Mastermind Meets The J'Red 2188

[Mastermind]

The owner of this saw asked about some pics........welp, here ya go Alex.

All the way from Alaska......

 

[Mastermind]

This saw is basically a 390XP.....

 

[Mastermind]

A little machine work to kill several birds with one stone. The 390/2188 is another one of those 90cc saws that has too much exhaust duration. By cutting the squish and base, I lose exhaust duration, gain intake duration, and raise compression in a single step.



If you look closely you will see that I cut the cylinder extensions while the jug is mounted this way.......saving time.



I like to check squish clearance after I cut the band to determine exactly how much to cut the base.



.046"......so I take .028 from the base to end up at .018".

 

[Mastermind]

Next step is to indicate the mandrel so the base will be cut dead square. I use a live center with a flattened point, that way I can tap the jug around to get it just so.



Then to check our new clearance.



.019......that will make the squish velocity pretty high on this engine. The band is not very wide, so I can run it a little tighter that on some other engines.

 

[cgraham1]

opcorn:

 

[Mastermind]

Now moving to the port work.....



Transfer height on this engine is 120 degrees from TDC. Here the transfers are roughed in......lots more to do to them.



Almost got tunnel vision and forgot to take pics.

Here I'm reshaping the intake port......I don't like an overly wide port so I just widen out to the edge of the factory bevels. Proper shape and opening height is my goal here.

 

[Mastermind]

Now for the exhaust. On this engine I don't widen, or alter the height of the exhaust port at the cylinder, but the outlet is worked over pretty heavily.

Remember, we wanted less time/area on this engine. To widen the exhaust port would defeat the trouble we just went to to lower it by machine work.

Matching to the muffler...





Creating a scavenging step.







This is just the sizing......finishing comes later.

 

[Mastermind]

Now the lowers.

Lots of people really work over the lowers. I'm not a fan of hogging stuff out on a work saw. Flow velocity means more to me here than sheer volume.

Just some blending of sharp edges.



Nice little pile of chips from this jug.

 

[Mastermind]

Now here's the jug during the finish work.





And after.....









I'm gonna be putting this back together now.

 

[Marshy]

opcorn:

 

[sld961]

Nice work. I always enjoy these threads. Thanks for taking the time to stop and take pics.

 

[Ironworker]

Hey Randy do you wear gloves while your grinding?

 

[blsnelling]

Nice saw. I luvs me some 2188/390!

 

[madhatte]

Holy cow, that is some clean work. Bravo!

 

[Mastermind]

Hey Randy do you wear gloves while your grinding?

When I work with steel I do. Not with aluminum.

 

[redfin]

Beeeeeutiful. Thanks for da pics.

 

[Mastermind]

Here's a few more details.

The carb adjusting screws have locks that require special tools to adjust. I defeat those so that the customer can properly adjust their carb with just a tuning screwdriver....

 

[Mastermind]

Then the coil.....

The 390XP and the 2188 come with a coil that is rev limited to 13,000.



I swap that out for one that is limited to 13,300.



I recommend that the saw be tuned to 13,100 after mods.

 

[Ironworker]

When I work with steel I do. Not with aluminum.

No burrs with aluminum?

 

[redfin]

Does the original limited coil start cutting out before 13k? Just wondering why you would switch for 100 more rpms.