prop synch

JeffAxel · #1 04-30-08, 02:38 PM

The prop synch on my '77 T337G is not working, at all. I believe it has been updated to the '78 and later configuration. Has anyone had problems with their prop sync, and does anyone have a recommendation regarding a shop that is familiar with this set up?? I understand it is shared with the 310. Any suggestions, and help would be much appreciated, the droning is driving me nuts!

Thanks!

Pete Somers · #2 04-30-08, 04:48 PM

Ok, just a little bit more info.
Does the SYNC lite come on.
Is this a Prop sync with a phaser control.
The sync box is mounted in the port center roof panel check the plug.
There is a breakout box to checkout the system, with this box it is very easy to tie it down to a component.
The sync box is the usual problem, however wiring to the pickups on the governors are also a problem.

Regards
Pete

JeffAxel · #3 04-30-08, 10:32 PM

Pete,
The prop sync light comes on, it blinks, never burns steady. The set up I have has a two position switch (off-on) and a knob. Neither seems to do anything, except turn on the blinking light! The sync meter on the panel works, and when you sync the props by hand, the meter indicates this as the needle stops moving back and forth. I have JPI digital tachs, so getting the props in sync is easy. The problem is the rear prop never stays at the same RPM, it varies +/- 50 rpm or so, this drives one crazy after a while! if I could get it to stay, I wouldn't care so much, but it refuses to do so. Too much slop in the rear prop cable I suppose. I will see if anyone knows where to get a hold of the test box. The shop is looking at the pot on the rear governor. My set up is like the one in the Service Manual for P3370292 and beyond, it was modified with a service kit that came out in the late 70's. Any other suggestions would be most gratefully received!!

Pete Somers · #4 05-01-08, 02:55 AM

The pot does give problems and the only way to check this is to replace it.
It does sound like either there is alot of play in the gearing or there is something wrong with the front pickup and it is not sensing the front prop RPM so the rear will hunt.
Do a check of the front pickup and a resistance check.
There is a separate book for the Cessna sync systems and contains all the info for checking out the system and the info on the test box.

Regards
Pete

skymstr02 · #5 05-01-08, 08:44 AM

If his rear engine is varying ± 50 rpm when sync'd manually, maybe the rear governor needs a shop visit?

JeffAxel · #6 05-01-08, 12:51 PM

The rear governor was replaced recently as it turns out. I am wondering if there is a lot of slop in the prop cable, and that is something we are looking into as well.

Dale Campbell · #7 05-05-08, 10:06 AM

Hi,
I have a 337H 1978 and had the sync worked on 4 years ago. They found both the pots intermittant. So they replaced the pot on the quadrant and the one at the rear engine sync. next to rear engine. Also the little motor on rear engine sync was removed, cleaned and new brushes installed. It worked for 3 years, but now is acting up again. Dale Campbell