Main Bearing Clearance

[evanfrucht]

I was going to say as a joke sort of, just use a less accurate micrometer lol

It's like the secret to perfect health: as long as you never go to the doctor you'll have nothing wrong with you, right? lol

I'm using a set if old, but well maintained, Lufkin micrometers and some snap gauges to check everything. I dont think I would ever really able to identify with much certainty measurements past .0001" even then it can be +/- .0001" with my measuring skills

That being said, Its probabaly wise to atleast try to check if you have two halves on opposite ends of the spectrum. That's a full .001" of variation from side to side. That doesn't sound ideal exactly. I dont know what that kind of variation would cause in an engine in real life. Maybe it's not a big deal for most engines, since you have the rest of the bearings keeping everything true. It's only the oil gap that varies?

I think as long as the a final clearance of the split can be verified to be in spec. I can live with that, I can't afford to buy 10 sets of bearings... it makes sense if you build enough engines or sell parts tho.

I'm just thinking out loud here, I am glad you pointed this out so clearly with pictures and measurements. It is good to be aware of. Thanks!
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1967 Bug ( the daily rod )
1964 Fury Wagon ( the pavement shredder )

[StefACE67]

[orwell84]

[txoval]

The +/- bearings would also help with those who like to coat the bearings...

I hope you are able to make this happen.

[sailtexas186548]

[gtjones]

Can a standard split number two bearing be installed in the number three full circle main without modification. I did drill for another dowel. I have good lateral movement of the crank when the case is split. But when I torque the case halves together I still have good lateral movement at 24 ft lbs, but at 25 ft lbs it is very hard to move back and forth. I tried a different number 2 split bearing with the same results. I did measure the bearing thickness of both the number two and number 3 bearing. The split bearing is a little thicker which of what i read is normal specs. I split and reinstalled all of the bearings without the locating dowels with the same result, so I ruled out that the dowels were too long. The case is new from CB Perf, as well as the counterweight crank. the crank journals are all the same size as well as the main saddles in the case. I was hoping for a little insight on this before continuing. My next step is trying some plastigage on # 2 and #3 with the split bearing and comparing the results. As I said, I do have some lateral movement, but it is very tight. I can push it back from the flywheel end, but have to use a screwdriver to push it back towards the flywheel. Any suggestions??

[vwracerdave]

[Brian_e]

[gtjones]

Thanks for the info. I do have a bore guage but it only gives me the variances of the bore ( wrong bore guage). I utilized a snap guage and measured that with a vernier caliper. The following is what I arrived at when measuring the case torqued to spec with just the mains. #1 -0.003, #2 0.0025, #3 with the split bearing 0.0005.
Can I take and file a small amount off the ends of the split bearing in the #3 position to increase the clearance by eliminating some of the crush? Perhaps I am expecting too much by installing a #2 bearing in the #3 position.
I want to build this right and have the satisfaction knowing I am doing this right. Suggestions?

[modok]

What kind of bore gage cannot be set to a size?

[jimmyhoffa]

I think the kind that has an owner that doesn't also have a micrometer set.

Definitely understandable, but you'll need to pick up some mics to set the dial bore gauge with or you'll be going in circles. Everything will make way more sense and you'll be able to set the gauge to mics, or mic the crank and set the dial bore gauge to that to check clearances, etc. etc. and all sorts of other useful fun things having to do with holes and the things that go in them.

Fun activity list, for starters:
Cam drive gear size and fit on crank
distributor drive gear size and fit on crank
piston to cylinder clearance
rod end and rod journal roundness and size
bearing crush
distance between two surfaces that is otherwise hard to measure
_________________
1974 Chenowth 2RL #1244 Street Legal
My other car isn't ridiculous.

[Vanapplebomb]

[RWK]

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73 Type 181
63 Type 113
63 Type 261- 428 071
62 Type 241-378 025 178 530

[gtjones]

I have a micrometer 3-3 inches that came with a 2 inch standard. I checked and it appears to right on. I then miked the crank journals and came up with 2.1650. I utilized the mike to set the bore guage to this reading. I then zeroed it. With the block resting on spigot bore 3 & 4 I miked journal #1 and at the 8 o'clock and 2 o'clock diagonal and it read -0.0015, then 10 o'clock and 4 o'clock and another reading of 0.0015. If correct then #1 bearing is in the range, correct?

[gtjones]

correction, that is a 2-3 micrometer

[Brian_e]

That is the correct procedure.

You should sweep the bore gauge back and forth to se the smallest distance between the mic anvils.

Then zero the bore gauge to that number. The gauge will now ready your crank journal size, and the variance shown on the bore gauge will be your oil clearance.

You can do the same thing to check the bearing crush on your case. Measure EACH bearing and set the mic. You should have .001-.0025" crush on each bearing when the case is FULLY torqued as it would be when its running.

Brian
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www.type-emotorsports.com

[modok]

Thumbs up on the procedure.
Shame it's too small, maybe a mahle brand #1 bearing would be better?


I'm realizing I need to back off on expecting guys to know how to do this stuff.
Getting INTO the world of measuring and high precision is just not for everybody.
But if you want to get into it.... that's great.

[jfdestree]

[modok]

At this point IMO you don't really need to be overly concerned about marks on bearings.
There are a lot of different kinds of bore gauges, some have large radius anvils which work good on soft materials or others have small carbide anvils which work well on hard materials. And then how SMOOTh are the anvils?
Very common these days is Mitutoyo 511 clones, and those aren't very gentle with soft bearings, but great tool for the $.

We have discussed this a few times before and many agree the spring force on some is a bit overkill. May want to reduce the spring force or maybe take the spring out of it entirely. They have enough spring force in these things to work upside down.... but how often is that needed? Measuring holes in the ceiling?
You can stand the case up so flywheel side toward the sky........much easier IMO, and then gravity is doing the work of the spring so you may not need one besides what's in the indicator.

So even tho I said don't worry about it, you want to get specific....
The mark has a dimension. These marks might be 0.00007" deep, or it might be 0.00015" deep, so, to get REALLY precise that starts to count.
So your .0015 reading might be .00135 actual, but PROBABLY lots of other reasons you could be off more than that so no need to focus on it initially.
If it starts reading .003" quit measuring that spot and work on the rest of it
that's a joke but... on a long enough timeline it could happen.

Only the center #2 main has a thin surface plating usually.
1,3,4 mains are just solid material.

[jfdestree]