Bad parts

[Guest]

Re: Bad parts

I am not following the firing order discussion.

O-145 and A65 both have 1-3-2-4 order and both using a cylinder number sequence such that even number are on one case half and odds are on the other.

They start the numbering sequence from diagonal corners of the cylinder matrix but the physical firing sequence will be similar.

A65 ; RH_rear->RH_front->LH_Rear->LH_front->RH_rear->RH_front...

O-145 ; LH_front->LH_rear->RH_front->RH_rear->LH_front->LH_rear...

By similar I mean that two cylinders fire in sequence on one side of the case then the two on the other side then start over again.

The difference is the A65 fires the aft cylinder first and the O-145 fires the forward cylinder first but both share the characteristic that when firing moves from LH to RH it also jumps from one end of the engine (fore/aft) to the opposite end.

These sequences seem essentially and effectively the same to me.

[wmfife]

Re: Bad parts

That was how the last A&P mech to do the annual on it before the sale and who had done all maintenance on it for the previous owner explained it to me. Two fire on one side then two more on the other side.

I am not an A65 expert but do have an original manual and can look this up. In any case I do hear a difference in the two when in idle to taxi settings. Maybe I am the only one. My father had his for twelve years and I flew with him often. But I am still learning stuff he never knew.

I am also hearing arguments made about my choice to which I am having difficulty seeing much point. Unless I am horribly mistaken it is my understanding that as a matter of historical record the reason for the popularity of the O-145 was its smoothness, or apparent perception thereof, that customers preferred despite the slight sacrifice in displacement over the other two choices.

Anyway the some ten pounds saving in weight over the Continental is just one more perk. Now if I can get a set of mags to replace these Bendix dumbells! I think each one outweighs the prop.

But all said, having cylinders that can't separate from the crankcase seems radical by most flat-four standards, making this little brute a real tough trooper if properly taken care of. And finding a full original packed and sealed supply of shielded plugs was a big plus seeing as they can be installed with no mods to the cowl.

As this seems to be one of if not *the* last BL12 on the U.S. registry with the original engine I am planning on keeping it that way for the foreseeable.

Bill

[Guest]

Re: Bad parts

I used to have a BL-65 and I agree that the engine was very smooth and I recall older mech./pilots commenting that it ran smooth and that O-145 typically did that.

I just don't know why.

Dave

[wmfife]

Re: Bad parts

I love mysteries. The truth is out there.

[3Dreaming]

Re: Bad parts

I think the smaller displacement leads to less rotating mass. Also I think the cast iron case does a better job of holding things together. A third thing is because of the smaller displacement and higher operating RPM you have smaller combustion events at a higher frequency.

[wmfife]

Re: Bad parts

You beat me to it Tom!

I was about to say from my Navy experience working on and flying behind P&W Wasp and Wright Cyclone engines the biggest difference in the sound and feel was all about displacement of individual cylinders. You can only smooth out combustion so much and the bigger the bang the bigger the shake. It's simple physics as someone said. The Prats had a smoother sound and feel than the Wrights simply because of smaller piston /cylinder displacement.

Stepping up the RPM's to account for the difference in both cases places the firings at closer proximity as to time leaving less space in between for a response in the airframe.

Could be one reason mine his an unusually high-time airframe yet still holds together almost like new.

[Guest]

Re: Bad parts

I think the smaller displacement leads to less rotating mass. Also I think the cast iron case does a better job of holding things together. A third thing is because of the smaller displacement and higher operating RPM you have smaller combustion events at a higher frequency.

Good points Tom,
I see the engines weights are the same.

If the moving parts are smaller then the base (case) is probably heavier on the O-145 so we have the less "energetic" events that you describe happening on a heavier base.

That would help.