schokshi

Folks,
I am new to gas engines. i have purchased RCGF 15 CC & am planning to install it in H9 Pawnee 40. It requires me to shorten engine box length by about 20 mm. I have never done this before & would like to ask you the following questions:

1) I am planning to cut existing engine box by 20 mm & build a new box with 1/4" thick plywood, is that fine?
2) Are there general guidelines as to how to build engine box so that is strong enough? is there any Dremel attachment that will let me cut 1/4" plywood easily?
3) H9 manual does not state right & down angle thrust that is build in current engine box, how do i find out what they should be

Thank you very much for your responses.

ahicks

My Feedback: (2)

I haven't done one that small, but have done several 30cc size with the same problem. On yours I would cut a 20mm section out of the middle of the box holding the firewall, then splice the front back on if that makes any sense? That way I don't loose the original angle the firewall is installed at?

I use a hand held 1" X-acto razor saw to make the cuts. It cuts straight and clean. Sounds like a lot of work, but actually the cutting, doing it a side at a time, only takes maybe 15 minutes.

schokshi

Ahicks,
Thanks for your reply. Actually cutting 20 mm from middle section is very good idea that way i can maintain thrust angles. However when i join them together, can i just use 30 min epoxy? or i have to come up with some sort of interlocking cuts to make sure it is strong enough.

MTK

For me, the simplest way is to mark off the box from the front of the firewal. Measure exactly 20 mm all around and cut carefully. The correct angles will be cut into the sides of the existing box

Then take the stubby section and remove the side pieces, revealing the original firewal, with all hardware in their existing location. Reglue with 30 minute, reinforcing the inside with triangle stock. I typically will use clamps to hold while theglue cures. Re- pin if the original arrangement was pinned, or use some 6 oz glass cloth to reinforce the outside of the box corners. You might want to round off the corners to allow the glass to lay down easier and then cover about 3/8" all around

ahicks

My Feedback: (2)

Like MTK is saying, you would want to reinforce that splice. My reinforcements generally include triangle stock wherever I can, and I use plywood at the joint. Maybe overlap each side of the splice by 1/2" or so, whatever you feel beefs it up to original or better strength. Just don't get carried away...

While I have that all apart, I usually take advantage of the good access available and beef up that whole area - including the landing gear mount. I'm really hard on those with all the screwing around I do anyway.

3136

What I would do is
Cut the top, or bottom of the engine box so you can slide your new firewall in.
Get another spacer timber and slide that between the new firewall and the old one.
That way your angles will be spot on.
Glue, pin and triangle stock the new firewall.
Take out the spacer.
When the glue has dried cut off the old firewall and excess engine box.
Perhaps fibreglass the inside and outside for extra strength (and fuelproofing)