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Engine basics => Engine set up tips => Topic started by: frank mccune on June 09, 2014, 05:20:06 PM

Title: Prop keeps blowing off when starting.
Post by: frank mccune on June 09, 2014, 05:20:06 PM

     Hi All:


      I have an engine that blows the prop, prop nut and washer off each time I flip it to start it.  It fires on the first flip but there is nothing on the shaft after the first flip.  It will also do the same thing when using an electric starter!

      Does this mean that I must add some head gaskets to lower the compression? If not this what is the cause?

      The engine is an older Fox .25 from the 50's.  It runs very well but what is with all of the starting problems!  I can not think that there is enough 'carbon build up" to raise the compression of this sport engine to provide a very high compression ratio!

     I used both wooden and plastic props is various sizes.  I used a lock washer between the prop washer and the prop nut.  I double nutted the prop nuts.  Perhaps Loctite is the answer.  Yes, I applied a large amount of torque to the prop nut.

     I have seen this happen with a .40 racing engine that had some severe mods for racing but a sport engine?

     Has anybody used a drop of Loctite to keep spinners and prop nuts from coming loose when being started? 

    Any suggestions?

                                                                                    Tia,

                                                                                    Frank

Title: Re: Prop keeps blowing off when starting.
Post by: RknRusty on June 09, 2014, 08:47:12 PM

The only Fox I have any experience with, a Stunt 35, has blown the prop off. With hard plastic APCs I have used a sandpaper disk behind the prop to help hold it. Woody's are probably worse about it. But I have had better success by back flipping mine. I rotate it to the beginning of compression(so it has a half turn of free swing) and smack it backwards with the chicken stick and it starts easier than forward flipping. Plus it's less likely to unscrew when hitting it in that direction. I wouldn't ever whack a wood prop like that though.
Rusty

Title: Re: Prop keeps blowing off when starting.
Post by: Akihiro Danjo on June 09, 2014, 11:11:40 PM

As Rusty san says, I recommend you to use (a) sandpaper disk(s) behind or both sides of the spinner backplate like this:
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXKDJ0&P=7
This item is too large for our use. Smaller one (1"OD 1/4"ID) is sold here in Japan from OK Model Co, and it is called 'Grip washer'.

Good flying, Aki

Title: Re: Prop keeps blowing off when starting.
Post by: Brian Gardner on June 10, 2014, 08:21:09 PM

Between the prop driver & spinner backplate (if aluminium) I always ran some 0.5mm high temp gasket material.

Title: Re: Prop keeps blowing off when starting.
Post by: Steve Helmick on June 11, 2014, 06:58:33 PM

This is a common problem with spinners with plastic backplates. Avoid them like the plague. If you're not using a spinner at all, I'd guess that it's overly wet. Try doing what you've been doing, followed by flipping the prop backwards about 6 times before you put the battery on. Well, I would try that, anyway.   y1 Steve