Megatron

You want to lock the piston where the crank throw and con rod are at 90 degrees to each other. The position with respect to the top of the cylinder will vary depending on the stroke. Impact wrench is the best, using only the compression of the engine. Take the flywheel off first to prevent shearing the key.

IMO, it is to support their dealers. How many people go to a dealer with the intention of just buying a saw (or anything else) but come out with PPE equipment, extra chain, bar oil, 2-stroke oil, files etc. If you were to order online chances are you would have just got the saw. There is no way dealers could survive without the footfall through the door. The Stihl policy is worldwide AFAIK. Husqvarna shafted their dealers when they changed their policy. I believe they are appearing in some of the "big box" stores in the US now, only downhill from there. The only thing I don't understand about Stihl is national parts availability. Why can't we get 3/4 wrap handles etc

Yep, no reason to change the 460 brake handle (unless you want to fit the catalytic muffler). For the 660; In 2008 the shape of the 3/4 wrap handle bars was changed and they standardised the 1122 790 9101 brake handle so that it would work with the new 3/4 wrap handles. Hence, For the newer 3/4 wrap handles 1122 790 3611 (unheated) and 1122 790 3610 (heated) you can use the newer (post 1998) standardised 1122 790 9101 brake handle. For the older 3/4 wrap handles you have to use the 1122 790 9102 brake handle. Which you also do if you have the full wrap handle.

There is a type of compression tester that does not have a check valve at the end of the hose. Hence, the volume of the hose is added to the combustion chamber volume. Compression readings are only good like you say at comparing with another known good saw, measured with the same gauge. As a result of the many variables involved including the opening pressure of the valve etc

Oops, forgot to say check the tank vent first.

Not exactly. The oil pump for these saws is press fitted into the plastic housing instead of screwed to the crankcase and both the pump and oil pick up hose are accessed from underneath the saw instead of from the side on the 036. Is the leak coming from the sprocket area or from underneath the saw, above the handle?

IMO there isn't much point in the longer clutch cover unless you have the 3/4 wrap handle and you can't get the standard wrap handles for the MS460 in this country. However, you can get the 3/4 wrap handle that fits the MS460 rescue saw, which will fit.

Like already mentioned it is quite possible the ignition or even the impulse hose is collapsing. Are you sure there aren't any adjustment screws? It is possible to richen the saw up by bending the inlet control lever slighlty up (or drilling the jets ever so slighlty bigger on a fixed jet carb).

With regards to the piston, the MS640 and MS650 pistons don't have the same Stihl part number which usually means they aren't compatible. However, since the MS650 is the successor to the MS640 it is possible the pistons are in fact compatible with the MS650 piston part number being more up to date. Unless you find out for certain then I would recommend; Contact STIHL – The Number One Selling Brand of Chain Saws | STIHL Select technical question. Don't mention the word "aftermarket" and you will have to make up a US zip code.

So it looks like the conrod seized instead of the piston. That black dust will most certainly have been a contributary factor. What air filter did the saw have, the wire mesh one? To rebuild you will need a way of extracting the crank out of the case without causing damage to the cases. The Stihl tools are £££, if you can weld you can relatively easily make your own tool to push the crank out of the clutch side case. Then you can either use a press or big clamp to push the crank out of the flywheel side or again you can make your own tool. (I wouldn't recommend using a mallet to extract the crank out of either side). If the bearings stay in the case you can push them out with sockets and a big vice and if they stay on the crank then use a bearing splitter or jaw puller etc You can reinstall the new crank and bearings into the case using heat...

Do you have a spur or rim sprocket set up at the moment? I am not aware that there is a 0.325" spur sprocket that will fit. You can however get a 9 tooth rim sprocket. You can get higher teeth numbers but you would probably have to get it from a saw racing specialist. The 066 uses the standard 7 spline like many of Stihl's saws. The part numbers for the rim only (9T 0.325") (no clutch drum); Stihl 0000 642 1239 Oregon 13624 I wouldn't have thought the strength of the chain would be a problem. Chip clearance might possibly be an issue but with only 20" you will probably be OK.

What gives you that idea? Like a lot Chinese produced cheap saws it is the YD-52 type; YD52 chainsaw products, buy YD52 chainsaw products from alibaba.com or just google (images) "yd52 chainsaw"

If you get the dual spikes you should get the roller chain catcher, part number 1122 650 7700. Then remove the stock one. I am pretty sure you can't get those parts in the UK as they are meant for other markets. You can get the dual port cover though. You shouldn't need a bigger semi-fixed jet or bigger carb when just installing the dual port cover. The H, L and Idle screws will need adjusting though and depending what carb the limiter caps will need to be removed for this. Don't install the dual port cover if you are still under warranty, wait until it runs out. Power increase would likely be about 0.5hp.

