NE 346XP - Affects of Cat Muffler & Muffler Mod - Porting & Popup To Come

[bjorn773]

Ok, off to the hardware store.

 

[TRI955]

Keep us informed, if you need, send me a PM and I'll give you my # and you can call me.


Mike

 

[bjorn773]

Thanks Mike, I'm hoping to pickup the bit tonight. Reassembly time depends on how long the honey do list is this weekend. I'll post as soon as I hear it run.

 

[bjorn773]

I picked up a .030 number 68 drill bit. I put a hole in the original vent bore with the bit on an angle. Now, I'm trying to figure out which way these screens go. In one direction, gas seems to seep out, I can hear hissing as I move the tank around. I flip them both over and it seems to seal with no hissing. However, is this going to vent. It looks like one side is more solid than the other. Basically looks like pourous plastic of some sort, not brass like some of the other's I've worked on.

 

[TRI955]

I don't recall that, maybe I just got lucky and put it back in the correct way. I wouldn't think it would make much difference....


Mike

 

[bjorn773]

I've tried every combination but it seems to seep. However, I have the tank on a bench with the fuel line plugged. Pressure building in the tank has to go somewhere, so I suppose out the vent is where it would go.

 

[bjorn773]

I started reassembling the saw at lunch. I have a strange bind at BDC. I know it was not binding before when I was degreeing it. What should ring end gap be on these, perhaps the ring is hanging on a port. Everything is bevelled, but I never felt the bind until I put the ring on. The bind doesn't occur when the ring passes a port, just at BDC. Any ideas?

 

[blsnelling]

You probably need to trim the bottom of the cylinder "skirts" that go into the crankcase recess. They're probably bottoming out and being forced inward by the case, pinching the cylinder. Make sure you didn't crank the "skirts" or base flanges where the bolts go.

 

[bjorn773]

Makes sense. I'll take a look tonight. Thanks.

 

[bjorn773]

There appear to be two problems. First, the piston skirt is dragging on the inside of the crankcase. It has shaved the slightest amount of crankcase material off. Second, the flywheel seems to be dragging ever so slightly on the underside of the piston. The first is most likely due to this being a larger piston than stock. It's an aftermarket version of the NE piston. The second is probably just poor casting. I will have to relieve the underside of the piston a bit to allow more clearance.

 

[bjorn773]

Maybe this is common sense, but better to ask before grinding. I plan to put some blueing on the flywheel and rotate to mark exactly where the piston underside is dragging. Then I will relieve the underside of the piston equally on both sides of the rod. Will this create a balance issue?

 

[blsnelling]

Skirt to case clearance is not real uncommon on aftermarket pistons. Just relieve whatever's hitting.

I'm not real clear what you're saying is dragging on the underside of the piston. You mentioned the flywheel, which isn't possible, and you mentioned the rod. How would the rod be hitting the piston?

 

[bjorn773]

I'm sorry, you're right. It appears the crank counterweight is rubbing the underside of the piston at BDC. I can just make out some slight marks on the crank weight, but need to remove the piston to get a better look. I will put blueing on it, rotate a few times then remove the piston for inspection. I suspect the underside of the piston will need some slight relieving.

 

[Cowboy Billy]

Awesome Brad

Now I want to mod my saws!

Billy

 

[bjorn773]

Skirt to case clearance is not real uncommon on aftermarket pistons. Just relieve whatever's hitting.

The piston was hitting the crankcase at BDC. Relieving the case did the trick.

 

[TRI955]

Well, does it run???

 

[bjorn773]

Not yet. Between two jobs and a family, my chainsaw mod time is pretty limited. I hope to have it running this weekend.

 

[bjorn773]

I'm working on my saw and noticed that looking through the exhaust port with the piston at BDC, about 3/32 of the piston is still visible through the port. The piston does not drop completely below the port. Is this going to be a problem. I did mill .030 off, but I have three times that much piston still in the port.

 

[bjorn773]

I reinstalled the oe p&c to see whether the piston dropped completely below the port and it did. So, my aftermarket cylinder exhaust port was slightly lower than the oe. I have raised the top of the port, so my duration is increased. Will the piston in the port at BDC be a problem or is this common on aftermarket cylinders?

 

[blsnelling]

I wouldn't sweat it. There's nothing you can do about it anyway. As long as port timings are correct, the piston sticking up a little at BDC is not an issue.