ALFIEV

Sounds very familiar to me. Best I can get out of a XOAR 18x8 laminated 2-blade is 7100. Just enough for my model.... just.....

simone76

moved cam shaft 1 tooth backwards, lost more than 1000... will try to move a tooth in the other direction. It's becoming a challenge.

ALFIEV

Did you advance or retard the cam timing. When you say you moved it back a tooth, I guess you mean away from the front of the engine, or towards the direction of the rotation of the cam (clockwise?). Of course, we have to be bloody careful tinkering with this least we end up with valves open at TDC, possible contact with the piston head, etc. The fact that you lost RPM suggests you moved in the (anti-clockwise?) direction. I did that, and got a smoother idle, but lower RPM at the top. I believe there are pictures on this thread showing the position of the valve cam. About post #37 I think it was. Fairly much lined up with the "web" on the engine casing.

It could be that around 7100 rpm is all we'll get out of our engines with the propellor we use, and the fuel we are using, in our particular environments.

Good luck and take care with that engine!

Basil Yousif

My Feedback: (3)

On the YS 110FZ I they said to put the cam dot at 11 O'clock I put it at 12 and the engine ran much better. Higher RPM's. Although on a gasoline engine that may result in it running hotter, try going one tooth ahead and see what happens. My YS ran like a bat out of hell after I made that adjustment, but it is glow.

simone76

exactly, moved dot a tooth away from propeller when it is at bottom. Will try to move a tooth forward and see. It became a challenge, i prefer having fun with cheaper engines than messing with expensive ones, i own as well. 7100 sounds enaugh to me, but atm im far away from it (6600 with 18x8 biela)

simone76

i recognize doing this i advanced it. Well, anyway i wanted to try both one tooth ahead and one tooth backwards. Btw here is a pic of original cam shaft with the newer one. Cams have slightly shape and... a different angle to the dot. This concerned me, so i'm going to find the best by trials...

simone76

With valve timing advanced by 1 tooth, it passed from 6600 to 7050 rpm with biela 18x8. Will test fly it like this because ran out of time. In future i will test a tooth ahead more.
Anyone uses a 18x8 Biela and want to share rpm it is peaking at?

SJN

So the old cam, and the new cam are the same, but the timing dot is located at a different place ?

Basil Yousif

My Feedback: (3)

By moving the dot one tooth forward your advancing the timing so the engine fires closer to Top Dead Center. The higher the compression in a engine the further you want it to fire from TDC but since these four strokes don't have great compression they will run better with the timing adjusted closer to TDC. If the engine is broken in you should be okey just watch for too much heat. If it's not overheating then your good!!

simone76

To me it seems so. Yyou can see that in picture and, to me the cam has a slightly different shape also. BTW im seeking for the best valve timing by trials... then will report.

simone76

I'm experimenting on valve timing. That has nothing to do with Ignition timing. It is matter to play with valve opening to get the most mass of air/fuel mix in the cylinder for best performances.

Basil Yousif

My Feedback: (3)

The valve timing does effect the ignition timing. Remember on this engine you can only max out the ignition sensor at 40 degrees for the ignition sensor. You can counter that by moving one tooth forward . The piston will be closer to the top of the cylinder when you move that dot forward.

simone76

Nope. Advancing the cam shaft causes the Inlet valve to open a bit earlier.

SrTelemaster150

Unless the trigger is mounted to the cam shaft, cam timing will n ot affect ignition timing.

CapMan

My Feedback: (219)

I have an NGH-38 on a R/C Guys Decathlon. The engine runs very well, starts easily and best of all sounds great. I have seen zero temperature issues. This engine does not look as fantastic as a Saito, but I can buy 2 NGH-38 for the price of one Saito 36.

SrTelemaster150

And the Saito will probably outlast 3 NGH-38s. You can also readily get any part for the Saito.

ALFIEV

Yep, my thinking with the moving of the cam shaft timing was that I was changing the point at which the engine developed peak compression prior to ignition. My idea was that, as I had an extremely lumpy idle and a lot of trouble getting the engine turning over to start, that getting the valves fully closed a little later would move the maximum compression closer to the point of ignition. This did indeed seem to work, easier to start, smoother idle, but a loss of top end performance.
Now I have moved the cam back to its more advanced position I am getting better top end performance, the idle is o.k, and I have a good strong starter to turn the engine over with so no problems there. I was also getting a lot of back-firing and loosened propellors initially. That also went away. Once again, the good strong starter and a better tuned engine seems to have sorted this out, I no longer have the back-firing issues even though I have advanced the cam back to it's original position.
This might defy Gas engine theory. I understand the theory surrounding advancing and retarding ignition. Advancing and retarding valve timing is a little less clear to me. I have tried to explain my thinking on this above. What I can say is that I did practically observe the outcomes of moving the valve timing cam.

Always learning....

Alf

tyor

I have had a saito 36 about the same effect as ngh38. but could never trust it. could not get it to go well in the air. Gave it away to a friend after crashing three planes due to engine failure in the air.

Basil Yousif

My Feedback: (3)

Your forgetting that the crank shaft will also be in a different position with the dot one notch forward. The crankshaft moves the piston up!!

simone76

The ignition trigger is on drive shaft, the dot is on cams shaft. There is no way changing valve timing will affect ignition timing to the piston. Have some mumbling with this engine in hands and you'll get it.


Btw inflight tests gone fine, engine did well, giving scale performances, performing quite reliable, pulling in air my heavy beaver on floats. At slightly more than 7000 rpm the 18x8 Biela should pull almost 7Kgf (>13 lbs). This may be the top limit we could expect from this engine.

ALFIEV

Finally got the Corsair out for another flight. NGH GF38 turning at 7100 rpm on a 18x8 laminated Xoar prop. Flew really well, enough power and good speed in the air. Never missed a beat!!!

Sadly my second flight ended in a rubbish landing so I have retract and wing damage...... again. Will repair over xmas and look forward to firing up the NGH GF38 again!!!!

drummaker

so.... in my imagination... I was thinking that the mounting standoffs would go directly to the back of the engine, then the mounting plate would go on the other end... Then the plate would be mounted to the firewall with enough spacers to allow for the heads of the bolts...

hmmmmm Would it fit like that? It would allow for perfect alignment of the standoffs

SJN

the mounting plate spreads the standoff out to the sides to the footprint of the engine is larger i guess.

But 1 of the backplate polts is alto covered by the carb ventury...the 3 others are clear.
You could probably remove the blue ventury......but the standoff would run close over te intake I think.

Try it, and see what happens :-)

captinjohn

What are we doing here? I hope it is getting all the bugs out of this engine before it hits the production line......

discus-fly

Thinking of using the GF38 in a Flair Tiger Moth. However lack of a muffler is putting me of. Aware several posts have addressed this issue in the past but not sure if available hardware will be compatible with the narrow cowl of the Tiger Moth.

Would therefore welcome any advice on suitability and the source of an exhaust stack.