Olddevonstihls

Rebuilding my old 051 after a loose screw was ingested through the carb and wrecked the cylinder and piston. Crankcase eventually came apart, leaving old bearings on the crankshaft. Now got them off which was a job in itself. However I don’t have a reference for the depth to which the new bearings sit in the crank case housings. I’ve got the small ignition side one in as far as it will go, using a flypress and also a socket and hammer (which is what the manual says, perhaps I should have heated the case and frozen the bearings) but it sits slightly proud of the housing. Can anyone tell me if this is normal? On the other side, the bigger one, the depth of the housing to the circlip is exactly the same as the width of the bearing which suggests it ought to be flush if hard against the clip. Thank you.

Thanks for this clarification. I’ve been using chainsaws for about 15 years now but it’s only in the last six months when things have started going wrong that I’ve had to learn all this stuff about two strokes. Been mucking about with four strokes and diesels for 40 years, and so when things like hot running occur I could figure out the mixture might be lean, but this vacuum and pressure business was a nasty revelation. Anyhow, a cheap vacuum tester and a home made pressure tester means I’ve now got all the saws back on track, just waiting for the next thing to go awry.

New cylinder and piston fitted and it roared into life first pull of the cord. What have I learned from this (at times miserable) experience? 1. Lots of fantastic help and support on this forum. 2. No necessary correlation between cause and effect. The saw probably did stop due to an earthing fault causing no spark but this was unrelated to the fundamental problem with deeply scored piston and cylinder causing catastrophic loss of compression. 3. Thumb being pushed off plug hole doesn’t indicate adequate compression. 4. Scoring, or in this case, gouging is not necessarily revealed through the exhaust port. 5. Lack of compression might cause inadequate fuel draw leading to dry plug and so wasted time suspecting carb (?) 6. Aftermarket parts are often of dubious quality. Feedback here about the piston circlips/snap rings which I hadn’t read before might have saved my original cylinder, for the sake of £1. Interestingly, the replacement Wartec cylinder didn’t quite fit my case, each hole being out by about 1mm. It was identical in all other respects (I thought I might have been sent a 52mm magnum part in error, but no). Using a genuine Stihl gasket to mark the exact position of the holes and a chainsaw file allowed me to elongate the holes slightly to make it fit. Only time will tell if this is another disaster waiting to happen. However original Stihl parts like the cylinder and piston are just not available for an old saw like the 038, but having said this, my dealer and L&S do still stock many other parts. Thanks again to all who offered help and guidance. Now to finish sawing up the horse chestnut after a two week interregnum.e

And that was a phone call worth making. After some discussion about the cause of the problem they are sending me a new piston and cylinder foc. Excellent service. Highly recommended. But they’ve always been good: many years ago I had an ancient Winget dumper that went wrong and parts were obscure, and service methods more so. After a short discussion, a director of the company came on the line and said he used to work on them in the 70s, and this is what I needed and this was the way to do it.

the L&S one is Wartec. How do they rate?

Mine is an 038 super. 50mm. Not many of those around. More 52mm for the Magnum to choose from. Greek guy has a 50mm branded Episan but no cylinder to match. L&S has a kit with cylinder at around £100 inc vat but no brand indicated. Saegenspezi in Germany has a kit for a bit less, also unbranded, inc all gaskets. What to do? There are various forum threads around suggesting its possible with a bit of fettling to make the 52mm magnum fit the 50mm super which will give increased power but I just want my super back.

Are we happy that the score line on the crankshaft is something I can ignore rather than replace it (it is the original and I’d prefer not to)?

The German site has stuff that l&s or other Uk suppliers often don’t. Brexit doesn’t seem to have affected them and delivery is free once you get to 150 euro which, unfortunately, I will. Otherwise it’s 10 euro delivery.

I suppose the wear on the crank web/counterweight might have been caused by part of the circlip or other parts of metal once the damage occurred rather than being out of centre. The question remains therefore is whether such wear would imbalance the shaft so much that it needs to be replaced (I will replace the bearings anyway). I bought the last piston from L&S Engineers as aftermarket but they have previously been reliable. I’m currently looking at the stuff on the German site Saegenspezi. I really like the saw.

