Bearing fits?

[Terry Keeley]

Having a closer look at my new CMB 45's and the rear bearing is so tight you can hardly turn it with your finger. When the crank is installed it just turns in the inner race. I know my Picco's came like that too but are the CMB's just as bad? I though it might be that the WIB's were bigger than the installed Jessa's but they're the same.

In the past I've just taken some 320 grit paper wrapped tightly around something close to the bearing size and just "massaged" it a little to loosen the fit. This time I'm going to do it "right" and make a brass lap and use 600 grit AlOx lapping compound to get it right. Any engineer's out there that know the size difference between too tight and just right? :blink:

 

[Tim Kish]

Hi Terry

All the bearings that I fit at work are size for size ,whatever measurement we get for the bearing we make the housing the same.

That will be plenty of interference to hold it in place , you definately don't want any load on the bearings O.D .

Tim K

 

[dave roach]

Terry

I have seen some dum engineer's in my life time.

 

[Mark Bullard]

Terry,

What size bearings are in the motor. I can tell what size the housing should be if I had the sizes of the bearings.

Mark

 

[Brian Schymik]

Terry,What size bearings are in the motor. I can tell what size the housing should be if I had the sizes of the bearings.

Mark

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Terry, I will tell you that I have a CMB 67 greenhead that allows the crank to spin inthe inner race. I thought this was terrible, so i got new Ron Byrd bearings. Still spins inside the inner race. So I got a new crank. No difference... Still spins. So I got stock CMB Bearings. Still the same. What next?? I put some green loctite in there between the crank and inner race. It has held up for two races and lots of practice so far.

Brian

 

[Tim Kish]

Typically when fitting a male part into a female part ( :blink: ) you need a minimum of .0003 to .0004 clearance on ground surfice finishes for the male to fit in without any preasure.

This is why a size for size fit works well on bearings the .0003 to .0004 load seems to be just right.

.

If you are not in a hurry Terry I can take my CMB housing and WIB bearing to work tomorrow and measure them to see what interferene they have.

P.S.

To bad you didnt make Collingwood last weekend , sixty hydro was STROLLINNNNN.

Tim K

 

[Terry Keeley]

Thanks for all the replys!

I borrowed a good 1-2" mic from a buddy (not a tenths mic though) and was able to get some measurements with my bore gauge. I measured the bore about 1.1020" and the bearing is about 1.1023 (28mm). With what Tim said that's a little too tight.

The odd thing is that I decided to fit the bearing one last time before I lapped the case. As soon as the bearing went in the phone rang and when I got back to it the case had cooled and the bearing was free! :huh:

Got to thinking what I had done and what the difference was. When I installed them before I used a little alcohol in a squirt bottle to cool the case quicker, the only explanation I can come up with is that I caused the bore to cool out of round slightly therefore binding the bearing. Sound reasonable?

 

[Terry Keeley]

Terry,What size bearings are in the motor. I can tell what size the housing should be if I had the sizes of the bearings.

Mark

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It's 28mm....

 

[Terry Keeley]

Terry,What size bearings are in the motor. I can tell what size the housing should be if I had the sizes of the bearings.

Mark

101416[/snapback]

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Terry, I will tell you that I have a CMB 67 greenhead that allows the crank to spin inthe inner race. I thought this was terrible, so i got new Ron Byrd bearings. Still spins inside the inner race. So I got a new crank. No difference... Still spins. So I got stock CMB Bearings. Still the same. What next?? I put some green loctite in there between the crank and inner race. It has held up for two races and lots of practice so far.

Brian

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Keep an Eye on it and if it feels rough change it quick, it's gettin' ready to chip a ball or two in my experience.

 

[Don Ferrette]

Got to thinking what I had done and what the difference was.  When I installed them before I used a little alcohol in a squirt bottle to cool the case quicker, the only explanation I can come up with is that I caused the bore to cool out of round slightly therefore binding the bearing.  Sound reasonable?

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Yup. Been there, seen it happen. I let all cases cool naturally now. I also drop the crank in & snug the flywheel & collet on while it's still hot. Allows the crank line up things even better.

 

[Mark Bullard]

Terry,

Housing fit should be 1.1020 to 1.1024. This is right out of the book. I would lean to the bigger number because of the RPM's of our motors. The bearing will last a lot longer this way. Hope this helps.

Mark

 

[Tim Kish]

Hey Terry

I am sure the interference you are measuring is the allowed tolerance for manufacturing.

It is impossible to mass produce castings without some reasonable tolerances.

All of the bores that I have ground for bearings typically have a tolerance of

+.0000 - .0002 , this is to ensure that the bearing will not float in the housing.

