After a dozen flights with my WH ultimate powered by a 3W-75 single, I decided to do an engine change because I was not happy with the vibration levels of the large single. I was planning to replace the 75 single cylinder with a 3W-70 twin.

After removing the engine, I noticed that all of the glue joints on the firewall had failed and the firewall was loose in the "tongue and grove" construction. There was no danger of the firewall pulling out due to the tongue and grove construction plus the additional dowels which I always use to pin firewalls on ARFs. However, the glue joints had failed.

This glue joint failure may have been caused by the pounding of the large single cylinder or poor factory construction. I would advise each of you to take a screwdriver and check on the glue joints by prying on them.

I was able to remove the firewall with a screwdriver with a little prying pressure which worked to my advantage since I wanted to make a new firewall for the replacement engine.

But, for those of you who want to continue to fly with the existing engine, you need to check the glue joints. Perhaps my plane was the only one in the batch with this problem.

Elson

Did the dowels you glued in come lose or were they still glued?

I am going to run a poulan 60cc on mine , very little vibration on this engine, I already have one on my eadge and all seems to be fine on it.

It's always a good idea to reglue the firewall, this is one area that all ARFs sometimes have problems.

TF

Ive learned to get the CA out and pour it into every thing that matters. I tryangle stock or in the case of the fire wall I use a hard wood square stock behind the firewall. Depending on the construction of the kit Ill back up the servo tray with another chunk of light plywood or even 1/4 square stock. I like the servo screws to be all the way into a piece of wood another thing i found very informative was this video on prop balancing http://www.dodvideos.com/don3.wmv this might have saved me some glue.