MS170. Rebuild a waste of time?

[Conn]

Hey all. Long time lurker, first time poster. (I registered in 2007! Ha!)

My little MS170 developed a no idle condition about a month ago. I've used it on occation since then but believe it has developed low compression. The rope requires VERY little effort to pull. I'm hauling it to work with me today to test the compression with a real tester. I've owned it for a decent while. Probably 4-5 years. Maybe longer. It's always had the Stihl Ultra oil ran through it.

I wouldn't even consider rebuilding it if I hadn't just stuck a new bar and chain on it.

I love to tinker and have never rebuilt a saw before but I don't want to sink 100 bucks into a 180 dollar saw. I hate to get rid of it as i was attempting to grow the herd a little bit. (wanting an MS261 soon to keep the 170 and a 250 in good company)

Is it worth the effort to rebuild it just for the learning experience and the opportunity to tune it a bit? Or should I just scrap it, buy another 170 and keep it for parts?

Any advise appreciated.

Conn

 

[Chris-PA]

It's not even a saw I particularly like, but you may as well take it apart and see what's up with it. Maybe it can be fixed for less, and you'll learn more about it. The worth of things is not always measured in $, and that saw would probably be worth more to you if you fixed it (and maybe modified it) yourself than a new one would.

 

[2dumb4words]

Seems to me there would be little to no risk in tearing it down for inspection? I know very little about the 170. If a set of rings saves the day, could be a cheap fix. Won't cost much but time to see what gives.

 

[o8f150]

if it does need to be rebuilt the meteor piston is only about 30.00 or so,,, take that sealed carb and throw it in the garbage and get you a wt 215 fully adjustable carb for it

 

[excess650]

Low compression could be as simple as a loose sparkplug, but could be stuck rings, scored piston/cylinder, holed piston, etc. Site sponsors Baileys and Northwood Saw both list pistons (017 piston will fit 170) for $30 or so. Take the muffler off and look at the condition of the piston/rings/cylinder. Take the plug out and look into the cylinder with from there as well (if possible). If the cylinder is salvageable, its probably worth putting a piston kit and seals into the saw. If the cylinder is beyond hope, you might be able to find a useable shortblock and replace the engine.

 

[Conn]

Low compression could be as simple as a loose sparkplug, but could be stuck rings, scored piston/cylinder, holed piston, etc. Site sponsors Baileys and Northwood Saw both list pistons (017 piston will fit 170) for $30 or so. Take the muffler off and look at the condition of the piston/rings/cylinder. Take the plug out and look into the cylinder with from there as well (if possible). If the cylinder is salvageable, its probably worth putting a piston kit and seals into the saw. If the cylinder is beyond hope, you might be able to find a useable shortblock and replace the engine.

Compression test this morning revealed 110 PSI cold holding it WOT. The saw starts, runs, and cuts good, but will not idle to save its life, and only re-starts when holding the throttle.

I took a peek into the spark plug hole. I can see 6 distinct lines in the cylinder wall. I inserted a pick into the hole and could not "feel" them.

 

[brokenbudget]

Compression test this morning revealed 110 PSI cold holding it WOT. The saw starts, runs, and cuts good, but will not idle to save its life, and only re-starts when holding the throttle.

I took a peek into the spark plug hole. I can see 6 distinct lines in the cylinder wall. I inserted a pick into the hole and could not "feel" them.

time to take the muffler off and have a look.

 

[Bushmans]

Compression test this morning revealed 110 PSI cold holding it WOT. The saw starts, runs, and cuts good, but will not idle to save its life, and only re-starts when holding the throttle.

I took a peek into the spark plug hole. I can see 6 distinct lines in the cylinder wall. I inserted a pick into the hole and could not "feel" them.

pull the exhaust off and you will get a good look at the piston. Sounds scored to me! Especially if your seeing marks on the cylinder

 

[o8f150]

110 is a tad low,, 150 would be a lot better,,, as far as the idle goes that sounds like you might have a carb problem,, if it was me i would throw that carb away and get a piston kit,,, 70.00 bucks you can have a new piston and new wt-215 carb

 

[nstueve]

Compression test this morning revealed 110 PSI cold holding it WOT. The saw starts, runs, and cuts good, but will not idle to save its life, and only re-starts when holding the throttle.

I took a peek into the spark plug hole. I can see 6 distinct lines in the cylinder wall. I inserted a pick into the hole and could not "feel" them.

110psi is too low for a properly functioning saw. You want at least 130+... Anything less than 130psi cold and I replace the rings minimum and most likely the piston and rings. tear it down and throw a new P&R's in!

