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Post by arrudings on Apr 30, 2021 10:11:24 GMT -5
Hey guys!
I'm here just to ask you a question and expect receiving advice from you. My 2017 2stroke Peugeot Kisbee AC has been whining and I need to replace its crankshaft bearings. I'm looking at the SKF bearings, but don't know if I should buy the polimer cage or the steel cage ones. Can you guys help me with the pros and cons? Can't find info about this anywhere.
Thank You from the Azores.
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Post by captincvmn on Apr 30, 2021 11:22:58 GMT -5
If it were me, cost being equal I’d take the steel cage bearing. Simply because it’s tougher and they’ve been making stew cage bearings a long time. As to which is actually better? 🤷♂️
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Post by aeroxbud on Apr 30, 2021 16:59:32 GMT -5
Stage 6 do both, here is what they say:
Stage6 offers you these high quality crankshaft bearing kits in 2 versions, with metal cage or with polymer cage. Both types are rated for use up to 20,000rpm with C4 clearance and are suitable for use with the highest end cylinder kits on the market.
The version with polymer plastics cage has higher elasticity and a reduced friction coefficient as compared to the metal ball cage, the metal cage bearing is more resistant than the polymer version, but also generates more friction and hence more heat, which results in a shorter life expectancy.
The reason I have always fitted metal cage bearings is they are probably easier to fit. Metal shrinking more when it's very cold.
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Post by arrudings on May 1, 2021 14:01:15 GMT -5
Thank you for your POVs and opinions!  |
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Post by Lucass2T on May 3, 2021 8:37:06 GMT -5
I've always been told that polymer cage bearings are better suited for performance engines.
Steel if its just a stocker.
Steel is also more foregiving with heat. Polymer can start melting without any signs. Steel will need more heat and will start to discolor first before it get distorted.
Personally I always stick to the rules above. Steel for stock engines and polymer for anything performance oriented.
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Post by ThaiGyro on May 3, 2021 18:24:45 GMT -5
I love these type of threads. As a former racer, builder, tuner...I focus on bearing APEC numbers. Not "exactly" the same beast.
In our engine builds of say...11,000 plus rpm expectancy, APEC 4+ is well worth the cost.
If you do not expect near that? APEC 3 is quite OK, 4 is better, if you are close in rpm. (conservative)
Your question of steel versus not? It is buried in the rating. Failure is all heat related versus time versus rpm in OMG rpm land. Understand OMG for your engine...I run cheap'os in engines 10,000 or less. (properly maintained)
My three cents/pence/peso/bitcoins
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Post by repherence2 on May 6, 2021 14:08:09 GMT -5
I love these type of threads. As a former racer, builder, tuner...I focus on bearing APEC numbers. Not "exactly" the same beast. In our engine builds of say...11,000 plus rpm expectancy, APEC 4+ is well worth the cost. If you do not expect near that? APEC 3 is quite OK, 4 is better, if you are close in rpm. (conservative) Your question of steel versus not? It is buried in the rating. Failure is all heat related versus time versus rpm in OMG rpm land. Understand OMG for your engine...I run cheap'os in engines 10,000 or less. (properly maintained) My three cents/pence/peso/bitcoins Have you ever used ceramic or hybrid ceramic bearings? |
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Post by Lucass2T on May 7, 2021 16:30:23 GMT -5
I love these type of threads. As a former racer, builder, tuner...I focus on bearing APEC numbers. Not "exactly" the same beast. In our engine builds of say...11,000 plus rpm expectancy, APEC 4+ is well worth the cost. If you do not expect near that? APEC 3 is quite OK, 4 is better, if you are close in rpm. (conservative) Your question of steel versus not? It is buried in the rating. Failure is all heat related versus time versus rpm in OMG rpm land. Understand OMG for your engine...I run cheap'os in engines 10,000 or less. (properly maintained) My three cents/pence/peso/bitcoins Have you ever used ceramic or hybrid ceramic bearings? Some time ago I've read into ceramic bearings but end of the story i've learned they're not suitable for engine applications. Maybe wheel bearings but nothing engine related. I think they're used in super high end road racing bicycles. Please excuse me the explanation but this is what I remember very clear. Ceramic bearings are awesome, expensive but awesome. But not for engines. Iam curious what your findings are! |
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Post by repherence2 on May 7, 2021 17:21:10 GMT -5
Lucass2t, i just remember when they came out with turbochargers with silicon nitride ceramic bearings. All i know is that ceramic bearings came about from the aerospace industry for turbo pumps on rocket engines.
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Post by Lucass2T on May 8, 2021 2:31:01 GMT -5
It's rocket science, nothing for us simple scooter folks  |
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Post by ThaiGyro on May 10, 2021 14:43:51 GMT -5
Hi reference2 and Lucass2T...yes, we have used them. may have posted some info about a build we worked on pre-Covid. They were hybrid with stainless cages and silicon nitride balls. ABEC 5.
Most of my current road race friends use them in their engines, as well as wheel bearings. Very robust compared to the older ones. One of our test engines in Thailand has a set. (Crank, counter balancer and tranny.) We souces them from Lilly, which is Chinese, but high end and half the cost.
They were worth the money for our efforts over there. Road race and super-moto bikes. The CBR 300 engine had 7 bearings in total at ~$290.
The Thai scooter drag guys use them if rich enough. Fun to watch!!
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Post by repherence2 on May 10, 2021 15:56:48 GMT -5
Hi reference2 and Lucass2T...yes, we have used them. may have posted some info about a build we worked on pre-Covid. They were hybrid with stainless cages and silicon nitride balls. ABEC 5.
Most of my current road race friends use them in their engines, as well as wheel bearings. Very robust compared to the older ones. One of our test engines in Thailand has a set. (Crank, counter balancer and tranny.) We souces them from Lilly, which is Chinese, but high end and half the cost.
They were worth the money for our efforts over there. Road race and super-moto bikes. The CBR 300 engine had 7 bearings in total at ~$290.
The Thai scooter drag guys use them if rich enough. Fun to watch!!I had a feeling that you probably had experience with ceramic bearings. That's why i asked.  |
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Post by ThaiGyro on May 15, 2021 11:16:51 GMT -5
Much discussion about them these days. Their reputation in the '70's and early '80,s not so great. The use in street cars/trucks today is quite common. Near anything turbo'd or supercharged has them.
However, if doing a torque motor, there is really not much to gain, except a lighter wallet. I still want to do a Honda GX single with them. We were trying to do a small bore, 4T, FI outboard setup, but never got that far. For economy more than power.
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Post by wesolydzik on Jun 1, 2021 11:39:44 GMT -5
There is also one thing to keep in mind. In case the steel cage fails, it will ruin your cylinder, piston and head. It did happen to me once. Since than I always fit in SKF bearings with a plastic cage. Havent had a problem with them.
Depending on how you intend to install your bearings onto a crank, I would advise to be careful not to overheat the polymer cage bearings in order to fit them on the crank. I would not use a torch or heat gun to heat the bearings. What I do instead is put a bearing in a hot (about 150 deg. Celcius) bath of oil, and "cook it" for about a minute at that temp. Than, take the bearing out of the bath and drop it onto a well frozen crank. Works really well.
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