Husqvarna 550xp pop up

[WoodsliverDan]

So, after doing some research and not finding much on making a pop up piston for the 550xp, I have decided to make one to try and post my results. After measuring the squish, (with gasket) and finding it to be .030" I have decided to turn .030" off the base of the cylinder and .020" off the piston. This should put me right at .020" squish with gasket. I hope to have more time this week to turn the base and possibly reassemble saw for a test drive this weekend.

I have decided to do pop up vs squish band cut due to the fact these pistons are so heavy! Figured they could use the diet??! Anyways, I think dropping the cylinder with the pop up should give me pretty good timing numbers as well. We'll see

 

[WoodsliverDan]

So tonight at work I had a chance to turn the base on the cylinder. I took .030" off both the base and the cylinder skirt. I have a new piston ring and circlips ordered which should be here Friday. Stay tuned.

 

[WoodsliverDan]

I have been asked if I'm going to make a stock saw for comparison. What does everyone say? I have another 550xp laying around I could use.

 

[WoodsliverDan]

Awfully quiet in here. Suggestions on ignition timing advance?

 

[huskihl]

Awfully quiet in here. Suggestions on ignition timing advance?

It'll be snappier and probably cut faster. But the autotune may not like it.

 

[WoodsliverDan]

It'll be snappier and probably cut faster. But the autotune may not like it.

Have you tried it?

 

[huskihl]

Using the popup, your exhaust and transfer timing will only change by a degree or so. Your intake timing went up by about 2°

 

[huskihl]

Have you tried it?

Yes

 

[Red97]

I have been asked if I'm going to make a stock saw for comparison. What does everyone say? I have another 550xp laying around I could use.

Won't hurt a thing to have a baseline to compare against.

Never been in a 550 so not sure what they like.

 

[WoodsliverDan]

Yes

I'm confused. You said the autotune may not like the advance. Have you done timing advance on a 550xp or not?

 

[WoodsliverDan]

Using the popup, your exhaust and transfer timing will only change by a degree or so. Your intake timing went up by about 2°

Yes, close

 

[huskihl]

I'm confused. You said the autotune may not like the advance. Have you done timing advance on a 550xp or not?

Yes I have.
It cut faster with the advance, but seemed to have a hesitation while accellerating. Not sure if it was due to the AT system not being calibrated or needing an update or not. That hesitation bothers some folks, others not so much

 

[WoodsliverDan]

Ok thanks. How was the heat? Not looking to make a cookie cutter, rather a saw that will burn a gallon of gas a day.

 

[huskihl]

Ok thanks. How was the heat? Not looking to make a cookie cutter, rather a saw that will burn a gallon of gas a day.

The AT seemed to allow enough fuel to compensate for it. But I wasn't burning tankfuls at a time looking for it either. No pinging or loping after long cuts

 

[huskyboy]

I found my 562 responded a bit better to advance than the 2253 (550). Both gained torque from it though. Make sure you copy that cooling slot in the topcover the new saws have if yours don’t already have it. Gut the muff as much as you can. It’s worth the temperature reduction.

 

[WoodsliverDan]

Half the key a good starting point?

 

[mdavlee]

The AT seemed to allow enough fuel to compensate for it. But I wasn't burning tankfuls at a time looking for it either. No pinging or loping after long cuts

If you’re talking about mine we used it pretty hard in the end of May logging. Never had a problem on 90 degree days

 

[huskihl]

Half the key a good starting point?

I'd start at about 1/4 of the key. About 1/4" of movement at the perimeter of the fw. If you like it, take another 1/4 of it and try it again

 

[huskihl]

If you’re talking about mine we used it pretty hard in the end of May logging. Never had a problem on 90 degree days

Yours acted the same way up here. You mentioned it not acting up at all for you. Difference in the fuel, oil, temp, humidity....

 

[mdavlee]

Yours acted the same way up here. You mentioned it not acting up at all for you. Difference in the fuel, oil, temp, humidity....

It is odd but al those changes do affect it. The timing wasn’t too bad for me. It ran awesome as is.