HaveBlue

Hi, I'm just giving my SJ90L/jett stream muffler turning an apc 11 X 7, its on it's second running on the bench, I'm using 7% nitro, 20%castor, 73% methanol, I ran it up to peak rpm than back off a turn, my tacho is registering 13950 rpm, is this a bit low , or is it just my low nitro content + it still being tight???( I know my oil content is a bit high being pure castor.. I think I'm just to weary of synthetics still)

being only the second tank going through the engine, should I keep it rich enough to only be turning 13,000?

bob27s

My Feedback: (19)

Hi,

Thanks for writing......

Running the 11x7 around 14K is ok for the new engine on 7% nitro. Worry not. Run it some more. If you have a smaller prop (11x6 or a clipped 12x6) use that for a few tanks. Get the engine up over 14,500 rpm for a bit.

A baseline setup, 12x6 on 15% nitro will run between 14K and 14.3K when breaking in. Will eventually get up to 14,500 peak. On 7% fuel about 500 rpm low is to be expected. On an 11x7 starting at appx 14K is pretty much on the money.

The engine and muffler run best over 13,500 ground peak. Prop accordingly for your fuel/altitude/aircraft.

The fuel/oil is ok, but you really do not need that much. Synth/castor blend is just fine. Usually 15% syth and 3% castor is good. I run 13+5 (total 18% oil by volume). Full castor may actually slow things down a bit. Ive never personally run full castor lube in any of my engines (At least not since the Fox .35 stunt days)

Best practice is to break the engine in on exactly the same fuel you will run the engine on for flight.

Let me know how things go

Bob

HaveBlue

ok Ive run my engines ..so I have a handle on what I'm doing.. but I was out at the feild for a change I had three of my Jetts with me..I made a portable running in bench out of an old air compressor platform.. I was far away from everybody doing my final break in on my first 90L... one of the guys came over ..basically calling me an idiot for running it as per your instructions... there are times I hate this hobby..but anyways after I politely listened to his way of running engines ..( I have to be patient I'm new at this club and they snob me a bit but I dont care..I'm a loner type anyway)...the thing that is concerning me and a point this guy made is that the engine felt very hot... I dont have a temp gauge.. but can you give me an idea of a suitable temp range...

fuel is homebrew 15% nitro, coolpower 15, castor5, balance methanol
prop 11X 7 apc
rpm achieved max 14200 average 13900..but then again this is with a globee..it seems inconsistent so not sure what to think here..
I'm having a hard time getting it up over 14,000 as I have to run it at absolute peak to get over 14,000 ..use a 11X 6?
I want to get this right as I cant afford to stuff this engine

one other thing is no matter how lean I turn the needle there is always a strong plume of smoke now , ..but I did take it back like the instuction say, I have run 32 oz of fuel now ..yeah not much, but should be ready for a flight ?... at what stage of this break in process would you say I can start to tune my mac's pipe?(it's just an experiment at this stage I like the muffler as is too)

any help appreciated
Roger

bob27s

My Feedback: (19)

Hi Roger.......

seems ok to me so far.... you are doing ok.

Forget temperature measurements. They are meaningless.

If the engine is reallllllllllly hot, clearly that is not good. A few things to check if that is happening. Also, do not use the exhaust 'smoke' as an indication of the engine's mixture. It is more likely vaporized oil, not un-used fuel.

The reason for the light prop is to get it to the correct rpm while being just a tad rich and slightly cool - taking it to near loaded temperature while breaking-in is ok. Maybe drop off to the 11x6 for a while, or use the 11x7 but clip the tips about 13mm each (and balance it). Get it up around 14,000 - 14,500. The engine may still be a bit tight yet. Run it a bit there. Find peak rpm with the 11x6, back it off about 800-900 rpm (should settle in at 14.5K or so). If it does not easily get there, something is wrong - see below for some things to check.

Running it too rich is not a good thing either. The cylinder and liner will not match up properly. That will keep the engine tight, and can actually cause it to get hot (from friction). If it is slightly rich, and still gets hot - that is an indication of fuel/lubrication problems.

As for your issues....

First.....
Politely direct your club member to the jett web site, and ask him to read our instructions and proceedures in the TECH section. If he has any further questions, he is always welcome to contact Dub or myself.

