Engine Rebuilding help

[9VDXN]

Anyone competent enough to rebuild a OS91 SXH engine?

Piston and ring is a sure gonner...might need help to evaluate what else is needed for replacement.

[9VDXN]

Still no time to strip it up....
here's how badly blown...

Check out the piston head, viewed from the exhaust port.

[Brandon Chng]

i managedt o change some parts last time...
here's how...
take off the cylinder head and the backplate

from the backplate hole, push out the liner...

now take off the piston from bottom dead center at the backplate hole.

replace piston and ring VERY VERY carefully. the ring is EXTREMELY super brittle. so any force will crack it and you'd have to buy another $20 overpriced ring.

reinstall the piston and liner the same way as above, but make sure the liner is in the correct direction or else the exhaust port will chipp off the ring and you'd have to buy another $20 overpriced ring.

[9VDXN]

Thanks Brandon for the note......I guess stripping it up is not an issue, but it's the checking that I'm concerned with....

Dunno if the internal walls of the chamber is still good though....imagine having so many tiny bits of alu fragments scratching the whole internals of the engine...

Might end up buying a new OS91 C Spec.

[X34]

Check the conrod and piston pin for wear, replace if the conrod holes are elongated. Same goes for piston pin.

Both bearing should be change as well.

If the head is pitted it need replacement as well.

Before u buy all the parts check the price. It may not be worthwhile to overhaul it if too many parts are gone,

Don't worry about the chambers, would not affect that much.

[9VDXN]

thanks man....still in the mist of stripping up engine at this late hour...

darn fan still stuck on engine shaft.... dang...

Will continue tomm in my effort to break lose the stubborn locktite.


Looking at the condition and my lazyness, i think i'll get a new normal CSpec with any pumps...

[9VDXN]

Looking at the condition and my lazyness, i think i'll get a new normal CSpec with any pumps...

i meant WITHOUT...

Ethinger actually suggested YS91.....anyone tried it yet?

[genexis]

you should use a proper tool to hold the crankshaft in place when taking out the fan. Hope you have the tool, try not to use hte back of a plier as people on other forums have pointed out that the material underneath the rubber will still damage the engine.

[Art]

dix..get a new one...

YS91 should be good..but the gaskets will leak from time to time....

OS91 is a PITA to start

[9VDXN]

you should use a proper tool to hold the crankshaft in place when taking out the fan. Hope you have the tool, try not to use hte back of a plier as people on other forums have pointed out that the material underneath the rubber will still damage the engine.

Well, in the first place, the engine is already damaged, so it makes not much of a diff...

If there's a tool more proper than this original stupid plastic from OS, i'd like to try out coz i still can't get the fan unit out...heheheh..

[9VDXN]

whoops, no pic..

[9VDXN]

Anyway, stripped out the head block....this is how badly blown...

[9VDXN]

Still can't get the fan out....anyone got 'gu-luck' (cow strength) to help me try?

[yapjy]

Try using a really powerful hair dryer to heat up the fan assembly but take care not to melt the fan.

Looking at the pictures, it's not so bad. Try washing the internals with fuel.

YS 91 is much easier to start and mere mortals like us will not notice the difference in power. However, YS 91 is very particular about fuel. It is recommended to drink 30% nitro fuel. I'm not sure if there's any "gasket" problem. I don't use gasket and there's no leaking. In addition, you have to practise proper shut down and maintanence of the YS 91 as it is a well known problem that YS 91 rear bearings rust easier.

[Brandon Chng]

oh man!!!! the horrors and nightmares of the amount of red loctite we put on the fan is back to haunt us!!!