Rod bearing clearance yielded .0012 after grinding crank .010 and resizing rods. Using Clevite 010 bearing (CB 542P-10). I'd like to have .0022-.0024. Are my following assumptions unanimous among experts here:

'69 400G stock-to-moderate perf build:

1. .0012 too tight for this particular combo (heavy crank, big journal, stock rod)
2. .0022-.0024 would be good target
3. Polishing crank might get .0003 but won't get me to the target numbers
4. There's no work-around solution and crank needs .001 ground off (if that's even possible).
5. Or mic new .020 bearing and grind crank to that ( last resort in my mind)

Thanks
Adrian Jacobs

 

Hey Adrian
Yes, they ground the crank on the high side it seems. Typically going to or even under the low side is the only way to get the correct clearance. And since you’re using stock rods I wouldn’t hesitate to add a few more tenths, maybe .0026-.003.

 

You will have to take the crank to a very highly competent machine shop (good Luck finding one) and have them grind another .0012 to .0015.

A good grinder can grind this small amount out, but no, you can't effectively and accurately (concentrically) polish this much out of the journals.

Use of an "Arnold Gauge" by a good crank grinder can show if your crank is currently ground concentric on all journals or not, and if not can grind the crank to .020 and give you proper clearances. Don't have your crank ground by any shop that can't or won't test for concentricity, as this is probably one of the main reasons olds rebuilds fail with their sensitivities to oil pressure.


As for what are proper clearances for a Big Block Olds using oil-restricted pushrods:
I recommend performance stock engine builds at .0022 and up to.0026 on the rods if using oval-honed stock rods and a high volume oil pump with a deep pan, otherwise, I recommend against a high volume pump but a higher pressure standard volume pump is better than stock.
Good Main clearances with the 1/3 oil groove main bearings is .0029-.0031 on journals 1 through 4, and .0033-.0036 on #5

You get better oil wedge with the 1/3 groove main bearings than the full groove clevite bearings.

 

First of all..... How are you measuring the clearance ?

How thick are your present bearings ? You need a bearing or "tube" mic to really measure them properly.

King makes a rod bearing for Oldsmobile and if you call them they will try to find a set that is on the low limit of thickness, giving you a little more clearance. Or even just try a different brand. Its amazing how much difference there can be from brand to brand and even from batch to batch. You could also try a set of the Clevite performance bearings, CB542HN-10 The H bearings seem to run on the thin side.

Polishing should never be used to try and gain clearance. It is pretty much impossible to polish material off a crankshaft evenly. It is also darn near impossible to grind .001 off. A real good crank guy might be able to do it if he ground the crank to begin with but it is still very very difficult.

 

I pretty much agree with Bill K. A "tube mic" is best, but there are other ways. Most "average Joe's" are not capable of accurately measuring .0005". Let a skilled professional do it.
An excellent crankshaft grinder could get .001" off, but you would pay for it. Its easier to grind .010" off than .001" or less. Polishing journals for clearance is never accurate or a good idea.
...Just my two cents worth.

 

I really appreciate the comments. I used these measuring tools. It took me most of saturday measuring and re-measuring to get the feel of these tools. I’m no machinist so not sure how snug or loose to set the mics but have been using the thimble dial to set tension.

I’m getting .067 for bearing thickness. I used the method of measuring crank with mic...then calibrating bore gauge to the mic...then use bore gauge to measure the rod saddle. Which showed .0011-.0012 repeatedly. I know this method can scar the bearing but i bought an extra pair of sacrificial (but new) bearings.

The crank guy was indeed somewhat non committal about grinding .001 but was will to try. Couple more questions for ya’ll:

1. Is removing .0015-17 just as difficult as.001
2. If I go down to .020, would I need rebalance? I balanced at current .010
3. Does .020 require re-heat treating crank

 

I know you don't want to hear it.... but I had the same quality Mitutoyo tools as you, and the dial bore gauge that looks similar, and I got within a .001 on my measurements, which isn't accurate enough to really know much.

I will say this, the bearings are soft enough and the mandrels with the ***** are hard enough that they do indent and cause false readings on these types of bearings and this type of measurement equipment.



My recommendation is to number/label torque up the main bearings in your block, and assemble and torque up all your rods with rod bearings in them and mark the bearings with a number and letter corresponding to the top and bottom, and the journal/cylinder number to keep them matched up (example 8T/8B).

Take the Block and the assembled rods with the crank to your machinist.

