Re-assembly of Husqvarna 50 (51/55) need timing and muff mod advice

[PogoInTheWoods]

Nice job on that jug.

 

[BGE541]

View attachment 507539 this is what it looked like when i got it.. cylinder cleaned up real nice like. Also resurfaced exhaust port.. saw must have run with loose muffler for a bit. Haha View attachment 507540

All in all, im pretty happy with my $35 find.. saw is actually in great shape and covers are all in good condition!

Didnt mean to take over the thread btw. Ill have to create my own for the full build. Thanks guys..

What did you use to clean that up? Looks like a nice CP cyl!

 

[sweidish445]

Why not include photos of the porta so we can tell you? Those 55s can be very strong saws with a little love. You may even be able to run a 350 piston that's designed to run with closed ports but you may have to trim the skirt some. Be sure to check your squish because the piston top above the ring groove is usually a few thousandths taller then the 55/51.

So i happen to have a 45mm dished 350 piston laying around and it is nearly perfect in dimensions. The skirt height and the distance above ring groove are the same. Although without base gasket, my squish measures .036in. Original piston was closer to .026 without base gasket.

Has anyone compared the crown height/ squish from the dished 350 epa piston and the flat 353 pistons?

Another question would be to go quality single ring piston, or suitable replacement with double ring? Both will likely require cutting bigger windows.

 

[BGE541]

The 350 is about .005 taller then the 44/45 that's what I go with it ya don't want to cut the base but get compression up.

 

[thefarmboy21]

Here are my timing numbers I've came up with, best I can tell with a flashlight. All numbers are with no base gasket, haven't checked the squish yet, but I will as soon as I get a chance. Didn't have the right size solder.

Intake:
Open 71 deg before TDC
Close 71 deg after TDC
142 deg duration

Exhaust:
Open 75 deg after TDC
Close 75 deg before TDC
150 deg duration

Ports:
Open 56 deg before BDC
Close 56 deg after BDC
112 deg duration

Do these look right?

 

[PogoInTheWoods]

http://www.arboristsite.com/communi...or-p-c-performance-build.271310/#post-5170531

There are several others as well.

 

[PogoInTheWoods]

I guess the question is..., where did you start and what are you aiming for?

 

[thefarmboy21]

I have no idea what the factory specs were...I have no idea what to aim for. I'm a V8 guy. I just figured there were enough ppl on here that have built saws, that someone could tell me if that was in the norm.

 

[thefarmboy21]

Also my squish with no base gasket is .030"

 

[thefarmboy21]

Ok, so I've read a little more (just enough to confuse me really) and I realize now that those numbers aren't correct in the 2-stroke world. This numbers are the LITERAL numbers that read on my degree wheel. With that being said, how do I figure those numbers into what the chainsaw world goes by? I saw somewhere that I had to subtract something by 180....but do I subtract degrees read, or duration? Also how do I figure blowdown? I just don't understand why we have to take the literal numbers read and re figure them? 2-strokes are over my head haha.

 

[PogoInTheWoods]

There are some good YouTube vids by some of the more reputable builders that explain the setup and interpretation stuff very well. Mastermind and Tree Monkey come to mind...

 

[sweidish445]

Well, yesterday was admittedly my first time using a degree wheel. It seems to work great actually. I have more homework as far as the numbers go but here's where im at..
-This is the 55 45mm closed port cylinder with dished 45mm 350 piston.
-No base gasket, squish measures .033

Intake
Open 70° btdc
Close 70° atdc

Exhaust
Open 70° atdc
Close 70° btdc

Ports
Open 52° abdc
Close 52° bbdc
Or something like that.. ive found like 3 different ways to calculate duration.. a few dont match up?? Definitely have more studying ahead of me, but our initial numbers seem very close.


http://www.arboristsite.com/community/threads/port-timing-questions.113678/

this thread describes blowdown.

 

[thefarmboy21]

Yea I'm gonna do it again and pay more attention with a flashlight and I am admittedly dyslexic, so I found myself when I was reading the wheel, reading numbers as say 85 when in reality it was 75 degrees or something like that. So I'll make sure this time.

 

[sweidish445]

you mess with your muffler yet? Heres mine. Reblued and everything..

 

[Chainsaw Jim]

Dump the dished piston and go with the flat top. Lil red barn has a good two ring one that really wakes that thing up.

Fresh crank seals will make a loose crankshaft tough to turn with one hand.

 

[sweidish445]

I do plan to get the flat top piston.. the one i have is actually not usable.. just using it to get a head start on my porting.

 

[thefarmboy21]

I have only taken apart the factory muffler. The 50 muf is slightly different than the 55's and 51's I belive. I'm getting a spare shipped from China, only because I got it for $6 and I have a 55 I got for parts that I believe just needs a Heli-coil in the spark plug hole. So I'll ise one for this saw and one for the 55 later.

 

[sweidish445]

Almost 3 months later and i finally got the correct replacment piston for my closed port 55! Ordered from lil red barn. I originally bought the flat top 353 piston from lil red barn, but i wasnt happy with the squish. It was in the .045 range, so i figured id save it for my 350... the squish with my new piston measures .034. Not exactly where i want to be, but im happy with the timing numbers and dont have to hack the skirts! Still have a little grinding to do on the transfers, so maybe in another 3 months ill have a running saw!

 

[Chris-PA]

That looks like some fat solder you are using - it may be giving you artificially high readings. What diameter is it?

 

[sweidish445]

That looks like some fat solder you are using - it may be giving you artificially high readings. What diameter is it?

I dont think thats the case. The solder is .061. I have thinner .028 stuff but its too thin to get a reading... Also, the distance from wrist pin to top of piston on the original measures .552. The 350 dished piston i was laying out ports with measures the same.
The new flat top 353 piston measures .542 which is where the wider squish band comes from. Im assuming the manufacturer does this as added insurance that their product will fit without modification. My new cp replacment piston is pretty close at .555. While id love for my squish near .020in, im going to opt out on the decking process for now.