De-catting the Makita 6421

[Lootbug]

Hey all, just thought I'd share some pics on how I removed the cat from a 6421. This was my first time so it was a bit experimental. Any constructive criticism is welcome.

Here we are with the regular cat muffler.

I used MAP gas to heat up the left side crimp (if your looking at it from the front), then used a flat head screw driver to bend out the crimp. After a little experimenting, it seemed to work best to just heat a small 1 inch section at a time and bend it out, rather than trying to get the entire side all at the same time. Also lost a good screw driver because it got hot and bent...oops...should have seen that coming . Restarted with an old screw diver, and before long had the side and the bottom crimp pried out.

Next, the muffler comes apart into four pieces. Just pry up and slide out one piece at a time...

The cat


The baffle/front section

The inner plate? not sure what this is even in here for...

The rear

Might as well do some grindy while it's apart... Removed part of the baffle, figured it'll breath just fine with only half removed. Also keep some structural integrity by leaving half.

 

[Lootbug]

Open up the exits a bit.


Put it back together minus the cat. For re-crimping I applied heat in small intervals again, then tapped the crimp back into place with a small finishing hammer.


Pics of the front...not too bad! Just some minor discoloration do to the heating.


The end result with the spark screen installed, and the dead cat next to it. RIP poor little cat.


Cat weighed in at right around 5oz. No biggie but it's something.


OK that's it! Now I just need to get a 7300 piston and I'll be good to go .

Also, thanks to everyone on the site who's contributing info made this possible. Cheers!

 

[madhatte]

Nice work!

Five bucks says the inner plate is in there as a heat shield. Catalytic converters get red-hot.

 

[wudpirat]

Thanks for the excelent write up Lootbug.
I was planing to gut my 6421 muff yesterday but got side tracked. The town dropped a large Maple (30") Friday.
They leave it for a couple days before its haulded away. It was gettin while the gettin is good. I got most of the top.
I was using my new to me Husky 455 rancher 20". I like that saw, lots of grunt, easy to restart and good fuel economy.
Be back today with the Dolly 7900, (32")to get some of the big stuff.
Talked to the land owner to get the OK to trespass and he said," You want wood? I got a pile (2 cord) you can have.
Want me to load the tractor and haul it to the end of the drive?" Bear **** in the woods?
Talk about stepping in it. A double score.
Be a couple days before I can gut that muff, no hurry got a dozen other saws I can use. Don't relesh the tought of firing up the MAC 10 -10's or gnawing that big trunk with the 024 or 026 , maybe the 6400 with a 24" bar.
To many saws and not enough time or wood.