lfinney

My Feedback: (44)

the vibration can be helped, simply windowing or trimming the skirt, on rear exhaust simply leave the skirt at its stock length where it covers exhaust port. after Xmas i will post some pics of pistons and weights in stock configuration. the key to cutting abc pistons is to remember they are very high silicon content, so they don't carve well unless using carbide or diamond cutting tools, some pistons have silicon content as high as 21 percent, and you can see the difference in the surface.. the silicon minimizes expansion as well as reducing wear. the next way to alter balance is to use a tungsten or mallory metal slug that is larger , K&B engines used this on their 6.5 and 7.5 engines. I would cut the skirt on the rossi 81 engine, but for me it would be more for performance, than vibration, for speed planes vibration isnt as critical as say a pylon racing engine. rossi .81 engines go cheaply on fleabay and here under the buy and sell section.. NIB engines average 125-140$

combatpigg

My Feedback: (3)

Pot calls kettle black. Re-read my post that you attacked and your response makes you look like the guy with the ego problem...in other words you did a "Barney Fife" there.
I answered your gangsta-punk-wannabee challenge to "put up or shut up" with a good offer. I would gladly take time away from a car project to take this Rossi .81 "pattern engine" challenge if you've got one lying around that you wouldn't mind receiving in return with some internal work done to it by either me or a local machinist.
The ball's in your court.
It makes no sense for me to take several steps backwards in my speed program to buy one of these engines, so if you aren't just shooting smoke out of your tail pipe send me the engine in question, [in decent shape] and I'll have a 1 month deadline to get it running faster than 155 mph [with video, audio doppler and onboard telemetry] or else I'll send you $100 plus your engine back. If I beat 155 mph, I expect nothing in return from you.

combatpigg

My Feedback: (3)

Thanks for the reply LF. That's what I was hoping to hear. Trim the skirt and install heavy crank metal if needed. If I could find a NIB engine for that amount it would be tempting, but after buying the exhaust system the actual turn key price would hurt a little. I'm at a point with my junk where in order to add anything to the pile, I've got to first subtract an equal amount beforehand. In other words I don't want to end up with a more ridiculous looking estate sale someday than what it will be already....

BTW..I lightened a K&B 6.5 piston enough to cause vibration and had to lighten the crank with a little divot afterwards. All those micrograms do add up at 22,000. IIRC the crank web was a full circle..so there had to be mallory plugs in it come to think about it.

speedracerntrixie

My Feedback: (29)

Actually the " Challenge " was for you to tell him in your opinion how to correctly set up the engine. What plug, fuel, prop, pipe length the same as I have done and then back it up with some proof that that supports your information. I gave him specifics and proof that those specifics work. The only information you gave him was to " do some work on it " with no real direction.

combatpigg

My Feedback: (3)

All you were able to do was show how to get mediocre performance [155 mph] and then take the opportunity to brag about your NorCal pylon racing exploits.
BTW...It's been at least 10 minutes since you last posted a picture of that plane of your's...what's up with that..?
Did you break your "Up Load" button...?

Next to Piper Chuck's Sig Wonder with the K&B .21 in it, that plane of your's must have the 2nd most photos uploaded in the history of RCU....

proptop

My Feedback: (8)

Hey...Merry Christmas guys...!

What did I get myself into by posting in this thread...?[X(]

Sorry I mentioned anything about vibration...

combatpigg

My Feedback: (3)

Merry Xmas to you, PropTop....and nothing but good vibrations for 2013.

Yak13

My Feedback: (17)

Thanks guys for the good info and passionate discussion. I think the fisrt thing should be to test the engine. Lets see how it behaves with different props. Honestly, I am sure we can get around 170 mph with no mods, on the right airframe. I have one that I desugned a few years back that doing 155mph on a stock YS60 and 10x10.

Let's see how this works out.

Thanks again and I'll let you know how it goes.

Ed

combatpigg

My Feedback: (3)

Merry Xmas Ed.
As what has been asked elsewhere, this is what I would do.
1. Tear the engine down and give it a sonic cleaning. You can do this by taping a glass jar to an orbital sander filled with cleaning solvent.
2. Do a detailed fitting of the crankshaft to the bearings / case. It should be velvety smooth, no radial slop or catches. with just a flick of the prop the crank should spin with no effort and come to a very gradual stop. It should never stop in the same place twice.
3. Obtain timing / porting specs from the D/F version and do my best to duplicate the same.
4. Lighten piston / wrist pin to the best of my abilities. Trimming the skirt, especially to unshroud a clear path to the schnuerle port[s] is a way to increase pumping capacity and improve the engine's redline in one fell swoop.
5. Open up crankshaft bore to what I deem as max. Grind closing edge of intake window to DF spec. Grind reverse oil control groove in main journal if none exists.
6. Place carburetor in my carburetor trash box and replace with venturi. Use servo actuated fuel shutoff instead of throttle.
7. Balance engine as required..even if I need outside assistance.
8. Perform engine testing per lfinney's outline. Use cheap wood props to get ballpark figure on pipe tune and for range of CF props to order for further testing.

