Jabiru compression test
New to being a jabiru owner with a gen 2 33A model. I’m doing my first annual and I had a question. Is there any guidance by jabiru regarding compression leak down test specifically regarding maximum Delta between highest and lowest compression numbers during the test. Section 9.8 of JEM0002-11 speaks to the leak down test. It talks about no more than 25% allowance in pressure loss or 80/60 psi but nothing on the delta between high and low psi readings. Traditionally I’ve heard of 10 percent in order to keep them balanced I was just wondering if jabiru had any guidance or opinion on this topic. Thank you in advance!
We don't have a criteria for the differential between cylinders. Each cylinder is assessed individually. That said if you notice that one cylinder has significantly lower leakdown than the other cylinders it could be worth investigating.
@jabiru-support would you be able to provide an example of what significant might mean to you? In addition, I noticed 50hour checks require differential checks this is definitely more consecutive than other engines like continental or even Rotax is there a specific cause for this or Safety Bulletin? I understand creating a pattern of data to identify errors early but seems excessive specially if you were to put over 100 hours I one year you might be doing leak down test 3 or 4 times a year costing you more maintenance money because the mechanic certification requirements. Can you provide more information on this?
For example if you had 5 cylinders showing 75-76psi and 1 showing 60psi, it would be worth investigating why that cylinder was different to the others.
Leak Down test data can be used to establish a trend for the engine as you have said. The more time between the data the longer the time to see a trend. With recreational flyers of all aircraft on average accruing only 30 hours per year, this will mean trends will be difficult to establish because only one a year will be performed. Flying schools can accrue 1,000 hours in a year. They usually have someone on staff who is qualified to do the leak down test and the time required to perform the leak down is not a financial burden for them. Services are a good opportunity to have a good look over the engine as per the checklist at the back of the engine manual with reference to the specific sections of the manual. Leak downs tests are part of the service regime and good practice. They are quick and easy to perform by an experienced person. They are not a Service Bulletin. Can't comment on the procedures for other brands.