OS105 bad vibes

[datatools]

Hey guys, I just replaced the engine in my N7 with a brand new OS105. The previous 105 in this heli needed a rebuild after countless jugs of fuel, so rather than wait for the parts I had a brand new 105 in box which I installed. I've had a heck of a time trying to tune the new engine, runs rich then lean, and constand bad vibes. I removed the head and when running the engine at at any speed the heli shakes like mad, and I've reduced the culprit down to the new engine. Replaced all fuel lines, exhaust vent line, etc, and finally rebuilt the old engine and put it in, now the vibe is gone. So it appears the new 105 was the cause. Any ideas what could be wrong with it? I cranked down on the crank shaft bolt really good when assembling it, is it possible I bent the crankshaft? How do I check to see if the fan is running true and clutch, etc (since I replaced the clutch and fan when reinstalling the rebuilt engine). Is the new 105 a paper weight now? Any ideas are much appreciated.

[Glenn Goodlett]

Dial indicate the crank, fan hub, and clutch to narrow the problem down.

[Rob43]

Also, not sure why the interest to crank down so much on the crank nut. Just not necessary. The fan hub split is what is critical to fit the journal on the crank shaft. The nut goes on last, and only needs to be snugged. As Glenn said, check hub runout. Better chance the hub was distorted on the shaft. Use some threadlock on but, and tighten it just to snug it up.

[Icanfly]

I'm interested to know if those rc motor companies balance the crank and piston assemblies or smack em together for the quick buck. Would it be unreasonable to think the crank is for a 120, shouldn't it have 105 stamped? and just how does one know the counter balance on the crank is accurate anyway?

I had some decent luck with my os32 and wanted to possibly balance the crank, I don't see any info on doing that with nitro rc motors.

[mdu6]

This is more or less the process to check fan hub/clutch runnout

1- Remove the engine back cover
2- Mount the engine in the vise (I use a homemade holder that simply clamps on one of the engine lug)
3- Mount the fan/hub on the engine and while pushing the crankshaft forward you put the engine nut on the crank and just tighten a little bit so there is no play possible on the crank
4- Start tightening the 2 clamping bolts. (2 bolts at the same time)
5- Check the runout - indicate the inside of the hub (page 13)
6- You want to slowly tighten the clamping bolts and check the hub to remain true (little runout as possible)
7- If the hub does not remain 'true' - you can
a) backoff the clamping and start back one bolt at a time
b) turn the hub on the crankshaft (using a crankshaft locking tool)
c) tap the hub using a soft hammer
d) etc etc
8- Repeat steps 4-7 until satisfied with the result - this can take 10 minutes or 2 hours
9- Once you have the result you want, snug the engine nut and put some loctite on the crankshaft/nut
10- Lay the engine so the crankshaft is upright (loctite will slip down)
11- Keep the engine like this for 2 hours while you take a beer to cool down ;D
12- Mount the clutch on the hub
13- Indicate the clutch (on the N7 - the only option is to use the one-way bearing) and write down the runout
14- Remount the clutch 180d - indicate the runout and decide which side is the best one
15- On some helicopters, I have use a file to create just enough clearance on the clutch bolt holes to 'move' the clutch around and zero in the clutch
16- Remove one clutch bolt at a time to apply loctite and tighten completely

Page numbers are relative to the N7 build book I made

https://drive.google.com/file/d/0B0y...it?usp=sharing

[datatools]

WOW, now thats good info. Very nice. Now I need to find one of those dial indicators, any idea where to get that tool?

[mdu6]

Numerous places - in Alberta for example you have many Acklands-Grainger outlets that should carry indicators.

https://www.acklandsgrainger.com/AGI...Ns=P_Price%7C0