Anyone heard of someone changing the crank dampers on a J1a5d from one fifth order and one sixth order, to two sixth orders ? It looks like they slide right out without having to split the case, just held on with two circlips. That's the only difference I could find fir what's needed to safely spin 2700 for 260hp... More with 9:1 pistons From what I've read, some people say it's safe to spin 2575 as is . Anyone have any info?

I'd bet that only Lycoming has all the info and they probably won't want to share. If you don't already have it, I can send you a copy of SI 1012G with counterweight and roller part numbers and which engines they go to.

You probably already are aware, but when installing the circlips, be very careful that you put them in in the correct orientation. Apparently they have a tendency to vibrate out after 800-1000 hours if they're in backwards, and I hear that leads to counterweights punching holes through the case.

that would be awesome. Send it to ydna7@hotmail.com

My dampers have LP11 written on the side.

thanks

https://www.dropbox.com/s/3r6f4ivnwnffi ... -58-36.png

Found an interesting report on a crank dampner failure. It shows vibration through rpm ranges before and after a overhaul. This graph shows that for the vibration of a fresh engine, anything over 2600 increases vibration at a high rate. In his case, it fatigued the accessory drive gears through transmitted vibration from the crank, and snapped the manual fuel pump shaft.

I think the 235 has not only lighter crank dampners than its 260 Hp counterparts, but a lighter crankshaft. Possibly why Thus the engine being 30lb less than other similar models.

In conclusion... 2575 looks like a good max rpm for experimental J1a5d engines in my opinion, but I'm usually wrong.

And if gears show wear, check crank dampner bushings for wear or out of round.

I wonder what engine model the crank and dampers came out of for these 300hp maules in the experimental section here.

I'd give Lycon a call- They do a lot of experimental stuff including Blueprint and balance, High Compressions, Porting and flowing Cyl's, etc...

http://www.lycon.com/ly-con/specialitys.html