Magnum 91 XL rebuild problem - How do I remove the conrod? - RC Groups
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Mar 06, 2012, 12:48 PM
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Magnum 91 XL rebuild problem - How do I remove the conrod?

I am in the process of rebuilding a four stroke engine. I'm attempting to remove the con-rod from my Magnum 91 XL 4 stroke. It moves about a third of the way off but seams to not want to move any further. there are two holes at the base of the rod at about 5 and 7 o'clock. I don't know what these are for, and they do not appear to be housing any set screws.

Any ideas?
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Mar 06, 2012, 12:52 PM
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gkamysz's Avatar
Remove the sleeve if you haven't already. The crank pin may need to be positioned about 30-60 down from TDC if there is a groove in the crankcase. If it still doesn't come out, the rod needs to be pushed aft in the piston.

Mar 06, 2012, 01:11 PM
If I'm not mistaken, the wrist pin needs to come out in order to remove the conrod.
You will have to remove the cylinder and place the teflon bushing of the wristpin on the crankcase hole in the back. remove that bushing with a thin pointy screw, being carefull not to damage it, then do the same to pull the wristpin out through that hole.

Good luck!
Mar 06, 2012, 02:15 PM
Registered User
I'm trying to remove the connecting rod from the crank. I can't get to the piston without removing it, and the connecting rod prevents this. There is very little play at the top of the connecting rod but I did pull it as far aft as i can. Still no good.
Mar 06, 2012, 02:32 PM
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gkamysz's Avatar
Right, as eluded to above, there is a hole for the piston pin to be removed in the rear of the crankcase. The OS FS-91 does not have this hole.

OS FS-52 Four Stroke RC Glow Engine Disassembly (9 min 26 sec)

Mar 06, 2012, 02:59 PM
But the magnum has, Greg.

Good ideia on posting your disassembly video, I'd forgetten about it ;-)
Mar 06, 2012, 03:02 PM
Registered User

I removed the sleeve and was able to remove the connecting rod. I now have to remove the crank shaft. Time to heat the oven or go buy a torch. This is fun.
Mar 06, 2012, 03:05 PM
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gkamysz's Avatar
Yes, it does. I forgot.

Hmm, so did you need to pull the wrist pin through the hole?
Mar 06, 2012, 05:42 PM
Registered User
First the two holes in the bottom of the conrod are lubrication holes.

Second to remove the crankshaft you will have to remove the cam first. It is driven by helical gears on the crankshaft. No amount of heating will get it out until the cam is removed. Once it is removed then the crankshaft will come out. That is the time to heat it to remove the main bearing from the crankcase (tight fit). Sometimes just a smart rap with a block of wood over the prop end of the crankshaft will get it out. Others it will take heat to get it out.
Mar 06, 2012, 06:00 PM
Registered User
I removed the cam before I tried to remove the crank shaft. Figured that one out for myself ;>) The videos I viewed were great, although not for a 4 stroke. I now have all bearings out and soaking in fuel. The Main bearing appears to be fairly rusty. The engine has only been run for a lilttle less than 18 months. I use after run oil after each day's flying. Not sure why the bearings look that bad, but they do.

RC-Bearings has replacement bearings for the Magnum. Putting everything back together should be fairly simple.

Thanks for the advice.

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