Rebuilding a Chainsaw Run on Straight Gas

[Tropical Sawyer]

Hi All! I have a few questions about rebuilding a Stihl ms381 with severe piston scoring.

A neighbor asked me to look at his chainsaw which wouldn't run. After a pull on the starter handle the saw seemed to lack compression so I removed the muffler to find severe scoring on the piston. Looking at the Madsen's piston failure analysis website it looks like the saw was run with straight unmixed gas. The neighbor had lent the saw to his brother which could have been when unmixed gas was used :.

I am considering rebuilding the saw with a cheap Chinese piston and cylinder. I was wondering however if the lack of oil has damaged the crank and bearings in the lower end. I could probably find out by removing the cylinder and looking but its not my saw and i'm pretty busy already.

Any advice would be appreciated. I'm sure that this has been discussed before on the forum but a quick search didn't find anything so I decided to start a new topic.

[Air Lad]

There are some super cheap knock off's that I wouldn't touch with a 10 foot pole 
but there seems to be some better quality options around.
I have used an Italian product called Meteor that seems to be regarded as good quality at a cheaper price. I also discovered genuine brand gear that has to come from Italy..Eg: Ms039 cylinder and piston kit $ 175 aus. It's cheap but freight $111 and a month wait. But for genuine this isn't a bad option.
Horses for courses I guess.
Good luck with you'r decisions mate

[Allar]

Majority of the time new p/c kit is all you need for a straight gased chainsaw.

If you're getting chinise p/c, i'd go with a farmertec. I wouldn't trust any other unbranded chinise parts.

[Tropical Sawyer]

Thanks for the replies, i will probably rebuild the saw with a new piston and cylinder. I'll definitely check out the options which you recommended first.

[Air Lad]

Majority of the time new p/c kit is all you need for a straight gased chainsaw.

If you're getting chinise p/c, i'd go with a farmertec. I wouldn't trust any other unbranded chinise parts.

Farmertec kit goes for $82.50 Aus. There are others here for more $
Tacsum $125. Hyway Nikasil $150. Meteor $200 (Italian made). The no name stuff goes for $30 to $90 .
These prices are for an 039/390 .. 49 mm
I need to replace the original as it is scored beyond rescue.
You like the Farmertec ?

[HolmenTree]

From the straight gassed Stihl saws I've worked on just the piston and rings need to be changed. 
A little elbow grease will clean that cylinder up nicely.
That OEM Stihl cylinder is way more valuable and precision made then any aftermarket stuff on the market.

[Air Lad]

From the straight gassed Stihl saws I've worked on just the piston and rings need to be changed.
A little elbow grease will clean that cylinder up nicely.
That OEM Stihl cylinder is way more valuable and precision made then any aftermarket stuff on the market.

Don't know what happened. Bought this one real cheap. Tried cleanup with fine wet and dry and kero. Replaced piston and rings . It runs ok but on inspection there is some slight cylinder grooves and some burning on either side of the rings. The elbow grease worked fine on a little 170 which was gifted to me looking terrible inside. Might run it some more to see if there is improvement. Only had 4 or 5 tanks.
Cheers

[Mad Professor]

From the straight gassed Stihl saws I've worked on just the piston and rings need to be changed.
A little elbow grease will clean that cylinder up nicely.
That OEM Stihl cylinder is way more valuable and precision made then any aftermarket stuff on the market.

What Holmen said.
Use wet/dry sand paper and scotch brite , and hydrochloric acid to remove aluminum smear on cyl. Be careful using acid, don't get on self or inside ports/aluminum that should be there.  Read up/search on how to do this.
I'd suggest an OEM piston rather than any Chi-Com stuff made of chinesium/beer can parts.

[HolmenTree]

Hi All! I have a few questions about rebuilding a Stihl ms381 with severe piston scoring.

Speaking of cylinders, here's the newly introduced MS382.
Similar to the MS461.
We'll never see this saw in North America unfortunately. 


 

 

 

 

 

[Mad Professor]

Interesting MS 382 Holmen.  Any more pictures? Maybe the whole saw.  What is cavity at base of cylinder for on ex side?

Is bolt pattern and bore/stroke same as a 038M (I'm thinking a swap possibility)?

What was that poor saw running?  30W at 16:1?

[HolmenTree]

Interesting MS 382 Holmen.  Any more pictures? Maybe the whole saw.  What is cavity at base of 22cylinder for on ex side?

Is bolt pattern and bore/stroke same as a 038M (I'm thinking a swap possibility)?

What was that poor saw running?  30W at 16:1?

MP, that was a MS382 that showed up in Joe Indies shop. It shares alot of the MS460 parts and has a similar cylinder scavaging setup as the MS461.
Same cc as a 038 Magnum,  even has flippy caps and a side chain tensioner.