os 40 la help!!

I took my os40 la apart to clean it in the crockpot with Anti Freeze. It came apart relatively easy and cleaned up real well with the anti freeze but now I'm having problems getting the engine back together.
I can get the piston onto the crankshaft in one direction but when I put the liner in around the piston it moves the connecting rod back about a 1/16 on an inch and the rod doesn't clear the crank case. If I reverse the direction of the piston (so the connecting rod is closer to the front of the engine)I can't get the connecting rod onto the crankshaft. Should I have some movement on the wrist pin for the connecting rod? Or is there a technique for putting the connecting rod on the crankshaft that I'm not doing.

Help!!

Yes, you should be able to move the connecting rod back and forth on the wrist pin. And I am pretty sure that there is a front/back of the connecting rod (so it clears the crankweb), so make sure you get it right! Usually you put a scratch mark on the back of the rod so it will be obvious as reassembly time.

Also you don't want to rotate the piston by 180 degrees since it has a wear pattern with the cylinder liner, which will be spoiled if the piston gets put back in 180 degrees off. Just in case you remove the wrist pin, put a mark on the top of the piston so you know how it reassembles with respect to the rod.

What should I do to loosen the connecting rod on the wristpin? Heat it? Please advise, and many thanks for your instructions.

Mccoy40

Absolutely!

What Alan said and if you leave the wrist pin tight on the con-rod, it will wear out the piston.

If you look closely at the bottom end of the con rod, you will see that one side of the crank throw pin hole has a chamfered (beveled) edge and the other is plain. The manufacturer chamfers the edge to make it easier to assemble and disassemble the engine and the chamfered side should go toward the front of the engine.

The con rod should slide easily on the wrist pin. This also gives you some clearance when you are reassembling the engine. use Marvel Mystery Oil or Mouse Milk to loosen it up if necessary.

Finally, and I'm sure you are doing this, the piston and con rod have to be placed over the crank throw pin before you slide the liner down into the crankcase. It's like a Chinese puzzle. There's only one way to take it apart and put it together.

Hope this helps.

Ron King

Thanks Ron,
I'll try loosening the con rod on the wrist pin with some marvel oil before I go too much further with the re-build. I noticed the beveled edge on the connecting rod and put that face forward. Then I hit this little snag, so I took it apart again and have been tenderly trying to get this back together. I've never disassembled an LA40 before so I'm not certian about the little details in re-assembling it.

McCoy,
I've taken apart a number of grungy engines bought off Ebay that had their connecting rods frozen to the wrist pin. The ones with minor sticking could be loosened up by using penetrating oil. However, some were stuck really bad but I was able to free them up by first heating the piston/pin/rod with my Monocoat heat gun. And then using a wooden dowel rod (same diameter as the wrist pin) to force the pin out. Be careful not to use excessive force or you might deform the piston. Also the parts can get very HOT so be sure to use gloves!
DennisV

I think McCoy has attempted to force the big end of the rod onto the crankpin and that's why it's stuck.

This could get real ugly before we're done...

Why do we never seem to learn that taking things apart is no big deal, but putting them back together properly actually begins with doing the disassembly to a higher standard?

I include myself in this group, having scratched my head when reassembling my first 20FP.

Dirty Dan,
Nothing has been forced by myself, the previous owner, though, may well have forced some parts together. (I hope not!) the wristpin and the connecting rod seem to be stuck to each other and I need to try the heat/oil process to see if this will loosen this connection.

The engine was an ebay special that had a broken back plate - minor problem since I'm going to replace it with a tower 40 back plate.

This is one of the older La40's because it has a Boost port cut into the sleeve. Something I've heard that OS is no longer doing.

>The manufacturer chamfers the edge to make it easier to assemble
>and disassemble the engine and the chamfered side should go
>toward the front of the engine.
The chamfer is there to give a clearance from the slight radius machined at the crank pin/crankweb junction. The other end of the rod must slide freely along the wrist pin and when assembling you slide it back so it's against the rear wrist pin boss in the piston. This puts the rod as far to the rear as possible to get the clearance to slip it on the crank pin. I usually hook some soft wire behind the rod to hold it to the back on the wrist pin.

I'm sure you are correct about the reason for the chamfer. It was pointed out to me about 40 years ago that it also made life easier when you were trying to put it back together.

The LA40 is a very easy engine to take apart. After I pull the sleeve, the con rod usually falls right off. I've never had to use anything stronger than a pair of tweezers to lift it off the crank pin.

Ron King