LOP dilemma

[lr172]

Superior mentions in one of their talks that having 80 compression (or very close to it) on a mid time engine is a concern that the rings were not installed correctly. he sounded like it's a bigger concern than if you see 60s.

Yes, if you get 80/80 there is a good chance you have a 0" ring gap and cracked rings are in you near future. It is theoretically impossible to get MORE than 80 PSI of measured pressure with an input pressure of 80, assuming the piston is not moving, hence the comment about inaccuracies in the gauge. This is an issue with superior, as they ship their rings oversized and expect the installer to file them down to size. Major opportunity for errors, as Lyc ships them pre-sized. Easy to forget if you usually use Lyc.

Very easy to create offsets for gauge inaccuracies. With the tester not connected to plug adapter, run the input up to 80 and read the other gauge. Your offset is 80 +- whatever the indicated gauge reads. Mine reads 2 PSI low, so I just add 2 to each measured result.

 

[Carl Froehlich]

My GAMI spread is about 0.5gph. I really want to put a slightly larger orifice on #4.

I suggest the preferred approach to balance cylinders is to always go leaner (smaller nozzle) on the rich cylinders. Don Rivera discusses this from time to time. I do not go bigger than the stock 0.028” nozzle.

On an IO-360 my experience is two new nozzles and GAMI is down to 0.0 to- 0.1gph. My first IO-540 took ~4 new nozzles.

Side note - on the IO-540 I was using a plenum without turbo nozzles. This caused me to do more nozzle iterations to get the desired GAMI spread. It started off at 1.5 GPH but it too got down to 0.0 - 0.1 GHP. Still deciding if I want to put turbo nozzles on the new RV-10. Phase One will provide the needed decision data.

Carl

 

[skirting_virga]

I suggest the preferred approach to balance cylinders is to always go leaner (smaller nozzle) on the rich cylinders. Don Rivera discusses this from time to time. I do not go bigger than the stock 0.028” nozzle.


On an IO-360 my experience is two new nozzles and GAMI is down to 0.0 to- 0.1gph. My first IO-540 took ~4 new nozzles.

Side note - on the IO-540 I was using a plenum without turbo nozzles. This caused me to do more nozzle iterations to get the desired GAMI spread. It started off at 1.5 GPH but it too got down to 0.0 - 0.1 GHP. Still deciding if I want to put turbo nozzles on the new RV-10. Phase One will provide the needed decision data.

Well, I was a dumbass and got GAMI injectors for certified prices instead of going to AFP. I couldn't figure out if the restrictors were removable, but I have certainly considered turbo-style injectors plumbed to the snorkel for max ram air pressure differential.

So what this boils down to is I have no idea what the orifice sizes are. I believe the front #1/2 injectors are GAMI's minimum size and no smaller size is available, so it is only possible to make 3/4 larger. If there's a way for me to investigate orifice sizes, I would like to do that (but that assumes the value is stamped somewhere and the orifice is removable).

 

[[email protected]]

Yes, if you get 80/80 there is a good chance you have a 0" ring gap and cracked rings are in you near future. It is theoretically impossible to get MORE than 80 PSI of measured pressure with an input pressure of 80, assuming the piston is not moving, hence the comment about inaccuracies in the gauge. This is an issue with superior, as they ship their rings oversized and expect the installer to file them down to size. Major opportunity for errors, as Lyc ships them pre-sized. Easy to forget if you usually use Lyc.

Very easy to create offsets for gauge inaccuracies. With the tester not connected to plug adapter, run the input up to 80 and read the other gauge. Your offset is 80 +- whatever the indicated gauge reads. Mine reads 2 PSI low, so I just add 2 to each measured result.

Ya I'm in the cracked/broken ring group on somebody else's over haul in the past. I always check the ring gap per manufactures rules and don't create problem not needed. And yes I run LOP as much as possible. TRUST AND VERIFY!!!
The OP's mechanics are out to lunch on this one.
My luck varies unless I am the one screwing it up. FIXIT

 

[Carl Froehlich]

So what this boils down to is I have no idea what the orifice sizes are. I believe the front #1/2 injectors are GAMI's minimum size and no smaller size is available, so it is only possible to make 3/4 larger. If there's a way for me to investigate orifice sizes, I would like to do that (but that assumes the value is stamped somewhere and the orifice is removable).

I would hope each nozzle has a stamp on orifice size. I do have any experince with GAMI nozzles so see if you can pull out a nozzle and look.

Carl

 

[Treekiwi]

So who makes this claim?

I really don't want to name the shop, but suffice to say they've been doing this a long time, and have a good reputation. Which, of course, could make them even more susceptible to OWT I suppose.
It didn't sound quite right to me, which is why I threw it out there.