Here's what you'll need:
Piston, add the piston to your cart and then search and add the remaing item numbers.
Replacement Piston for Stihl 017
$30
Threebond: for resealing the piston to the base:
No. 1184
$8
Torx 27 "tee-handle" for removing the torx screws at base of cylinder.
SKU: A150
$5
Piston lock: for taking the flywheel and clutch off (take these off before removing the cyldiner)
SKU: A175
$5

--------
Total of $48 +S&H


I'd also ask on the swap meet forum if anyone has a fully adjustable wt215 carb. I've also heard some good things about the chinese repop carbs for smaller stihls. Fully adjustable carb for $20 shipped!
New General Walbro Repair Carburetor Carb for Stihl MS170 180 017 018 Chain Saw | eBay

 

[Ozzie]

if it does need to be rebuilt the meteor piston is only about 30.00 or so,,, take that sealed carb and throw it in the garbage and get you a wt 215 fully adjustable carb for it

I found out about 3 years ago that it was cheaper to buy the new carb than buy a rebuild kit. Having said that, I went back with original sealed carb and now wish I'd went with the WT 215.

 

[Conn]

pull the exhaust off and you will get a good look at the piston. Sounds scored to me! Especially if your seeing marks on the cylinder

Yep. It's scored.

I've looked into the adjustable carb a long time ago. Dug up a thread this morning on converting the MS180 to the WT-215 and looks about like the same process.

I think I'll give rebuilding it a whirl. No harm in it I guess.

Thanks for all the help guys!

 

[jughead500]

Don't forget Crank Seals.That could be part of your problems too.

 

[Bob95065]

Don't forget Crank Seals.That could be part of your problems too.

+1

When I rebuild a saw like this I replace anything rubber - crank seals, carb boot, impulse line, fuel line, carb kit, etc. It doesn't make sense to tear down a saw and not replace these parts. I don't want to put a piston iin a saw only to have it ruined by faulty rubber parts.

You should do a vacuum and pressure test before and after you rebuild it. If the piston is scored because of a lean condition you should know why. After it is rebuilt you should repeat the test to be sure the problem is fixed and no new leaks have appeared during assembly.

Bob

 

[casual cutter]

Rebuilding a disposable homeowners saw is a good start. Even if you muck something up, there is typically little loss if you have to throw it away...

 

[Conn]

Done!

Finally got everything put back together tonight. MMed, widened ports, and a WT215.

I had a bugger of a time getting it to run initially. Then I realized that I didn't install a new clamp to replace the cheapo "one use" plastic clamp on the intake from the factory. A nice heavy zip tie did the trick.

Mixed up some 32:1 Klotz and it has a nice little haze four stroking at WOT.

I spent about 100 bucks by the time it was all said and done. Had to buy a $25 flex hone to finish the job.

It really wasn't worth investing $100 into a saw I can buy new for $180, but it was worth it to fire it up after I had its guts all over the workbench.

 

[elanjoe]

110psi is too low for a properly functioning saw. You want at least 130+... Anything less than 130psi cold and I replace the rings minimum and most likely the piston and rings. tear it down and throw a new P&R's in!


Piston lock: for taking the flywheel and clutch off (take these off before removing the cyldiner)
SKU: A175
$5[/url]

shame on you, don't you know that piston stops can cause damage, use a piece of ROPE !!!!!

 

[ckelp]

a wt215 wakes that little saw up..
IMHO it's the best upgrade for that saw

 

[lumberjackchef]

+1

When I rebuild a saw like this I replace anything rubber - crank seals, carb boot, impulse line, fuel line, carb kit, etc. It doesn't make sense to tear down a saw and not replace these parts. I don't want to put a piston iin a saw only to have it ruined by faulty rubber parts.

You should do a vacuum and pressure test before and after you rebuild it. If the piston is scored because of a lean condition you should know why. After it is rebuilt you should repeat the test to be sure the problem is fixed and no new leaks have appeared during assembly.

Bob

+1

 

[brokenbudget]

Finally got everything put back together tonight. MMed, widened ports, and a WT215.

I had a bugger of a time getting it to run initially. Then I realized that I didn't install a new clamp to replace the cheapo "one use" plastic clamp on the intake from the factory. A nice heavy zip tie did the trick.

Mixed up some 32:1 Klotz and it has a nice little haze four stroking at WOT.

I spent about 100 bucks by the time it was all said and done. Had to buy a $25 flex hone to finish the job.

It really wasn't worth investing $100 into a saw I can buy new for $180, but it was worth it to fire it up after I had its guts all over the workbench.

hope that 'zip tie' likes heat. another problem with a zip tie is they dont clamp perfectly round. they have a 'pinch point' which could lead to an airleak.