PaulSwany

My Feedback: (45)

I've been breaking engine mount bolts in my SuDoKhoi. It's powered with a MVVS .40 with a mini tuned pipe. I've got an 11x4 apc prop on it, swinging at about 14,700 rpm. I've balanced the prop.... I have about 2 deg of right thrust added with a tapered shim that covers the entire mount lug on the engine.

These are 6x32 socket head cap screws mounted to 1/2 hardwood engine bearers with nylock nuts.....

Any idea's why I would be breaking soo many bolts? I break one about every 2nd or 3rd run.

Kevins_RC

My Feedback: (1)

Paul, did you drill out the holes in the motor casing for #6-32's? Make sure that there is clearance there, about 1/64" on the diameter.

Check the grade of the bolts you are using. I usually use a No. 5 (3 tick marks on the head). Ensure that you are not using a No. 8. The higher the number, the harder they are, and more brittle. If you are using No. 5's, go to a standard bolt, which is a No. 3. A No. 3 is more elastic and will absorb more shock.

You may also want to check the alignment of the engine's mount holes with the mounting rails and ensure that they align. I would think that the rails are hardwood, thence this should not create the problem even if there was some alignment.

You are obviously experiences some unusual vibrations or harmonics. I would suggest that you try and run an APC 11.5X4. This is the prop that I am running on my MVVS 40 with the mini tuned pipe without incident, plus I prefer the perfromance over the 11X4 APC.

I hope that this offers some help.

PaulSwany

My Feedback: (45)

I did open up the holes on the engine... I'll check to see that they have proper clearance.... I'm wondering if the shims I'm using might cause a problem... they are aluminum and there's black dust on and around them.. I'm assuming from the vibration. I couild use a little high temp silicon to create a cushion between the shims and the engine.....

I don't have any idea what the grade is for the bolts... I'll call the fastener company..

11.5 x 4!! Wow... and my buddy said that a 11x4 would be too much... I'll try it. The needles on this thing are VERY finicky... couple of clicks on the low end makes a huge differece... I'm running 5% nitro in this.

SitNFly

My Feedback: (54)

Same thing happened on mine, but I have a Saito .56 so it's not just a two stroke thing. My local fastener outlet told me that the socket head cap screws are high alloy and are actually harder than grade 8. Brittle stuff. I replaced them with stainless bolts and haven't had a problem since. Stainless is probably overkill, you could just use lower grade slot head machine screws as recommended in the previous post and get the ductile properties needed.

Rein

PaulSwany

My Feedback: (45)

I just talked to the fastener guy and he said that the alloy bolts are the equivelent of grade 12.... wow.. that's hard!!! Something like Rockwell 39.... Anyway, I explained my problem and he said he would send me a bag of 6x32 stainless socket head cap screws to try out. He said that the stainless is better with vibration. Not as hard and more ductile.

All he wants is some feedback... Pretty cool guy.... Their url is: Micro Fasteners

I'll let you know how I fare out.

dyerstown

Is your prop balanced well? That kind of vibration could be caused by a prop that is significantly out of balance, or if the bolt hole in the prop is oversized and allows the prop to be mounted slilghtly off center. I have a ST .51 that has a vibration that I cannot pin down. I indicated the crankshaft, and it is right on. Hope you find the problem. In my opinion, no socket head cap screws should break, at least not often. I use them on all my planes, and I don't remember ever breaking one. Best of luck.

Balsageek

How does that MVVS engine run? I'm trying to decide on my next fun fly engine. I have it narrowed to the TT.46, the Morris Powerhouse .45, or a MVVS .40 What do you guys think? Low weight and high power is my main goal.


Matt

Kevins_RC

My Feedback: (1)

Needless to say - Balsageek, you are asking an opinion - which is dangerous! The Powerhouse is a Rossi. The Rossi is known for its great mid range power band, though is HEAVY!!!! You would think that you have a heavy 60 size motor in your hand, but its a 45. The casing on these motors are huge! They offer great power (I'm told - mine still hasn't proven that to me and I have since replaced it and its going to the Swap meet here shortly). On a FunFly you don't want weight. Despite its supposed power, I don't think that it is worth it. You normally have to add weight to the tail to compensate for the nose weight that the engine creates.
There are people that love the MVVS, and others hate them. I have a 40 MVVS, that is not boken in yet, and believe that it out performs most 46s (including the TT 46). The TT 46 is heavier than the MVVS 40. I have compared them on a double pan scale.

I like the Webra 50.

I would suggest on investigating on what others are running in your area, and what is supported thru your LHS.

Hope that this helps you out!!! Good Luck!

PaulSwany

My Feedback: (45)

My MVVS .40 is a real power house... It really moves that 4.5 lb plane around.... I am finding that the carb settings are a little finicky. 1/8 turn on the low side make a HUGE differece on throttle response...

