RCU Forums - Engine Disassemble guide

I don't have an LA but it's quite a simple engine to take apart. However there's a couple of things to watch for which mostly apply to any engine.

First take off the cylinder head, easy..just undo the screws. You'll see it's symmetrical on the inside which means it can go back on anyway you like but it looks better if the fins point the right way :)

Next, undo the screws holding on the back plate but be a little careful as there's likely to be a thin paper gasket that can get torn fairly easily.

Now comes the trickiest part, removing the cylinder liner/sleeve. It's a very close fit but some will move upwards by putting your finger or a bit of wood inside the crankcase and pushing it up. If it won't push up then I resort to my next method. Put on a prop then get one or two matches that sit on top of the piston and get squeezed against the top edge of the liner when you slowly turn the prop around. Usually this works but sometimes it'll simply cut through the matches without causing any damage if it's still too tight. The next step is to heat the crankcase so it'll expand slightly more than the liner but I try never to go much hotter than the boiling point of water (OK..so I put a bit of spit on it :) ).

I'm not sure about the LA but there might be a tiny roll pin in the recess where the liner flange sits and this locates it by a matching notch in the liner flange. It's foolproof except for the guys who don't see it and try to tighten the head back down without aligning it...it happens....

Once the liner's out there's enough play to slide the rod off the crankpin but it's a good idea to first use a marker pen to mark the side of the rod that faces you because the rod only goes one way. To get some extra play, slide the rod as far as you can along the gudgeon/wrist pin until it touches the piston (every little bit helps!). Once the rod is free then slip the piston/rod out the top of the engine. Now have a close look at the big end of the rod. You'll see that the end of the bush (on the opposite side to the mark on the rod) has a chamfer while the other side is flat. This chamfer is to give a clearance for the slight radius ground between the crankpin and the crank web. Also, if there's only one oil hole in the rod then it'll be slightly off to the left hand side of the bottom with that mark facing you. These are the two ways you can figure out which way a rod goes but the chamfer is a positive way.

If you're going to take the piston off the rod then first mark the top so it mates with the mark on the rod or any other way that ensures the piston goes back in exactly the same way it came out. Then check to see what might be retaining the piston. This could be tiny little circlips which will almost certainly end up on the other side of the room so take them out inside a plastic bag. Some pistons have only one retainer because one end of the gudgeon hole is slightly smaller to stop it moving in that direction.

Well that's the hard bits done so all that's left is the crankshaft. Take off the nut, washer and drive washer and then you'll see a thin steel washer that sits between the drive washer and the crankcase. This is very important on a plain bearing engine like your LA because it seperates the two alloy parts when an electric starter is used (make sure there's some lubrication around it before you use an electric starter too!!). Now you can just slide the crankshaft out the back and you're done (I wouldn't bother taking off the carb unless you want to).

Assembly is just the reverse...crankshaft...piston/rod assembly (right way around)...cylinder liner (slide it gently over the piston so it doesn't lay over and bind) and aligning the roll pin if fitted...back plate (don't overtighten the screws cos it's plastic)...then cylinder head. Coat all running parts lightly with an after run oil, ATF oil or even some fuel if that's all you've got before assembling each part.

But a couple of things on assembly. If the liner hasn't got a pin to align it you'll notice 3 ports (if yours is a later LA, earlier ones have 4 ports). Look for the port that goes the highest up the side of the liner (and in your case it's the one that doesn't have any angles machined in it) and that's the exhaust port. Centre it as accurately as you can in the crankcase exhaust. When tightening the head screws put them all in just barely finger tight at first then tighten them bit by bit in as best a criss cross pattern as you can to get an even pressure down on the liner. It's not necessary to tighten them to the point they're almost stripped but firm pressure on a suitable driver is all that's needed.

And that's it...it sounds complicated in words but do it once or twice and it's dead easy :D