If I do it with aftermarket cylinder kit and crankshaft etc it’s about £150. That is worth it as it is a good powerful saw (when not wrecked) and is a fraction of what it would cost to replace. But if those aftermarket circlips wreck it everytime it doesn’t look like such a sensible thing to be doing.

10 out of 10. Just inspected the circlips and what do I see?

Also, what’s the assembly trick to avoid recurrence? I’m pretty sure the bearings were fully seated (case heated up and they dropped straight in), and crank was frozen and assembled easily into the case but the wear suggests either the bearing was proud of the seat or the shaft was not properly centred.

I think I’ve found the cause. Side of crankshaft is scored from rubbing against bearing, clutch side. I did replace the bearings so obviously didn’t reassemble carefully and/or correctly enough. Question now, is the crankshaft ruined with this scoring due to imbalance, even assuming it can be correctly reassembled?

Well, well, well. What a shocker. That piston is not just scored, its gouged. As is the cylinder, which I’ve never seen before. I’m gonna have split the case aren't to see what’s gone on? When I first took the airfilter off it was evident that there was sawdust detritus on the wrong side, but can woodchips have done this? There’s clearly bits of metal in the bottom of the crankcase but that could just be the arisings from the damage to the piston and cylinder. All bearings appear intact. photos for your amusement.

Right. We can add one more time to Spud’s having heard “it’s got compression”, and then maybe not. Tested it with a draper generic tester which is not specific to two stroke so might be inaccurate…but showing 60psi despite pushing thumb off. To compare, a known good saw is showing 120 with the same tester so even if not entirely accurate for either, the 038 is much lower. Will take the head off to inspect the scoring but as I’ve secure pressure and vacuum I am wondering if the carb problem may have been causing it to run lean before it cut out.

Having looked again at the carb and the parts diagram, which/where is the check valve on a Bing 48?

More helpful suggestions, for which many thanks again. carb has been completely stripped and drenched in cleaner at least twice, inc H and L screws out and while they look identical, put back in the same holes. Light is visible through many of the holes so no visible obstructions. I haven’t put compressed air through as past bad experiences. Will explore possibility of check valve. Carb repair kit arriving imminently. I’m also going to do a proper compression test today as it drops on the cord quite quickly despite palpable pressure at the plug hole against thumb. I expect I am be confusing cause and correlation. The initial cut out was HT related but something else was going on as well which has now come to the fore as a result or despite of fiddling around with the electrical side. More work required. I will report back. All very annoying as it’s the saw I need to finish the job I was doing when it died. Meanwhile there is a lot of horse chestnut hanging around, flowering on the ground.

Lots of thoughts here, thank you. if I understand correctly having fuel in both chambers of the carb is good so I can move on from worrying about that. pulling the cord several times on full choke leaves the plug dry. Squirting carb cleaner both in the plug hole and through the carb wets the plug but it won’t start it as you’d expect. I haven’t measured compression, but it is enough to push my thumb off, and I have checked the exhaust port: the piston is moving freely and while there is some scoring the rings are intact. It was pulling like a train before it cut out, and had just felled a 40” wide horse chestnut. Vacuum and pressure tested with testing devices with exhaust and carb blanked off and using adapted spark plug. Crank seals were replaced not long ago with split case and new bearings, plus new boot and impulse tube. plug is new and is specced for the saw. Breather pipe is new and was venting properly until the electrical cut out. the spark is as blue and strong as I’ve ever seen. so I have compression (and it was running fine before it suddenly stopped), I now have a spark, but despite fuel in the carb chambers it doesn’t seem to be getting fuel into the cylinder, yet even with carb cleaner directly into the cylinder, its not kicking. All I can think of is the timing has gone out of whack but I don’t see how, and anyway that doesn’t explain the apparent lack of fuel. Something just isn’t right.

