Leak down test

[rhtrudder]

Quote

 

Noticed a soft compression one one cylinder so ran through a leak down test sat the gauge on 80 , three read 77psi but the sick one was down to 75 psi , I guess not a lot of difference, could hear a faint bubble in the oil tank , engine has 1850 hrs up, would a set of rings an a hone fix this , back in my 2 stroke days rebored to get everything round , engine is a 914

[derekliston]

14 minutes ago, rhtrudder said:

Noticed a soft compression one one cylinder so ran through a leak down test sat the gauge on 80 , three read 77psi but the sick one was down to 75 psi , I guess not a lot of difference, could hear a faint bubble in the oil tank , engine has 1850 hrs up, would a set of rings an a hone fix this , back in my 2 stroke days rebored to get everything round , engine is a 914

As a retired LAME I would be quite happy with those numbers. Anything above 60 is considered acceptable although on my own engine I’d investigate if it is down to 65!

[RFguy]

I would think those numbers are within the normal range of the test precision. Sounds fine. 

 

If you get low leakdowns , WHY is just as important as the numbers to whether or not it is airworthy.

Tank gurgles are normal.   For a high hour  914, good numbers- nothing to be concerned about at all. Many rotax go 3000 hours+ without rings being done.

Check if the leaks are happening on the exhaust valves- there was a SERVICE BULLETIN for 914  on the exhaust valves (in recent times) . 

 

Footnote- For Jabiru- Jabiru engine are not tolerant to brewing troubles like other engines. 

For Jabiru- Suggest investigating the WHY  if leakdowns are lower than 70, and ground the aircraft if lower than 60. A leakdown lower than 60 on a Jabiru engine may indicate imminent engine failure will occur.    (valves not closing (and will separate) , stuck/ broken  rings, cracked piston)

 

Edited August 12, 2023 by RFguy

[derekliston]

1 minute ago, RFguy said:

I would think those numbers are within the normal range of the test precision. Sounds fine. 

 

If you get low leakdowns , WHY is just as important as the numbers to whether or not it is airworthy.

Tank gurgles are normal.   For a high hour  914, good numbers- nothing to be concerned about at all. Many rotax go 3000 hours+ without rings being done.

Check if the leaks are happening on the exhaust valves- there was a SERVICE BULLETIN for 914  on the exhaust valves (in recent times) . 

 

Footnote- For Jabiru- Jabiru engine are not tolerant to brewing troubles like other engines. 

For Jabiru- Suggest investigating the WHY  if leakdowns are lower than 70, and ground the aircraft if lower than 60. A leakdown lower than 60 on a Jabiru engine may indicate imminent engine failure will occur.    (valves not closing (and will separate) , stuck/ broken  rings, cracked piston)

 

I fly behind a Jabiru and I agree with you, hence my 65 comment! Good engines, but you have to look after them.