Bearing Istallation

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Al Hobbs

Legend of the NW
Vendor
Joined
Aug 25, 2009
Messages
1,932
I am not an engine guru, but I have met some model boaters and manufacturers that really know their way around an engine. I paid attention to what they had to say. Your engine will give you many years of service if you take the time to maintain it.

Many model boaters don't know some simple engine maintenance, such as replacing the crankshaft bearings. It is not difficult. Different boaters have different thoughts as to the best way to remove the old bearings and install new bearings. This is how I do it.

First disassemble the engine. If the engine uses needle bearings on the crankpin, count how many there are so you will replace the correct number of needles. When the engine is disassembled down to just the crankcase, crankshaft and bearings, I put it into a toaster oven at 350 degrees for 20 to 30 miniutes.

Many people heat their crankcase with a torch. This is fine if you know what your are doing. It is easy to heat the crankcase unevenly which can make the crankcase warp a tiny bit. Heating in an oven, heats the parts evenly. Never exceed 400 degrees F as a lot of aluminums begin moving around at 400 degrees F. So much depends on the what the manufacturer uses and how much silicon is in the aluminum itself.

After taking the crankcase out of the oven, the bearings normally fall out. If they do not, put them back in the oven for another 10 to 15 minutes. If the bearings still refuse to fall out. I rap the large end of the crankcase against a piece of wood. The big bearing should just pop out. If the small bearing does not want to fall out, I use a wooden dowl to push the bearing out. Normally with a rubber or plastic mallet. Remember that the crankcase is still very hot. I use heavy leather gloves to hold the hot crankcase.

Then let the crankcase cool as it is quite hot coming out of the oven. When it is cool, I use a toothbrush and lacquer thinner to clean the crankcase inside and outside. When it is clean and dry, I put it back into the oven at 200 to 250 degrees F for 20 to 30 minutes. The aluminum crankcase will expand evenly.

Now, it is time to install the new bearings. Again other people have their own ways of installing the new bearings. I first install the small bearing, using an arbor press. Some people use a vise, but I think it is too easy to damage the engine that way. Make certain that the small bearing is fully inserted. The K21 front bearing actually is inserted further into the crankcase than the edge of the crankcase.

Next, I press the big bearing into place on the crankshaft. Put a film of oil onto the crankshaft and slide the crankshaft into place, extending through the front bearing. Put the flywheel collet and flywheel onto the crankshaft and draw it tight. You can look through the crankcase to see if the big bearing has been drawn into place. If it isn't, I use my arbor press and a socket to press the big bearing fully into place. The crankshaft pin should be lined up in the center.

To make sure that the new bearings are perfectly aligned on the crankshaft, I hold the flywheel, and only the flywheel. Then using a wooden or plastic mallet, I strike the cable nut squarely in line with the crank shaft two or three times. The crankshaft should spin freely. Then I pour oil into the crankcase around the big bearing.

Holding the crankcase upright, the crankshaft should spin freely and always stop with the counter weight at the crankcase bottom.

If you are uncomfortable replacing the bearings, don't keep running with worn bearings. Your engine will not perform properly. There are several people on this forum that do work for other boaters, including replacing the bearings. Don't hesitate to contact them to get your engine back to peak performance.
 
All sounds good. Do anyone need bearings. LOL This is my cabinet that I keep my bearings in. Notice the rubber pads under the bearings. You will be surprised how much vibration comes from the floor. This is just what the earth does all the time. You can measure it with vibration equipment. And by putting the bearings on the pads prevents the vibration in the balls and races. On electric motors stored on the shelve in our warehouse we turn the motor shafts a quarter of a turn every month because of this vibration. The weight of the rotor will flat spot the bearings in time.
 

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All sounds good. Do anyone need bearings. LOL This is my cabinet that I keep my bearings in. Notice the rubber pads under the bearings. You will be surprised how much vibration comes from the floor. This is just what the earth does all the time. You can measure it with vibration equipment. And by putting the bearings on the pads prevents the vibration in the balls and races. On electric motors stored on the shelve in our warehouse we turn the motor shafts a quarter of a turn every month because of this vibration. The weight of the rotor will flat spot the bearings in time.
And nobody wants flat balls…. 😁
 
Thanks Al, to add to the info here's how I do it but I now also put the case in the oven at 250F. You can use a torch but you havta be careful how much heat you use and the most important thing is to let the case cool naturally.



edit: crank sizes (from CMB at least) have gotten better so no need to loctite the rear bearing anymore.
 
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Anybody have a methed to fix a case that has loosened up around the front bearing. It's spinning in the case. I'm thinking of machining it to accept sleeve but that will probably fall out during future bearing changes. An oversized bearing would be ideal then I could just machine the case to that size. Any ideas?
 
I found some 16100 2z bearings that are 10x28x8. I'm going to try machining out the case an extra 2mm and see how it goes. Anyone know the interference tolerance for these bearings?