Second.....
Im not sure if you removed the high speed needle. But just in case, do this anyway. Remove the needle and packing nut. Slide the packing nut OVER the needle up onto the non-threaded part. Start threading the needle into the NVA assembly. Once it threads in a bit, slide the packing nut down and thread that on snug by hand. Turn the needle all the way in, back it out 3.5 turns. Just a starting point for your next run. Then tighten the packing nut so you have to use some bit of effort to turn the needle with your fingers (snug, but not locked down).

Third.....
look into the exhaust port - make sure the liner ports are lined up with the case. (If they are not, remove the head, rotate the cylinder liner so it lines up, and tighten the head back down). If the engine simply will not turn up with the light prop, this is probably what is wrong.

Fourth.....
Make sure the cylinder head clamp (head bolts) bolts are snug and tight. Best to check these when the engine is still warm. Check the backplate too. If they are loose, please see #3 since it is possible the liner rotated.

Also, even though this is on a test stand, make sure the fuel tank is mounted on foam or something to prevent bubbles or fuel foam.

Let me know how you make out
Bob

HaveBlue

Hello Bob,
I have some time this weekend to run this engine some more, just wanted to make sure of a point you made in another post , regarding the threaded stud that screws into the crank, and that was to keep it about 2 or 3 turns(?) from stopping hard when being screwed in... I had to unscrew it to get the prop off.

As for the four recommendations(post above) I do those prior to going out and running it as I do notice the liner moves a little bit and check it first. The main difference will be the 11 x 6 apc prop , 15% fuel, and a tnc tach for a better measure of accuracy!..just wanted to double check this crank stud distance first..


thanks
Roger

bob27s

My Feedback: (19)

hey there..

yes, you want to avoid bottoming-out the stud in the crankshaft. Just run it all the way in, and back it out a turn or three. If it bottoms out, there is a possiblility (rare, but it happens) that the stud will not be properly aligned to the shaft, and if the prop hole is tight over the stud, its possible to mount the prop slightly off center. You would want to avoid that condition.

HaveBlue

just a note to say thanks for all the advise...after changing to an APC 11 x 6 I had her happily running at 14,400 peak was a tad over 15200..I gave her 4 x 5minutes runs with total cool down in between..she has a definite squeak at TDC and she still feels a bit tight but I'd expect that..I think I might give her one more bench run with a slight increase in rpm on the last two sessions around 14,500 14600 all going well I should be bolting her into something for a flight

one question I do have is on the bench, even though my tank sits on a big rubber foam block, I seem to get a few bubbles in the line between carb and RNV.. the foam isnt secured and the prop wash moves the tank about a bit..(probably the cause) the only hiccup I have is priming her on the 2nd, 3rd and 4th run makes it slightly(only slightly ) difficult to start eg three or four flips if not a total re prime.. the first start up of the day is the best..just prime and she fires ..but I do have slight trouble on consequent start ups... any advise here???...
as a side note I shoot a small mist of silicone spray(armorall) over my fuel mix to stop frothing but the bubbles do persist.. its a TY1 16oz sealed tank which is exclusively used for this engine/test stand

many thanks
Roger

bob27s

My Feedback: (19)

Hi Roger,

Yeah, sounds like the engine is coming in ok. Squeek is good

If you keep that 11x6 on it, definately take it up near 14,600-14,800 for a run - push it to 15K+ for a minute. (stay out of the prop arc). Then on the next run, install an 11x8 or 12x6 - This will better load the engine. Find the peak rpm (what ever it is), back off 300 or so---- run it there. See what it does then.

Sometimes micro-bubbles form in the fuel. Even with good installations. When they go through the pressure-drop of the needle valve, then can combine as larger bubbles - which is what you see in the feed line. One thing that has shown to help reduce these, is to mount the needle valve off of the engine... on the airframe, firewall, etc. Doing so reduces the effects of vibration and some heat transfer at the needle that can sometimes assist that bubble formation.

Prime..

Usually the first start of the day tends to be when I need to prime the engine. After that, just the vapor in the cylinder will get it to fire next time. To prime, I leave the glow battery off ..... open the carb to full throttle, place my finger over the exhaust outlet, and turn the prop through 5 or 6 times. Then remove my finger, pull it through 5 or 6 more times. Close the throttle to high idle... put the battery on, and it will almost always fire on the first flip.

For subsequent starts, usually the problem is the engine is too 'wet'. Open the throttle, pull the prop through two turns to get some air in there, close the throttle - add the glow battery. Should fire right up. You will instant fuel flow as soon as it fires. Give it a try.

Careful with the armoral. Sometimes it can help. Too much can cause problems.

Bob