Stihl 038 not starting mystery

[Muddy42]

9 minutes ago, spudulike said:

L&S are a decent outfit. I have never had any issues with them over the 12 years of using them.

On bit of advice is to fit OEM circlips and make sure they are 100% in their grooves and the gap in the clips is to the top.

L&S and Garden Hire Spares are now in business together....Wartec were a GHS brand.

agreed and helpful and knowledgable over the phone, if you need to call.

 

Ive had an unbelievable bad run of breakages, repairs and saw destruction recently - L&S should offer me a loyalty discount !

[Trailoftears]

23 hours ago, Trailoftears said:

'Dont send them on a spa weekend',I like that-a lot 👏

I'm left with a slightly troubling mental picture of jaded crankshafts sipping a g&t on adjacent treatment beds at Champneys animatedly discussing whether to go with the bikini line wax treatment, or just stick with the cheaper eyebrow threading option.

[Trailoftears]

Interesting re: L&S/wartec/ghs.I've always found l&s to be excellent-and God forbid they ever go belly-up,it would be a great loss.I've also bought a lot of parts/bits from ghs/wartec-generally via Ebay.Usually decent enough/functional aftermarket stuff at fair prices.Reminds me of Oregon stock-its ok/does the job if you need to save a few bob or can't justify throwing silly money on oem parts for older machines.

[Olddevonstihls]

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

[spudulike]

Great, glad you got it going and thanks for letting us all know.

On your point 5)  : -  the dry plug will be down to lack of vacuum in the crankcase....the fuel vapour is pulled in to the engine as the piston rises in the cylinder, this causes a vacuum in the crankcase to increase and pull fuel/air vapour in from the carb and enter the engine via the inlet port. Because your piston was so scored, the piston rising in the cylinder caused a substantial lack of vacuum in the crankcase so no fuel on your spark plug.

 

An engine can get a big air leak in the crankcase and still have "secondary compression" (combustion chamber compression) but total lack of fuel due to the above. A bit different from four strokes and is why I bang on about vacuum and pressure testing the engine as well as a compression check on the top end  - The crankcase has both vacuum and "Primary compression", the top end is known as "Secondary compression" but is often the only type mentioned.

[Trailoftears]

Grand to hear the old beast lives again 👍

And spuds technical pointers re: compression (or not) are of great value for those of us that dont fully understand the inner workings of these 'simple' machines.

[Olddevonstihls]

1 hour ago, spudulike said:

Great, glad you got it going and thanks for letting us all know.

On your point 5)  : -  the dry plug will be down to lack of vacuum in the crankcase....the fuel vapour is pulled in to the engine as the piston rises in the cylinder, this causes a vacuum in the crankcase to increase and pull fuel/air vapour in from the carb and enter the engine via the inlet port. Because your piston was so scored, the piston rising in the cylinder caused a substantial lack of vacuum in the crankcase so no fuel on your spark plug.

 

An engine can get a big air leak in the crankcase and still have "secondary compression" (combustion chamber compression) but total lack of fuel due to the above. A bit different from four strokes and is why I bang on about vacuum and pressure testing the engine as well as a compression check on the top end  - The crankcase has both vacuum and "Primary compression", the top end is known as "Secondary compression" but is often the only type mentioned.

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.