IMO you want to be looking for 140+ psi on a chainsaw. Anything less there is usually a problem. 150 should be fine but if you have reason to believe your piston and cylinder are deteriorating then pull the muffler to check. Compression doesn't tell the whole story... the saw in the picture was pulling 170psi. The rate at which you turn the engine over (within reason) shouldn't influence the compression reading. There is no need to peg the throttle open either as the saw will just draw air through the exhaust port instead of the intake. Just keep pulling the rope until the compression reading won't go any higher. I believe there are two types of compression gauge. Those that have the schrader valve at the end of the hose (what you want for testing saws) and those that have the schrader valve next to the gauge. Using the latter would mean the volume of air in the hose would count as part of your combustion chamber volume and you would consistently get lower than expected readings. Wouldn't make that much of a difference with a car engine cylinder, with a much larger combustion chamber volume.

088, MS880 before 2009 and the post 2009 updated MS880 all share the same recoil.

I think the "standard" (recommended) for the 066/MS660 is 8T and 7T for 064/MS640/MS650... (3/8ths, of course)

Parts for these saws are getting scarce as they are being phased out by Stihl. I have listed a few examples below, the column headed "year" denotes the last year in which the part was/will be available from the factory. However, this doesn't necessarily mean you can still get the parts up until that date, it differs from country to country. But unless your distributor still has some in stock, beyond the date, you are out of luck...

Didn't pay much attention to the pic, just followed on after you were talking about the 026 I see the motivation in trying to mend the tank now seeing as it is off an MS880 (or MS780). £80 excl VAT is quite cheap by MS880 standards though. (I'm assuming it is pre 2009 model, if newer then £105 excl VAT)

I'm assuming you mean the MS 441 C-M ? (A model with C-E means it has ErgoStart/Easy2Start) Without getting into to much detail; The MS441 C-M has a fully electronic M-Tronic engine management system. When working correctly it regulates the ignition timing and electronically adjusts the fuel flow, taking external conditions into account. The dealer is right in some respects. Stihl are supposed to be making software based diagnostic equipment for the M-Tronic saws but it hasn't been released yet. (Husky are no better with Autotune). It isn't tuning equipment though rather diagnostic equipment. However, until then he should be able to test with a multimeter in conjunction with the M-Tronic test lead, part number 5910 840 0903. There are "target values" in the Tech Bulletins for the Solenoid Valve, Micro Switch, Wiring Harness etc. He may have been doing this though... did he try swapping components for known good ones?

024 and 026 saws of the same age share the same tank...

You can get a good used 024/026 tank off ebay for £24.50 not including delivery. You would have to modify the tank vent and more than likely get a different fuel hose though as it is from an earlier version. The two stroke drill looks to be a BT 45. Shares exactly the same engine as equipment from many of Stihl's ranges including; BG, FC, FS, HL, HS and others. Pretty sure it has a spark arresting screen which can clog, both UK and US versions. Also similar to the MS200T (and many other models) it has an accelerator pump on the carb...

I can see what you mean about the cost. Realistically you would be looking at about £100 incl VAT for the parts I mentioned above. New OEM parts except aftermarket piston and good used flywheel. I think it is next to impossible to balance a flywheel by removing material from the other side... they tend to not be symmetrical. You could probably get quite close but at 8000+rpm, the flywheel side bearing isn't going to thank you. Picture of bearing with cracked polymer cage, spins freely; (note; some bearings are installed with the cage inwards, others outwards)

A saw is tuned/jetted mainly for operation at idle and full throttle. Letting a saw warm up on idle should be fine, in cold weather if you don't warm a saw up you can cold seize it. The piston heats up and expands faster than the cylinder. Warming a saw up on part throttle is not a good idea in my opinion as depending on the model carb and the exact throttle plate angle, this can cause the saw to run lean. I am aware that "modern" saws are tuned leaner (at idle and full throttle) but it should still idle without starving the saw of fuel and oil. If you are milling a long hardwood log it is common place in my experience to stop periodically to allow the saw to return to idle and cool. As a general rule the ignitions on chainsaws don't like heat! Keep the holes in the recoil housing, the flywheel fins and around the ignition module free from crud. (and the cylinder fins, to keep the cylinder cool)

My main worry with the crank bearings is although they may spin freely the polymer cages may have been damaged. More so with the acid theory though. The flywheel appears to be missing at least one fin...

It looks like someone tipped acid or the like in the plug hole to try to unseize it. Can't imagine where else the grey precipitate could come from? IMO needs at least a new piston, bearings, seals, gaskets, carb kit, hoses and flywheel... If you want a saw you can rely on.