Originally Posted by pilotyoung (Post 1330744)

Scott, when you say "Being casual about maintaining a proper carb. sync is a sure way to cause gear box wear.", can you explain what you mean. Do you mean checking and ressetting it every 100 hours? More often than 100 hours? Other inspections besides just syncing the carbs?

I would like some guideance on going forward so I will know I have maintained it properly.

Thanks.

John

Originally Posted by rvbuilder2002 (Post 1330819)

Yes
Checking and adjusting it every 100 hrs.

My "being casual" comment was based on the large # of comments I see that mention initially running the engine without doing a synch (don't have gauges yet), "it felt pretty smooth but I sure could tell the difference after we got it synched properly, etc.

Assuring that the carb's are and remain well synched at idle and low throttle settings is crucial to gear box longevity. If at any time between the 100 hr inspections the engine seems to not be as smooth as it has in the past, it should be checked and the problem resolved ASAP.

Originally Posted by NinerBikes (Post 1330867)

So, with the 912 iS package motor on the 2018 and later RV-12iS builds, if the idle speed is kept above 1800 rpm, the gearbox causing vibrations should be a non issue anymore, due to lack of synching the carburetors? Any other considerations to be aware of to prevent gearbox wear?

Originally Posted by pilotyoung (Post 1332099)

Jolly,

Thanks for your list of possible causes. I worked through most of them in an effort to properly diagnose my vibrations. I finally concluded it was the gear box, and disassembly confirmed my conclusion. The dogs were worn as well as he spring washers. They were all replaced, the greabox is reinstalled and I will fly it as soon as the annual condition inspection is over, hopefully Wednesday.

The one item on his list that I would never have thought of was the wheels being out of balance. So as I get mine airplane back together, I will be eager to see the results. If it is not smooth, I will have the prop balanced, then the tires balanced. I can do the remainder of the items on the list.

But I do appreciate your providing a comprehensive list for us to use to trouble shoot.

Originally Posted by TomVal (Post 1332124)

John,

Hopefully the gearbox was the culprit. Another item for the comprehensive list is to consider re-clocking the prop one prop flange bolt hole forward or back from present position.

Originally Posted by pilotyoung (Post 1328366)

I have been having vibration problems with my RV-12. It ran smoothly at cruise, but when I reduced the power from about 4600 to 3000 there would be a vibration. I tried several possible solutions: 1, did the friction test on the gear box; 2, weighed the floats to see of they were too heavy; 3, sycnhed the carburetors; 4, replaced the soft engine isolators; and 5, replaced all the muffler springs. Since those didn't fix the problem I then decided it was the Gear Box. Ronnie and Morris Smith of South Mississippi Light Aircraft agreed with my thoughts.

Today I took the gear box to them for repair. The dogs were worn and the disks were worn. All were replaced and Ronnie says my vibrations will be gone. I will be out of town next week so I won't get the gear box back on to know for sure for a week or two. But if any one is interested, here are some pictures of the worn gears and dogs.

The aircraft has 450 hours on it. I ask Ronnie is this was from abuse, bad parts, etc. He said there was no way to tell. I have flown it 120 hours and I have not let it idle at slow speeds.

I am posting these pictures in the hope it will help others understand the problem if they experience vibrations like this.