Barn find.... The Mill.

[JDT]

So we got to the engine.

Two stroke engines all work the same whether they have one,two, three or four cylinders. They can be configered as horizaltaly opposed, vertical or rotory.
They all need three things to run. Compression, spark and fuel.

Compression. Depending on design compression can be as low as 30 lbs or as high as 200 plus PSI. Most engines are in the 120 to 150 range. Knowing what is suppose to be will tell you if you have a problem once you test it. On multi cylinder engines compression must be relatively even. Readings of 140 and 150 are ok. But 120 and 150 is not. If it is off by over 10% you have yet another adventure ahead of you. Cylinder compression has nothing to do with the condition of the crankshaft seals. Nothing. Seals are a key factor in the condition of any engine. It may start and run but with a bad seal it will not run long.
Spark. Having spark is important but having that spark at the correct time is critical. If your timing is a little off you will be robbed of power. If it is a lot off you will melt the engine or it will not run at all. If you do not have the proper tools and insturments to set timing, start with the stator in the center of the adjustments and pay very close attention to operating temps and spark plug color. Other factors like air/fuel mixture and gas/oil ratio can effect color so make sure everything is where it is suppose to be. Spark plug gap and point gap have to be set to specs. A common problem is a engine that will not start but only backfires when you pull it over. It may be firing 180 degress out of time. A quick test would be to switch the plug wires around. If it then starts the fix would be two reverse the two wires going to the external coils.
Fuel. Again the ratio of air to fuel is critical. Too lean and the engine will run hot and melt down. Too rich and it will smoke, foul plugs and run poorly. The gas oil mixture is imporatant also. Too much oil and it smokes and carbons up the plugs. Too little oil and the bearings run dry and the engine will overheat and seize up. Old gas will not burn right. If you have 3 year old gas in the tank it may not run at all. Always buy premium gas. The benifits are worth the extra 20 cents a gallon.

So testing the engine has determinded that it needs some quality time on the workbench. The best way to go is a complete engine tear down. Every single piece taken apart. Every nut and bolt. If you do not know the history of the engine, if it is stuck, if it has noises when you roll it over, if you can see damage on it or in it, if there is a hole in the piston, if there is white aluminum deposits on the plugs or the exhaust manifold or if you are just bored some weekend... grab your tools.
The only tool you may not have is a puller for the flywheel. A harmonic balancer puller is the tool you need. You can buy one for $50, rent one or barrow one from a friend or a garage. But you need one. A three jaw puller may work to remove the flywheel but if you go that route you will need a new flywheel. If you take a torch to the flywheel to remove it you will be looking for a new flywheel also. Even if the flywheel has never been off the crankshaft it will come off with the proper puller and some patience. In some cases patience is spelt BFH.
The primary clutch also requires some finese to remove. Again the tool to used is the proper puller. Buy one, rent or barrow the specific puller for the clutch you have in front of you. There are 30 some pullers out there so make sure that the one in your hand if the correct one. Never reach for the torch to help with a stuborn clutch. A heat gun is ok but as clutches are made from die cast metal and some clucthes have plastic pucks in them the torch will turn them into a puddle.
A service manual is a must if this type of work is new to you. It will offer step by step instructions and pictures. Specs and tolerences that have to be met are important. Sure some things are obvious but others require careful measurements. As you remove parts from the engine put them in a pail so you don't loose any small pieces like woodruff keys and smaller fasteners. Once you are down to the crankshaft you are done. Now the cleaning starts. It takes me at least three hours to clean an engine. Every part gets soaked and brushed and then is inspected. All carbon deposits are removed. Ports cleaned with a small brush. Oil passages checked. It is very detailed work but a clean engine is happy engine and even a tiny spec of rust, dirt or metal fragment in a bearing means you get to tear it all down again in a week. Once every part is clean the inspection begains. Heads need to be damage free. Spark plug threads chased. Rings inspected and spec out or better yet renewed. Pistons carfully examined. Look for cracks, scars, groves, sign of overheating. Look closey at the flywheel magnets. Are they loose or damaged? Wrist pin bearings and pins. Any damage to the circlips when you removed them?
The crankshaft needs very close inspection. This is one component that you may have to place in the hands of a pro if service is needed. You can chase the threads in the PTO end where the clutch retainer bolt was. The threads for the flywheel nut can be chased it they need it. There can be as few as two main bearings or as many as six on your crank. If any are noisey, loose or stuck you have gone as far as you can. But if you have a press and some shop tools you can change the outer bearings. If the problem bearing is in the middle or the connecting rod bearings are flaking, rough or questionable off to the pro the crank must go. Look very closely at the centerseals. If they are sloppy on the shaft or the springs are missing then you have to see the crankshaft doctor.
At a minimun you will need a complete engine overhaul kit. This will include all seals, gaskets and O-rings that are needed for a rebuild. Once you are ready for reassembly open up the package and lay out all the pieces in the set. Account for each part. Note that some kits contain extra parts that may not be needed in your engine. Again having the service manual open on the bench is the way to go.
Sort through all the hardware that you cleaned. Put all like pieces in sepearate piles. This will help make sence of it all as there can be over 100 nuts, bolts, and washers in the pile. Put one of a kind parts and spacers in a seprate pile. For example having all 8 mm washers in one pile and all 6mm nuts in another will help. If you sort through all the hardware beforehand this really does help.
I use a muffin pan. Sometimes two. For example if you put all the 6mm bolts in one pile and sort through them by length you can see that the two long ones are for the coils, the three shortest ones are for the starter cup, the four sloted ones are for the recoil, these 8 must be for the shrouding and these four are for the intake manifold. When you are looking at the bolts for the case halves note that there may be 12 bolts but they not be all the same length. Inspect all the threads on the studs and bolts. If they are damaged replace them or chase the threads. If you have a blown out hole on, for example one of the recoil holes in the fan housing, you can install a heli-coil to make it good as new. Don't mess with damaged hardware as it will be a problem when you go to torque everything down. Used just enough sealent when you put the case halves together. If it is ozzing out on the outside it is also ozzing out on the inside. Sealant does not make a good lubricant for bearings.
Coat base gaskets with oil. Prelube all bearings with oil. It will smoke big time on first startup but it will be well lubed. Torque heads slowly and evenly and retourque after the engine is started, warmed up and than allowed to cool down.
After all this is said remember that the keys to a successful rebuild are clean parts, close inspection and attention to details. It is not rocket science but it does require time and patience. You may find it neccesary to use some emory cloth here and there, file a nick off of something, hone the cylinders, ect but when you do that please reclean those parts.

Ok so what did I miss?