As a home hobbyist using cheap ""precision"" equipment** measuring the bore, then the bearing shells, then the crank is extremely difficult due to stackup of errors. 1/3rd of a thou error at each measurement - width of the bore + 1 shell width + 1 shell width - crank journal width - leads to 4/3rds thou error. I couldn't get repeatable and valid numbers that way. You also need a separate tube mic to measure the bearing shells. You end up using three ""precision"" devices - two different mics plus the bore gauge's dial gauge. If it's all calibrated Starrett then I bet it's a joy. Buy for me it's Shars from Amazon. I even have two 1" standards that are a half thou different length!!
My preference is to measure the crank with a mic. I write down that number as just a reference, but really use that as a set position to zero the bore gauge. Then the only measuring device is the dial gauge on the bore gauge directly measuring the difference between the crank and the distance between the shells. Sometimes I check the accuracy by opening the mic by 1 thou according to its dial and see if the bore gauge shows 1 thou.

Measuring the bare bore is good to ensure it's round. It should be very evenly round **without bearing shells!** The bearings have eccentricity build into them so they're thinner near the parting line.
I always check the final size with the bearing shells. Yes, the bore gauge will scuff the outermost coating on the bearings. It "looks" bad, but it's just fine. There's an extremely thin coating on all bearings that is sacrificial and very easily rubs off. It's even fine on coated bearings (e.g. Calico). Just be careful and don't dig into the bearing.

Oil only is definitely a good preference but you just never know. My "plan" with my last assembly was to fire up the engine within 2 weeks. Due to various disasters that engine sat for 4 months before I started it. I'm just always liberal with the Lucas sticky snot goop and do an oil change after a few heat cycles.

 

A lot of guys laugh at this method but for a DIY that wants to just double check their measuring methods take a .002" feeler gauge and slide it in to the front main as shown in my picture and then torque the cap. If you can pull the feeler gauge out you know for sure that you have at least .002" clearance. I used the .002" as an example. Depending on the clearance you are shooting for it might be something else. In my case if a .002 will pull out but a .003 wont, it gives you an idea of what you have.

Of course you can only do the front main but it might make you feel better about your measuring method.

I will also add that Plastigage is actually pretty darn accurate on the mains.

 

This is a very interesting discussion, thanks to all the contributors.

This is how I did the rod bearings, for exactly that reason - it removes the accuracy/inaccuracy of the micrometer from the equation. The wheels and plunger on the bore gauge left witness marks on the rod bearings (which are coated) but I didn't think too much of it. That's when I ran across discussions of measuring shell thickness on the mains. After the discussion I ordered ball end tips for my micrometer in order to measure the thickness of the main bearings, but it still bothers me that, like you said, it isn't as direct a method as measuring the shells installed in the bore. I also wonder if measuring it in the bore would catch some other issue w/ a defective bearing that only shows up when installed. Probably very low probability, but still. oddball, when you measure as you described have you noticed damage to the bearings from the bore gauge?


This is another topic I'm interested in - I don't know the spec for roundness or taper. I can measure and get numbers but they don't mean anything to me. I found an apples-to-orangutan comparison of an LS7 roundness spec for main bore is +/- 0.0002". With my understanding of how line honing is done (not boring, but honing) I'm curious if this is even possible on a worn 50+ year old block? If not, what is realistic, and/or acceptable for a daily driver vs an occasional track car that sees 6500 rpm max, etc... Or, since that's probably a tough (impossible?) question to answer, what number is "too bad" in terms of variation in measurements around the bore?

 

Ok. let me be a "devil's advocate"
#1. "Standards" are accurate to MILLIONTHS of an inch.
#2. Because one standard is .0005" different than another standard doesn't mean either standard is correct.
#3. Stack up error happens when you stack up 2 or more items. Because you are placing one bearing shell on each side of main bearing bore, there is no stacking of anything.
#4. You don't need a "Tubing Micrometer". An accurate 0-1" Outside diameter micrometer and a ball bearing (that you measure and write down the diameter, .250" ball works good) gets you down one less "precision instrument".
***A "tube mic" is a micrometer head and a series of tubular extensions or caps. Tube mics usually are used to measure bores from 4 to 40".
#5. I hope you check calibration of the micrometer before you measure the main bearing journals, otherwise you could have an unknown error.
#6. Of course you do wipe the anvils clean after each measurement ?
#7. Dial bore gages vary. Some have about 1/8' diameter plunger and corresponding smaller conical surface. Larger diameter (1/4") have a larger conical radius that is less likely to gouge a bearing. Plunger spring pressure also has an effect on gouging softer material.

 

I am just rambling ..........

