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Engine basics => Engine set up tips => Topic started by: frank mccune on October 13, 2020, 06:44:40 AM
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Hell All:
I am attempting to replace the bearings in a HP .40 SS engine and would like to have input.
What grade should I purchase?
Should I purchase a shielded bearing for the front.
What would be a good choice for retainer material?
Where is a good choice to purchase these rings? There is a bearing supply store near me.
Suggestions/Comments
Tia,
Frank
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Hell All:
I am attempting to replace the bearings in a HP .40 SS engine and would like to have input.
What grade should I purchase?
Should I purchase a shielded bearing for the front.
What would be a good choice for retainer material?
Where is a good choice to purchase these rings? There is a bearing supply store near me.
I wouldn't attempt to mastermind anything, just get the original parts - in the extremely unlikely event that your current bearings are bad.
https://www.mecoa.biz/shopexd.asp?id=411
https://www.mecoa.biz/shopexd.asp?id=412
Both show in stock.
Brett
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Hello Buck:
WOW! That was a fast reply! Thanks bigly.
I think that I can say that the rear bearing is more than likely to be need replaced. One half of one of the retainer is missing along with two balls are missing. The front bearing is very dark in color so I will also replace it.
I have run this engine for any flights prior to discovering the bad bearing. I finally noticed a bit of noise when the shaft was turned back and forth near bdc. It ran in the plane like a champ with no problems. ???
Be well,
Frank
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I have run this engine for any flights prior to discovering the bad bearing. I finally noticed a bit of noise when the shaft was turned back and forth near bdc. It ran in the plane like a champ with no problems.
One wonders how the parts got out the exhaust without wrecking something.
Brett
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Hello:
Thanks for the replies! I have new bearings on their way to me as I type this post.
It will be interesting to see if there is a marked difference in performance when the rear bearing is complete. Lol This engine turned 13,100 rpm on a wide wooden 10-6 prop in the past.
Be well,
Frank
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It has to be a million to one that a rear bearing shedded parts while running and they exhausted without extensive engine damage. You may want to play the lottery.
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Hello:
An update about the bearing replacement on the HP .40.
I called Bocca Bearing in Fla. I spoke with a female who answered the phone and she knew all about my needs! She checked to determine if they had the bearings in stock, they did and they would be be in the mail that afternoon. She also said that they would remove one seal from the front bearing free of charge. I did not suggest this mod but she knew this was the thing to do. When I told her what bearings I needed, she said, “O, for a HP .40.” She impressed me!
The bearings arrived in less than a week and now, all is well.
Great service!
Stay well,
Frank
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Make sure you install a rear bearing with a phenolic cage, and make sure you install the front bearing ALL THE WAY IN, many do not, this will KILL the bearing when you tighten down the prop, YOu also will want to make sure the rubber seal is facing frontwards.
Randy
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Thanks for the replies:
Why are phenolic bearings recommended?
Tia,
Frank
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Frank,
A phenolic ball cage (also called a ball separator, because that is what it is in there for) is a good overall choice. Separates the balls, has reasonably low friction, holds oil well, and withstands high speeds at the material temperature. The phenolic does not fatigue like a stamped steel ball cage will. The wear on the balls should be less with phenolic than with a steel cage. Less noisy. And so on. It is a well-proven component in this application.
I might mention what the ball separator is there for. When you load or stack a bearing, you place both races on the bench and pinch them on one side. With the large gap between the races on one side, you can now start feeding balls into the groove. The more balls you try to put in, the more centered the two races will become. When you can't get another ball in without forcing things you have arrived at a "full complement" bearing. If you want more balls, you're going to need a split ball bearing. Not something most applications want or need. Now you need a ball separator to keep the balls spaced out so they don't rub on each other, and so the rings will stay concentric. Note that the balls roll inside the bearing and if they touched they would scuff because their surfaces are going in opposite directions. To install a one-piece cage, you space out the balls evenly, and snap the cage into the clearance space and over the balls. Done.
There are lots of variations and materials used in specialty bearings. What we need/use for engines is pretty standard stuff.
