Stihl MS250 rebuild.

[ArlyA]

Here is a fuel story that might not apply to you Dodge. We take our machines into the field to be used by volunteers so with each operator, we've give them some extra fuel in a red 22oz camp fuel bottles. Since we had 2 and 4 stroke machines with us, I'd mark some with a large "MIXED FUEL" to help keep them straight. Helping us we had a super smart university employee who'd never make a mistake in his life, fill the bottles and as you might guess, put straight fuel in the ones marked MIXED FUEL. I happen to fill my machine 1st that day and noted the fuel was not the correct color and ran around finding the miss filled bottles.. It happens to even the really smart folks. :laughing:

 

[ericm979]

Other two stroke assembly tips: check the port edges and gently round the sharp ones. Very gently if it's nikasil instead of an iron liner. On Chinese saw cylinders I will clean up the ports to remove any dingleberries or other weird stuff and make them symmetrical. I use small stones to round the edges.

Piston skirt edged get slightly rounded (on like a 1mm radius) if they're sharp. I want oil to stay on the cylinder wall not get scraped off.

I measure the piston and cylinder to check for the correct clearance. I have had manufacturers ship mis-marked parts.
I already mentioned checking the ring gaps.

Assemble with generous squirts of two stroke oil on the bearings and bore.

I check the squish clearance after it's assembled. You can't do much to reduce it on a clamshell engine but it'd be good to know if it's too tight. You could file down the piston crown in that case.

 

[ruffdog]

Thanks for all the answers. How do you pressure test? Plates to cover up the ports?

Yes, plug intake, exhaust, and pulse line.

Also....3 bond 1184.

 

[dodge man]

I got the new parts in today, hopefully get it put together this weekend.

 

[dodge man]

All back together. I have not started it yet, I wanted to let the RTV dry overnight. Took me about 4 to 5 hours to get the piston installed on the old rod and crank and get it put back together. One problem, I got one leftover torx screw, there are several that hold parts together, such as the handle. I looked the saw over good and can not find where it goes. Ericm was nice enough to send me several manuals a few months back and I looked through them and could not find where it goes. The pic is the saw after it is back together and the leftover screw in the tray.

 

[ruffdog]

Silicone sealers are not fuel proof....keep the screw for next time....

 

[ericm979]

Yea, you need something like Yamabond #4 or Dirko to seal crankcases.

Did I send you the parts list? It shows the size and length of the screws.

 

[ArlyA]

According to a google search concerning rtv gasket chemical.

RTV works quite well for gaskets because it has very low shrinkage when cured, and the material remains compliant without being hard or brittle. It is also resistant to gas, diesel, oil, or other automotive fluids, so it won't disintegrate over time when exposed.

 

[dodge man]

Yea, you need something like Yamabond #4 or Dirko to seal crankcases.

Did I send you the parts list? It shows the size and length of the screws.

You sent a parts list but it didn’t list the size of the screws or the length. There was a lot of torx, maybe 12, and they were all the same except one. I do not think any are critical except the 4 that hold the crankcase on the cylinder and in the saw.

The Hiway kit had nicely rounded ports, I did not need to do any smoothing.

The kit also had a warning about fixing what went wrong the first time. One of things was using ethanol gas. At one time I ran ethanol at 10% but it was 91 octane. Then I switched to pure gas at 87 octane. A couple of years ago a station started carrying 91 octane pure gas.

 

[ruffdog]

According to a google search concerning rtv gasket chemical.

Oh....Okay........:laughing:

https://441py33rout1ptjxn2lupv31-wpengine.netdna-ssl.com/wp-content/uploads/tech_docs/tds/81160.pdf

Chemical / Solvent Resistance
The product retains effective properties in contact with automotive fluids, such as motor oil, transmission fluids, alcohol, and antifreeze solutions. Note: Not recommended for parts in contact with gasoline.