Basic top end swap /Solo 665 becomes Solo 681

As the title says, I am going to pop the top on the Solo 665 (65 cc) and make it a Solo 681 (81 cc).

While I am at it? I will explain (somewhat briefly) how to do this yourself. If you ever decide to do a saw yourself? Post a thread, ask questions, and take pics.

There is quite a few steps involved. But nothing the average homeowner can not do.

For this saw? You will need a 4 mm allen, 5 mm allen, a T-25 torx bit, and a flat head screwdriver. I may have forgotten a few small things I used, but these are the main tools for this saw. A Stihl will use the T-27 mainly, and a Husq uses a lot of 4 mm and 5 mm.

Here is the saw and parts in question. Even though this saw is gaining 16 cc, it would be the same swap if it was an aftermarket top end or OEM top end of the same size.




First, we have to remove the plastics and the wrap handle (you don't have to remove wrap.. But taking it off makes life much easier).





Once all the plastic and the wrap are off, your next move will be the jug. On a Dolkita or Solo, removal of the entire assembly (carb, boot, cylinder) is the easiest. But you can remove the carb, boot, and jug, a separately.





You need to make sure the fuel tank is empty before the next step. Remove the fuel line and loosen the four 4 mm allen bolts that hold the cylinder down.

(Notice the visible oil 36:1 )



Once you have the cylinder off, if your going to "up" the size of the saw? The piston has to come off. So you need to remove one of the circlips (these can be a PITA).




Then pull the wrist pin.. a small deep well socket works well for this.




And finally, the A/V spring has to come off the old jug and be put on the new jug..




Now you have the saw broke down and ready to get all the new parts ready for assembly.

 

Remove the carb and impulse from the old cylinder and place on the new jug.




Then install the A/V spring on new jug.






Before you reinstall the cylinder bolts, clean any Loc-tite that may have been on them, be sure to reapply some before you install.





This pic shows the difference in size of the Pistons






Now it's time to put everything on. I use good 2 - cycle oil as an assembly lube. Put some on the needle bearing, wrist pin, and piston skirt/ring. Put the piston on and install circlips (I install one before getting it on saw, then install the other after wrist pin is installed). Make sure the arrow on the piston, points towards the exhaust port.. Always..



Because this is a single ring saw, it's pretty easy to compress the ring and place the jug over top of it. Make sure to apply some 2 cycle oil on the cylinder walls before sliding piston in.





Then torque the cylinder bolts down to 14 NM (on this saw). Please refer to your specific saws torque specs.

After a few heat cycles, it's a good idea to check the torque again. Just to be sure.

 

The only thing I did to this saw, as far as a mod goes? Is to clean up the window casting. There is a thin casting flaw that's about 1/64" around the O.D of the windows. I used a dremel and cleaned those windows up..






And here. You can see the the Big Bore jug (81 cc) is lighter by over 3 oz, over the 65 cc jug.





I know I probably forgot about a dozen things (like the gasket, checking squish, etc). But I have promised this thread for 2 days and it's getting late. Took a while to build the saw and a while to do this thread.

Here is the finished saw. Was a 665.. Now a 681!

 

Here are the videos. The 665 was about broke in (half dozen tanks).

The 681 only had about a half tank (couple heat cycles and retorqued cylinder bolts)

I timed them twice and these are the numbers I got

665
1st cut 4.0 and 4.03
2nd cut 3.7 and 3.75
3rd cut 3.69 and 3.60
4th cut 3.60 and 3.65





681
1st cut 3.0 and 2.90
2nd cut 3.07 and 3.09
3rd cut 2.94 and 2.96
4th cut 2.81 and 2.74


Here are the videos

Solo 665 before putting on 81 cc kit (681):


Solo 665 (now a 681):

Now open for replies..

 

And for those who are worried about putting something back where it went? You can take pics along the way? Or before cell phones, in my early shop days, we were taught to use little pieces of paper and write down, what went where.

Or in the case of cylinder head bolts, lifters, valves, or any other important wear fit part? Place in order in a cardboard template.

Here I did a small example to show how you can organize parts.



After doing several, you won't need to mark anything. You'll just be able to break it down, throw it all in a container, and put it back together

And the last pic is the compression of the 65 cc jug. I want to give the new jug some time to seat before taking a reading.

 

Most people think they can't accomplish something like this? But it is much easier than most think. A few tools were needed but they were not expensive.

Some of the tools I bought for this project were cheap! A 6" long t-25 torx in 1/4" drive was less than. $5 shipped!

 

Great Job, Dex! and some nice gains too...

 

I only put some back on, because they had some on from the factory. All the Stihls I have ever worked on, never got any.

As for the base gakset? I don't like to push my luck. The jug is pretty thin around the outer edges of the transfer ports. So I used the metal gasket that comes on the Dolmar 7900.