RCU Forums - os 91

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- - os 91 (https://www.rcuniverse.com/forum/glow-engines-114/8288160-os-91-a.html)

do you have to have a pully to pull the bearing out of a os 91 4 stroke?

NO

If you force the bearings in or out of your engine, you not only risk ruining the bearing, but ruining the surface that it fits into also.

http://www.youtube.com/watch?v=TuzEco3EDUM

not sure if there are any pullys readily available to pull the rear bearing? I heaten up the crankcase with an air heat gun and then use a piece of aluminum pipe to push/force the old bearings out. Start with the front bearing.

The front prop drive hub will slide off and there is a Woodruff key that drives the hub that you don't want to loose. The crank will slide out

The bearing - you heat up the case with a Monokote gun and shake the rear bearing out by slamming the case against a board while hot

The front bearing you must stick a dowel up through the case from the rear and against the front bearing. Holding the hot case, slam the dowel against the board to knock out the front bearing

Putting the crank case in the oven at 300 degrees for 10 minutes heats the block evenly. Whether it make a difference versus the heatgun I can't say but I replaced the bearings in an OS .91 fs 2 months ago that way and they came out with very little effort.

When installing the new bearings, reheat block and freeze bearings, they pretty much fall in that way and when everything cools a little, you can start putting the crank back in.

thanks alot for info

By the way, where are you getting your bearings? Here are bearings just as good as the OS brand at 1/4 the price. This is what I put in th OS 91 fs I rebuilt and they work fine.

http://www.rc-bearings.com/catalog/p...05034e4df41254

If you really want the best bearings, the ceramic bearings are supposed to be better but the do cost more but are still cheaper than the stock OS steel bearings.

do you have to set the timming on a90fs4stroke if you chang the bearing in it?

Yes. The cam has to come out for front or rear bearing replacement. It is easy to set. There is a dimple on the cam gear (inside side of gear, you can't see the dimple when the cam is installed IIRC) that goes straight up when the piston is at TDC. If you even get it off 1 tooth, it won't run right. Just point the dimple straight up and you should be set. If you want to make it easy on yourself, make your own mark on the outside of the cam gear and case while the cam is installed and piston is at TDC. Then line up the marks when re- assembling engine.

Quote:

ORIGINAL: GhostRider32

Yes. The cam has to come out for front or rear bearing replacement. It is easy to set. There is a dimple on the cam gear (inside side of gear, you can't see the dimple when the cam is installed IIRC) that goes straight up when the piston is at TDC. If you even get it off 1 tooth, it won't run right. Just point the dimple straight up and you should be set. If you want to make it easy on yourself, make your own mark on the outside of the cam gear and case while the cam is installed and piston is at TDC. Then line up the marks when re- assembling engine.

The timing for the cam is not straight up! The dot that is visible from the outside when the cam cover and exhaust cam follower are removed, goes in line with the cam followers/ push rods as in the picture. On the OS 91, there is a + mark on the prop drive hub that indicates crankshaft top dead center when aligned with the crankcase seam behind the hub. The gears on the cam are spiral and the cam twists as it is inserted so you will have to allow for the twist and lead the position a little.
http://image2-6.rcuniverse.com/e1/ga.../lg-163571.jpg
http://origin-images.rcuniverse.com/.../lg-163571.jpg

Glad someone caught that.

how to take bearing out of zdz80rv

I think they service the ZDZ line at troybuilt models now.