I probably have left out some other details...but I do not do this stuff for a living....
I would consider 170 mph a waste of time, since there are so many easier ways to do it. Especially with a larger model than .40 sized..because 170 with a 40 sized model looks quite a bit faster and more impressive than when you see 170 with a big model.

Yak13

My Feedback: (17)

What would be a good replacement carb for the .81, in order to squeeze more power/rpm out of it? I have an OS 7D as well as a Picco 80 DF engine and a Rossi 90 DF engine.

The 8mm throat will surely choke the .81

Thanks!!

Yak13

My Feedback: (17)

To clarify my last post. I can use the carbs of those engines for testing. The DF engines will not fit in the airframe I will be using.

Ed

lfinney

My Feedback: (44)

the 10.00 MM rossi carb is good, as well as the three needle 10.5 MM Os carbs from the heli engines as well.

speedracerntrixie

My Feedback: (29)

Yak, I have a Picco carb on mine and it works well. It took a little fiddling to get it to idle. It was a combination of leaning the low end screw and rotating the whole fuel inlet assembly. Being that yours is an 81 you may not have to do that. Once set up I have not had to mess with it ofther then set the high speed needle to the conditions.

Yak13

My Feedback: (17)

I just found an old OS 108 in my engine chest, with an OS 7D carb. Do you guys think it might be an option?

speedracerntrixie

My Feedback: (29)

If it fits, it should work. The only thing I am worried about is some of the larger OS carbs came ith an adapter/heat insulator made from some kind of brown plastic. It looks like Bakelite but I'm not 100% sure if it is. If your carb has that then the Rossi " draw pin " design of attachment could easily damage the plastic before you get good carb attachment. I have even gotten ahold of Rossi and other makes of engines where this method is used where the pin had been overly tightened and damaged the aluminum carb body.

lfinney

My Feedback: (44)

the carb insulator is actually urethane and is pretty tough, and is expensive to replace.. but.. the OS heli engines us a drawbar method to clamp the carbs just like the rossi engines so if the diameter is correct the install clamp and use..the heli carbs from os are the best simply...10-10.5 diameter throat size with mid range needle which is the cats azz for pipe users. I am using them on 61 SX-WC engines in fixed wing planes...love them.

SpeedBoy

lfinney how do you set the 10mm Rossi carb ??

I have had a hard time trying to have normal transition with this carb that comes with the Rossi 53 VP engine , I can't leave the engine on idle for more than 10 seconds and have a good response when transition to full power , the only way to achieve this is closing the high needle when I pull the trhotle stick to full power , and at this point the low needle is completely close , the engine seems to charge in idle even when low needle is completely closed.

I have had this symtom on 3 carbs of these.

What Im doing wrong with this carbs ??

speedracerntrixie

My Feedback: (29)

Speedboy, what I have found with the 10mm carb is that if you have transition problems then the low speed needle is too lean. If opening the needle some causes idle reliability issues then go to a slightly hotter plug. In both my Rossi .45 and 61 I have found OS #8 or Enya #3 plugs to work the best. When I first started running my .45 with a 10mm carb I too had transition problems. It was acting like it was loading up so I would lean the low speed. Made it worse so I went the other direction. Transition was fixed but now wouldn't idle so I replaced the Rossi #5 plug with an OS #8 and it ran great.

Petrovsky

Good points from speedracer- I've had exactly the same problems with the Rossi #5 plug. A Rossi #3 solved the problem. Probably in the same heat range as the OS #8. In fact it works well with straight 80/20 fuel. Speedboy are you using low or no Nitro?

SpeedBoy

Thanks for the advice , I was using OS R5 plug (cold) as this one was running perfect on my Rossi with the 8mm carb.

I'll play with the needles and change the plug to see if I can solve the problem.

Petrovsky , I was using 5% nitro.

speedracerntrixie

My Feedback: (29)

The 8mm carbs work great but IMO Rossi got the taper on the low speed needle wrong with the 10mm. The mixture is not liniar so at part throttle the engine leans and will not transition. By richening the mixture you will overcome this transition issue but create an overly rich idle. The hotter plug compensates for this but you will need to run slightly richer on the high end too. This will cost you a few RPMs. The needle can be modified but is kind of a trial and error thing and really needs to be done on a lathe. The racing circut that I run in requires that we demonstrate a 4,000 RPM or lower idle for 10 seconds. This is verified just prior to model release in the first heat. For the first heat I run an Enya 3 plug for idle reliability. All heats after that I run with a cooler Glowbee plug so I can get just a little more top end. All depends on what your goals are I suppose. If idle is important to you then stay with the hotter plug, if speed is the main goal and your not concerned with idle then the cooler one is the way to go.

speedracerntrixie

My Feedback: (29)

double post

lfinney

My Feedback: (44)

if you contact rossi USA they will send you a different taper low speed needle, for the 10 MM carb.. the early production new style 10 MM carbs had the taper wrong on low speed needle

speedracerntrixie

My Feedback: (29)

Do you know when that was impemented? My carb is only a little more then two years old.

lfinney

My Feedback: (44)

you may have the new taper on the idle side, but a call to sahak will do the trick