Have them take measurements with a Sunnen dial bore gauge and a setting fixture based on the crank diameters for each journal coresponding. Even better yet, and the most correct way, have the machinist measure the bores of the rods and the mains without bearings installed first, so you know where the numbers are at for bearing crush (if you are on the low side and super tight or high side and the bearing crush is loose). If the diameters are outside of the high side, you will have minor or less than minimum bearing crush and you can spin a bearing much easier when there isn't enough bearing crush.


This is the only way to do this correctly and get it right when you have this type of problem. Ask me how I know, and I will tell you this is how Vortecpro was able to help me get our engine right and you might have seen how my long story turned out. VORTECPRO was the key, and with his extreme knowledge, craftsmanship, and skills with his precision tools to fix our hot mess of an engine.

 

Those measuring tools are about as good as you can get. The Sunnen bore gage that batten mentioned also has ball ends and will not be much more accurate.

As far as grinding the crank goes you have to remember that in order to grind .001 off the crank size you are really only grinding .0005 all the way around. Pretty hard to set up and do that but it can be done. Just very time consuming.

As far as going to .020 you will not need to rebalance. The .020 bearings will be thicker than the .010 ones and the difference in weight will make up for what is taken off the crank. It is minimal anyway.

Personally I would rather have the clearance on the loose side for a performance engine. Clevite has always said the .001 per inch of diameter is a good starting point. That would mean .0025 for a 455.

 

If you the use the same mic to set the dial bore with as you do to mic the crank, it could read 5.00”, it doesn’t matter. It’s a reference of the difference that’s all.
However if you’re using two or three different mics then there’s an opportunity for error. If at possible mic up everything with the bearings installed, setting the tension on the dial bore to as little as possible so you don’t dig into the bearings.
And the thickness difference between a P bearing and an H bearing is minimal. An H bearing simply has no tin protective layer, which can come off easily even using just newspaper. And besides, I wouldn’t use an H bearing in a stock rod anyway, it’ll be more likely to pinch at the parting line as it’s more concentric than a P bearing is..

 

I'm new to Oldsmobiles, but Big Block Chevy you can get .oo1 oversize bearings and use both halves or just 1 half of bearing to get clearance correct. People may think there is a step if you use 1 half of a bearing but I have never had a problem. This was on my 454 then ran 8200 at the finishline.

 

My thoughts are above and below in bold font.
#1 There is an anvil cap for a 0-1" that has a larger radius and not as likely to "dent" soft bearings.
#2 I don't care for dial bore gauges with "wheels". I don't think they "center up" reliably in bores. Starrett makes a similar thing and they are also clumsy.

 

This comes back to my point about the “Arnold gauge”

If your crank grinder doesn’t have one and won’t show you the concentric runout on each journal, they aren’t who you want.

If I were you, I would go ahead and buy all new .020 bearings to have them ready to go for your crank grinder.

there are no .001 extra bearings sold for oldsmobiles unfortunately.

you can also fine tune clearance by precisely sanding the bearing backs (count your strokes and make even for both halves)with sand paper and checking clearance for taking as much as about .0005 out

 

You don’t want him to polish the crank to get more clearance but you’re willing to have him sand the back of a metal bearing shell? What’s the difference? Nothing, don’t do either one.
And yes Clevite used to make a +.001 for the mains and rods but in std only I believe. It was their HXN series.

 

There is a huge difference if done correctly, and “used” to make means they are scarce as hen’s teeth.

Again, it is really only to get to a finite clearance of an extra few .0001’s.


Telling the poor guy that he can get this fixed using his own measuring tools and a shop that ground the crank wrong in the first place though is the wrong way.

Consistency means having the machinist measure everything with their own tools and then using the setting fixture to measure and grind the crank to get the proper clearance.


I for one hate to see anyone’s project get sidelined by poor machine work and practices, so I was sharing what I know works.

No offense meant, I just see a train wreck coming for another ruined oldsmobile engine build if we don’t direct him on the best path here to save money and heartache later.

 

The suggestions and comments have all been helpful to me. I digest and scrutinize all comments through my own scope.

I take responsibility for all of the decisions i make...even if that decision was erroneously listening to the wrong person or selecting the wrong shop or part.

The machine shop gave me exactly what i asked for...turned the crank .010 and i believe they hit it dead nuts.

The pickle I’m in is my fault. i should have measured rods and bearing first, then specified crank to be turned a bit smaller.

And even more my fault is the fact that I l’ve read that advice on sequence of events numerous times and still decided to grind crank to a generic .010.

BTW since my bearing were sacrificial, I originally tried sanding backside for kicks to see result before discarding them.

Thanks again for words of wisdom. I’m not done asking questions yet.