SC 52fs

[Simon UK]

Hi guys i'm not a nitro head so when i recently bought a 2nd hand sc 52fs i was really suprised to find i had absolutley no problems in getting it started, i even manageed to set up the idle so it ticks over nicely.

 

My concerns are these, firstly there is virtually no compression when turining it over by hand, and thats with the trottle fully open. Secondly the final 1/3rd of the throttle band does not provide a noticeable increase in rpm. I am also not convinced that i am getting full power from the engine. Although it's fitted in a H9 Cub and it's plenty powerfull enough for the model.

 

So my questions are these, is it a worn piston ring/s? and if so are these easily replaced and aquired? I am not sure how old the engine is but it was a bargain and it runs so i'm not complaining, just trying to get the best from it

 

Cheers

Simon

[Peter Miller]

Ringed engines often do not have much compression at low speed, i.e when hand turning the engine. I had an Enya 46 that was in a sorry state, there was no detectable compression when turned over but it still turned an 11 X 6 at 10,000 rpm.

 

Some four strokes with reings do have more compression. Just ckeck the rpm if you have a tacho,

 

Most model carbs have very little effect  at the wide open end. They don't start throttle]ing down until about a third closed. so in effect opening them over the last third will have little effect.

 

If you have exponential on your Tx for the throttel channel you can overcome this. I set 30% negative exponential on my Futaba FF8 for a much more linear response.

 

Alternatively you can set the output arm on the servo at an angle so that it moves the arm the greatest linear distance at the open end of the travel rdeucing towards the closed end.

[Simon UK]

Thanks for the fast reply Peter

So you don't think that the engine needs a new set of piston rings then, good news as it saves me a few quid and some time. A tacho is a piece of equipment i will have to pick up in the next few weeks. Should i be looking for specific numbers from the tacho, i'm currently on an 11x6 prop but i may go to a 12x5/6 or a 13x4 to try to get a stighlty more scale appearance.

 

I don't need exact numbers just a ballpark for me to use as a guide.

[i12fly]

I bought a similar used SC52FS, compression embarrassingly difficult to find when its hot. Starts OK on the starter, tickover fine and seems to run fine full on. I get 8300rpm on 12x6 and 9500rpm on a 12x5, Both are APC props on 10% nitro and with a blunt 5inch radial cowl. Don't know if this is typical but it pulls my plane about OK.

[Peter Miller]

I wouldn't worry too much about a tacho if you haven't got one.

 

Personally I find that the SC four strokes (and others) tend to be happier on props at the mid to lower end of the range.

 

My current model flies aerobatics happily on the SC 52 FS with a 12X6 but it has a low wing loading.

 

On a Piper Cub you could go to a 13X4 as you don't want a fast model and that will give you a steady pull.

 

Think of the pitch as gearing. A higher pitch is like drivng your car in top gear, Hight top speed and poor acceleraton while a low pitch prop is like runnignin a lower gear.

 

5 lbs, 700 sq. in. SC 52 on a 12 X 6. Fully aerobatic.

 

 

[Peter 'Ivanna Crashalot' Savage]

ah, I did not know ringed engines have low compression at slow speed, this explains why my os 48 fs is so uncompressiony

[Myron Beaumont]

The leakiness does however allow oil/mixture to get to the crancase to provide lubrication .It's the only way it gets there! Crude but it works  

[CARPERFECT]

If you need parts http://www.amerang-group.com/contact.asp these are the importers of TT engines. I bought  a 52 off flee bay that ran the same as yours. required new liner and piston  as it would only manage 4000 rpm. sent it back to seller for full refund as he discribed it as fully working. Parts for TT engines are like rocking horse poo in the Uk i contacted 6 uk TT engine suppliers all said the parts i required were special order 4 to 6 weeks at a cost of over £35

[Peter Miller]

As this is an SC engine you can get all your spares very easily from any J.Perkins Stockist.  or John D Haytree

 

You can easily check the spares situation at the J. Perkins Distribution website

 

Since it is flying the H9 Cub I doubt if it has anything wrong with it.

