Husqvarna 562 MK2 beginner porting

[lindahl85]

I have always wanted to try porting a 2 stroke engine so I decided to start with my saw. Something will be the first and this is it. I don´t have much skills so I only want to use file, no lathe. The plan was to start easy and measure what I do. I would like some kind feedback of what can be done better and why
I started with muffler mod and keeping the original mesh.
My exhaust opened at 104 degrees, but I missed to check total duration.
My intake opened at 72 degrees but I didn´t check total duration.
Squish 0,62mm (0,024 inch)

The plan was to be easy and open at 102 degrees but I chamfered a bit much so it became 98 degrees. Port is really open at 100 degrees.
I also lowered the intake floor to 79 degrees. Things happened much faster than expected.
I took away a little bit material from the lower transfer.
All edges cleaned. The exhaust could be polished better but I don´t know with what.
This is how it looks so far.

 

[srcarr52]

You don't want to read the chamfer on the port opening numbers, you want when the port roof will open. Some people use a really thin feeler gauge and read right when it's bending into the chamfer.

With the exhaust so high you'll want to raise the transfer to support it. Strato saws, with the back filled transfers, really like short blowdown. I like around 116.5° opening on shorter exhaust than you have which yields 13.5° blowdown.

 

[lindahl85]

You don't want to read the chamfer on the port opening numbers, you want when the port roof will open. Some people use a really thin feeler gauge and read right when it's bending into the chamfer.

With the exhaust so high you'll want to raise the transfer to support it. Strato saws, with the back filled transfers, really like short blowdown. I like around 116.5° opening on shorter exhaust than you have which yields 13.5° blowdown.

If so, the exhaust opens on 100 instead of 98.

The issue with blowdown is that i have read both. Claims that MK1 is like you say with short blowdown but some claims that the MK2 prefer long blowdown. So I decided to ship it at this point and start it first.

 

[dangerousatom]

Not too terrible for 1st time....

Pull the transfer covers off, there's a few ruff bits in there and it lets you get to the lower transition angles that you can see in your first pic.

 

[lindahl85]

Not too terrible for 1st time....

Pull the transfer covers off, there's a few ruff bits in there and it lets you get to the lower transition angles that you can see in your first pic.

The angles makes me a bit afraid so I don´t mess things up.
I haven´t tried it in wood yet, it runs stable on idle and revs good so far but I was thinking of two extra things.
Transfers - Make them wider instead of adjusting blowdown and the effects of that.
Exhaust - Widening that from where I am and effects of that.
In both cases, how much is okay? How much is too much. Measured in mm or inch.

Polished transfers - Is it good or mess up turbulence?
Polished exhaust - Does it do anything else than keeping dirt away? It´s still too rough for my taste but I don´t have any good file that cuts less.

If I measured correctly I currently have 180 degrees exhaust duration and 150 intake duration

 

[EFSM]

The angles makes me a bit afraid so I don´t mess things up.
I haven´t tried it in wood yet, it runs stable on idle and revs good so far but I was thinking of two extra things.
Transfers - Make them wider instead of adjusting blowdown and the effects of that.
Exhaust - Widening that from where I am and effects of that.
In both cases, how much is okay? How much is too much. Measured in mm or inch.

Polished transfers - Is it good or mess up turbulence?
Polished exhaust - Does it do anything else than keeping dirt away? It´s still too rough for my taste but I don´t have any good file that cuts less.

If I measured correctly I currently have 180 degrees exhaust duration and 150 intake duration

Don’t widen transfers much at all, as that reduces their ability to direct the airflow properly. Widening the exhaust definitely can help, but most builders stop at 65 or for sure 70% of the bore width to reduce ring wear. Widening the exhaust and transfers could lead to short circuiting of the A/F mixture from the transfers right out the exhaust instead of sweeping the combustion chamber first.

 

[lindahl85]

Don’t widen transfers much at all, as that reduces their ability to direct the airflow properly. Widening the exhaust definitely can help, but most builders stop at 65 or for sure 70% of the bore width to reduce ring wear. Widening the exhaust and transfers could lead to short circuiting of the A/F mixture from the transfers right out the exhaust instead of sweeping the combustion chamber first.

Sounds like I should leave the transfers? But since I opened the intake, are my transfers limited somehow?

I will try to measure the width of it now, i think the piston is 46mm, so exhaust width of 30mm is safe and 32mm maximum?

 

[EFSM]

Sounds like I should leave the transfers? But since I opened the intake, are my transfers limited somehow?

I will try to measure the width of it now, i think the piston is 46mm, so exhaust width of 30mm is safe and 32mm maximum?

You can raise the transfers if you pull off the transfer caps. That will increase your torque band.

 

[lindahl85]

You can raise the transfers if you pull off the transfer caps. That will increase your torque band.

But this is the issue. I have read that mk1 want less blowdown and mk2 more blowdown. If I raise it will have less BD.

 

[srcarr52]

But this is the issue. I have read that mk1 want less blowdown and mk2 more blowdown. If I raise it will have less BD.

Probably because the MK2 lacks the crank stuffers so the crankcase compression isn't as strong as the MK1. They still don't like more than stock blowdown.

 

[lindahl85]

Probably because the MK2 lacks the crank stuffers so the crankcase compression isn't as strong as the MK1. They still don't like more than stock blowdown.

So mk1 have less volume in the crank? I have a 560 från 2022 and like the characteristics of that better than mk2.

What will happen with blowdown if I widen exhaust?

 

[EFSM]

So mk1 have less volume in the crank? I have a 560 från 2022 and like the characteristics of that better than mk2.

What will happen with blowdown if I widen exhaust?

Crank stuffers fit over the counterweights and fill the rest of the rotational space that the counterweights take up.
Blowdown doesn’t change unless you lower the cylinder (machining the base or deleting the base gasket), raise the exhaust, or transfers, or a mixture of these. Simply widening the exhaust doesn’t change the blowdown, but it can vent the cylinder more quickly, allowing more charge into the cylinder. That difference will be hard to notice without other changes.