My shrinking stack

[Flat47]

Has anybody else run into this:

The stack or stack collar on my 2x4 Grimm appears to expand and contract with use. The stack is all new this season (3' base and 12' of 8" all galvinized). The collar is vintage ('80s? maybe). When I set up the new stack, the base stack was sitting on the arch collar. After a couple days of boiling, I noticed it wasn't on the arch collar anymore, so I checked the arch for level (it was) and went up on the roof and tapped the stack down until it rested on the arch again.

Guess what? It's not on the arch again. And I've been watching it grow during boilings. At start-up it's about 3/4" up off the arch collar. By the end of the day it's in contact again. Let it cool overnight, and it's 3/4" up off the collar again.

It's bugging me. The rig hasn't moved out of level. Is it my stack or my stack collar? I really don't like the idea of an ember shooting out of the stack inside the sugarhouse.

[michiganfarmer2]

Im not sure. Heating and cooling causes expansion and contraction, but Ive never seen what you are describing.

Id be temped to strech the stack base somehow, or put a split in it so it doesnt fit so tight on the arch collar. Then the expansion and cotraction cant push it up because it isnt tight enouhg for any friction. I mean it might move a little, but with no friction, gravity will keep it down instead of it "climbing" up the collar

[Dennis H.]

How is the stack held going thru the roof?

On my evap the stack sits on the evap. Where the stack goes thru the roof it is sitting there and is not attached to any part of the flashing or roof.

It almost sounds like you have the stack attached to the roof or flashing or it is a very tight fit up there so when the evap and stack come up to temp and expands a bit that it pushes up and once everything cools down the tight fit and attached stack up at the roof prevents the the stack from "falling" back down onto the evap.

I can't beleive that the arch is getting higher when your boiling but I can believe that the stack getts longer with heat.

Heck my arch goes in lenght about 1/4" when I am boiling, the pans are a tight fit between the arch front and the stack collar at the back but after about 2 hrs of boiling I can shove the syrup pan back about 1/4" to keep remove the gap between the syrup and flue pan.

[Flat47]

The stack goes through a roof jack, which is really snug. The roof jack is actually Metalbestos brand and intended for 6" insulated Metalbestos stove pipe, and then a storm collar over that. Otherwise, the only other thing the stack contacts is the arch collar, which the base stack is loose on.

So maybe the roof jack is the culprit.

[Dennis H.]

I know where my stack goes thru the roof jack I have about 1/8" all the way around it. Then above that is the storm collar that is attached to the stack.
So there is a little wiggle room up there.

[Flat Lander Sugaring]

My whole stack is screwed together with 5/16 self tappers No problem here

[Flat47]

My whole stack is screwed together with 5/16 self tappers No problem here

Same here, except it's not screwed to the collar on the arch. The collar is cast iron and it'd be tough to drill and screw into it.

I guess I'm going to get up on the roof and create some play around the roof jack. That's the only place keeping the stack from moving up and down.

[3rdgen.maple]

Just a thought but do you run a blower? Is there a cap on the top? If so I was wondering if the stack is undersized and the draft is pulling it up. You can always put support wires on the top and anchor it down to the roof. Seen that done many times to keep the stack up in place.

[Flat47]

Just a thought but do you run a blower? Is there a cap on the top? If so I was wondering if the stack is undersized and the draft is pulling it up. You can always put support wires on the top and anchor it down to the roof. Seen that done many times to keep the stack up in place.

Funny that you mention the blower. I did run one, until I forgot to turn it back on after adding wood and it boiled better. Now I don't even bother with it. I've got a GH Grimm 2x4, so my 8" stack is already larger than the 7" they recommend. I thought of adding wires, but I was thinking more to keep it standing up, not holding it down. We're in a mostly exposed area (lots of surrounding farm fields) and we get lots of wind. I'll go up and create some play around the stack/roof jack tomorrow and see what happens.

Thanks to all for the input.

[Flat Lander Sugaring]

Same here, except it's not screwed to the collar on the arch. The collar is cast iron and it'd be tough to drill and screw into it.

I guess I'm going to get up on the roof and create some play around the roof jack. That's the only place keeping the stack from moving up and down.

pre drill the holes then stick the self tapper through, its cast not stainless its softer than you think.