Husqvarna 55 numbers

[Ronie]

I'm putting a closed port 55 cylinder on a 51 and was wondering if these numbers sound like they would be good with a 16" bar.
EX 105
TR 125
IN 75

 

[David Young]

Wouldn’t be terrible. Normally you want to tighten the squish and reshape the intake. They take a little timing advance ok. The muffler is easy to open up. Widening the ex a little will help Careful you don’t get too wide and flat

 

[Wood Doctor]

I put a 55 top end on a 51 and suddenly I had a chainsaw that would run with my 257 and pull a 20" bar and chain.

 

[Ronie]

Wouldn’t be terrible. Normally you want to tighten the squish and reshape the intake. They take a little timing advance ok. The muffler is easy to open up. Widening the ex a little will help Careful you don’t get too wide and flat

I going to bring the squish down to around .016 and may do a small pop up, opening the exhaust to 65% of the bore and square up the intake. I'm also going to try and bore out the carb to 15mm. Hope that will make it a good runner.

 

[Ronie]

I put a 55 top end on a 51 and suddenly I had a chainsaw that would run with my 257 and pull a 20" bar and chain.

I had a closed port 55 with a 20" bar on it, it didn't do to bad for what it was.

Edit: I just wanted to add that it had an Oregon BPX bar and chain on it, I think that's narrow kerf.

 

[David Young]

I going to bring the squish down to around .016 and may do a small pop up, opening the exhaust to 65% of the bore and square up the intake. I'm also going to try and bore out the carb to 15mm. Hope that will make it a good runner.

I’d stay closer to .018 a popup works well but be careful you get in a pinch taking much off the base and the impulse passage will open up. If you have the stock piston I think skirts are only 60% just be careful there.

 

[Ronie]

Finished up porting the closed port cylinder I got from @GoBigBlue1984 , thanks again, now I just need to go around the ports again and put a better bevel on them. As it stands now the numbers are, EX 104, TR 126 and IN 77. I'm waiting on a cylinder gasket and with it the numbers should be close to what I was shooting for. It will also be getting a popup.

 

[Ronie]

This didn't start off as a build thread but I thought I see it through and put up what I've done. The muffler was very restrictive, so I opened it up a bit.

 

[Ronie]

I rechecked the numbers using a ring and the fist numbers I gave were a little off, now without the base gasket they are 105-125-78. With a base gasket I think they will end up 104-124-76. When my parts come in next week, I'll get it together and post how it runs with those numbers.

 

[drf256]

I know little about this conversion, but being you already have the JB weld out, I’d fill this area in and smooth it



I am assuming you had to match a side fed jug to a case fed lower case. I’d want it smooth personally. In addition, I think you added case volume, so I’d bring the transfer roofs up to 120 myself. You’ll still have 45* of cranking compression. It’s a dual port, so it needs more time to flow, plus the uppers look a bit big and lazy (no offense I hope-just what I see).

 

[Ronie]

I know little about this conversion, but being you already have the JB weld out, I’d fill this area in and smooth it

View attachment 258493

I am assuming you had to match a side fed jug to a case fed lower case. I’d want it smooth personally. In addition, I think you added case volume, so I’d bring the transfer roofs up to 120 myself. You’ll still have 45* of cranking compression. It’s a dual port, so it needs more time to flow, plus the uppers look a bit big and lazy (no offense I hope-just what I see).

I read in the porting threads that the dual ports need less blow down but I wasn't sure on how much less they need. Filling that area with JB Weld is a great idea, I'll pick up some and get that area filled in. Thanks for the suggestions!

 

[Ronie]

@drf256 I was looking at the cylinder and it it would break through if I bring the roof up to 120. Would it be better to angle it up and get it there or get it as high as I can and keep the roof flat?

 

[Ronie]

Since I can't raise the transfer roof much I'm going to raise the exhaust side of the transfer at an angle towards the plug.

 

[Ronie]

I started grinding on it with the plan
of just doing half of each transfer and decided to do all of it as flat as possible and hope I didn't break through. After grinding I checked it with a ring and it was at 121, I'm not going to push my luck anymore and leave it there. It's not perfectly flat but it's close. I'll get it together by the end of the week and post how it does with those numbers. Thanks again @drf256 for helping me out.

 

[drf256]

People will argue, but you don’t have to go perfectly at a 90* roof. I can’t remember which, but angled vs 90* is supposed to differ in more peak vs broader power.

Many of the strongest saws I’ve done are simply raised and the plating and smoothed into the factory roof. Some saws I’ve done actually don’t run as well at 90*, plus is changes the finesse of the factory transition from the tunnel to the roof of the transfer.

Your uppers look cleaner BTW.

 

[Ronie]

I filled in those areas that drh256 suggested with JB Weld, just need to smooth it out a little more.

 

[Ronie]

Got it back together this afternoon. Final numbers are, EX 104, TR 121, IN 76. It needs a little more tuning and a chain sharping but it don't run to bad for an old 51/55.

 

[Ronie]

Second cuts, it ended up at 13,800 rpm wot.

Edit: Just adding a final video after readjusting the carb and putting a new chain on it.

 

[Ronie]

Just wanted to add that it's got a popup and that I wanted to try open the carb up, I figured I would try it on an aftermarket one before I risked screwing the OEM one up. It has the aftermarket one on it now, I opened it to 14.70mm, drilled out the hole at the back of the high needle and drilled out the holes at the top of the jet. I couldn't find any info on the Walbro 170 so I just winged it. I was just trying to get more fuel and it seemed to work. I also advanced the timing a little.

 

[drf256]

Looks damn good I’d say. Now you’ve got the bug.