Replacing Air Chamber Jotul 602 CB (again): Best metal to use?

[nola mike]

So when I got the stove, the secondary air chamber was warped. I removed it and straightened it, and it lasted until 2017. At that point, I replaced the whole air chamber and partially rebuilt the stove. Last year developed an air leak and a couple of bad overfires, which warped the metal in the chamber again. New air chamber is now $280, which includes the cast upper housing (which is fine on mine). I think I'm going to just fab a piece of sheet metal to replace. I measured the old, and it's about 1mm, so 20 gauge. I thought it was stainless, but it's magnetic, so now I'm wondering if it's just mild steel. Does anyone know what type of metal can/should be used in this application? I'm going to go the local sheetmetal place tomorrow to get their input. Then of course, I'm going to need to figure out how to bend it...

 

[begreen]

Do you just need the bottom, stepped plate with the secondary air holes? That is the Air manifold. It's stainless and may be magnetic.

 

[nola mike]

Do you just need the bottom, stepped plate with the secondary air holes? That is the Air manifold. It's stainless and may be magnetic.

Yeah, that piece. Strongly magnetic though, ss I think should be weakly magnetic at most

 

[begreen]

I'd definitely have it made up out of stainless for this application.

Stainless steel grades 409, 430, and 439 are also known as ferritic stainless steels because they have iron in the alloy. They are magnetic. Austenitic stainless is not magnetic.

 

[nola mike]

Stainless steel grades 409, 430, and 439 are also known as ferritic stainless steels because they have iron in the alloy. They are magnetic. Austenitic stainless is not magnetic.

Yeah, thought they'd use a more common 304 or 316. Those are the only ones readily available that I've found

 

[nola mike]

Ok, so that was a giant PITA. Brought the metal piece to a shop. They were convinced that it was just 16g mild steel. The piece that I had cut seemed a bit thinner. We'll see how it holds up. Unfortunately, removing that manifold again required me removing the top, front, and back of the stove. Took forever to reassemble because of cleaning off the old cement. I ended up grinding the edges of the air chamber before reassembly so that it can be removed in the future if needed. Worst case, I'll need to remove the top and the rear baffle. Bending the sheet metal was a trick as well. The sheetmetal brake that I have couldn't handle making the middle bends in opposite directions, nor could it handle the edge bends. So I ended up using a vise and BFH, which is not a precision method. It came out pretty good in the end though, and if a secondary burn is possible on this stove, it's going to happen now.

Old sheet metal. It had warped and separated from the edges of the air chamber, essentially not routing any secondary air.


I ground down the front edge and the relief in the middle (where my finger is) so that it could clear the mounting shelf. It looks like it was designed to be removed without all the drama, but I had to disassemble the last time I did this as well. Not doing that again.


It ended up fitting the cast iron pretty well. Not going to win any beauty contests, but I think it will work fine. The fit from the factory was pretty sloppy; when I bought the whole chamber 5 years ago I ended up re-cementing the seams.


Finished product. My hole drilling also wasn't pretty. I was starting to run out of patience...
Most important thing is that the air chamber is leak free and seals with the rear baffle.



For $30...I dunno, a lot of time. Hopefully won't be a next time, but I'll be able to do much quicker if I do.
Now just need to sweep the chimney, and we should be ready to roll!

 

[Todd]

Those side shields look pretty beat up?

 

[nola mike]

Those side shields look pretty beat up?

That's the side, I ordered new shields that aren't on there yet.

 

[nola mike]

Finally fired it up today for the first time. Worked well, easy to control (but still pretty warm here). There was a very little bit of secondary action, but I've never had much on this stove. We'll see how long it lasts. I had a hell of a time getting the side shields in. The bottom shield was warped, so there wasn't enough clearance. Used a grinder on the lower shelf and a touch on the shields to get them in there.

 

[EatenByLimestone]

So how's it running?

 

[nola mike]

So how's it running?

