How to access cylinder head on husqvarna rider?

It will be similar to the saw. Only the cylinder head needs torquing. The other, hand tighten and then cinch them up.

https://www.google.com/search?q=husqvarna+128ld+trimmer+bolt+torque+settings

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Try this. Remove the solenoid from the mower, this makes access to test it easier. Apply 12 volts to the two SMALL terminals on the solenoid. You should get a clear "Click" as you turn the power ON and again as you turn it OFF.
With the power ON use a multimeter set to Ohms or Resistance and test across the two LARGE terminals. you should get no resistance. When you turn OFF the power it should change to a resistance reading.

The cylinder base bolts should be tightened to 15nm

I assume you're refering to cleaning the inside of the crankshaft and 'big end' to only way to access tis without splitting the crank case is to remove the cylinder head, to give you access to the crank shaft where you can flush it out with fuel.

Never worried about torque setings on any of the saw's just get them good and tight.

Hi,
Thanks for posting your question and I will do my best to provide an accurate answer.
The symptoms you describe lead me to believe that you have a defective head gasket on one or two of you cylinders. The head gaskets fail between the valve pushrod area through which oil passes to lubricate the valves and the cylinder bore. this allows oil to pass into the combustion chamber causing the oil to burn and cause the smoking.
It is not uncommon and is a relatively inexpensive repair. The head gaskets cost around 20 dollars and the labor to remove the engine shrouds, carburetion, intake manifold, exhaust system to access the cylinder head should be three to four hours. It is very wise to replace both head gaskets since the labor to change the other is 1/2 hour or so vs. three or four again if the other fails a short time later.
I hope this answers your question.
Kevin

I think it is in hex ( 494841 ) or (444 33d)in hexadecimal

450 does not have a cylinder head. The cylinder assembly is one piece. The cylinder assembly is connected by 4 bolts installed from the bottom of the saw.

here are the manual for the rider 820-8
http://www.husqvarna.com/ddoc/HUSI/HUSI1990_AAaa/HUSI1990_AAaa_I9000235_.pdf

whats rough the motor if so you could have bad gas or bad plugs or somethin els you may need to get that to a shop