Hi All, Which is the best way to bolt the engine mount to the fire wall ? I was thinking of using bolts and nuts with a cotter pin to prevent the nuts from comeing off.


Thanks
Jim

that sounds like overkill to me. i used just some bolts and lock nuts. a few washers to prevent the firewall from getting crushed would help. i even put some rubber fender washers in the mix to help with the vibrations....works reall well.

What size bolts should I use to bolt the engine mount to the firewall ?

Thanks
Jim

i believe i used something like 10-32 bolts and they never worked loose. depending on what kind of plane you are mounting this on.
i fly exclusively spads and with a poly firewall it was rock solid.

http://spads.mattclement.com

I drilled the holes for 1/4" bolts. I will be mounting the engine on a Dynaflite Flybaby.

Thanks
Jim

jb foster:
In my engines I could NOT find the same bolts for the rear plastic cranckcase piece that holds the carbs in the ryobi, so i used some 3/16 bolts , but obviously forcing the situation. Do you mean you actually enlarged the holes in the rear of the crankcase to accept 1/4 bolts!!! Quite a solution that I was afraid to use, but if it worked for you....
tato

Tato,
Actually I was talking about the bolts that go into the firewall. I used the screws that came with the mount on the crankcase. I was not sure how big of bolts to use to bolt the mount to the firewall.

Jim

The factory bolts for mounting the 'carb plate' to the case are #10- 24tpi. I would suggest that you find some allen heads bolts that are longer and trim them for max length including the thickness of the engine mount and do not forget the LOCKTITE. Ask me how I know on both items. BTDT

AFTER having bolts vibrate and break the thread sleeve out of a blindnut on the test stand, I decided to put a nylock on behind each of the 4 #10 bolts that hold the motor mount to the firewall.
(I have now had all three blindnut 'spikes' shear off. I'm liking the nylock locknut idea even better! )

1/4 may be a bit large and if it bothers you enough, run a countersink on inside part of the holes fill with epoxy and a filler (talc if nothing else is available) and redrill smalller hole thru the filled area. That will make a H#$$ for stout holes in the firewall.

1/4" is overkill for something like this. Four #10 bolts, hardened or not, are plenty strong enough for even the most powerful Ryobi 31cc.

How strong you bolt your engine to the firewall should be matched by how strong your firewall is tied to the rest of your airframe. Most of the crashes I see, the firewall always get ripped out of the fueselage along with the engine block.

Volfy: great tip about the bolts type. Around here nobody could tell what kind they are..so imagine how hard is to me have my ryobis running at acceptable rates.

Mikenlapaz and JBfoster, thanks for the answers.
Now I have to get at least 16 socket head ( allen) Nº 10- 24TPI to add a engine mount at the rear of each engine.

In the case I could not find the bolts here around...where can I get them??
Thanks
Tato

Ask around and find out where the auto mechanics go to get replacement bolts for suspension parts, and lug bolts and nuts.
After haugthing the local hardware store with no success, I ask an auto repair shop and sure enough there is a very small specialty shop that has ONLY nuts bolts and washers.