Running great so far and easy to control, but not super cold out yet,

 

[nola mike]

Well, that experiment failed (you were right BG). Worked well until a week or 2 ago. Noticed it running hotter. Then got real hot. Noticed a giant hole in my new manifold. I did have a pretty significant over fire earlier in the season, dunno how much that contributed to it. I made a sheet metal patch to limp to the end of the season (we're pretty much there). Now need to figure out if it would be better to find an actual metal fabricator to make it with some thicker stainless or just bite the bullet and but the whole stupid $275 part. I wish they just sold that sheet metal part...

 

[begreen]

It's a small piece. Bring your part to a decent sheet metal shop as a template and have them cut some stainless and bend it up.

 

[nola mike]

Ok, so did as suggested. Got a piece of 14 or 16g 304 SS. MUCH more robust feeling. I had the shop fabricate it for me for $70. I told them not to bother drilling holes. After ruining 10 bits and ending up with zero holes I brought it back to the shop and they punched the holes for me for $30--told me it would be less had I had it done originally. Don't know how these jokes will work out. I wanted 15x 3/32" holes like the one I made last year. They ended up doing ⅛" holes, which is more surface area. Curious how this will affect things, I can fill holes if need be. Hoping this will last longer than the last one. Will fire it up whenever it cools down.

 

[nola mike]

OK, I'm getting some secondary action (again, not a ton). This thing must just draft like crazy though, even with air closed down still have a lot of turbulence in there. I put some more gasket material on the airwash, which helped. I'd still like to be able to damp this down a little more, especially when I'm burning some bricks in cold weather. I have a key damper installed, but that seems like cheating . I'd like to see if I'm drawing in too much secondary air. @Todd (or anyone else with this stove) be willing to measure the size/number of holes in your manifold? I can then plug up some of the holes to keep the surface area the same as stock (although that might affect burning due to different air velocity through the holes, but I'm probably overthinking).

 

[Todd]

2 rows each with 17 holes 1/8” diameter. You may also want to try blocking some of the secondary air hole in the back of the stove. I used to run mine on a 22’ straight chimney and it drafted like a Hoover til I blocked the secondary by about half with a couple magnets. She runs great on my 14’ straight chimney in my workshop with no mods.

 

[nola mike]

2 rows each with 17 holes 1/8” diameter. You may also want to try blocking some of the secondary air hole in the back of the stove. I used to run mine on a 22’ straight chimney and it drafted like a Hoover til I blocked the secondary by about half with a couple magnets. She runs great on my 14’ straight chimney in my workshop with no mods.

Thanks! Well, 15 x 1/8" is what I have, so that's pretty damn close. I have a 5" x 25ish' chimney. I think I'd want to keep the secondary air coming at the expense of the primary. I'll close the key damper a bit to see how that affects it. The secondary action was definitely better after blocking the airwash some. I'd just like to have a bit of wiggle room if she starts to run hot (the key damper isn't too accessible behind the stove once it's up to temp).

 

[Todd]

Yeah these stove can really take off! There were times when I would just shut her all the way down right after reloading, especially if you reloaded on a good bed of coals.

I’ve been playing with the secondary air on my F45 this fall and so far I like how it operates blocking it 30-40%. I’ve tried more but it sometimes leaves chunks of unburnt wood in the back. There’s a sweet spot in there somewhere.

 

[nola mike]

Well, solved that problem. The issue was that the slide for the primary air intake was leaking. Don't know how long it's been like that, and strange that I didn't notice it sooner--considering the difference in burning, I'm guessing it's been a while. The slide is pushed up against the door by a couple of springs, and if loose a ton of air can get around it, even when appearing closed. I could hear the air, and thought it was from the air wash. Completely closed the air wash inlet, and could still hear it. I was able to stretch the springs and reinstall. Huge difference. I opened the air wash inlet all the way, opened the key damper fully, and am still able to run at 800' peak stove temp with the primary somewhat open. I can get it to smolder if I close it all the way.