Echo 490 to ported 4910…to cs-5484

[thompsoncustom]

Never tired this but what about making your own boot out of castable polyurethane rubber?

You would have to take the larger boot and the stock boot and cut/glue them together to make the mold shape you wanted and you could adjust the length to whatever you wanted, I just don't know how long they would last or if it would work in this application at all but may be a option but I've put poly bushing in cars without any issues.

 

[Ketchup]

Never tired this but what about making your own boot out of castable polyurethane rubber?

You would have to take the larger boot and the stock boot and cut/glue them together to make the mold shape you wanted and you could adjust the length to whatever you wanted, I just don't know how long they would last or if it would work in this application at all but may be a option but I've put poly bushing in cars without any issues.

Well, mold making is a skill I don’t have but yes I have considered it. I was thinking silicone because of its high melting point and ease of pour. I also wonder how long they would last.

 

[Ketchup]

Well, I just couldn’t leave it alone. I just couldn’t see how this 4910 was going to catch up with a 346. But having torn it apart and built it up so many times, I’ve come to appreciate how easy this saw is to work on, and it’s feather light.

Pretty early on I looked at what it would take to fit a 346 jug on there instead of the 4910. The extra MM of stroke was attractive, but the layout wasn’t great and the wrist pin bearing is a problem. 346 is 10mmID x 14mmOD. 4910 is 11mmIDx15mmOD. I couldn’t find an acceptable 10x15. I could probably have shimmed it, but it seemed like a lot of work for a minor gain. But then I realized that the most common husky bearing is 12x15…

Including 359/357.



And the bolt pattern is a lot closer. That’s a $17 white box 359 jug that I started my experiments with. You can see where this is going.

 

[Ketchup]

There’s enough flange on the 357/9 jugs to shave them down and drop them on the case. It takes a lot of clearancing. The flywheel needs thinned. The magnets shoot sparks everywhere when the carbide hits them.


And the case needs ground away on the PTO side. This photo is from before I got busy. The screw boss right of the piston has to be taken down flush and the lower humps and ridges need slimmed a scoache.

The plastics and brake won’t fit if you don’t take off a lot of fin.

And the transfer flares are a lot wider. Belt sander mode took over…


Not pretty. The fins and some casting wall needs ground away at the bolt holes for the head bolts to have a straight shot at the threads. There are also some case deck bits that stick up and the jug needs trimmed for those.

 

[Ketchup]

Something I forgot to photo is the jug spacer. 357 is a 34mm stroke, 4910 is 33mm, but either the deck is lower or the con rod is longer on the 4910. I very crudely fabbed a 0.1” spacer. Effectively it’s a super thick base gasket. That got me to right at -0.005” squish. I cut the band to 0.022”, which seemed like a conservative port job amount. Next one I would probably take a bit more out of the band and make a shorter spacer. Sorry for the crude craftsmanship and rough numbers. I was just groping along hoping this would work. Here’s fairly far along in the port work and the stretched bolt holes.

The fine chaps on this forum helped me a bit with numbers. I’ve never ported a 357. Here’s that thread:

Staggered uppers on 357?

Hi guys! I’m porting my first 357. Target numbers are 106/124/80. Maybe a bit higher on the exhaust. My question is has anyone left the secondaries low and just brought up the primaries? @huskihl, @Stump Shot, @Mastermind , @drf256, @srcarr52, @Red97, and anyone else! Open to any advice...

opeforum.com

 

[Ketchup]

So the carb may have been the trick that would have brought the 4910 jug to life. But as mentioned above, there is very little room in the carb box. I wanted a hda199 to go in, but I found the layout backwards and the intellicarb metering system makes it too tall. Turns out a hd12 goes in a lot better. Unfortunately, it’s 5mm thicker than the WT carb, and the bigger jug protrudes into the air box a bit. Luckily, the 357 intake boot is almost as short as the stock 4910 boot. 357 left, 4910 center, 372XT right (372OE is the same length as XT).


But you have to buy 5mm. You take 2 off the spigot.

You stretch another off the air horn bolt holes.

There’s yet another MM you can shave off the carb side of the air horn. Sorry, no photo there.
Then there’s the boot flange. It ain’t pretty. I got 1.5mm shaved off here. I had to trim the intake boot to fit and the inside bore of the flange needs opened up considerably. You gain the rest by gently cramming everything together. It crushes the boot an unfortunate amount.

 

[Ketchup]

But it all fits. The best part is the throttle and choke linkages are a near direct fit! You have to take the cable fitting off the throttle shaft and grind a spot for the travel of the remaining plate. The choke wire is a little sloppy, but stays put. Throttle linkage is a perfect fit. No mods.

 

[Red97]

I like it!

 

[Ketchup]

Last one for tonight. The Muffler. It turns out to be surprisingly easy as well. The original muffler is folded together. Just grind away the outer fold and keep the top as a retainer like an 026 can.
You have to cut the bolt hole pipes as they don’t line up with the new pattern. I just left them for now as outlets. Then you need a bracket shaped like the 357 exhaust. Turns out the chinese 357 mufflers are all loose inside and have the perfect bracket. Just port match and drill new holes in the back of the can. I filled the gaps with liquid exhaust gasket.

The stabilizer bolts at the bottom of the jug clamp it all back together. It does stick out a tad, but not enough to interfere with cutting.