Dave
PS--It would likely be helpful if you read this prior thread. Some questions covered that you probably have asked, or might want to ask....
https://stunthanger.com/smf/engine-set-up-tips/engine-ball-bearing-high-grade-replacement-suppliers/msg572973/#msg572973
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Since I'm commenting on this thread, let me suggest the reason Randy has cautioned us about properly seating the front bearing lest we ruin it when we tighten the prop is due to Brinelling.
The engine should be set up by the manufacturer to create proper axial fits using close tolerancing of all of the pieces: Case (shoulder to shoulder); crank (web fillet to front bearing seat); main bearing (width as measured across the two races in preloaded condition); and, the front bearing (width s measured in preloaded condition).
The bearings in your engine are back-to-back or "DB" preloaded. This tells you the contact angle direction. This orientation is used for higher moment stiffness (can handle the pounding of the rod better without the crank tipping in the bore) but it does not like misalignment. If you change the internal clearance of the bearing, because all of the other geometry we've mentioned here is fixed (ie. machined in), you've changed the preload. A lot of factors here are interrelated.
If you fail to fully seat the bearings, then cranking down tight on the prop nut will cause a large axial load to be transmitted thru the balls while things try to draw up. There are fewer balls (and sometimes smaller balls) in the front bearing, and it also has a smaller radius of curvature, so you will damage it first. This is called Brinelling. You are causing surface damage (and subsurface damage) to the balls. Making flat spots in the balls, in colloquial terminology. Nothing says in aggressive instances that the main bearing won't be damaged as well.
Perhaps the most common reason that a bearing is not fully seated is that the case was not hot enough prior to installation. A secondary reason might be that a proper tool that pressed only on the outer race was not used and the installer "was trying to be careful." But the worst is if the race gets cocked in the bore due to an improper setup, potentially galling the bore, creating a burr, etc. I have seen this with bearings installed using a hand-held tool and hammer. It could also happen if your press has a crooked armature or if your daisy wheel isn't seated. This later situation almost guarantees bearing damage unless you are suspicious enough about the feel after it all cools off to take it back apart before wrenching on the crank. In general when properly heated, the bearing should drop all the way to the shoulder without the need for hammers, presses, etc. If they don't, realize that you are on that slippery slope towards eventual damage.
I might also note that in some instances the preload is modified by the tuner when either the parts are non-standard (bearings) or something about the parts is not dimensionally correct. I bought one speed engine that was like this. Since I don't have the drawings, and many of the parts had been "reworked," it would only be an educated guess why it needed bearing shims to get the axial play back to a reasonable amount.
Hopefully I have not misinterpreted Randy's comment. In any event, any errors in the above description are my own....
Dave
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Hi Dave:
Thanks for the reply.
Stay well,
Frank
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Phenolic cages are old tech, you can still get them but, the latest bearings use polymite plastic retainers. Don't get them confused, they are different.
Motorman 8)
Propably this goes to "Princess & pea" or "Lipstick for Pigs" -level, but the ultimate cage material is phenolic impregnated *rolled* cotton, more accurately Tufnol RLF1.
In stunt it's irrelevant but in higher speed the injection molded polymer cages tend to start rubbing due to centrifugal forces.
Tufnol also absorbs oil and provides kind of emergency lubrication when needed.
I do cages for F2A engines, and also to front bearing of our stunt engine. Because of rear intake, the lubrication of front bearing *may* sometimes be compromised. L
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Phenolic cages are old tech, you can still get them but, the latest bearings use polymite plastic retainers. Don't get them confused, they are different.
Motorman 8)
Actually I was telling him to not use the stamped steel, and to use Phenolic Plastic, YES phenolic is also a "plastic"
(Phenolic plastic (phenol-aldehyde resin) is considered to be the foundation of the plastic molding industry. ... Most applications of phenolic plastic materials benefit from a thermosetting reaction created by a one or two-stage process. Phenol and formaldehyde are the two major components of phenolic plastic.)
Either cages are OK, the ones you talked about, or any of the ceramics, The POINT was to stay away from the steel cage
Randy