Where to get all these shims everyone talks about

[marked23]

Everybody seems to be shimming the head on OS 91csps. Where do you get these shims? I see people mention .004 and .008 and even larger ones, but never any source to buy them.

I bought a spare "gasket kit" for my engine, but it's just going to come with a second stock-sized shim. So how do I get the non-stock shims?

What's a likely good setup for the os91csps, CP30, MPII on an Extreme at sea-level? Does lower density altitude need thicker shim?

-Mark

[DavidH]

http://www.ronlund.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=heli&Product_Code=SHIM91SX2

http://www.ronlund.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=heli&Product_Code=SHIM91SX4

[marked23]

Thanks, I ordered a couple .004s.

Are they safe to stack? I would guess that two stacked would be ok, but more might get sloppy.

-Mark

[WillJames]

I have stacked I think 5 with no problem. Are you running the Viper Head?

On CP 30% I think if I remember right we were running 12-16 thousandths on CP30 and 16-20 on Magnum 30% with the VH. Probably 4-6 thousandths less with the stock Hyper Head.

PM Shannon Davis or Clintstone for the exact specifics.

[marked23]

No, just the stock head.

So I should stack three or four .004 shims. That seems like a lot.

-Mark

[WillJames]

Go to 12 or 16 and see how it runs. Should help the leaning at midrange tendency especially with the MP2 and make it a little easier to tune the top for more power without causing the mid to lean out so much. Let us know how it goes please.

[DavidH]

What's a likely good setup for the os91csps, CP30, MPII on an Extreme at sea-level? Does lower density altitude need thicker shim?


With the PS motor I only used the stock shim (.008) with the stock blue head. I never had any problems with detonation. And I flew the heli in Florida at nearly sea level and then also at 1000' ASL. Motor ran the same. I am still using the stock blue head on the Cspec PS. Only difference now is those motors now have the 60K carb on them with Cline setup and OMI magic dust sprinkled on them.
I really doubt you will need to shim the stock head on the CSpec PS any more than the .008 that comes with it. The blue CSpec PS has the combustion chamber shaped for a wide range of nitro content.

The new SZ has a different shaped combustion chamber in the head. So that motor has to be shimmed more to run 30% nitro. That is why OS sends an extra .008 shim with the SZ.

David

[marked23]

Everyone at the field says I'm running my engine on the very rich side. So I lean it out a little and the tail starts to kick (predetonation?). They say it still seems rich, but I'm getting that kick that I didn't get when it was even richer.

I tried using a cooler plug (to retard the timing), but what I could find was too cool (OS A5) and just went out. So now I'm looking at trying a shim. My regular plug is OS8.

I'm getting about 8 minutes on a full tank of CP30 in a Fury Extreme. I'm hoping to get around 12 minutes, and a bit more power, by setting a proper mix.

Am I barking up the wrong tree?

-Mark

[DavidH]

Yep I would say you looking in the wrong direction.
With the stock Fury tank and the motor on 7.75 gear ratio. I was getting 13 minutes or more on the fuel in the main tank.

Everyone at the field says I'm running my engine on the very rich side. So I lean it out a little and the tail starts to kick (predetonation?)

Which needle you leaning out? Also have you taken the carb apart and checked for trash in the carb.
How many clicks do you call leaning it a little? My experience with the OS 60M carb, it took close to 1/4 turns of the needle to make a difference in the mixture.
Also do you have the mid range needle installed?
Do you have the return line from the check valve running directly into the main tank? Also are you sure the pressure line from the muffler is allowing enough air to get into the tank? That can be a problem with the motor running too lean when a vaccum is created in the tank by the pump pulling fuel from the tank.

I used OS 8 plugs and Enya 3's.

[marked23]

David,

I have the third needle.

I took apart my carb last week, looking for trash in the carb. Didn't see any.

I'm using 8.18 ratio.

I'm going about four clicks on the main needle from where it works, to where it starts running rough and kicking. Note that it's not running lean, it's detonating/kicking while it's still on the rich side. The third needle seems to have almost no effect on leaning the mid range, only richening it. I have the idle needle set at about the middle.

