Stihl ms 460/660 Hybrid. 469e

[NateSaw]

Preface :

-This build was @drf256 's idea. We were talking hybrids, and he said he'd always wanted to try this. I doubt I'd have ever thought of it, even with my lathe fixture plate being marked 460/660. I pounced on this because of boyish excitement, and timing. I had just been given a 460 with no jug and no plastics. The tank had weeds growing in it. With that, a pair of red lever 026's and the clincher, a 660 jug. So I had what I needed to get started.

-On certain parts of this build, especially the muffler, my craftsmanship was lacking. I took a "means to an end" approach on certain things to get to the goal of running the saw to see if this hybrid was even worth doing. There is also some chineseum employed here.

- I wasn't going to do a thread on this saw. Half way in, I felt guilty pouncing on Doc's idea. I'm a squirrelly monkey sometimes and I don't consider the big picture and how my actions effect others. The man has no time for, in my opinion, heroic reasons. He's a family man and a health practitioner of MONUMENTAL commitment. I on the other hand am a saw addict, for now, and we know how selfish addicts are. I take hostage an unfair, unreasonable amount of time to work in my saw dungeon. When I'm not doing tree work with Gailey's, I'm neglecting my home life widdling away at saws. However... Doc said I need to do a thread. And less selfish than my saw addiction, is my desire, if this build warrants, to see you fine fellers on here that have REAL skills porting saws, grab this and run with it, making REAL power. Doc will... @Canadian farm boy , I know you'll make this run stellar. Your hybrids inspired me! Anyone. So that's the purpose here. Grab it and run with it fellers. I did the footwork, now y'all get some slick port work goin!

 

[NateSaw]

Chapter 1: The piston..

-The 460 stroke is 36mm
-660 stroke is 40mm
-660 intake is notoriously early
-We knew we had to drop the jug a fugton to make up the stroke difference... And that's no Bueno for the intake... So, we knew we needed a piston with tall compression height, and longer skirts...
In digging, I landed where most of you probably have already... The plethora of 125cc dirt bike slugs. They had more than enough skirt, and most had compression height for days... But they're all Reed valve, bottom fed transfer slugs. Full circle, with no windows, and very little meat around the pin to open up and trust. Many had interesting notches and holes on the intake side that we couldn't use. So, it had to be a saw piston.

 

[NateSaw]

The 288 slug is shorter on top than the 660... No dice. Longer skirts but by hairs. Welding a top on would putty the metal. I took to looking at pictures. There really was only one slug that looked taller and longer. The echo cs900evl. And, Lil red barn had em cheap so I got one.
As you can see, it's a fat fugger.

But.... There's alot to do here so let's put it on a diet.

 

[NateSaw]

Using the pin for alignment, you can see the blank canvass this slug could be.

 

[NateSaw]

Not only is it taller, with longer skirts, but the skirts are MUCH wider...
.... Widening ports to a dangerous width is more than possible

 

[NateSaw]

Also note that the ring pins are still both on the intake side..

 

[NateSaw]

I started with clearing the case for 54mm slug. And then some for the longer skirt. I wanted to keep the skirt for options for intake timing.
Barely fits...

 

[NateSaw]

Next I had to relieve the skirts ID to make room for crank throw... I set my compound to 22* arbitrarily, then to 10*, also arbitrarily. I eyeballed it. I did use some Prussian blue to see the contact areas.

 

[NateSaw]

Now that the piston fit the crankcase, I could bolt the jug on and try to aquire a squish picture. Unfortunately, in my haste I didn't take a picture of the solder crushed. I had to braid fat solder. The point I focused on was at the very edge of the domed piston. That was all I had to work off of. I took multiple readings with the base gasket and consistently read 0.1035". I knew I'd cut the dome off, and also knew I probably wouldn't be super accurate landing squish first attempt. I wanted to get close enough to see where the ports would land. So... I cut the dome off leaving the very edge of the piston, probably a band of maybe 0.005". This would make the height of the slug closest to my readings, so I could "math" my way into cutting the squish and band.
This picture is not my final pass. I swapped out the insert for a new one for proper finish. Idk why I didn't take a picture. Haste makes waste.

 

[NateSaw]

Back tracking a bit... For the benefit of science, here's the difference in compression height...

 

[NateSaw]

Some relieving I had to do to get the jug to bolt down. Nothing new here. You guys know the drill.

 

[NateSaw]

Nope. More relieving.... Lots. Fins, base, watch the flywheel etc... Again, nothing new here. Just different.

 

[NateSaw]

Now for some dietary supplements. We want big windows, and less weight. Voila. But it's still fat. No worries, I make a discovery later you all can probably see already.

 

[NateSaw]

Now let's drop this jug... I like big flats and I cannot lie. They sit nice and true when I flip them, and this thing needed a haircut for sure, to get the top cover to even consider taking a seat.

 

[NateSaw]

Lemme backtrack my *pretty boy again. I had to knock 0.030" off the base to even GET some semblance of a squish reading. Sorry. Very important. My reading of 0.1035",with gasket, was after already taking 30thou off the base.

 

[NateSaw]

So... 35thou from squish, as my focus... With an 18thou squish as my goal, I took I think a total of 0.1265" off the base
As you can see the lowers got lower....

 

[NateSaw]

Beautiful symptom... The 660's notoriously lazy, fat uppers, at bdc. So raising them won't necessarily make them unusably huge.

 

[NateSaw]

I didn't go crazy on exh. I mean, I took alot just to get to 100.5*. But I widened the acceptable 65%. I used the rings that came with this piston, which are an unknown. I didn't want them over extended. I also kept the roof tame. I'll give this slug another thing, it uses 1.5mm thick rings. So, if cabers were acquired, I'd have more faith in them holding form with a wider, flatter port, than the 1.2mm rings. But that's my novice theory.
This picture is a rough in. Not shaped yet. I'm not slick with a grinder yet, but I'm better than this

 

[NateSaw]

 

[NateSaw]

I don't know what came over me. I just kept grinding
Thanks the saw gods for this stove pipe rtv.