Older McCullochs had that small groove cut at the top of the exhaust port to act as a sort of decompression device, at low RPM like starting up a saw it would lessen compression a bit, with the saw turning WOT it hardly mattered.
Did finger ports kill this 394?
- Thread starter marti384
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Really don't know why they did that on that particular saw; but we can speculate a bit as some of that slot in the bottom will be exposed to the bottom end at TDC, almost like the dreaded freeport issue we all observed then realized didn't matter much on those 56mm Huztl's. So what happens? Maybe a bit of fresh mix from the lower end gets pulled in there? Possibly helps lube or cool that area??
Rx7man
Cattle Rubbing Post
I think it looks more like fatigue than ring snag... My 064 snagged a ring and it's evident where it happened..
drf255
BAD CAD
The porting on that jug looks very nice and well done.
I wouldn't want a ring gap going over any open space. I'm sure whoever did that nice work knew that, so it's likely the piston was replaced incorrectly or the wrong piston was used. Like JJ said, replacing it with the correct 394 piston in the correct orientation would be incorrect with the mods.
That teardrop cut in the exhaust floor is odd. I can think of only 2 possible reasons. One would be to make the jug usable after there was damage to the floor of the port. Second is intentional freeporting. Some people believe that freeporting at TDC will create a Venturi effect and allow the case to fill betterer.
I wouldn't want a ring gap going over any open space. I'm sure whoever did that nice work knew that, so it's likely the piston was replaced incorrectly or the wrong piston was used. Like JJ said, replacing it with the correct 394 piston in the correct orientation would be incorrect with the mods.
That teardrop cut in the exhaust floor is odd. I can think of only 2 possible reasons. One would be to make the jug usable after there was damage to the floor of the port. Second is intentional freeporting. Some people believe that freeporting at TDC will create a Venturi effect and allow the case to fill betterer.
Big Block
WFO or I don't go
How hard did this thing run compared to a stock 394?
I think you are right about wanting it to Freeport. The groove continues into the floor of the exhaust port. Not very deep or wide, but probably just enough to create a free port situation. It is hard to tell though, since I don't have a good piston to put in there and see if the exhaust skirt is short enough to free port.
Don't know, it came to me broken. I might throw a 395 piston in it and run it, then put an unported 394 jug on it to see the difference. I want to know where the location of the ring end pins are on a 395 piston first before buying one. Anyone have measurements or photos of 395 pin location?
Chris-PA
Where the Wild Things Are
That notch does look like an intentional freeport. Can't see that it hurts, nor how it would help. When the piston gets toward TDC it's not pushing or pulling air anymore, but there will be some high pressure in the exhaust port and low pressure in the case. Due to momentum and the mass of the air column its response to the piston motion will be delayed. So you'll get a little EGR.
Big Block
WFO or I don't go
What about a Weisco?
Haven't looked into them, but I think they cost more than I would want to spend.
Big Block
WFO or I don't go
Just a thought since you have a badass finger ported monster
Maybe if I knew I was going to keep it, I would go all out. But I have a really nice 288 I hardly use, so when this is done I need to figure out which one to sell. I only need one saw this big as a backup for my 3120 on the chainsaw mill, and to make large rounds smaller to lift onto the log splitter.Just a thought since you have a badass finger ported monster
zogger
Tree Freak
The piston in my finger ported 394 is indeed installed backwards.
Rx7man
Cattle Rubbing Post
I could see that groove being useful if the saw had a pipe on it that could potentially create a significant vacuum and draw more air/fuel mix into the crankcase.. On a standard muffler I can't see any benefit to it except perhaps lubrication as someone already mentioned
Big Block
WFO or I don't go
Anything new on this ?
It runs great, the little bit I have had a chance to run it. I don't really have anything worthy of using it on right now. I put a 395 meteor piston in it with the finger ported jug, and no problems. I had planned on testing this setup vs a regular un-ported 394 jug just to see the difference, but haven't had any large logs to make it worthwhile yet. It will pull a 34" full comp with an 8 pin through a 36" willow without slowing down, but willow is really soft. I think I will be keeping this one and selling my 288.
it came to me in a failed state, so I can't answer that. It is back up and running now, but with limited run time so far.
