Conical Lycoming Rubbers

[Chris Iriarte]

No, I meant "horizontal" and "vertical". With the engine at TDC, the prop was at the 11-5 position (looking from the front). I took it off and rotated one position CCW, so that it was now (mostly) horizontal. That is, the prop is now in the 9:15-3:15 postion (since we've already established the crankshaft flange holes do not allow a completely horizontal position at TDC ;-) ... ).

Now, when I pull the mixture, the engine stops with the prop in a vertical position, which would be (off the top of my head) about 90 deg BTDC. The engine itself is stopping in the same spot ... it's just the prop that's different.

Chris

"Advanced it from 11-5 one more position to horizontal" . . . . "I just have to get used to the prop stopping completely vertical" I think you meant say Vertical in both wordings. Anyway, I think you need your prop to go to the prop shop for tracking and balancing. You seem to not be achieving success in stopping vibration. Also, stopping the prop completely vertical will impede the momentum of the first cylinder firing and taking the prop "over the top" to a position where you are using the inertia of the prop swinging down to bring the next cylinder up on it's compression stroke.

[Jim]

Hi,

When my old 290 was torn down after a prop strike we found one piston was a completly different casting than the other three. No way they could have all been the same weights. We found cracked things almost every annual, baffling, oil cooler mount, heat cuff tab, primer lines etc. My prop was earlier confirmed not to be my vibration source. If you can't position your prop to fix things, or you trust it, you might consider looking into dynamic balancing everything all at once.

[Steve Pierce]

I agree with Jim. People change cylinders with different weight pistons and over sized bores. Lots of things effect vibration besides props.

[Chris Iriarte]

As I recall, my engine had a cylinder R&R'd a few hundred hours after a field overhaul (before I was the owner). When I did the valve wobble test a few weeks ago I noticed on half the cylinders, the rocker arm shafts were full length, the other half the shafts had the plastic buttons on the end. So, there's no telling what's rattling around in that engine!

Chris

[59pacer]

Our son is building a full size WW1 Albatros fighter, but since there's no spare 180 hp Mercedes engines available, he's having to do an automotive conversion. I've suggested that he uses conical mount rubbers same as in our PA22/20. I can't find anywhere what the taper is on the O-320 crankcase to take the conical mounts. The rubber mounts themselves go fairly close to 45 degrees (i.e. 90 degree included angle), but most probably Mr Lycoming has a more accurate number.
I see that the Continental O-100 specifies a 78 degree included angle.
Anyone know what the answer is, or where I can get it?

[gliderman]

"the rocker arm shafts were full length, the other half the shafts had the plastic buttons on the end."

that is an old style rocker arm shaft and a new style.. any required replacement of the rocker shaft( cylinder overhaul) would result in this condition

Shane-o

[59pacer]

I replaced the conical engine mount rubbers on my O-320 today.
The lower left one had 'collapsed' to the point where the bolt was just starting to rub crankcase housing. On the others, the holes in the rubbers were a little 'oval', but nothing like the lower left one.
Any ideas why the large difference in condition?
I did some experimenting with the 1.84" dimension, and 40inch/lbs of torque.
A torque of 40"/lbs gave a dimension less than 1.84".
If the engine was supported by the block and tackle, the dimension came out at about 1.80".
If the engine was unsupported, the dimension came out at about 1.82".
I used the last option and torqued to 40"/lbs against the weight of the engine and left it at that.
Am I doing anything incorrectly here?

[Steve Pierce]

I made a measuring tool that will reach around the baffles and tighten to the 1.84" dimension. Had no issues that I know of and have been doing that for many years. I doubt that it makes a huge difference but that has worked for me.

[wyandot jim]

Hey Guys,
Grandson and I plan on changing out rubber bushings in the O-290D-2B in the Champion this weekend.
It appears the 290 has a different bushing than the O-320s. Is the torque and dimension the same for the O-290?
Thanks,
Jim

[59pacer]

Yes, Steve, I'd made up a couple of 'tools' and callipers to set up the 1.84" dimension. I'll just fly it for an hour or two then recheck it.
I did a bit of a search about the unusually worn left lower rubber. It seems that that event is not particularly unusual. I'm curious as to why. Looking at the engine mount itself, the two upper arms are quite light and unsupported, so the lower rubbers may get more of the load, and with torque, the left one would get even more. Who knows?

I made a measuring tool that will reach around the baffles and tighten to the 1.84" dimension. Had no issues that I know of and have been doing that for many years. I doubt that it makes a huge difference but that has worked for me.