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Open or sealed case/crankshaft bearings.

8K views 14 replies 7 participants last post by  BeatsMe 
#1 ·
Hi guys,

Well the urge to pull the motor apart and take a die grinder to it is just too much. I want to have a bit of a play with the ports and just do a general freshen up of the bottom end too. Nothing new for me as dad and I did this many times with my old pocket bikes and even chainsaws. We always got an improvement out of them. Sometimes only a little bit and sometimes a lot depending on the amount of material that could be removed.
Anyway most of the engines I messed with had sealed bearings but I remember couple also being open. Also noticed that the CY/Zenoah engines also have both choices. Which would be better and why? Since the engine gets it's lube from the fuel/oil mixture and that passes through the case then it seems reasonable to me that the open bearings would get plenty of lube. With sealed ones they will basically rely on lubrication that has been put inside them at the time of manufacture. That worries me a little as the grease will eventually be broken down or even slowly leak out. Really can't decide but I am leaning towards the open ones. Could you guys sway me in either direction.
 
#2 ·
I personally say open bearings, for the reasons that you stated yourself, and if running the third bearing as well then that one should be sealed.
 
#4 ·
Awesome. Thanks for confirming my thoughts guys. Going to place another order from DDM tonight and hopefully over the Easter break I will get something together. Reason why I really want to do it is I also noticed that the head gasket is weeping. It isn't blown out as the motor rips along but I doubt it will last much longer. Might as well do a little fiddling with the head while I have everything apart and why not freshen up the bearings and seals while I am there. Thanks gents.
 
#5 ·
dont bother getting ya bearings from ddm. go buy good quality bearings from a good bearing shop. half the price and just as good if not better.
 
#6 ·
That means I will have to get my arse off the chair and drive to a bearing shop. You have no idea how lazy I am Matt. Anyway it doesn't matter mate. Only a few bucks and it's just a 23cc mill. If I was building something serious than I would do as you suggest. Just looking forward to doing it.
 
#9 ·
HAHAHA I know what ya mean. When ya gunna bring it out my way n give it a run. I still need to play around with mine. Might have a crack at it tomoz.
 
#11 ·
Here, I will throw a spanner in the works. Open or Closed? It depends, but always use what the manufacturer recommends for that engine, if they say closed, use closed. My personal view is go closed, if you have a proper rebuild cycle on your engine you have no worries about the grease deteriorating leading to bearing failure, you know your bearings are properly lubed and are less likely to be a failure point at any time. Also, if you manage to do something like put a ring over a port, or cook a piston, those bearings being closed are not going to fail also because of metal flakes getting in there, or run out of fuel you are not going to cause damage because of lack of lube or because your tune goes out and your running lean at high revs and dont pick up on it in time.

On our race bikes, rings, cylinders honed and pistons if required were done every 6 months, bearings done every 12 months, and apart from the time i broke a rod, i never had an engine fail because of one of those things. Everything has its pro's and cons, even the open bearings. :)
 
#12 ·
Having recently destroyed a near new G290 my advice is thus...the 2 bearings closest tot he crank use the good quality japanese ones. The 3rd bearing closest to the clutch housing be it sealed or open, pull it out and toss it in the spares bin then fit a good quality seal, genuine Zenoah or the more fancy Alannach Zero Drag seal.

My reasons are thus...running the G290 out on dusty dry track with an open clutch carrier there was enough crankcase vacuum to suck very fine dust into the bearings as theres enough clearance on the crankshaft to allow talc like dust to get sucked in. This is a well known modification that the SSME guys run due the track getting dusty when drying out.

Luckilly I got away with replacing the 2 bearings with 1 bearing and a seal, no other damage luckilly.
 
#13 ·
Have they improved the zero drag seal. I remember reading something about them AGES (as in maybe a few years ago now) ago that they were the fault of some failures on dusty conditions as they dont seal 100% either.

I know most boats run them as mine do as there isnt much dirt out on the water lol.

Also BB I am working ALL of easter. Starting most likely the monday before and working right through easter weekened to the following weds or thurs. Have a BIG shutdown at a factory and 16mtr switchboard to be installed and wired within a VERY slim time frame. Maybe the weekend after or something. Not sure. My family want to catch up too so not sure when I will be free.
 
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