I agree, Bill.
While the example shown was not an aircraft rotor, I did indeed loose the triangular bit of the apex seal during reassemble. It fell between rotor and side housing into one of those lightening/balancing divots cut into the rotor - Just my luck. If it had not fallen into the divot but had simply got between the rotor and side housing, I doubt seriously that the engine would have turned over at all. As, it was, it did turn over, yes, with resistance - because I was in a hurry to get my aircraft back from the unattended airport, I convinced my self the "resistance" was just sign of a "good rebuild" with good solid compression.
Here are a few things that I should have paid attention to:
1. It took a bit of effort to hand turn the flywheel
2. While cranking it, was turning over slower than normal
3. When I fired it up it would not idle below 2000 rpm (obviously due to the high resistance)
4. After the first hour of running everything was "normal" in that it would now idle at lower rpm and the resistance was "gone"
Of course by step 4 the hour of running apparently wore the seal piece down and the rotor housing had already incurred the damage that the friction caused - which later led to my rebuild while stuck in Louisiana for 4 weeks.
Clearly having a dial torque reading to compare would have helped. In fact, Bruce Turrentine and several folks told me something was not right - and I should have listened, but just in too much of hurry to get it done and into the aircraft - so I got to do it again, correct this time {:>)
So your suggestion certainly has merit.
Ed
----- Original Message -----
Sent: Wednesday, January 30, 2008 1:04 AM
Subject: [FlyRotary] Re: Emailing: damage24.jpg
Ed and group,
This assembly problem is vexing. We really need to avoid these types of foul up! When I built race cars and motorcycles the assembler (usually me) would try to learn what kind of force it should require to turn over a newly built engine. That is, how much friction to expect when turning over a brand spanking new engine for the first time. Cosworth even has a torque table that suggests you use a dial torque wrench for that first rev or two. If you see higher than suspected torque do not turn the engine over or even through the tight spot! Learning these forces saved one of my best customers a completely mangled engine! (Anecdote warning!)
Guy M. my customer informed me that he would do the basic assembly of the "long block" including putting on the head so all I would have to do was time the cams. (Engine was a Kawasaki 900 with considerable modification to run in an SCCA C sports racer.) Guy was an EXCELLENT mechanic in his own right so I thought, "great that part is easy but tedious so I won't have to do it." I installed the cams correctly, and did the all important first revolution by hand. At TDC there was a very small change in friction, that would have been easy to miss if I had not been super familiar with that engine. Guy wanted to just run it, but I wouldn't do it because that is where the engine has nearly no piston movement for about 20 degrees. I made him pull the head and was super glad I did. Guy had installed all four pistons reversed on the piston pin. The large valve cut out was on the exhaust valve side rather than the intake as was normal. The "tick" was the intake valve rubbing on the side of the piston cutout! If we had started the engine it would have run for a few seconds until the intake valves bent! We corrected the problem, and thankfully the intakes were not even bent. Believe me we checked. The result was a few hours lost rather than a destroyed engine.
We need to develop a data base here. So if you do a new build up, or any build up for that matter, do us all a favor and put a dial torque wrench on there and record your max turn over torque. Oh yea, do that with the plugs out of course. On a rotary with plugs out you should get a pretty even torque with no compression so if you get any spikes in there you may want to pull it apart again before you do some serious damage. Mistakes can happen even to very competent mechanics so it would be a great help to everybody and might even save you some cash. Just a good idea. My $0.02.
Bill Jepson
I agree, Bob, there is no way that apex seal could come out of its recess without that part of the rotor being broken off. Those small parts can be illusive, particularly when you turn the rotor upside down to place it on the e shaft - make certain you use good Vaseline or halomire stickum {:>).
Ed