Brent
 
Anybody have a methed to fix a case that has loosened up around the front bearing. It's spinning in the case. I'm thinking of machining it to accept sleeve but that will probably fall out during future bearing changes. An oversized bearing would be ideal then I could just machine the case to that size. Any ideas?
Years ago, a friend of mine ran 3 piece case OPS’, he intentionally opened the bearing pocket and then used Loctite Bearing Mount on the O.D. of the bearing. He used the crank as an alignment tool and later machined a tool.
 
Years ago, a friend of mine ran 3 piece case OPS’, he intentionally opened the bearing pocket and then used Loctite Bearing Mount on the O.D. of the bearing. He used the crank as an alignment tool and later machined a tool.
I used to chuck them up in the lathe and use a knurling tool to raise the aluminum and press in the bearing with a drop of red locktite…
 
I found some 16100 2z bearings that are 10x28x8. I'm going to try machining out the case an extra 2mm and see how it goes. Anyone know the interference tolerance for these bearings?

Brent

Most quality bearings will have all that information available from manufacturer for the specific bearing you are working with.

Aside from that .0025" interference I believe would work
 
I found some 16100 2z bearings that are 10x28x8. I'm going to try machining out the case an extra 2mm and see how it goes. Anyone know the interference tolerance for these bearings?

Brent

CMB's bearing to case fit on most sizes is between about 5-7 tenths, the tight side of M5-M6:

https://www.skf.com/ca/en/products/...ring-interfaces/tolerances-and-resultant-fits

If you were somehow able to press in a bearing with a 2.5 thou interference fit it wouldn't even turn as the high end of C3 internal clearance for that size is 1.1 thou.

How are you going to do the job? How are you going to measure the bore?
 
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I'm going to shoot for .0007-.001. Of course my old mill and other factors may (will) give me trouble on holding that tight of a tolerance. I used the crankshaft and the old bearing to line the case up in my mill vise then I plan to use the boring head to cut it with. Measuring it will be the trick, I'm thinking of making some kind of gauge pin or something to creep up on the final size. Maybe I can just put the new bearing in some dry ice and use it as the gauge. I'm hoping to get some ideas and look forward to this project.

Brent
 
I'm going to shoot for .0007-.001. Of course my old mill and other factors may (will) give me trouble on holding that tight of a tolerance. I used the crankshaft and the old bearing to line the case up in my mill vise then I plan to use the boring head to cut it with. Measuring it will be the trick, I'm thinking of making some kind of gauge pin or something to creep up on the final size. Maybe I can just put the new bearing in some dry ice and use it as the gauge. I'm hoping to get some ideas and look forward to this project.

Brent
I could understand if this was a rare motor with no parts available but 67 cases are everywhere. Why not just change out the case
 
I'm going to shoot for .0007-.001. Of course my old mill and other factors may (will) give me trouble on holding that tight of a tolerance. I used the crankshaft and the old bearing to line the case up in my mill vise then I plan to use the boring head to cut it with. Measuring it will be the trick, I'm thinking of making some kind of gauge pin or something to creep up on the final size. Maybe I can just put the new bearing in some dry ice and use it as the gauge. I'm hoping to get some ideas and look forward to this project.

Brent

A bore gage would be the best to measure it I'd think, the pockets are deep enough for my run of the mill Mitutoyo unit, maybe borrow one?

I never had much luck boring to tenths on the mill with my old Criterion head, it's easier with the Wohlhaupter but still challenging. I'd do it on a lathe if Ihad to, much easier to hit your tolerance I think. I just bushed a 45 case that started to gall, maybe you could make a similar fixture? Wished I did my 91 VACs too before last weekend in Indy. :(


45 case.jpg


45 bushing.jpg


91 VAC.jpg
 
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A bore gage would be the best to measure it I'd think, the pockets are deep enough for my run of the mill Mitutoyo unit, maybe borrow one?

I never had much luck boring to tenths on the mill with my old Criterion head, it's easier with the Wohlhaupter but still challenging. I'd do it on a lathe if Ihad to, much easier to hit your tolerance I think. I just bushed a 45 case that started to gall, maybe you could make a similar fixture? Wished I did my 91 VACs too before last weekend in Indy. :(


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Terry, do you have a dimensioned drawing for a cmb 67 case? I like that fixture it would make the job easier.

I could go buy a new case but to me this kind of stuff makes the hobby more interesting and fun.

Brent
 
Best bet to fixture is a 0.001 slip fit to a mandrel and a drop of CA glue to fixture. Or a shrink fit to a steel mandrel. Heat to 350 to remove mandrel. I'd be careful removing 2mm from race. May weaken the case. If case breaks while running there won't be much that is salvageable. Have you considered using bearing retaining compound? Locate makes several. But go easy on it, a drop goes a long way.

Terry, is that a pcd tipped boring bar? PCD cuts aluminum like butter.
 
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