Edited By Peter Miller on 21/06/2010 07:53:47

[Simon UK]

I think i will pick up a 13x4 prop from my lhs this week. Thanks for all the advice guys, and especially thanks Peter for the tips including the way of thinking about prop pitch as car gears. That actually makes things much clearer in my tiny brain.

 

As you correctly state top speed is unimportant to my cub, i would much prefer better acceleration

[smudgetsgreatadventure]

Best little 4s ever made to be honest, i have two, one has done at least 80-90 hours run time in various models, compression feels the same now as when it came out of the box, always used contest 10 and os f plugs, nevr put rings in or any thing else, but do keep valve clearances checked, this keeps performance, and stops the valve train getting sloppy and rattling itself to an early grave,  brilliant engines, even have the 400 radial, in a yak, have yet to run that baby. only better engines are saito, but oh, the price

[Stephen Grigg]

I always feel a four stroke doesnt sound as if its quite revving enough compared to a 2 stroke, but its all about extra torque with a four stroke isnt it.I recently tested an SC52 4stroke I also bought off E bay.Ive had it a year.Started instantly and ran perfectly.I was having trouble trying to figure out why i couldnt get a models engine to run properly in the  model,so put this engine into the model and it started and ran perfectly.I then knew the model want the problem.

[Ian Skeldon 1]

Hi,

 

I tinker a fair bit with engines and have to say that the advice about low compression is bang on (pun intended). Your four strokes often don't show much compression when turned by hand, but as mentioned it's nowt to worry about if it runs ok on a reasonable size prop.

 

Again I sometimes increase the loading with a bigger prop and then taco it to see how it's doing. My advice would be to stick with about a 12 -13 inch prop and anything between 4.5 - 7 pitch, you can get more revs (and noise) with a smaller prop but be carefull of underloading your fourstrokes, the top end can let go.

 

I tend to use hot(ish) plugs again mentioned was a OS 'F' plug, these work well. As for spare parts for them, I find that Perkins can be real slow here and nearly always use Just Engines. They don't do Super Custom but they do sell ASP and the parts are mostly identical. I have to admit that I have now started to use more ASP and some SC engines as the Jap ones are so expensive. I do sometimes buy from ebay and always allow for the cost of rings, con-rods and bearings as a minimum when bidding. Laser Engines are great and do tend to have a bit more compression when hand turned, they also start easy and WILL BITE if you over prime them.

 

For fuel I tend to use Model Technics Contest 5 or 10. After a days flying my engines are treated to a little squirt of two stroke oil (as used by the little mopeds etc) through the crank breather. I never use any tubing on the breather nipple and I use fuel clamps, locking them after each session and leave any fuel thats left in the models tank.

 

I hope you get many happy and trouble free hours of flying from your engines.

 

Ian

[Derek Gray 1]

I have a SC52fs, it runs fine, even tickover. The issue is the last half of the throttle does not produce much in the way of a power/rpm increase. At half throttle it's pulling 9400rpm at full throttle it pulls 10000 rpm but sounds a bit uneven in the air at full throttle.

I am using contest 10 fuel, os f plug and a 12x5 MA prop. The needle settings are

High end 1 and a half turns out, and low end (idle) 1 and three quarter turns out.

The engine is quite new, only had half a gallon through it but it picks up well from a 3500rpm tick over even if the throttle is opened quickly and smokes as expected.

I have tried a richer needle setting (rpm 9300 on ground) but the model is under powered and staggers around in the air. I have opened up the idle setting making it richer but it causes the engine to cut in the air after a few mins flying. I have been told a 12x6 or 7 prop will help as it will load up the engine?

At the moment the aircraft flies well at half throttle with full throttle only slightly effecting vertical climb performance. I cannot lean out the needle as it may damage the engine and spoil the good throttle response at the bottom end. I have the tank center inline with the needle valve and have even tried a smaller 6oz tank and plumbing.

Any suggestions guys