Stihl MS170 non starter

[ipbr21054]

Picked up a MS170 for cheap from a guy who found it in his fathers garage.
Pulling the cord doesn’t start the saw.
I have a spark at the plug.
I have removed the old fuel & replaced with new.
I’ve cleaned the carb but unable to undo the screw that holds the viton tip needle jet in place. Testing it shows it’s doing its job.
I wanted to replace the air filter & spark plug anyhow & for £12 it also comes with a new carb.

Hopefully once new carb is fitted it will then start but should it still not start are we then looking at compression ?

I don’t have a compression tester so I put my finger over the spark plug hole & pulled the cord. I know this is basic but I could feel the pressure / resistance when doing it.

Also with the saw on the ground I held the pull cord & started to lift it off the floor. Some of the come was allowed to come out but then the saw was lifted off the ground. So my guess is that if compression was low the saw should not lift at all ?

Any advice so I can continue once carb is here.

Thansk.

 

[Burnerman]

Take the exhaust off, and post a pic of the piston and rings down there.....this gives an excellent clue as to the condition of the engine.
John

 

[ipbr21054]

Ok will do tomorrow.

When the carb was off I did look in the bore and piston was not scored etc & both rings where in place.
The condition of the piston was pretty good.

 

[ipbr21054]

Here we go.
The inlet side is smooth but exhaust side has some marks.
Using my finger through the port it doesnt feel rough etc

 

[ipbr21054]

I also noticed that the exhaust side didnt have any kind of gasket between cylinder & exhaust,maybe this also helps you

 

[lostinthelight]

Can you post another pic with the piston top edge and ring visible in the port?

 

[Burnerman]

At an initial glance that piston seems to be badly scored.
There should be a compressible gasket between the cylinder and exhaust.
Pattern pistons and cylinders are available for a good price.
John

 

[ipbr21054]

There was no gasket betweenctlinder & exhaust.
Photos of top of piston as requested

 

[Burnerman]

Not looking good! I’d suspect the rings are stuck in their grooves too.
John

 

[ipbr21054]

So do you advise a piston with rings ?
If so I need to get things ordered so so I just order the following items.

Piston with rings.
2 crank oil seals.

What do I use for a gasket sealer when I split the case.

Can I use Instant Gasket ?

Please advise on the above so I can order items.

Thanks.

 

[Burnerman]

The barrel is likely to be in the same state as the piston, so maybe budget for both?
The crank seals are best replaced with bearings.....feel for any play first. Oil seal failure will be evident by oil on the outside.
Use paper gaskets for the crankcase ( if you split it), same for the barrel base, plus an exhaust gasket too.
To shift the piston from the con rod, heat it up hot with a hot air gun and the gudgeon pin will slide clean out.
Don’t lose the circlips into the crankcase!
John

 

[ipbr21054]

Think I will get it apart and see.

You mention gaskets if I spilt it.
I assumed the cylinder was joined to the lower section.
Hence why I mentioned seals.

 

[Burnerman]

Scratching the brain cell regarding the MS.....the bottom of the crankcase may unbolt, so the con rod and bearings just lift out.
If that is the case I think the seal is made with silicone, but you’ll still need a cylinder base gasket.
Just post more pics with the thing dismantled and I’ll remember better.
John

 

[Burnerman]

My correction! The cylinder forms the top half of the crankcase too.
John

 

[ipbr21054]

Hi
I’ve now got it apart.
The crank has a cap which is held by 4 T27 bolts.
There are 2 seals either end of the crank and held in place by the cap.
When I pulled the piston out of the cylinder I could see the rings then expand a touch so they were not stuck. I can move them easy enough and aren’t broken etc.
The piston has some marks on the exhaust side & also in the cylinder.
Inlet side is fine.
Looks maybe more dramatic than when I feel it with my finger or nail etc.
The cap has orange sealant making a seal around the edge.

Video clip in next post