 

[Ketchup]

Oh yeah. Nothing amazing, but for the weight…

 

[thompsoncustom]

Oh yeah. Nothing amazing, but for the weight…
View attachment 370526

I think it's amazing to see what is possible when someone puts in the work.

 

[Dolkitafreak]

I had looked into 346 swap just never did as there’s a few things I struggled to justify the time with. I dig this build, looking forward to cut vids!

 

[Ketchup]

I had looked into 346 swap just never did as there’s a few things I struggled to justify the time with. I dig this build, looking forward to cut vids!

I think this is the easier build and it gains more displacement. My hope is I can get 346-like performance out of the 357 jug. They’re very similar. Still chewing on how to scale the design of the 346. I think the transfers are smaller relative to bore on the 357.

Right now I’m still working out the kinks. I’m pulling pulse from the spigot and it keeps leaking. I also don’t like how crumpled the boot is. And I’m sort of glad I don’t have photos of the spacer. It’s a sandwich of homemade gaskets and steel body panel I scavenged off a dead drill press. 1184 was the condiment of choice. That will have to be improved as well.

I should mention 359. It’s possible and would gain some displacement. The main extra hurdle is the transfer covers. They’re thin and have a weak interface right where you need to grind the most away. If you go with a AM jug there’s plenty of meat to grind away, but then you have all the other problems of an AM jug. And personally, I find the transfer lowers on 359 to be completely cattywampus. Is it side fed or bottom fed? Why all the squared geometry at the base? Is the tunnel divider helping or hurting?

Still, 57cc is appealing. More grunt in the cut is what I prefer in all work saws.

There may be a diminishing return there though. Effectively this is a de-stroked saw. Increasing the bore makes the saw more and more over square. 33mm is a pretty small stroke. Maybe a 4910 stroker is possible? That’s a lot farther down the rabbit hole…

 

[Dolkitafreak]

I think this is the easier build and it gains more displacement. My hope is I can get 346-like performance out of the 357 jug. They’re very similar. Still chewing on how to scale the design of the 346. I think the transfers are smaller relative to bore on the 357.

Right now I’m still working out the kinks. I’m pulling pulse from the spigot and it keeps leaking. I also don’t like how crumpled the boot is. And I’m sort of glad I don’t have photos of the spacer. It’s a sandwich of homemade gaskets and steel body panel I scavenged off a dead drill press. 1184 was the condiment of choice. That will have to be improved as well.

I should mention 359. It’s possible and would gain some displacement. The main extra hurdle is the transfer covers. They’re thin and have a weak interface right where you need to grind the most away. If you go with a AM jug there’s plenty of meat to grind away, but then you have all the other problems of an AM jug. And personally, I find the transfer lowers on 359 to be completely cattywampus. Is it side fed or bottom fed? Why all the squared geometry at the base? Is the tunnel divider helping or hurting?

Still, 57cc is appealing. More grunt in the cut is what I prefer in all work saws.

There may be a diminishing return there though. Effectively this is a de-stroked saw. Increasing the bore makes the saw more and more over square. 33mm is a pretty small stroke. Maybe a 4910 stroker is possible? That’s a lot farther down the rabbit hole…

Agreed on transfer relative to bore.

I’d pull pulse from a transfer tunnel or cylinder base. I wanted to keep mine 346 for competitions with cc restrictions. I’m excited to see your saw finished.

 

[Ketchup]

Here’s how she sits now. I think this is stock appearing? Too many muffler outlets?
Shindaiwa 500sx air filter. A stack style filter may ultimately be necessary.

 

[Ketchup]

Agreed on transfer relative to bore.

I’d pull pulse from a transfer tunnel or cylinder base. I wanted to keep mine 346 for competitions with cc restrictions. I’m excited to see your saw finished.

I don’t know diddly about racing, but I think you’re over 3cube with the 33mm stroke and 44.3 bore.

I’m a long way from finished. It runs but needs a lot of small touches. I’ll probably get this one close and just start a second one.

 

[Ketchup]

Agreed on transfer relative to bore.

I’d pull pulse from a transfer tunnel or cylinder base. I wanted to keep mine 346 for competitions with cc restrictions. I’m excited to see your saw finished.

I don’t know diddly about racing, but I think you’re over 3cube with the 33mm stroke and 44.3 bore.

I’m a long way from finished. It runs but needs a lot of small touches. I’ll probably get this one close and just start a second one.

 

[Dolkitafreak]

I don’t know diddly about racing, but I think you’re over 3cube with the 33mm stroke and 44.3 bore.

I’m a long way from finished. It runs but needs a lot of small touches. I’ll probably get this one close and just start a second one.

33x44.3 is 50.86cc which is allowed at every major race now. It’s bigger than true 3 but everyone allows 51cc now as no currently available saw is smaller than 3ci in the 50cc class. And someone may bring the issue and try and limit at 50.1cc, didn’t end up mattering as the 346 chassis and cylinder can go faster than 4910 imo.

 

[Ketchup]

The chain is awful and I may take the secondaries up to meet the primaries. That was a nasty chunk of knotty petrified Honeylocust. Some weird popping noises in the cut. Almost like too much ignition advance. May e I’ll put a light on it.

@Dolkitafreak, have you run into problems getting the RWJ butterfly to open all the way? I really have to mash the trigger on this HD 12. Feels like the linkage is flexing.

I don’t think I’ll ever be satisfied, but it’s a strong saw now.

 

[Duane(Pa)]

Sounds way too fat to me...