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Old 06-24-2012, 10:05 AM   #1
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Default Why do my main bearing fail

Dear fellows

I have two OS Speed 21XZ-R, and both have worn down the main bearings quite quick. Is this normal or do I do something wrong.

Engine was runned in by two tanks of fuel quick through the engine (3-4 min), 30 min rest with cool down, one tank through the engine idling at 80-85 degrees (15-20 min), 30 min rest with cool down, and the on the track. Two tanks with full throttle and fourstroke ... about half speed. 30 min rest with cool down, then normal drive for two to three times of two tanks with rest and cool down between. Leaning it form time to time to just about race setting. Going from about 80 to 95 degrees.

Then idle and LSN was ajusted correctly and runned in by race setting for 3-4 tanks of fuel and 95-105 degrees.

Both angines has worn out mainbearings - the first engine after about 3-3 liter of fuel and the second engine at about 6 liter fuel. Conrod chaged as well.

Best wishes; Jens
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Old 06-24-2012, 05:08 PM   #2
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Originally Posted by jensroland View Post
Dear fellows

I have two OS Speed 21XZ-R, and both have worn down the main bearings quite quick. Is this normal or do I do something wrong.

Engine was runned in by two tanks of fuel quick through the engine (3-4 min), 30 min rest with cool down, one tank through the engine idling at 80-85 degrees (15-20 min), 30 min rest with cool down, and the on the track. Two tanks with full throttle and fourstroke ... about half speed. 30 min rest with cool down, then normal drive for two to three times of two tanks with rest and cool down between. Leaning it form time to time to just about race setting. Going from about 80 to 95 degrees.

Then idle and LSN was ajusted correctly and runned in by race setting for 3-4 tanks of fuel and 95-105 degrees.

Both angines has worn out mainbearings - the first engine after about 3-3 liter of fuel and the second engine at about 6 liter fuel. Conrod chaged as well.

Best wishes; Jens
It's a VERY good chance it is your clutch.
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Old 06-24-2012, 05:21 PM   #3
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OS makes great motors but the bearings they use don't last forever. Replace them with a good aftermarket ceramic like TKO.
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Old 06-25-2012, 12:45 PM   #4
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I will change the bearings to ACER ceramic engine bearings since I have a couple af sets of these.

What specific is it about the clutch that stress the main bearing ... clutch engage too hard? clutch engage at too many revs? clutch slips? clutch engage too early? or something else ... mechanical issues?

Best wishes; Jens

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It's a VERY good chance it is your clutch.
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Old 06-25-2012, 01:33 PM   #5
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I will change the bearings to ACER ceramic engine bearings since I have a couple af sets of these.

What specific is it about the clutch that stress the main bearing ... clutch engage too hard? clutch engage at too many revs? clutch slips? clutch engage too early? or something else ... mechanical issues?

Best wishes; Jens
Slipping can make the clutch over heat and destroy the rear bearing.
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Old 06-25-2012, 01:39 PM   #6
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Thanks a lot for the replyes ... valuable information

Best wishes; Jens
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Old 06-25-2012, 07:15 PM   #7
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same prob =(
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Old 06-30-2012, 09:23 PM   #8
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I think because of the rather tough breakin process, most of the internals are under stress.
This is why typically alot of racers automatically change rear bearing and the conrod after a few litres of fuel. its also a chance to have a good look inside engine.
With the price of most bearings today and the great tools, its an easy job to do even at track. I'm using the reds motor bearing (swiss made).

Proper warm up, not revving too early or over revving, fuel quality, oil content, type of oil, time between runs (weekly/ monthly etc) plus other factors all contribute.
Lastly i could hear the start of the dreaded bearing noise on start up, so changed it quick smart. You can also hear when its going off during a run, funny when you mention to people during a run that there bearing sounds to be off, i get comments like "it always sounds like that! WRONG

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Old 07-03-2012, 12:28 AM   #9
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Dear Davo

Thanks for the information, wich make good sence. I have heard the bearing bee off/worn out when the engine was at idling, and at driving temperature.

