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