When I call it leaning it a little, it's four clicks on the main needle. I adjust it leaner and leaner until I see the tail kick in a hover or an agressive FFF turn. Then I richen it back up a few clicks and fly.

My muffler pressure line is suitably sized, but because of how I routed it, it's a bit long... maybe 14 inches.

The return line goes straight back into the main tank.

Enya 3s make this problem obviously worse than OS8.

Any thought on what I should try next, if not the shims? I've never seen a written procedure for correctly tuning a three needle carb with a fuel return.

-Mark

[WillJames]

How many turns open is your return needle? I think we had ours around 1/2 turn.

Try the shims. With the MP2, there are many of us who got some relief from that exact problem by shimming, and in some cases, the cateye neded a little modding as well. At one time I had 4 of the C-SPEC PS engines, and only one of them ran good out of the box, the other 3 needed shimming and also cateye work and third needles, although the one did not even need the third needle but I did shim it.

PM Shannon Davis, or Clintstone, and they can verify. Also since you are running the MP2 it exaggerates the problem over the Hatori Mufflers that David runs. I am not trying to take away from the advice David gave you, he is HUGELY KNowledgable, I have just had different experience first hand with 4 different PS motors and MP2's.

Here is a thread that talks about the exact or very similar problem to what you are experiencing and the fixes that were found. All these people were running the MP2 just like you are, and incidentally, all the ones I know are running the Hatori now...

http://www.helifreak.com/about898.html

Search for shim there are a few more threads as well.

Here is the direct link to the cateye mod video I shot with Shannon Davis demonstrating his expertise to cure this exact problem it sounds like you describe with in flight video where you can see the results of hte mod. I later added another 4 thousandths under the VH and it was even better.

http://www.moretraction.com/helis/images/Videos/S2DCatEyeMod_8-8-04.wmv

The PS in this video is one of the 4 I owned, in my first Fury Extreme. :)

HTH,

[DavidH]

Here is a thread that talks about the exact or very similar problem to what you are experiencing and the fixes that were found

How I fixed the PS was put an OMI 60K carb on them. Never looked back after doing that.



The third needle seems to have almost no effect on leaning the mid range, only richening it. I have the idle needle set at about the middle.


Which way are you turning the mid range needle to richen the mixture? Which way you turning it to lean the mixture?
How many turns do you have the mid range needle?

The Low end adjustment will also affect the mid range. I usually had to run a little on the rich side of the low end adjustment.

My muffler pressure line is suitably sized, but because of how I routed it, it's a bit long... maybe 14 inches.

Are you sure the pressure tap in the muffler is open and allowing enough air to pass thru it?

Will is correct, I was using the Hatori mufflers. Most I see running the OS's now are using Hatori mufflers.

David

[sumonzu]

I'm using .024 shim with OS C-Special + Viperhead and Cline + big bore carb. Fuel CoolPower 30%.
Is runs really cool, silky smooth and powerful.
I fly at an altitude of +1100 msl.

[DavidH]

I'm using .024 shim with OS C-Special + Viperhead and Cline + big bore carb. Fuel CoolPower 30%.


Have you tried .016 ? That is what most are using with that I have found with the above combo.

David

[marked23]

I got to try a .016 shim with my stock blue head. It really made a huge difference. Runs exactly how I want it to now. Seriously more power. I can't believe I didn't do this a year ago.

The biggest surprise was all the smoke. There's a lot more smoke now. I guess I was running so rich that the engine/muffler never warmed up suitably to make good smoke.

-Mark

[sumonzu]

David, .016 makes my engines always really too hot, only with .024 they run the smoth and cool. Maybe I can try in the future .020 but never less: I do not know it is possible that my setup depends on the altitude: as I said I fly at 1200 msl.

[boon]

could any body tell me 0.008,0.016 or 0.24 are in mm or inc"size? :?: :?:

[DavidH]

0.008 = 0.203 mm
0.016 = 0.406 mm
0.024 = 0.61 mm

David

[boon]

Thanks DavidH :D