Rattle

This for all the engine experts out there. I am going to check my timing on my 65, to verifiy as being correct, but have this question.
For the first 1/2 of flight the engine has a rattle to it and then will go away. First I thought it was piston slap, but it has four new cyls and pistons and the time frame is all wrong for this rattle to happen . The lifters are quiet at start-up and seem to stay that way. I started wondering about the 1/2 hour time frame and thought it would take about that long for the mags to heat soak. If I have too much advance and the mag parts expand inside to cause a slight retarding of ignition. Is it possible I'm hearing detonation in the first half hour? Like I said, I will check out the timing and rule it out, but curious if some-one else has seen this happen? They are the older Bendix mags, not the box mags.
Ron

is it like the impulse not kicking out, what is your mag drop?

rattle

The impulse is out at around 300 rpm. Mag drops are 50 on both. Turn either one off in the air at criuse, might get 25 rpm drop.
This thing was timed at 30/30 but with the slop in the hub key-way, it's possible it may be more. Used a t.d.c dial and found the hub markings with keyway slop were out about 3-4 degrees. Yup, I know you're suppose to use a degree indicator , but it is a 65 after all. Can't see the stupid thing being that critical as it was designed for less that 80 octain and now is running 100. But then again, may-be it could be.
Ron

I know you probably thought of this already. Have you tried running a auto gas or auto gas mix in her yet.
My 90 horse HATES 100LL. Plus she hates synthetic oil.

She was making weird noises last spring. I went back to 80%-90% auto fuel (w-MMO) and straight weight oil. Just like magic the noise stopped, the engine stopped leaking oil, and she runs cooler.

Ron,

Alex is right. I was running 100% avgas in the C75, and she made weird noises, actually started to iddle really weird. Now I put 50/50 in her, shes runes perfect, and has a nice exhaust color too.

With 100LL only, they tend to foul up on the plugs, need to clean them too many times...

Cheers

Fred

Retorque your prop bolts, especially if you have a wooden propeller. That is what it sounds like when a wood prop shrinks and the bolts are loose. ...Clyde

rattle

The prop is metal and the hub is tight. I was using 50/50 at first but the price of auto got higher than 100 at one point so I just fed it 100. Now that it has dropped again I'll go back to the mix and see if it changes the sounds.
Ron