I have a TT 46 as well... It is a great motor, but the throttle response isn't as good as the MVVS .40. It's also heavier than the MVVS. I have one in my Fazer and it will hover at 1/2 throttle. I've got a Tower .46 muffler on mine... was good for 500 rpm.

Hey Kevin... you don't want to get rid of one of those Webra .50's do you?

PaulSwany

My Feedback: (45)

Do you have any data on the Webra .50? Do they have a web site?

ReallyUglyStick

My Feedback: (5)

did you change the length of the header you have on your mvvs 40? is it the stock header? with the stock header i was able to get 33300 rpms with an apc 11X4. i figured this was a little low. still plenty of power, though. the stock header has been replaced with a macs header because it broke. i didn't do any tuning, but i cut the header to what macs recommends, 5.25"...i believe this is for one of their pipes, though. i tried it at that length and had no power. i've since cut it to 3.75", .50" longer than the stock header. i'll try it out next weekend.
what header are you using and how long is it?

Rotaryphile

I have run into this problem, but with glass-filled plastic mounts where the engine was mounted well forward on the mount, which makes the spring/mass system of mount and engine softer, lowering its natural resonant frequency. Sort of like a diver bouncing up and down on a diving board at the right frequency, forcing the board to oscillate up and down. Suspecting that the engine and mount combination was reaching its resonant frequency when the prop unloaded in flight and engine RPM increased, I fitted a one inch smaller prop, and ground ran the engine at full RPM. Eureka! The engine went into wild vibration that made the model painful to hold. The problem was solved by mounting the engine farther back on the mount, and placing a thick plywood spacer behind the mount, to place the prop in the same plane as previously. If your wood engine bearers are attached firmly to the fuselage sides, this explanation does not apply, but if they are cantilevered out from the firewall, I would strongly suspect a resonant vibration problem, that might be fixed by better restraint of the bearers.

PaulSwany

My Feedback: (45)

I'm using the stock header on my mvvs. I'm going to try putting a little silicon between the engine and the tapered shim to try to cut some vibration out.

PaulSwany

My Feedback: (45)

Hey... The stainless bolts rock!!! I've got 5 flights on it with no bolt breakage... My 6061 T6 gear is working out much better too. The 1/8 x 3/4 alluminum at home depo is butter!! the tempered gear had a nice bounce too it. Much better.

PaulSwany

My Feedback: (45)

Well, the stainless bolts are definately the answer for profile engine mounting. I've got about 25 flights on the stainless bolts without a break!! Perfect solution.

FIVESQUARE

You may have solved the problem with a bandaid.....
DYRESTOWN has you answer.....You prop is more than likely off balance.
Start with the simple thingds first....
VIB usually means prop out of balance.
5x5

PaulSwany

My Feedback: (45)

fivesquare...

I did that... I balanced the heck out of a 10x5 prop... Then I put a 11x4 prop on it... Again painstakingly balanced.... It seems like it has less vibration with 2 gallons thru it... It just keeps getting better and better...

IMHO... I think profiles are more prone to vibration that full fuselage planes.... the wood engine bearers and flexible fuze make for a vibrating combination.... The stainless bolts really helped....

uciflylow

Paul
That's really strange about the bolts breaking. I use 4-40 socket head alloy from Micro-Fastners on all my 46 to 60 size planes and have never had one break! I use the alloy 6-32 for the bigger engines and have never had a problem with them. I currently have 46 fx'es mounted in a Sudokohi, profile hotts and morris mustang, not to mention the stick, mid*40 and a coupla other planes and never a problem.

m.gramling

My Feedback: (8)

I am having the same problem with my YS 63 on my top cap arf. Yes my prop is balanced. I keep breaking the back bottom bolt. I can start my motor and it breaks within 5 minutes of the first flight. I am using Great Planes 4-40 hex bolts. It looks like I am going to have to find me some more bolts.

DonH21

My Feedback: (3)

Paul
I've always used 4/40 bolt on my MVVS .40 and .49.
Never have broken one. I had to drill the holes out a little in the motor.

Don

Rotaryphile

You can frequently help a vibration problem by deliberately unbalancing the prop, trying the heavy blade in line with the crankpin and 180 degrees away. If it helps, you can use a dowelled unbalanced spinner backplate. I used unbalanced backplates on 125cc McCulloch kart engines used on high performance drones. Really reduced crank runout at full RPM measured at the spinner backplate. Trial and error is needed to find the right unbalance.

PaulSwany

My Feedback: (45)

Michael - with that horse your gonna need 6x32 stainless bolts... and make sure you have plenty of clearance..... Check with MicroFasteners.. They have a web site.