Stihl MS 150C - Will not rev.

[arboriculturist]

I have a Stihl MS 150 C and a Stihl MS 150 TC.   Both are 12 years old.   The MS 150 C has become harder to start over a few weeks and now after getting it started it will barely run at low revs for more than 10 seconds before cutting out.   I stripped the carb, found nothing amiss and built it up again and re-fitted.   Same symptoms.    So removed carb and fitted it to the    MS 150 TC and this saw ran perfectly with the MS 150 C carb.   I tested the resistance of the coil, which appeared as specified.   So I removed the coil off the MS 150 C and fitted it to the MS 150 TC.    Pulled it over and it started 1st pull, revved up fine and ticked over perfectly.    I am thinking crank seals but have no way of testing crankcase pressure.   This saw has done a fair amount of work.   There appears to be the slightest of play on the flywheel end of the crank, which is the end I looked at.   If the crank seals need replacing what is the likely cost if I gave it to someone stripped already and is it worth it on this 12 year old saw ?     These are the only saws I have that Spud has not ported !    Any replies much appreciated.

[spudulike]

A few things to try: -

1) make sure the air filter is clean - replacing the flock paper one with the nylon one helps the saw.

2) make sure the muffler is clear of carbon. They can get pretty clagged up under the top cover held in place with the screw. Whilst the muffler is off, check the piston for scoring and the port for carbon.

3) On these saws, the flywheel runs pretty close to the plastic body and they tend to build up a fair bit of wood chip in this area and this can stop the saw idling. Just remove the recoil cover and clean with an old paint brush and compressor air line. Whilst in there - make sure the front engine mounts are OK - if the stop switch has stopped working, they are probably loose or knackered. They are located to the top and bottom of the clutch drum.

See how that helps.

 

[Joe Newton]

How much time do you want to spend on a saw that cost £300 when you bought it 12 years ago. Chuck it in the spares bin and replace. 

[arboriculturist]

10 hours ago, Joe Newton said:

How much time do you want to spend on a saw that cost £300 when you bought it 12 years ago. Chuck it in the spares bin and replace. 

 

I take your point and that was my initial thought, especially as many of the parts on that saw will fit the 150 TC's.

[arboriculturist]

10 hours ago, spudulike said:

A few things to try: -

1) make sure the air filter is clean - replacing the flock paper one with the nylon one helps the saw.

2) make sure the muffler is clear of carbon. They can get pretty clagged up under the top cover held in place with the screw. Whilst the muffler is off, check the piston for scoring and the port for carbon.

3) On these saws, the flywheel runs pretty close to the plastic body and they tend to build up a fair bit of wood chip in this area and this can stop the saw idling. Just remove the recoil cover and clean with an old paint brush and compressor air line. Whilst in there - make sure the front engine mounts are OK - if the stop switch has stopped working, they are probably loose or knackered. They are located to the top and bottom of the clutch drum.

See how that helps.

 

Thanks for replying :   1. New air filter fitted - no difference.     2. Muffler clear.  Piston perfect.  Port already spotless of carbon.   3.  Flywheel area clear as I had flywheel off to check keyway was perfect.   Engine mounts good and I took the stop switch out of the equation.           This may or may or not be relevant  - but the saw will only run for 10 or 20 seconds with the choke on and held on full throttle.

[Dan Maynard]

13 hours ago, arboriculturist said:

If the crank seals need replacing what is the likely cost if I gave it to someone stripped already and is it worth it on this 12 year old saw ?

Sounds like you should invest in a pressure/vac tester. Will cost similar to sending it to someone to test and then you have it next time.

 

Also I'd be surprised if paying someone to change the seals is economic but you seem prepared to spend time so have a crack yourself, otherwise its scrap anyway.

[arboriculturist]

A lot of sound advice from everyone thankyou.   Yes this is an old saw and I like to get a long life out of my equipment, saws included.   Spud fitted a new barrel / piston and ported the Husky 346XP which is now 26 years old. Better than the day I bought it. Yes replaced odd bits and pieces but that is still a tremendous machine.  I accept that the time does come when repairs become uneconomic and this is looking like one of those times.   I am not sure if I can pull those bearings without a puller though if I go down that road ?

[arboriculturist]

3 hours ago, arboriculturist said:

A lot of sound advice from everyone thankyou.   Yes this is an old saw and I like to get a long life out of my equipment, saws included.   Spud fitted a new barrel / piston and ported the Husky 346XP which is now 26 years old. Better than the day I bought it. Yes replaced odd bits and pieces but that is still a tremendous machine.  I accept that the time does come when repairs become uneconomic and this is looking like one of those times.   I am not sure if I can pull those bearings without a puller though if I go down that road ?

 Ok, so I have ' grabbed the bull by the horns ' like a lot of you would do.   Checked the impulse and fuel pipes - perfect.    Rubber carb manifold - perfect.    On close inspection with just the engine unit in my hands it is apparent that there is some end float movement and some lateral movement of the crankshaft.   I could see bubbles in soapy water around crank seals after sealing exhaust and inlet ports and blowing gently into inpulse spigot in barrel - so they are leaking air.    I could replace bearings and seals myself ( I have no bearing puller) or give to someone to replace ?   Parts are all lo-cost items as are the crankcase and barrel gaskets.   Any thoughts

[Botty Cough]

When we were kids we used to put stuff on the train track to get run over so try that....😁

[spudulike]

3 hours ago, arboriculturist said:

 Ok, so I have ' grabbed the bull by the horns ' like a lot of you would do.   Checked the impulse and fuel pipes - perfect.    Rubber carb manifold - perfect.    On close inspection with just the engine unit in my hands it is apparent that there is some end float movement and some lateral movement of the crankshaft.   I could see bubbles in soapy water around crank seals after sealing exhaust and inlet ports and blowing gently into inpulse spigot in barrel - so they are leaking air.    I could replace bearings and seals myself ( I have no bearing puller) or give to someone to replace ?   Parts are all lo-cost items as are the crankcase and barrel gaskets.   Any thoughts

Pulling the bearings and working on the crank is like working on a sewing machine. everything is super small on these saws and typical bearing pullers etc are pretty useless on this tiny engine. 

The plus point is that the saw is relatively easy to take apart.

The crankshaft should have no in and out movement as the bearings are a interference fit on the cank shaft unlike the MS200T. There should also be no up and down movement as the bearings are ball races. Don't confuse the sprocket movement as crank bearing movement.