Tim K

 

[Terry Keeley]

Hey Terry
I am sure the interference you are measuring is the allowed tolerance  for manufacturing.

It is impossible to mass produce castings without some reasonable tolerances.

All of the bores that I have ground for bearings typically have a tolerance of

+.0000 - .0002  , this is to ensure that the bearing will not float in the housing.

Tim K

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Sounds like you're doing some pretty close work there, I doubt if they hold 2 tenths, probably more like half a thou. (just guessing).

If I measured right at 1.1020" for the bore that's right on the tight side of acceptable, still seems a little tight for me but we'll see. :unsure:

How do you measure these bores at work? You don't have one of those $1000 "Holemikes" by any chance do you? If you have time I sure would be interested to know (accurately) what the bores are on some of these motors and how much press they're working with.

 

[Tim Kish]

Your probably right about the half thousand tolerance for production work , very hard to hold it any closer.

.0002 is really not that hard to achieve with the proper tools we use swiss bore gauges for most of our measurements and they are certified by our CMM 's.

Unfortunately I can't take any of the bore gauges from work to check your engines (very expensive) but after I get done with the moving into my new house thing I would be glad to measure some cases for you .

Our CMM's measure in microns so you won't get any better than that .

Later Tim

 

[Joe_Knesek]

Hey Terry
I am sure the interference you are measuring is the allowed tolerance  for manufacturing.

It is impossible to mass produce castings without some reasonable tolerances.

All of the bores that I have ground for bearings typically have a tolerance of

+.0000 - .0002  , this is to ensure that the bearing will not float in the housing.

Tim K

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Sounds like you're doing some pretty close work there, I doubt if they hold 2 tenths, probably more like half a thou. (just guessing).

If I measured right at 1.1020" for the bore that's right on the tight side of acceptable, still seems a little tight for me but we'll see. :unsure:

How do you measure these bores at work? You don't have one of those $1000 "Holemikes" by any chance do you? If you have time I sure would be interested to know (accurately) what the bores are on some of these motors and how much press they're working with.

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I would think a crank is ground in the same manner I ground ceramic. If that's the case, .0002 is not an issue. Some of the parts we made at Coors for Applied Materials had a tolorance of +-.00001. Dressing the wheel, setup and sparkout is key.

 

[Terry Keeley]

Your probably right about the half thousand tolerance for production work , very hard to hold it any closer.
.0002 is really not that hard to achieve with the proper tools we use swiss bore gauges for most of our measurements and they are certified by our CMM 's.

Unfortunately I can't take any of the bore gauges from work to check your engines (very expensive) but after I get done with the moving into my new house thing I would be glad to measure some cases for you .

Our CMM's measure in microns so you won't get any better than that .

Later Tim

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Wow, must be nice to have access to such expensive equipment!

Maybe you could bring one of your motors in an check it when it's time to change bearings?

 

[Joe_Knesek]

Your probably right about the half thousand tolerance for production work , very hard to hold it any closer.
.0002 is really not that hard to achieve with the proper tools we use swiss bore gauges for most of our measurements and they are certified by our CMM 's.

Unfortunately I can't take any of the bore gauges from work to check your engines (very expensive) but after I get done with the moving into my new house thing I would be glad to measure some cases for you .

Our CMM's measure in microns so you won't get any better than that .

Later Tim

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Wow, must be nice to have access to such expensive equipment!

Maybe you could bring one of your motors in an check it when it's time to change bearings?

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Terry I checked one of my Picco 45s on a CMM and it was scary how out of round everythink was. The rotor had a .003 low spot in it right at closing. Nothing a Blanchard grinder can't take care of but the piston and sleeve....

 

[Terry Keeley]

Terry I checked one of my Picco 45s on a CMM and it was scary how out of round everythink was. The rotor had a .003 low spot in it right at closing. Nothing a Blanchard grinder can't take care of but the piston and sleeve....

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Know what you mean. Years ago when I was running K&B 45's I couldn't understand why some motors would run great and others were dogs, even though I worked them the same.

Start poking around with a good mic and a bore gauge and you'll sure find out! I found some of the old sleeves that were almost half a thou out of round.

 

[Bob Finn]

It's all in the feel you use on the gauge. I used to machine mine to line to line fit on the big bearing, and a .0005 press on the little bearing. The bearings don't generally vary more than about .0001

 

[Terry Keeley]

It's all in the feel  you use  on the gauge.      I used to machine mine  to line to line fit on the big bearing,  and a .0005 press on the little bearing.    The bearings don't generally vary more than about .0001

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Hey Bob: When you say "line to line" do you mean make the case the same size as the bearing?