Getting the most out of the Fora .049
By Gene Pape
For High-Performance 1/2A Combat there have been three different engines in common use since I started flying the event in 2010. The black case Fora, the Cyclon, and the current Fora.
From watching others, I learned that the black case Foras had some reliability problems. The Cyclons seemed a bit more powerful and seemed to be pretty much bulletproof. I found a used Cyclon to get me started. I was immediately hooked on the event. In early 2012, it became apparent that the Cyclon engines would no longer be available. To preserve our unobtainium Cyclons, John Thompson and I each bought two of the then new Fora .8cc engines from aerohobby.ca in September of that year. When we got these engines, they seemed just a bit down on power from the Cyclons, but they were plenty good for anything but the Regionals and the Bladder Grabber.
As time went on, others started using the Foras also, and John had to replace one engine due to midair damage. We learned that while most of these engines run well, some do not. From Buzz Wilson we learned that the supplied rear bearings will wear out the ball separator after a bit of running. Because this happened over five years of me not paying much attention, I don’t really know how much running. Since no other engine has come along to take the place of the current Fora, it seemed the time had come to find out if the Fora can be a true replacement for the Cyclon and what it will take to make that happen.
The first hurdle to cross seemed to be the bearing problem. After much discussion with Buzz Wilson, whose problems with bearings got me started on this, Henry Nelson who took one look at a picture of a failed bearing and told me what the problem was, and Yaro from aerohobby.ca, I chose a part number MR689 TH9/C3C BG bearing from BOCA Bearings the replace the original. Fora number 2 in the chart has this bearing
For performance evaluation, I tached three Cyclon engines and two Fora engines using the same fuel and the same green fiberglass prop. With those results, I did the following to the second Fora to try to match the Cyclons for performance.
Below is the chart that includes all of the testing I've done. I still need to test the other fuels I have with Castor oil in them as I think these engines should have some castor oil in them for flying.
This is how I measure head clearance using a Nelson .36 as an example.
I measure down from the top of the head to the piston at TDC with a dial depth gage. The measurement here is .491”
Then I measure the head thickness. The measurement here is .4845”
.491 - .4845 = .0065”. Perfect for a Nelson. If it’s not what I want, I add or subtract the proper amount of shims. This works on any engine with a straight plug head with no engine-specific sleeves required. Since it is done with the head bolted on with the shims in place, there is no question that the measurement is correct.
Most people don’t have a dial depth gage sitting around, and they can be rather expensive. If this looks like a good way to do this and you would like to have a dial depth gage, I have local supplier that is selling them for $40.20 Let me know if you want me to pick one up for you.
The above is just part of the process several of us including Buzz Wilson, Lane Puckett, Jeff Rein, Pete Athans, Yaro Melnikov of YMS Systems, and I went through. This is what we all learned. The first step to a good engine is to replace the bearings with the truly proper units from YMS Systems.
The next step is to have a proper fitting piston and liner. This can usually be obtained by breaking the engine in carefully, but you may need to lap the piston and cylinder to obtain the proper fit. Last, set the head clearance to match the fuel you are using. Testing found these engines prefer fuel with 15% nitro and a bit of castor oil added to the synthetic. Run these engines with a slightly smaller prop than the Cyclon uses. They are much easier to set the needle if you let them rev. With the above, the Fora can truly be a competitive 1/2A combat engine.
This page was upated Feb. 22, 2018