This is my first season in nitro-racing, so theres a lot to learn. I just now getting the know-how to set-up the clutch, so I think the reason most likely is, that my clutch has bee set too soft up in the beginning when breaking in the engine, and that has caused the stress on the mainbearing.

Thanks and best wishes; Jens
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Old 07-03-2012, 08:51 PM   #10
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If replace with ceramic brgs, It probably ruin in quicker than the steel brgs.
I have to ask you, What is the measurement of engine end-play or Clutch end-play. Breaking in an engine it would running rich, rich so you cant blame on non lubrication. What fuel you useing. If engine are new, I cant blame on warped engine block. If second hand another story. Another possibility bent crank.

Think its error on end-play set-up. Average life of engine are 7 - 9 Gallons.
5 gallons I rebiuld it.
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Old 07-04-2012, 02:27 AM   #11
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I have the same engine and I found something strange when i put the flywheel. With other engines by placing the cone on the crankshaft and then tighten the flywheel, it has a bit endplay (bearing endplay). But with this engine is not true. When i pull the flywheel, it pushes the crankshaft cone and leaves not bearing endplay. For this reason I think that the bearings do not work properly and causes excessive wear. (The same occurs if the axis of a wheel put too shims)
To test, I tried to leave 1mm (excessive) clearance between the bearing of the engine and the cone, but to tighten the flywheel, the cone slips and tightens the cone against the bearing. I think this is not good.
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Old 07-04-2012, 04:58 AM   #12
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Originally Posted by Valerio View Post
I have the same engine and I found something strange when i put the flywheel. With other engines by placing the cone on the crankshaft and then tighten the flywheel, it has a bit endplay (bearing endplay). But with this engine is not true. When i pull the flywheel, it pushes the crankshaft cone and leaves not bearing endplay. For this reason I think that the bearings do not work properly and causes excessive wear. (The same occurs if the axis of a wheel put too shims)
To test, I tried to leave 1mm (excessive) clearance between the bearing of the engine and the cone, but to tighten the flywheel, the cone slips and tightens the cone against the bearing. I think this is not good.
Does cone and the flywheel have the same correct angle and not touch the nut??
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Old 07-04-2012, 05:35 AM   #13
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Yes, it is the same as with the cone that comes with the engine, as with the cone that comes with the clutch.
The same cone in a crankshaft nova works perfectly. Perhaps the treatment of the O.S. crankshaft makes its surface is more slippery...
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Old 07-04-2012, 02:10 PM   #14
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I had now replaced with ACER ceramic bearings, both main and front, even the front bearing was in fine shape. have saved it for spareuse.

Do ceramic bearings have shorter lifetime than steel ?

Endplay is 0,1 mm, and the clutcbearings are fine with no slup. Fuel are MLC 25%, so its top-notch fuel. several others are running the same fuel from the same batch and have no problems. Cranks are fine and 100% straight.

I think the mainbearing has ruined because I have driven with a too soft clutch set-up wich have caused vibrations in the clutch, transferred to the mainbearing, and that has stessed it too much.

When you rebuild it is this with piston and sleeve, bearings, conrod etc ?

I tend to shift the conrod every 1-2 gallons, and bearings every 3-4 gallons and buy a new engine after its worn out ... hopefully after 6 gallons or more

Best wishes; Jens

Quote:
Originally Posted by Geezatec View Post
If replace with ceramic brgs, It probably ruin in quicker than the steel brgs.
I have to ask you, What is the measurement of engine end-play or Clutch end-play. Breaking in an engine it would running rich, rich so you cant blame on non lubrication. What fuel you useing. If engine are new, I cant blame on warped engine block. If second hand another story. Another possibility bent crank.

Think its error on end-play set-up. Average life of engine are 7 - 9 Gallons.
5 gallons I rebiuld it.
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Old 07-04-2012, 07:29 PM   #15
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You said it yourself. Wearing brgs.. Vibration, Balance of thw clutch & flywheel.
replace flywheel & cluch system.
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