Stihl 038 not starting mystery

[Trailoftears]

I feel the o.p.pain.And these old 'vintage' saws were built so well,its unlucky to have an issue like this.Obviously people like spud etc know more than I ever shall.But again what a futhermucker when these small machines let you down.I like the quote from the late/great Bill Tilman-possibly the finest explorer/mountaineer/yachtsmen this Isle has ever produced. in one of his many expeditions to the Himalaya, when he expressed his exasperation to the Indian driver of the ancient truck that had just broken down for the umpteenth time with all his gear on board.The driver looked at him almost pityingly and pointed out "but Sahib,it is but a machine",we should perhaps take that deeply philosophical point on board!

[Trailoftears]

Deepest apologies to the o.p. and the mods too! But re: Bill Tilman quotes-which I just cant resist.(He visited and shared in many cultures) The wise man sits over the hole in his carpet.A wife's advice is often bad-the husband who ignores it is obviously mad.The sight of a pony makes the walker instantly lame.The camel driver has his thoughts-the camel has his.The well known Mountaineers foot syndrome (the inability to put one foot in front of another at extreme altitude).Again, apologies to all!

[Olddevonstihls]

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.

[Olddevonstihls]

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

[Olddevonstihls]

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.

[Olddevonstihls]

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.

[Trailoftears]

Jeez-those photos are pretty ugly.I do know that finding woodchip on the interior face is entirely normal-I mean the interior external face of the air filter if that makes sense!?The photo's do seem to suggest free-floating metal elements in there.What a shame,hope its viable to fix,should be loads of piston/combo's out there.Assuming yours is the standard 038 av @61cc's you might struggle to find the original 48mm setup.But should be loads of 50mm kits which should be a straight swap.Essentially then you're turning the 038 into a 038 super,so an upgrade you might say.

[Olddevonstihls]

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?

 

 

[Olddevonstihls]

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.

[Trailoftears]

I can only refer you to donny walkers series of excellent vids on YouTube re:tips and tricks/tools with assembly/case splitting/bearing seatings etc.Starts to look a v.expensive rebuild job now sadly.Unless you can find a decent for spares/repair saw on Ebay?Even then shop wisely!