nlappos

grind off the top half of the bump on the gearbox, both sides, don't shave the aluminum bracket, you'll weaken the support. These shots are my C box, showing the bump details and how they fit after trimming.

Pavement makes you work harder because the tires grip better, so any misalignment in yaw is multiplied a lot. In my many bad landings, I have found a few tricks to try:
1) learn what straight ahead is. Seriously, and be sure you are absolutely straight ahead at the last several seconds of the landing. Watch what the angle over the cowl is as you taxi, spot the picture and make it happen on landing.
2) work yaw like crazy. I found that “happy feet” is the best trick for me - wiggle your feet on the pedals rapidly in small oscillations so the nose wiggles at your command, maybe 200 feet on final. It’s kind of like the way a pitcher will shake his hands before he sets in his stance. You get ready for the rapid small inputs right after landing where you get to tell the Avid that YOU are in charge.
3) whatever your approach speed (55 in a big wing, 60 in a small wing) be sure you land 6” above the runway and hold it off until the stick is in your belly and the whole thing has been strangled into not flying. Done right, there is it not a prayer of it trying to skitter into flight once down, and the drop to the runway is less than an inch.
4) Now you are rolling out, the weight will be on the main wheels solidly, and the stick should be back in your belly so the tail wheel gets the weight it needs. The ground loop starts when you are cocked in yaw and the tail wheel isn’t loaded enough to help you stay stray, so keep stick in the belly.
5) In the rollout work the pedals like crazy in fast tiny inputs, don’t keep any input too long. Mostly you want to detect the first swerve, squelch it with a small pedal stab to stop the swerve rate, and stop the swerve even if you are t pointed perfectly straight. The trick is to stop the yaw rate first, and then put the pedal back to neutral, all in a half second or so (thus the happy feet practice.)
6) With idle throttle, stick in your belly and a brisk rollout, your speed will die quickly and you are home. Fly the beast all the way to parking, I have been run off the taxiway by a small gust when I relaxed for a few lazy seconds!

skypics, 
the 670 has 670 CC's, like the 582 has 582. That's the trick. The larger pistons and stroke of the 670 buy you the extra HP. The engine has been widely used in snowmobiles for decades. For aircraft use, the 670 gives 92 Horsepower at 6350 rpm, vice the 65 HP at 6500 for the 582 blue head.
The 670 weighs about 10 lb more (all inclusive) than the 582.
From the Rotax specs:
582 bore 76 mm, stroke 64 mm
670 bore 78 mm, stroke 70 mm
Here is Rotax Rick's specs page:  https://rotaxrick.wordpress.com/operate/
The 670 has "RAVE" valves that retune the exhaust with rpm, so the gas mileage stays low across a wider rpm range. These valves also add power, because they keep the exhaust properly tuned.

TJay,
I am getting 550-600 fpm at 6000 feet and 95 degrees, with about 950 lbs GW. That is a bit more than I got at sea level with the 582, with the same aircraft. That checks out, since I am now at about 9000 DA, so the 670 is putting out the same horsepower at this altitude that the 582 did at sea level. See above, I posted fuel flows as well.

skypics,
We are talking about a 670 installation, are you? What engine does your friend have in the Mk IV that works well without the belly radiator? The 582 has 41% less power thus 41% less heat, I think that's why you think it works, as you do. Have you run the 670 or are you speaking about your 582?
With a 670, in the new 1"  lower position (see photo below), the belly radiator works well, I can climb continuously at 60mph at full power on a 95 degree day at 7000 feet and engine water temp remains in the green.
I have blocked off the path around the nose radiators, too, so they get all the air, but with my 670 they are insufficient without the belly. I am thinking of removing the belly in the late fall and re-installing it in the spring.
Nick
 

TJay
parts for the 670 are all in production, there are thousands in use worldwide. In addition many quality after market items like pistons nd such are also made. Rotax Rick uses and stocks these parts.
As far as zero time, all I rely on is my engine’s log book.
Nick

Fred,
Yes, your Simonini looks like a great choice.
The snowmobile 670 is very popular, so I think most of the 670 unique parts are readily available. Rotax Rick stocks them too, and he has a 2 year warranty. My choice was easy, I needed an overhaul on the 582, so it was spend about $2200 plus shipping, or trade the core in and spend $3500 and get the zero time 670, plus $250 for the exhaust, and the engine was a drop into my existing FWF.

