Swapping Gearing from 8.18 to 8.45 for Fury Extreme

[ZR2Chevy22]

Hey guy's and gal's,

When I bought my Fury it came with both the 8.45 and the 8.18 side plates and a 90T and 93T main gear and YS motor mounts (square hole in mount). I'm currently running a YS91SR and 8.45 gearing. I was told the 8.18 gearing fit's the SR better then the 8.45 which suits the ST better.

To swap the gearing I swap the main gear out to the 90T BUT do I have to use shims between the motor and the mount or is it fine as is? Also what all's required to make the swap? Just change out the main gear and side plates? Do I need the round hole motor mounts?

Andrew

[WayneBrown]

Your mounts fit the engine, leave them be, unless you have clearance issues.
Change the side plates and main gear, realign everything to get the correct gap at the clutch driver and locktite it all up.
there's not a great deal to it.

[ZR2Chevy22]

Originally Posted by WayneBrown

realign everything to get the correct gap at the clutch driver .

What ya mean by this wayne? you mean gear mesh?

Andrew

[WayneBrown]

nope, you want an even gap all the way around between the fan and clutch driver disk.
Gear mesh will be set with the plate changes by moving over the clutch stack itself.

[WayneBrown]

to get the even gap, you *may* have to shim the engine from the mounts, or swap the mount itself. You cannot guesstimate, if its not lined up, it won't work, trial and error will tell what you need to do to get everything lined up.

[DavidH]

Andrew,
As I told you in the PM exchange. You will need two .030 shims(115-47) on each side of the 8.45 mounts to convert to 8.18. Main gear will need to be 90 tooth and clutch plates 8.18.

David

[ZR2Chevy22]

Yeah I know David. I got 1 set other set's on order. I just wasn't sure what he meant by clutch driver.

Andrew

[SlowWhite]

Is it bad to run the SR at the 8.45 gear ratio?

is the part number needed to switch from 8.45 to 8.18: #119-130
http://www.miniatureaircraftusa.com/...prod=119%2D130

[Caleb Phillips]

Originally Posted by SlowWhite

Is it bad to run the SR at the 8.45 gear ratio?

is the part number needed to switch from 8.45 to 8.18: #119-130
http://www.miniatureaircraftusa.com/...prod=119%2D130

The high end of the practical rpm rating on that engine is 17,000. With the 8.45 ratio, that would put the head at 2012 rpm. So hurting the engine, I doubt it so long as you're running less than 2,000 rpm on the head but I don't think you're going to be anywhere near the peak torque output. The 8.18 is a much better option (so I've been told).

As far as the needed parts to go 8.18, that does look right, but I've never done it before. Seems like you might need a different bottom plate for the engine though. Maybe Harkey can chime in and verify this.

[SlowWhite]

I just ordered my SR and new Hatori muffler. should be here by friday.

But I haven't ordered the parts from MA yet to do the swap. I just wanted to get the motor while someone had them, been waiting over a month now.

[Caleb Phillips]

I'm sure you'll also need some different spacer as well as the dimensions are probably different between the SR ans ST4.

[DavidH]

You can change from 8.45 to 8.18 by doing this.
You will need a 90 tooth main gear.
You will need 4 shims
http://www.miniatureaircraftusa.com/...?prod=115%2D47
Two of the above on each side of the 8.45 mount. The 8.45 mounts have 0.030 material machined off the mounting surface from the 8.18 mounts. So two shims on each side.

You can either buy new clutch side plates for 8.18. Or you can take the 8.45 side plates and slot the four holes 0.60 towards the main gear. I have done this on several sets of clutch plates and it is simple to do. Just oval the two holes that bolts to the upper bearing block and the two holes that hold the lower bearing block towards the main gear.

You do not need the 11 tooth pinion in the kit you posted the link to. 8.45 already has a 11 tooth pinion.
Here is what you will need if you don't want to do it the way I described above
115-50 motor mount
115-55 motor mount
115-47 you need one shim on each side with the 8.18 gearing
0865-90 Main gear
119-118 8.18 clutch plates

Personally I would go the less expensive route and just change the main gear and use the shims on the motor mount. Then oval the clutch plate holes towards the main gear. Up to you if you want to spend $30 for the change or $100.

David

[SlowWhite]

So I need the 2 motor mounts (115-50, 115-55) regardless? or can I just use my current YS motor mount and just shim it?

[DavidH]

Originally Posted by SlowWhite

So I need the 2 motor mounts (115-50, 115-55) regardless? or can I just use my current YS motor mount and just shim it?

The 119-50 and 55 motor mounts you have now on the 8.45 are the same as the 115-50 & 55 motor mounts. The difference is the 8.45 mounts have .030 less material on the mounting face.
You can use the 8.45 mounts you have now to change to 8.18. To do this you will need two of the 115-47 shims ( 0.30) on each side.

I personally would use the 8.45 clutch plates also and just open up the four holes that the screws go thru into the bearing blocks. You will need to open them up at least 0.60 towards the main gear. You can take a dremel and a small grinding bit and it is about a 2 minute job. 0.60 is not that much. I use to do this all the time when I was testing different gear ratios. The holes being slotted in the clutch plates is no big deal. You just have to line up the pinion to the main gear and the clutch driver to the fan hub.

David

[SlowWhite]

Got it now. Thanks for the help.