 

[Reflex]

I suggest the preferred approach to balance cylinders is to always go leaner (smaller nozzle) on the rich cylinders. Don Rivera discusses this from time to time. I do not go bigger than the stock 0.028” nozzle.

Carl

Carl,

I think I've seen you post this before. Would you mind elaborating? I'm not at all saying you're wrong, I'd just like to know why. The reason I ask is that I too used GAMI an they did just the opposite. They enriched the first cylinder to peak.....at least in my case (IO-390). I didn't think too much about it as I figured "balanced is balanced". That's why I'm asking the question.

Fred

 

[lr172]

Well, I was a dumbass and got GAMI injectors for certified prices instead of going to AFP. I couldn't figure out if the restrictors were removable, but I have certainly considered turbo-style injectors plumbed to the snorkel for max ram air pressure differential.

So what this boils down to is I have no idea what the orifice sizes are. I believe the front #1/2 injectors are GAMI's minimum size and no smaller size is available, so it is only possible to make 3/4 larger. If there's a way for me to investigate orifice sizes, I would like to do that (but that assumes the value is stamped somewhere and the orifice is removable).

is your engine an older one? The early injectors did not have removable restrictors. easy to tell. pull the nut off. if the restrictor is removable, you will observe a seam line about 1/8" down from the top, the part with the female flare. get your fingernail in that seam and lift it out. if tere is no seam line, it is the older version.

 

[lr172]

I really don't want to name the shop, but suffice to say they've been doing this a long time, and have a good reputation. Which, of course, could make them even more susceptible to OWT I suppose.
It didn't sound quite right to me, which is why I threw it out there.

they could be an excellent overhaul shop. skills to build an engine are VERY different than those necessary to understand engine wear cause and effect.

 

[lr172]

Carl,

I think I've seen you post this before. Would you mind elaborating? I'm not at all saying you're wrong, I'd just like to know why. The reason I ask is that I too used GAMI an they did just the opposite. They enriched the first cylinder to peak.....at least in my case (IO-390). I didn't think too much about it as I figured "balanced is balanced". That's why I'm asking the question.

Fred

i would agree that balanced is balanced. That said AFP generally recommends going smaller as a general rule, as it increases post servo fuel pressure, which can reduce instances of fuel boiling / roughness. AFP generally recommends .024 sizes for 320/360 and .025" for 540's.

 

[Carl Froehlich]

Carl,

I think I've seen you post this before. Would you mind elaborating? I'm not at all saying you're wrong, I'd just like to know why. The reason I ask is that I too used GAMI an they did just the opposite. They enriched the first cylinder to peak.....at least in my case (IO-390). I didn't think too much about it as I figured "balanced is balanced". That's why I'm asking the question.

Fred

i would agree that balanced is balanced. That said AFP generally recommends going smaller as a general rule, as it increases post servo fuel pressure, which can reduce instances of fuel boiling / roughness. AFP generally recommends .024 sizes for 320/360 and .025" for 540's.

This. Don Rivera recommends this approach. I tend to do a hybrid as many times just getting one or two smaller nozzles does the trick. But, I do not disagree with Don, just too cheap to get six new nozzles then 2-3 more slightly larger when the data comes in.

Why GAMI does what it does is beyond me, other than I’d guess it had something to do with spam can engine certification. But considering we usually do not have weird engines we can sharpen our pencils and dial in what is needed instead of making sure we still meet whatever is needed for odd ball engines.

Carl

 

[Bicyclops]

The choke doesn't happen from squeezing the barrel. This is purposely done via the boring and honing process. They put in that taper in the final machining. As freemasm stated, they do this so that the bore will mostly be a uniform dia at operating temp. That doesn't necessarilly mean it is bad to run in the smaller state, as long as the rings are sized correctly.

Larry, my fellow instructor at the A&P school had previously been a part owner and employee for many years at an overhaul shop specializing in Pratt & Whitney. They routinely overhauled P&W cylinders, removing the heads, weld repairing as necessary, and re-mating them to barrels. It was he who told me the the barrels were bored and/or sleeved straight, and that after the heads were shrunk on, the taper resulted. This jibes with the Powerplant textbook which states, as I described, the taper results from the interference fit of the head. The text also says that the cylinder will be straight at temperature, but I still don't buy that, at least not entirely. My opinion is that they sold the taper as a feature rather than a side effect and came up with theories to support the claim. Cylinders bored oversize could certainly be bored with a taper and might well be. Plated cylinders could also be honed with a taper. The taper is listed in the table of limitations so the overhaul shop is obliged to replicate it when boring. As far as I know, heads of Lyc and Cont aren't removed during overhaul.
Ed