I published a bunch of info above but here is a summary:
1)  The 670 starts and runs perfectly. It is smooth and feels in many ways just like a 582.  
2) The rave valves work well, when throttled back I can easily get down to 5 gallons per hour or less while the EGT stays nicely within limits.
3) The power of the 670 is amazing, here  at 6000 feet take off altitude and 9000 feet cruise I get about the same power in the 670 at this altitude that the 582 gave me at sea level.
4)  The 670 needs more cooling, so I added the belly radiator which increases drag and cost me about 4 mph. I can add throttle to overcome that slow down but at the expense of extra fuel consumed up to about 7 gallons an hour. I also added a small scoop on the right side of the cowling to blow cool air into the carburetors, since the under cowl temps rose with the bigger engine and this affected the carburetor fuel air mixture. The temps under my cowling went from 25° above ambient down to less than 10°. 
5) In my total configuration change (engine, prop, landing gear, double tail spring) I gained 20 pounds of empty weight but only about 10 lbs of that is the engine, radiator and exhaust.  I believe the rest is the highwing landing gear and the warp drive prop.
6) Installing the 670 in the 582 engine mount was a piece of cake. Everything fit perfectly so all it was was literally a drop in. I did have to add an electric fuel pump and the belly radiator but that is the only modification needed.
7)  I installed EGT, the hacman leaning device, and a fuel flow gauge and all work well with the engine and really help the experience. 
8)  Rotax Rick’s workmanship and support are first class. The engine looked beautiful and all items were accounted for. He was always available for a discussion and advice. 
9)  I think the 92 HP 670 is a very viable alternative to some of the really heavy higher horsepower engines. Those considering a 912 or one or the Subaru variants  might really consider a 670 instead  because you can get almost as much power and only about a 10 pound weight gain. 
 

Those little diamond cross section brass inserts are stocked in the compression fitting section of most US hardware stores. They can be sold individually and separate, but are also packaged with the entire fitting for each tubing inlet. The typical dimension is 1/4" OD for most Avids, although some use 1/8", I think.
If you can't find any, I can get you a handful at the local True Value hardware and pop them in the mail.

This is the Highwing LLC gear, made by Lowell Fitt. The springs are stiff - 1450 lbs per inch. In a max landing the gear moves up 4" and out 4" assuming no tire flattening (which would be at least 3" more, I think) as the spring closes its 1.78" compression. If the spring was softer, the gear is worse, since the spring will bottom earlier at less force.The gear is good for 12 feet per second sink rate, and about 4 g's when the spring is completely compressed. See below for the geometry.

North Idaho, I think you might try to install bigger carb jets, a bigger richer jet will cool the EGTs. As a quick fix you can raise the needle a bit to get more gas in. It is a real goat rope, but I suspect you are too lean and the prop is not the cause.

I now have several hours on this gear on my Mark IV, Lowell had to modify the cabane 7/8" wider for my Avid. It is fantastic, the aircraft is so stable on landing it is a whole different experience. For those who want, I have an analysis of the landing strength which says this gear is good for about 12 feet per second, and about 4 g's on landing before those yellow springs bottom. This makes the gear stronger than any Cessna.
Lowell was a pleasure to work with, and the gear was half the price of a Grove gear.
Fred, here is a detail of the cabane forward attach point, which runs to the outside of the fuselage ears.

