Yes, the expansion box is correct, only muffler is from 600cc street bike.

Hello, assume you have the correct shape exhaust expansion box on this, the wrong one will rob horse power.

Looks like muffler job isn't for me...   Or this YOSHIMURA muffler isn't for 2 stroke. It is almost as loud as without the muffler, but it looks cool 

I was patching underside of the hull with ABS slurry. You melt abs plastic in acetone to make slurry...

I won't dry to fix those old blades, they are what they are and let them be.
Fan side clearance is 16mm and top and bottom is 6mm.

Got engine back running again, need new air filter box and mufle and fun begins again.

ABS slurry? Ive no knowledge or experience with that -and  so close to arguably the most dangerous part of your craft- the blade tips. If any parts away-  it will destroy fan (lift and thrust) in a milli second, which can catapult the driver out. Ive seen this a few times in racing.
I didn't know the hull was ABS. I thought it was Glass resin.
Ho hum

As mentioned- close blade clearances are  not needed or advisable? IMHO
Your decision though!
Good luck

Definitely I will keep factory blade angle. Looking around in google, it seems best upgrade for Scat would be 9 blade fan with 6 blade what set to pairs.

https://www.youtube.com/watch?v=4mtq_oW9MZk&t=42s
Definitely I'm going to measure pulling force to ensure blade swap eficence.

I filled cracks with ABS slurry. Previous owner was trying to fix it with fiberglass and epoxy...

Altering the fan set up (away from standard) is best avoided, otherwise- the lift and thrust characteristics will be NOT as good.
Find out what it was set with- and go with that in my humble opinion.

Thank you for your answers.
Right now I'm overhauling rotax 503 engine (unfortunately it is from snowmobile) And paching ABS plastic. Unfortunately ABS plastic have many cracks and some holes in it.

I'm planning to buy 9 blade fan using with 6 white blade what is set in to three pair.

In winter I'm planning to overhaul hovercraft body and next summer maybe buy more powerful engine...

Yes, I would also ignore it and wonder if the Scats were ever built "with accuracy in mind" as they were one of the first
MASS produced hovercraft out of Kip Mcullums design board.
I used about 20 mms clearance as these craft can bottom out and the resultant shake can destroy the fan (and nearby people) quite easily.
Excess clearance is good, to little is bad!

I seem to remember reading a few years back, that black blades are more brittle than the whites and are prone to shattering under load.  But my memory isn't what it used to be, so I could be mistaken 

What are the clearances?  If less than 20mm or so I'd just leave it as its not worth the effort - and you need some decent clearance to avoid blade strike when the craft is bumped.

Hy!

I bought myself old Scat II hovercraft. And now I'm dealing with all the isiuse what it has...

I discovered that duct isn't round. It has deformed by time. What is the best way to re shape it?




Unfortunately picture doesn't tell the true story.
From the sides clearance between duct and fan are double the size compared to top and bottom.