OS .91 fs bearing replacement- Advice?
02-24-2005, 01:01 AM
#1
OS .91 fs bearing replacement- Advice?
I need to replace the bearings in my OS .91 FS Surpass engine. I have replaced bearings in 2-strokes before but never a 4-banger. Are there any secrets or 'tricks' to worry about or is it pretty straight-forward? Do I have to worry about the orientation of the crankshaft to the valve mechanisms? Or does it just work out when you put the crank back in?
Or should I get one of the 'old-timers' in the club to do it for me?[
]
Also, should I bench-run it after the repair? Or just stick it back in the plane?
Gotta get ready for summer![8D]
[8D]
Or should I get one of the 'old-timers' in the club to do it for me?[
]Also, should I bench-run it after the repair? Or just stick it back in the plane?
Gotta get ready for summer![8D]
[8D]
02-24-2005, 01:15 AM
#2
RE: OS .91 fs bearing replacement- Advice?
First remove the cam, followers, pushrods, and rocker arm stand.
Then it is the same as a two stroke.
When you get the engine back up to this point, One of us can talk you through it.
Basically to time the cam. Get the piston at top dead center. There is a mark on the drive flange that aligns with the seam in the case.
Drop your cam in with the dot in line with the cam follers. Or the dot right behind where the exhaust follower would be. The gears are spiral cut and the cam will rotate as it seats. So lead the position a little bit.
Set the valves at .0015" -- .004" we can talk you through this too.
In the 91 Surpass engines, the rear bearing is a MR6002 and the front bearing is a R6. (from Boca Bearing)
Enjoy,
Jim
Then it is the same as a two stroke.
When you get the engine back up to this point, One of us can talk you through it.
Basically to time the cam. Get the piston at top dead center. There is a mark on the drive flange that aligns with the seam in the case.
Drop your cam in with the dot in line with the cam follers. Or the dot right behind where the exhaust follower would be. The gears are spiral cut and the cam will rotate as it seats. So lead the position a little bit.
Set the valves at .0015" -- .004" we can talk you through this too.
In the 91 Surpass engines, the rear bearing is a MR6002 and the front bearing is a R6. (from Boca Bearing)
Enjoy,
Jim
02-24-2005, 01:15 AM
#3
Senior Member
RE: OS .91 fs bearing replacement- Advice?
Ho,
You are asking the right questions...
Of course you have to re-time the valve-train. There is no point in valves that open and close, independently of the piston rising and descending.
There are timing mark(s) (I don't know what they look like in the OS FS) that have to be aligned, with the piston at TDC. If non are found, the valves should both be slightly open (the overlap period), with the piston at TDC.
This coincides with the ending of the exhaust stage and the beginning of the intake stage, which must happen when the piston is at TDC.
I guess there are enough people here, who can tell you what to look for in your specific engine.
You are asking the right questions...
Of course you have to re-time the valve-train. There is no point in valves that open and close, independently of the piston rising and descending.
There are timing mark(s) (I don't know what they look like in the OS FS) that have to be aligned, with the piston at TDC. If non are found, the valves should both be slightly open (the overlap period), with the piston at TDC.
This coincides with the ending of the exhaust stage and the beginning of the intake stage, which must happen when the piston is at TDC.
I guess there are enough people here, who can tell you what to look for in your specific engine.