Any performance change?

from an old Chopndrag post:
 
Joey had a cargo bag made that's awesome. I plan on getting one soon. Here is the company info . Just say you want a Avid cargo bag that goes behind the seat.
Nate FisherFisher's Upholstery661 E. Beacon Light Rd.Eagle, ID 83616(208) 939-6513 11am-7pm MST

Turbo, I think you're right on with your understanding of EGT and mixture. The biggest problem we have is the relatively inept Bing 54 carburetor, which has really no mixture control at all. In carburetors with manual or automatic mixture control these conversations would be unnecessary. I think the Bing adaptation for flying is the worst part of the Rotax two stroke snowmobile engine converted to aviation.
In any case I have my 670 with the hacman mixture control which is really pretty effective for about 100 to 150° of EGT. I'm operating from 6000 feet and on hot summer day I had to take my jets down to 165 to lean the mixture to get the darn thing started. I did note before I switched jets, if I fully leaned with my hacman the engine would start and run well. That gives me some rough calibration that the hacman full rich to full lean is worth about 15 points on the jet sizing.
Obviously like any piston engine the EGT and mixture are directly related, so that extra gas cools the gas stream.  Before I lean at all, the cruise EGT runs about 980 to 1000, and as I lean,  I drive that up to about 1080 or 1100°. I also have a fuel flow gauge and I note that before I start leaning I'm getting 6.5 gallons per hour and when I fully lean in my 670 I get down to about 5 gallons per hour.
With the hacman and my 582, I had the same basic control over EGT (about 100 to 150°) and the gallons per hour would go from about 6.2 un-leaned to about 4.8 leaned.

Welcome, enjoy the group, and please contribute!

As I read it, is a toss up. No night flight, period, unless you have approved nav lights.  But an anti-collision light is only required if it was originally on the aircraft when made airworthy, so if you don't have an anti-collision light, the non-approved lights are ok. If you have an approved anti-collision light, you can certainly install the recognition lights, just don't remove the real AC light.

Just a reminder that the position and anti-collision lighting required for night flight, even in experimentals, must be FAA approved. That's why these are labeled "recognition" lights.

 I posted a bunch, with photos at :   http://www.avidfoxflyers.com/index.php?/topic/5734-new-rotax-670-install/

My 670 puts out at least 92 HP, and it added a total of 20 lbs to my 582 Mark IV, engine, prop, belly radiator and Highhwing gear, all  actual flying weight. And it cost a bunch less than a 912, $3400 and a turn in of the 582 to Rotax Rick.

The turtledeck aluminum makes a perfect ground plane, better than the foil. Let me know how the coax works (how quiet the radio is), I might upgrade.

I bought a well used 24" blade on ebay and it works like a charm, about $35. and this guy makes high quality BNC coax cables to order, don't buy the black Chinese ones, they are junk - I had a dead transponder for months because a brand new back cable was dead. https://www.ebay.com/itm/BNC-Male-to-BNC-Male-50-Ohm-RG316-Coax-Low-Loss-RF-Cable/272908120318?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

ebay 
 https://www.ebay.com/itm/Turf-Glide-Rib-8-00-6-4-Ply-Carlisle-Lawn-Turf-Tires-508-040/401339548793?epid=18017807239&hash=item5d71b38479%3Ag%3AVXsAAOSwubZZ56tg&_sacat=0&_nkw=carlisle+turf++tires&_from=R40&rt=nc&LH_TitleDesc=0

Yes, the 600 is half of 1200, because there are two gear! My MGW is 1150 but I rounded up.
I agree, you have to work the bungee spring rate which is hard, because it is all scrunched up in there and probably not linear at all. The rest of the Avid geometry is easy to analyze. I bet the bungee gear is dandy at this too, it is just a bit too narrow and therefore not as stable on the ground.
4 g's is a pretty hard whack, and involves 12 feet per second landing sink rate, which is 50% higher than Cessnas have to meet. I have hit the ground at 4 g's in experimental helicopters, it is not easily forgotten! 
 

I installed Lowell's Highwing gear and have flown it now for about 3 hours. It is a charm, stable and very low ground loop tendency, a marked improvement on the Avid original gear. During normal landings the spring compresses less than 1/2". The landings feel smooth and not harsh.  Lowell had to widen the cabane by 7/8" because the Avid is that much wider than the KF. It fits perfectly.
I attach a quick analysis of the gear (I am an aerospace engineer). note the sketch is not to scale, but the angles and dimensions are accurate. It says:
1) the gear is good to 4 g's and 12 ft/sec
2) the spring is not too stiff
3) If you make the spring weaker (less spring rate lb/in) then the gear gets weaker and damages the airplane at a lower landing sink rate.