Here is a link from King Bearings that has some interesting information:
https://www.kingbearings.com/wp-cont...e-bearings.pdf

One thing that nobody has brought up is the fact that if you give the same micrometer and the same crankshaft to 3 different people, they will probably come up with three different measurements on any particular journal. There is a good deal of "feel" involved and it takes a while to get it right.

Also every time you loosen the main bolts and retorque them the measurement will be slightly different. And ... is your torque wrench exactly the same as the guy who did the align hone ?

You can drive yourself crazy measuring this stuff.

 

BillK, you are kinda correct. Three "people" will get different measurements, but three "skilled machinists" won't vary more than .0002". It DOES take a "feel", no question about it. The worst thing in my book is those "thimble ratchet" micrometers. You can be cocked to the right or left a very, very small amount and the ratchet will click.

In my younger days, you were shown something to measure. You measure it and told the Journeyman what you got. If he said "wrong", you measured it again. If he said "wrong", you measured it a third time. If it was wrong, the Journeyman told you what it measured......and you were sent back to the "saw room" to cut steel for jobs and practice measuring things.

 

#1: Agreed, quality standards are. That's why I used all the quotation marks. The stuff that I'm willing to pay for considering how infrequently I use it and for the very imperfect usage I have for it, won't be at that level of quality.
#2: Right. That's my point exactly. Different standards and different measuring tools makes it really hard to get a "true" measurement which means adding a bunch of "relative to something" measurements results in error.
#3: Right, so you're saying these parts don't stack? The bearing doesn't touch the bore? The crank journal isn't aligned with the bearings? So the measurements have no relation to each other. Yeesh. Maybe it's not the precise definition of "stack up error", but if each measurement is incorrect by 0.0003" and there are 4 different measurements (personally I measure each bearing shell - there's no guarantee that both shells have precisely the same thickness) then after 4 measurements we've got a potential of 0.0012". And since the target clearance is usually around 0.003" then we're talking about 33% error. That's painful. I chased my tail for hours on this path years ago and finally had to realize that it wasn't going to get any better - I don't have the skills and tools to measure things reliably this way.
#4: So the ball bearing is guaranteed to be perfectly round? Interesting. Personally, I don't keep a stash of machinist-quality ball bearings for such a purpose. Frankly I would expect *another* error if I spun the ball around and now the width of the ball on the axis I'm using is 0.0002" different than the axis I measured! I agree that ball bearings "should" be highly precise, but that doesn't mean whatever I grab from the junk drawer qualifies.
Maybe it's not the "correct" term, but I've always seen them called - and sold as - "Tube Micrometers" that have one flat anvil and one ball/rounded/oval anvil and are readily available in small micrometer sizes. That way the anvil is known and the calibration is against that specific anvil.
#5: Yes! But if I'm using different micrometers, that means different standards. And as mentioned, we're talking about hobbyist quality here.
#6: yup.
#7: My assumption is we're talking about the typical 2" - 6" dial bore gauge.


Maybe a clarification: the bore gauges I've seen don't have enough travel to go from the crank size all the way to the bore size (travel covering both bearing shells and the clearance). Which means I have to measure the crank with a mic, measure the bearing shells, adjust the bigger mic to show crank+shell+shell, set the bore gauge to zero on that measurement, THEN measure the bore.

You'll see witness lines left in the bearings. It's OK.

Oh, there was a note about eccentricity. The bore (the cap+block or the cap+rod for rod bearings) should be **extremely** round. Swirling the bore gauge around should show close to no changes, certainly for hobbyist tools. I wouldn't recommend using a 10ths dial gauge - at best use a half-thou dial gauge, so you shouldn't see any repeatable or easily visible change in the reading. Once the bore is round then the eccentricity is set by the bearing shells. I usually check one measurement near the parting line just to ensure the reading is *wider* than the vertical reading. The specific amount of eccentricity is set by the bearing manufacturer and can vary a lot so the specific distance of eccentricity doesn't particularly matter unless you're REALLY in the weeks of tweaking a build. But checking this will tell you if there's a major problem. If the measurement is SMALLER than the vertical then there are big problems.
For example! There was a mention about line honing an old block. Yes, if it's done very very well then it can have a very good result. However, not all shops are going to spend that amount of time. I had a block line honed - original caps but adding studs and a 5 main halo - and the mains ended up sinking into the block by something crazy like 5 thou. It moved so much that the bearing parting line was BELOW the cap - not lined up with the cap/block parting line. It was hard to see visually, but an off-axis measurement showed a major crunch. The bearing shells were being forced inwards by the alignment tangs. The bore looked great! But trying to run it like that would have immediately destroyed the bearings. And this is from a well known and decently respected local shop.