First build questions

[Leerod83]

So I have a ms310 with a scored up piston. Saw still runs good but I picked up a huztl 390 short block for when it dies. Is there anything I need to do to the new motor other than bolt it in and go? Aside from tuning and break-in that is. Thanks and I'm new to here and saw tinkering for the most part. This will be a farm/firewood saw.

 

[Matt_Ellerbee]

Why was the piston scored? Need to fix that problem before bolting in new motor,or it will happen again.

 

[Leerod83]

Well, I'm not sure when it happened to be honest. Took it to the dealer when I noticed a gas leak between the tank and carb. Had that, the tank vent, filter, carb kit, plug and retuned. Was gonna do the muffler mod deal and when I pulled the muff I noticed the piston. It idles week and is snappy. Doesn't seem to be down on power. It wears a 20" full chisel and I cut mostly hardwoods with it. I did some trading with the brother in law for it who originally purchased it from e-bay. So there's no telling what happened to it before him. He works for a tree service (I used to also) so I don't believe he hurt it. I didn't run it long after the gas leak was discovered either.

 

[Leerod83]

Anybody help a guy out

 

[Matt_Ellerbee]

Have you checked impulse line? Why/where was fuel leaking from? Gas line I'm guessing.

Any pics of piston through muffler?

 

[Leerod83]

Have you checked impulse line? Why/where was fuel leaking from? Gas line I'm guessing.

Any pics of piston through muffler?

 

[Leerod83]

Best I could tell it was leaking at the tank from the fuel line/grommet. I assumed he changed the impulse line too as I told the dealer to check the saw over. I will however check it to be sure because the assume thing and my luck. I'll get some pics up after work. Thanks

 

[Leerod83]

So here's some pictures and the impulse line wasn't changed last service.

 

[Matt_Ellerbee]

Yuck. Not as bad as some tho. I'm betting that cylinder could be cleaned up,based off the piston isn't that bad as some on here that have been cleaned. Still gotta find that leak before rebuilding.

 

[a. palmer jr.]

Don't know about the Huztl kits but some of the engines require that the buyer seal up the bottom end before installation. Check everywhere that might have an air leak, like intake boot, pulse hose. Make sure the new engine has a little 2 stroke oil on the piston before start up. I use a few drops of oil on the rings through the ports before I install the engine.

 

[Leerod83]

I'll pick up a new impulse line and pressure check the old motor. Where can a guy pick up the right type of sealer? Will a hand pump work for the pressure check?

 

[a. palmer jr.]

You can buy Motoseal at Oreillys auto parts. Be sure to follow directions, it makes a big difference.

 

[grizz55chev]

I'll pick up a new impulse line and pressure check the old motor. Where can a guy pick up the right type of sealer? Will a hand pump work for the pressure check?

Bike pump with a guage, pump to 7 to 10 psi, no more or you'll blow out the seal between the pan and the cylinder. Lots of threads on pressure vac testing, both tests are important, I use pressure to find slow leaks.

 

[tomdcoker]

Anybody help a guy out

If you have the equipment and expertise vacuum and pressure test it for leaks. Most of the tie this is not necessary. Just be sure to do a visual for any leaks. Be sure to check the Gas line, impulse hose and the carb. to cylinder manifold for cracks or leaks, also be sure that the cylinder bolts are tight to prevent air leaks. I use an adhesive for the cylinder gasket, but I have a pressure gauge to check my work. If you do not have one just use a gasket and soak it in gas or use a film of adhesive on it and do not soak it. Tom

 

[blsnelling]

A gauge is the only way to test if it'll hold vacuum.

 

[Ted Jenkins]

Years ago I worked for a Stihl dealer rebuilding. Most of the saws that had scuffed pistons or scuffed cylinders were the fault of the operator. I saw no need to check bottom ends on current year models, so your saw probably just needs top end service. Since you did not mention that the thing rattles like mad or something that would indicate bottom end problems. Replace the top end and start cutting. Thanks

 

[blsnelling]

So just throw a topend on it and hope for the best?

 

[cedarshark]

It sounds like the gas line was the source of your air leak. The piston is scored enough to leave aluminum on the cylinder wall. This needs to be removed chemically (w/ muratic acid) or mechanically with sandpaper or a dremel tool before you install a new piston. As brad mentioned above, get a brake bleeder kit (w/ gauge) and test the saw before you fire it back up. Motoseal,Yamabond,Hondabond,Threebond or Dirko can be used to reseal the bottom cap on the crankcase. As you have easy access to the crank seals and bearings, I would consider replacing them at the same time.

 

[Leerod83]

Thanks everyone for all the insight here. When I get her back up and running I'll let y'all know how she turns out. Thanks again.