MS 170 Tear-down

[mountainlake]

Some saw impulse is fed through a small hole in the base of the carb, don't cover it or plug it up. That cylinder was lean siezed not straight gassed, find out why. When putting the flywheel back on there's a lot of slop in the key area, make sure to center it when tightening the nut or even a little advanced. If you get it retarded a bit it will be absoulatly gutluss instead of just gutless when advanced a bit. Steve

 

[JDNicol]

You notice this model has no impulse line? No nipple, no nothing. Did I miss it somehow?

The impulse passage is attached to the carb boot (inlet manifold).

Out of interest what make piston and cylinder did it have? I have seen quite a few of these with Mahle cylinders with Kolbenshmidt (KS) pistons in them from the factory.

 

[sefh3]

Your new kit should come with a pin, two clips, piston and ring(s)

They don't come with new rod bearings. So order a new bearing or reuse the one you have.

Acid should clean that cylinder up with no problems. Pay close attention to the seals. If you buy from Northwood they are a tad thicker than stock. Make sure when you align the pan up with the cylinder the seals are in straight and the correct postion. I have a 170 that I build with all new parts for Northwood and it runs great.

 

[Zombiechopper]

I use a dental pick and hemostat for takin out clips.

that cylinder will clean up. You can see from the piston that it will ne thick smear on the cylinder wall. sandpaper and acid

 

[roostersgt]

I haven't taken the flywheel loose yet, it's still attached to the crank. Bearings look and feel good. Replacing crank seals, even though they still look like new. The fuel line is in new condition/carb boot is in new condition. Inside of sprocket clean with very very little wear from clutches. IMHO, this saw hasn't seen much use at all. Heck, the plastic doesn't even have any scratches on it.

I took the guy's word it was straight gassed. Fuel resevoir had little fuel left in it and it was definately pump gas w/ no mix at all. Not sure where, or how it developed an air leak. Everything seems like new and was tight fitting. I don't have a vac/preasure tester, so I'll just be putting it back together very carefully. I'm sure with much more care than it was originally assembled with.

I'll get some more pics up of the muriatic bathing and massaging, as soon as I can find someone with some acid laying around. Gotta get to scrounging and bothering neighbors now.

 

[Zombiechopper]

go to any hardware store and look for acid used to etch concrete. It's like 10 bucks for a gallon, which will last your lifetime doing saws. Sometimes its labelled muriatic acid, sometimes hydrochloric. Same thing. Just the old name and the new proper chemical name

 

[roostersgt]

Thanks, I'll try that as a last resort. This is California, everyone except me, has a pool and the required chemicals. I just have to pick my lucky donor to this worthy cause.

 

[roostersgt]

Unsure of the make of piston. Can't see any markings other than a lazer imprinted "33" on the top of the piston. Cylinder is Mahle.

 

[mountainlake]

I haven't taken the flywheel loose yet, it's still attached to the crank. Bearings look and feel good. Replacing crank seals, even though they still look like new. The fuel line is in new condition/carb boot is in new condition. Inside of sprocket clean with very very little wear from clutches. IMHO, this saw hasn't seen much use at all. Heck, the plastic doesn't even have any scratches on it.

I took the guy's word it was straight gassed. Fuel resevoir had little fuel left in it and it was definately pump gas w/ no mix at all. Not sure where, or how it developed an air leak. Everything seems like new and was tight fitting. I don't have a vac/preasure tester, so I'll just be putting it back together very carefully. I'm sure with much more care than it was originally assembled with.

I'll get some more pics up of the muriatic bathing and massaging, as soon as I can find someone with some acid laying around. Gotta get to scrounging and bothering neighbors now.

The cylinder says it was lean siezed , if staight gassed the scoring would be all the way around. Steve

 

[roostersgt]

Agreed. Just don't see where it could have leaked. Not many possibilities. No carb adjustments unless you have a special tool and all the rubber parts are pristine. Won't make a bit of difference in the rebuild, as I am replacing the crank seals anyway and have thoroughly inspected the fuel line and intake boot. Will dunk carb in jar of mix and put preasure to it to check for leak there. Not much else can be done. BTW, the engine never "seized", it just wouldn't fire.

The saw is like brand new so it is very unlikely any of the rubber parts / seals degraded / shrunk / cracked. With no carb adjustments possible, other than idle, what else could I check for leaks.

 

[sefh3]

I would say it was straight gassed and lost compression and shut down. Usually if there is a filtration problem, then the intake side would messed up. When putting acid on the cylinder make sure you use a mask and some gloves. That stuff is hard on the lungs. Also, don't let it sit to long in one spot. Keep it moving around and use water to stabilize it. Keep us posted on the build.

 

[sefh3]

On the carb issue, there is one needle that instead of H and L to adjust it.

 

[blsnelling]

Never use rope in a 170 or 180. That's what caused the ben rod on mine. As THall showed, used the correct Stihl piston stop and you will not bent the rod. Personally, I'll use an impact gun next time. However, I would never do so on the clutch without removing the flywheel first. I made that mistake as well and spun the key out of the flywheel. Never use a screw in piston stop either. The crown of the piston is super thin and it'll poke right through. Definately not a robustly built saw. I won't own another, although seem to hold up well for many.

 

[roostersgt]

I got lucky and just used impact wrench with plug out. Came off easy enough. As for the carb adjustments, I'll try to post a pic later showing the H and L "holes", which lead to some really wierd looking "screws"? Very small hole. Smaller than any of my screwdrivers. Idle screw is easily identifiable and standard. It's a Zama carb.

Brad, this saw came to me. I wasn't particularly looking to buy one. Guy wanted to barter for a 30 pk of MGD. I was looking for a project, so,,,,,,the deal was sealed and I get to play with rebuilding a clamshell. Pretty easy so far.

 

[atpchas]

So you're the one who beat me to that saw - good for you. If you want some acid, let me know - I'll never use all of the gallon I have. I also have a MityVac if you want to check for leaks.

Good luck with the project!

Charlie

 

[roostersgt]

Thanks for the offer, I might take you up on it. Don't feel too bad about my beating you to the saw. You forget I'm the guy who bought your 028AV? The MS170 is in good hands and will be long after that guy has finished his 30 pk of MGD. You'd've loved getting this saw. Looks close to new as one could get.

Update = applying acid and it seems to be working well,,,,slow, but working.

 

[SPDRMNKY]

With no carb adjustments possible, other than idle, what else could I check for leaks.

on the 170 I fried a couple months ago, the tech said the throttle shaft was worn/loose and letting air/dirt in...might give your's a wiggle and see?

 

[roostersgt]

My throttle feels real solid. Still will be submerging the carb and applying air preasure to the fuel inlet to check for bubbles (leak).

 

[roostersgt]

Cylinder cleaned up nicely. I'm calling it good. Everything feels very smooth, nothing can be felt. Now all I have to do is await the arrival of the parts from Northwood Saw. I will be updating this thread as I test and reassemble the saw, hopefully the pictures will upload. I've been having problems with that feature lately.

 

[Rookie1]

Nice job Rooster. Keep up the play by play pics. I used acid to clean up a couple of cylinders and it worked great.:msp_smile: