Originally Posted by 12vaitor
I believe the flexplate/ring gear cracks are a sperate issue from the gearbox drive coupler failures. The flexplate is a stock Honda part with a starter ring gear welded to it. The welds are as good as any I have seen, they are uniform, and the plate shows no sign of warpage. There are no additional holes drilled.
The cracks appear to be limited to the 110 engines and not the 3-gear setup on the 130/150/190 engine which use the same part. Charlie Rosenzweig has the 3-gear version with the same flexplate/ring gear on his turbo 1.8L Honda, so it would be interesting to see if he has the same problem. If the cause is pitch/yaw induced bending it would affect every installation of this part.
So what is different about the 110 setup that could cause a bending vibration? The big difference is the bottom half of the flexplate is in the radiator airstream where it is subject to the prop pressure pulses. It may be the same phenomenon at work as cracked exhaust pipe-muffler joints because the pipe sticks out a bit too far from the cowling. The other engine installations use a horizontal radiator mounted under the footwells, vs the 45 deg angled 110's which is about 10" behind the prop. It could also be turbulent flow through all those holes are causing some resonance to occur.
Just one more thing to check during the CI.
I just stumbled upon this post. I do not have a viking supplied flex plate. I made my own, by welding a ring gear on a flexplate. I do agree this is far from ideal, IMHO, but I did not see another option at the time I did this, which is probably more than 5 years ago now. I do have a 3 gear Viking supplied gearbox, But nothing else in my set up was supplied by Viking. I have inspected my flexplate carefully and I do not see any cracking. I also do not have any measurable end play in my GB input shaft.