OS40FS

[Engine Doctor]

The link on piston pin removal is ok providing the pin is not siezed /gummed into the piston. Lots of heat , plus gas etc needed in those cases. Good luck .

PS a soak of all the bits in cellulose thinners will remove any Castor oil . It doesn't dissolve it if its gummed but pickles it a bit like putting cellulose paint on top of enamel and it then brushes off easily.

[Engine Doctor]

Posted by Doctor Chinnery on 05/08/2020 11:15:26:

Shame there don't appear to be Hayes or For Dummies publications on the subject.

That would be a popular publication but with Haynes manuals current quality probably not that good ,JMO.

[Jon H]

Posted by Doctor Chinnery on 05/08/2020 11:15:26:

Posted by Jon - Laser Engines on 03/08/2020 12:48:50:

Its a pretty simple job. backplate and head off, cam cover plate off, liner out, mark position then piston/conrod out (can be a fiddle), cam shaft out (photo position first), crank out with a few hammer taps, and then its time to toast it up with a heat gun or similar to get the bearings on the move. One they are out its the same job but backwards!

Sounds easy if you've done it a few/dozen/hundred times but to an engineering virgin: intimidating is the term that comes to mind, 'specially if despite much marking and photographing I get the piston & liner or worse (probably) the cam shaft wrongly aligned when putting it all back together.

Shame there don't appear to be Hayes or For Dummies publications on the subject.

I understand your trepidation but once you get into it they are simple creatures so if you get something wrong its rarely terminal and you can just take it to bits again and fix it. Your example of the cam (which can be a fiddle with its helical worm drive), if its wrong you will know immediately as it will not align with the photo you took in the first instance. To be totally sure, turn the engine over very gently the first time round so that if there is a problem and a valve donks the piston there is no load on it. Dont just go ham and crank it with a leccy starter!

And as much as i dont like to disagree with ED as we are normally on the same page im not a fan of using cellulose in engines.

 

Edited By Jon - Laser Engines on 05/08/2020 12:34:33

[Alistair Taylor]

If it's any help - fairy powerspray is a great remover of gummed up castor - but tends to dull the silver paint on the outside of model engines. Switch cleaner, sold by Maplin (online only) is also great for loosening gummed up castor.

This a great www for exploded views of most engines;

sceptreflight

I've taken apart and refurbished a few OS two and four strokes. Key tips that may help avoid a boo-boo;

- The cam has a mark / indentation to assist with getting the timing right marked on the outer face, i.e. there is a right and wrong way to reinsert it!

- There is a head bolt concealed under the rocker assembly you can't reach until the assembly is removed

- Use wooden rods / dowels to remove bearings to avoid damaging the engine case

- An appropriately sized socket is really helpful for reinstalling bearings (they are a tight push fit)

- To get the timing right, you need to hold the piston at TDC - you can make a tool to do this by finding a bit of broom handle / disk of wood that's a snug fit in the back of the engine case, and snading / drilling a slot just big enough for the conrod - this then holds the conrod/piston at TDC while you fiddle with the cam

- The cam timing is set like this (but feel free to google and watch a few other demos)- see also this from justengines

- it is difficult to get the conrod off the crankshaft until you remove the liner - then you can wiggle the piston to a position where the conrod will come off - NB remember this for reassembly!

- Make sure you have the correct replacement bearings!

Hope these help a bit

AlistairT