Any experts on 394xp chain brakes?

[Jon1270]

i couldn't get the spring in initially, it was too long. in doing a search i found a blog for huskys where they said the spring should be the 3.330" long. that looked more like it it & worked when i cut the new one down.

I've been letting this sit for a couple of days, but thanks. The spring I got is 4" long when relaxed, and it's a wrestling match to get it into the pocket where it's supposed to live. With the knee joint all the way forward into the tripped position, distance between the piston shoulder and the back of the pocket is about 3.25", so if I were to cut the spring to 3.33 inches it would be almost fully relaxed when the brake was engaged. Thoughts?

 

[turtle561]

at that point the spring has expanded(engaged) , expending it's energy clamping the band around the drum. job done. when you reset the brake the spring will be compressed. drum expands, drum turns.

 

[Jon1270]

I set this aside for a while in frustration, but have finally picked it up again and looked at it with fresh eyes. Since the brake was disassembled and missing parts when I got the saw, and since the brake flag didn't match the PN on any of the 394 IPL's, I decided there was a good chance that I had the wrong flag for the saw, and that even though it was possible to assemble it with the flag I had, the geometry might be just far enough off to cause problems. So I found a deal on an NOS 394 brake flag, and that did the trick with regard to the hairpin-like spring shown up at the top of this post. The one with small loop facing inwards, which doesn't match the IPL illustrations but is what you get when you order the PN shown on the drawing, works fine when you have the correct flag.

I was also having problems with the pressure spring. Most of the many versions of the 394 IPL that I found referred to PN 503717101, so that's what I initially ordered. It was far too long, and while I could force it into place it made the brake ridiculously stiff; the force required to re-set the triggered brake threatened to fold the flag in half. While researching possible solutions I found a few comments like turtle561's:

i couldn't get the spring in initially, it was too long. in doing a search i found a blog for huskys where they said the spring should be the 3.330" long. that looked more like it it & worked when i cut the new one down.

So I methodically went through every version of the 394/394xp IPL that I could find, and I identified three different part numbers for the pressure spring. They weren't expensive, so I ordered both of the two that I didn't already have. The lengths were significantly different, and like Goldilocks I found that the one in the middle of the range was the one that worked for me. For posterity:

503644901 is about 2 11/16" long.

503465901 is just over 3" long, seems surprisingly loose when the brake is triggered but also seems to work and is the only one of the three that is plausible in my clutch cover.

503717101 is 3 15/16" long.

The gauge of the wire, the diameter of the springs and the spacing of the coils seem to be the same across all three.

 

[turtle561]

bravo ! very tenacious analysis. I don't remember seeing a part no. in the post that mentioned the 3" length. searches are great things.

 

[big hank]

Who needs a chain break

 

[aswan]

Nice one.

View attachment 485298

Doesn't look 22 years old, does it? The air filter cover, one of its springs, the decomp and one recoil screw are new. Everything else you can see is original.

Nice saw

 

[Jon1270]

Well, here's where I have to admit I got it wrong when choosing a spring length. I took the saw for a test-run today and found that the medium-length spring was too loose, allowing the band to drag on the clutch even when the brake was "released." I switched to the longer spring, and while it was challenging to get installed, it works fine now that I have the correct flag.