Using my 038 for an hours hard work and it stopped instantly, suggesting no spark. Removed plug to check and indeed no spark. Area around the kill switch under the air filter was clogged up and when cleaned out, weak spark appeared, adjusted coil gap and then got a good strong spark. But… it still won’t start. Stripped down Bing carb and there was some detritus which is now cleaned out and reassembled. Still won’t start. When carb stripped again both chambers are full of fuel. Plug is not wet which suggests fuel/air mix is not making its way from the carb into the cylinder. Gaskets and diaphrams are ok. Carb is holding pressure. Saw itself is holding pressure and vacuum. I can feel compression. Saw won’t start when fuel trickled in and turned over. The flywheel is on the woodruff key so the timing should be ok. Do the flooded chambers indicate I’ve still got a blockage of some sort in the carb? Can anyone suggest what I need to be looking at here?

That’s helpful, thanks. I had hoped with the beds square with the side support dogs it would only be a blade adjustment but it sounds like I will have to do a full alignment if I get the bottom rollers tight.

I’m using an old LT40 for various milling projects. When we set it up it was more or less square, but over time it was not cutting perfectly square, so cants were coming out as parallelagrams, each cut being slightly out but over four cuts compounding to something more noticeable. We didn’t do a full alignment as described in the manual, but checked that the beds were level with one another and square with the side log supports/dogs. This was slightly out so the side dogs were adjusted on the cam bolts to bring them into square with the beds. So far, so good. Levelling the blade to the beds, with the plus 1/16” on the idle as specified in the manual, didn’t produce a square cut, however. In fact, to get a square cut we needed to raise the idle side 15mm above the drive side. This was done by adjusting the nuts and bolts under the bottom rail. Apart from the blade being out of spec, this also means that the blade guide alignment arm is also unlevel by about the same amount. As it is, we are getting perfectly square 6”-8” cants, and boards are uniform thickness (as should be the case when cutting through and through because each cut will be paralell to the previous), but, but… why is the machine like this? Can anyone suggest where we might look?

That confirms the manual and also what I’m experiencing now (though not for the many years of using the saw before the problems began). Seems to be running hot though - smoke coming off the cylinder when running for a few minutes.

I’m pretty sure the crank seals are ok. i’ve now got it running reasonably smoothly but it needs the half choke setting to start. When I look back at the original ms240 manuals, what I’m describing as half choke is what stihl describe as the warm start position, and the manual says to use this position for a warm start and, from cold, to use the full choke position to get the blip, and then move to the warm start position. I’m pretty sure that until I started getting problems I could start the saw by going from full choke to run, and to warm start directly from the run position without using the warm start/half choke position in either case. I’ve read recently that ms240s/024s are difficult to start. Is what I am describing normal? If so perhaps I’m worrying unnecessarily.

Thank you. Even quite big differences (and settings in between) on both H and L) don’t seem to overcome the fundamental problem. Carb stripped down again and inlet gauze/screen replaced (again) as there was some residue on it. Another new set of diaphragms and gaskets on the carb. New fuel line still ok, and tank/vent still passes vac and pressure test. But the half choke start remains and symptoms still suggesting air leak but where is it?

Thanks. Very helpful. I probably wasn’t being clear about the tests, sorry. Normal vac/pressure was with rubber seal behind carb (ie next to cylinder inlet), impulse sealed by the connection to the carb, exhaust sealed similarly behind muffler, and test hose connected to modified spark plug. Both vac and pressure holding solidly at 0.5 bar. Carb itself holding pressure separately. The other pressure test, when I sealed the air filter side with the carb attached was to establish if there were any leaks on the carb side, including at the gasket between carb and cylinder: there were not, other than at the throttle linkage. I look again at the other things you suggest, but there is new fuel line (a split in the original lead to starting difficulties and fuel starvation and so was replaced) and filter. Carb settings at the specified starting positions of L 1 turn/H 3/4 turns plus a small amount and giving the right engine characteristics but perhaps they need richening up more boldly.