Leak Test Results

D

dtreid

New member
Just did a leak test on the 165 Franklin in my Cruisair. Engine was warmed up prior to test.

3 Cylinders were in the 60s, with cylinder 1 being the lowest at 63. Other three were in the mid 70s. Engine seems to run fine.

Is this something to be concerned about. I've heard conflicting reports on the reliability of a leak test to determine engine health.
 
This can be an indicator of the general health of the upper end of the engine. It is not gospel as these figures change from time to time and subject to personal interpretation and technique.
Dan
 
Did you warm it up, or did you fly it hard for an hour? I was helping a friend with an annual a few years back, and the pressure were not very good. The IA said go out and fly it full throttle for an hour and we will check again. The pressures came up 5 to 10 PSI on all cylinders, and the IA was happy. I have heard this same sort of thing from a number of Franklin owners. It is worth a try. ______Grant.
 
You might want to look at:

http://www.tcmlink.com/pdf2/sb03-3.pdf

It is the TCM SB on compression testing. It is a source of great information, and while it may be kind or iffy if it really applies to Franklins, it is reflective of the fact that somebody finally took the time to update the old "pull them if they're below 60" mentality.

I do not know of any reference in any Franklin literature that says they must be pulled when less than 60, but AC43.13-1B does say in Section 8-14:
"If a cylinder has less than 60/80 reading on the differential test gauges on a hot engine...the cylinder must be removed and inspected." Note that section has a type where it refers to Para 8-15b(5)(i) should refer to 8-13b(5)(i).

So that conflicting information gives you some food for thought...and room to argue. What do the rest of you think?
 
The SB from Continental is an excellent manifesto on checking cylinder compression and IMHO should be adopted and wholesale replace the old (and useless) tribal take of "anything less than 60 should be replaced".
now that Textron owns Lyc too, maybe it'll be expanded to include them, as it should.
About a dozen years ago, a guy with a J3 taxied up to my hanger - the guy was distraught because his IA wouldn't sign-off his annual due to ALL of his cylinder being below 60... yet he flew it to my field. I hand-cranked it through and sure enough, could hardly feel any compression.. valves were good, just old rings. He let me fly it (It's good to be an IA). It got great static RPM and flew exactly like a cub flys.. I had him get the IA so sign the inspection with "a list of defects provided to the owner/operator", then brought it back to me to sign off the engine.
The below-60 lie must die.
 
One of the IA's at my field told me that when he went to TCM school, they demonstrated an engine with 0 (yes ZERO) compression from loss through the rings. They put it on a dyno and it developed full power!?? I haven't seen that, but that is what he told me. He is not one to BS. I do check my compressions after using a calibrated orifice on my compression checker, and we do use the SB to help us evaluate any low cylinders. I also borescope them while I have the plugs out. To many cylinders are pulled unnecessarily !!
LL
 
I did not fly it hard before the leak test. I did some high speed taxi's for 15 min or so.

I have been going back through the logs and that cylinder showed a leak test of 62r/80 (I'm not sure what the r was for) for the last 20 years.

I guess I'm just a bit apprehensive of my new bird until I fly it more and trust it more completely.


While on that topic of trust, I show close to a 200rpm drop during the mag check, with both mags being almost the same. Does this mean I'm looking at a mag rebuild before too long?
 
What type mags? Slick recommends a 500 hr check. Eismanns (sp?) not so much. Check timing. Do you have any idea how accurate your tach is?
 
They are bendix mags.

Timing was just set.

I have just installed an electronic tach that I am sure is very accurate
 
Apples, oranges and orangutans.

Constancy of method, and also of measurement equipment and having the same person do the
measuring will add some meaning to comparisons of readings year after year.

Not that I think that good mechanics using properly calibrated equipment can get very similar readings.

But cold one time, luke warm another, and rode hard and put away wet the next yields nothing from compressions
but confusion - taken alone.

Beyond whether an engine with 50/80 compressions will run.. is the REAL QUESTION;

How is it running, and How Safe Is It ?

I would far rather fly behind an engine with excellent valves, and sloppy rings with attendant blow by and oil consumption,
than I would with an engine that can lose a piece of an exhaust valve soon.

I wouldn't want to taxi and airplane with a loose valve seat, or disintegrated valve guide, or cracked piston.

So, as Larry said, you really want the Whole story of what the engine is doing.
Borescope inspection is fast, cheap, and tells you a LOT.
So will a squirt of oil in a low cylinder, and reading the plugs.

I just pulled a cylinder that was 68/80... which broke my heart , but when the lower plug came out and a bunch
of oil drained out on the floor from the plug hole... then I don't care about compression anymore.

The cylinder next to it was mid 60's when I bought it.. next mechanic read it as 70.. and this time it came in at 59
after flying around the patch. We pulled it too,because we could see the seat needed grinding or lapping.
Who knows how much longer it would have gone on just as it was. Another year or two ?

Taken apart, of course the rings and bore are worn, and in go the new guides, and valves.

It's only money, right ? :mrgreen:
 
Did a compression test on a hot engine this evening. Cylinders ranged from 109 - 111 psi. I would say this is good, would you?
 
yeah... in a low compression engine those are good numbers from an automotive type tester.

When parts are broken... and compressions aren't really at the bottom end of the 60's
as so many said above and quoted by continental.. what's the worry ?

Now.. you might have the same 60's compressions with a broken ring, and scored bore
and then it just flat needs to get pulled and repaired.. because it can cause bad things to happen in flight.

A static compression test might not reveal a loose valve seat.. but again.. just not airworthy.

So, it aint numbers alone.. it is numbers in concert with an Educated Borescope... and other diagnostic
inputs.

Sooner you start oil analysis, the sooner you establish a baseline.

If you oil is constantly being contaminated by blow-by.. then it is being diluted with fuel, and loaded up
with carbon... so the oil is going to simply lubricate worse and last a much shorter time.

Can you change it more often, and live with your old tired engine hundreds of more hours... probably,
with close monitoring. Do you want to cross the rockies with it... that is between you and your god.

Again.. what are the gauges telling you ?
when everything is steady freddy, formal and normal.. then that fine.

When it is pumping a quart an hour of dirty oil , running HOT in every way you can measure.
then who are we fooling ?

In the franklin... with no oil filter, and perhaps no EGT, and OH parts sometimes hard to get,
and the work required bound to be slow, do the limited number of competent folks who do it anymore,
My opinion (and it's just that)... is not to let anything go that will shorten the life of the rest of the engine..
and not to fix anything that "aint broke".... tempered with the practicality of doing marginal stuff just because
you are already in there fixing something bad..because you don't want to pay for the pull down and build up and test
time twice.
 
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