Need a little help porting a 346

[Ironworker]

Well I picked up a 346 oe with a new 50cc top end. Brad is nice enough to cut the base for me and do a pop up, I will be doing the port work once it's returned, I would appreciate as much info on these and some pics of work that others have done. I usually pick Randy's brain and he has been very helpful on a couple of builds already but I like to see a variety of stuff. I did a search but it's a PIA.

 

[sunfish]

I cut the base and did a pop up on one of mine (50cc) with no porting and it's strong as hell!

Other one (45cc) I did same but widened ports, matched lowers, hogged out the exhaust and it's strong as hell.

 

[Chainsaw Jim]

You'll be doing good to eliminate any edges that can cause turbulence or restriction to the air/mixture flow. You shouldn't need to change the timing of either the ports or ignition.
When grinding on cylinders it is key to focus on the surface you'll be leaving behind for the rings to travel over. The use of angled and rounded edges in the exhaust and transfer ports are to prevent too much of the ring coming in contact to hang up on, and all the edges are beveled or chamfered to further aide that.
Many open port cylinders have edges in the upper transfers that are left too sharp from the factory and will wear on the piston very hard.

 

[Ironworker]

Where are the saw gurus at.

 

[Ironworker]

Does anyone have any pics of the lower transfers after porting, I'm pretty sure I'm gonna match the case.

 

[drf255]

Not a Guru, but my $.02


With the popup and the jug drop, you're not changing the (already excellent) exhaust or transfer timing very much, if any.

Tightening squish alone will drop jug slightly onto piston, so there will be a slight difference in blowdown. If the exhaust drops 1*, the transfers will drop slightly more because of rod angle.

You're gonna get slightly more intake. Brad likes that.

No guru here, but I'd Widen the intake and exhaust and not change the timing at all. Square up the intake.

If the design is a 1 ring hoosky with a central ring pin above the intake port at BDC, then you can widen the intake to 1-2mm from the skirt edge. You won't have to worry about the ring gaps like you do on the Stihl 026.

I know on those, the lower inlet transfers need work.

Message Mattyo. He built a 350 with a 346 45mm top that was purely amazing. Plus, the guy that's doing your machine work builds an incredible 346, as you know.

Below is a pic of "squaring up the intake". In case you don't know what I mean. It's an unfinished 026 intake port.

 

[drf255]

Sent from my iPad using Tapatalk

 

[redfin]

What are your stock numbers?

 

[Ironworker]

Not a Guru, but my $.02


With the popup and the jug drop, you're not changing the (already excellent) exhaust or transfer timing very much, if any.

Tightening squish alone will drop jug slightly onto piston, so there will be a slight difference in blowdown. If the exhaust drops 1*, the transfers will drop slightly more because of rod angle.

You're gonna get slightly more intake. Brad likes that.

No guru here, but I'd Widen the intake and exhaust and not change the timing at all. Square up the intake.

If the design is a 1 ring hoosky with a central ring pin above the intake port at BDC, then you can widen the intake to 1-2mm from the skirt edge. You won't have to worry about the ring gaps like you do on the Stihl 026.

I know on those, the lower inlet transfers need work.

Message Mattyo. He built a 350 with a 346 45mm top that was purely amazing. Plus, the guy that's doing your machine work builds an incredible 346, as you know.

Below is a pic of "squaring up the intake". In case you don't know what I mean. It's an unfinished 026 intake port.

Good info

 

[Ironworker]

What are your stock numbers?

Didn't check them. I probably should but I don't bother being that the height of the cylinder is being changed.

 

[EvilRoySlade]

I have not learned port work yet but checking and recording timing would be very wise. You will have before and after numbers, database is what you build. Takes a little adventure out of it but I'm sure this won't be the last 346 you get into.

 

[drf255]

Someone's gotta have the stock numbers on hand here.

 

[Ironworker]

Someone's gotta have the stock numbers on hand here.

I have another one I could check, maybe I'll do that .

 

[Ironworker]

I have not learned port work yet but checking and recording timing would be very wise. You will have before and after numbers, database is what you build. Takes a little adventure out of it but I'm sure this won't be the last 346 you get into.

You're right, but I'm somewhat inpatient and more interested in the end product.

 

[blsnelling]

The following is my NE 346XP recipe. I've done very few OE, but something similar should work on the them.

As already mentioned, I turn a pop-up on the piston. IIRC, it's .035". Always measure the crown thickness above the top ring. As a rule of thumb, always try to keep it no thinner than .100". I then recommend deleting the base gasket on the 346, in order to minimize the flat area that will extent out onto the intake extension.

I always case match the base, then blend into the lowers. This requires removing some of the cylinder extensions. I also raise the sides of the cylinder by approximately .050".

Before

After

I widen both the intake and exhaust to 70% off bore.

You can also see in the pic above where I widen the upper transfers about .100".

After

Note that the intake is much more square, as rings do not move across it.

I don't have my numbers in front of me, but I believe they're:
Exhaust 106-107
Transfers 121-122
Intake 80

 

[Ironworker]

Wow Brad, thanks, those are some sweet pics. That's more or less what I had in mind. You sent me some numbers already and I got some from Randy. I just went to check the stock numbers on my other 346 and discovered that the P&C is scored pretty bad, my first bad eBay experience. No big deal, I'll either return it or get a new top end.

 

[drf255]

Brad,

You got some beautiful jugs.

 

[blsnelling]

Ummmm..........Thanks, lol

 

[CapitaineHaddoc]

I just put a Snellerized cylinder on a nice 346XP. These pictures are nice, but when you have the cylinder in your hands, it looks almost better. A real piece of art.

 

[drf255]

Why 70% of bore, not to skirt/ring gap limits?