Olddevonstihls

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?