Differential Compression Tester With 12Mm & 18MM Adapters

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Part# 15-05209
MFR Model# 12-01012


9590 Rotax 912 Differential Compression Tester. Find faulty cylinders quickly. Static test your Rotax 912 cylinder compression with 80 psi shop air. No cranking required. Just find TDC and pressurize cylinder to 80 psi. Left gauge allows you to regulate pressure with built-in regulator valve. Simply adjust pressure and slowly open built-in petcock and read differential compression. Pin point loss of ring compression (pressure exits crankcase) leaky exhaust valves, (pressure exits exhaust), or leaky intake valve (pressure exits Intake). Includes 12mm adapter that screws directly into spark plug hole and female pipe thread to accept hose.
California Prop 65 Warning Symbol

WARNING: Cancer and Reproductive Harm -

In The Box

  • Differential Cylinder Pressure Tester Model E2A
  • 12mm Adapter


It showed up in 10 day exactly as advertised. Swapped out the adapter with no issues and used it to annual our 912. It works great!

July 28, 2018

Best company, fast shipping and excellent tool. Recommend

May 15, 2017

Bought for use on Rotax, so the first thing I did was to attempt to remove the 18 mm spark plug adapter that comes pre-installed on the flex hose. The soft brass nut on the flex hose immediately rounded off as it was so tight. CPS sent another complete tester, and I very carefully used vice grips to hold the brass nut while removing the 18 mm adapter, to find that the threads had been cemented together (presumably to eliminate leakage) by a hard-setting cement. Spent the next hour carefully removing the cement from the brass threads on the end of the flex hose, then a couple of minutes filing the sharp edges cut into the flats with the vice grip. The next job will be to try to make a leak-proof connection, using Teflon plumbers tape, between the flex hose and the 12 mm spark plug adapter, which is a machined section of bar stock with no flats to accept a wrench and will therefore need a padded pair of pliers to hold it tight enough to apply enough torque to tighten without crushing it. They really should charge a few bucks more and supply two separate hoses, with spark plug adapters pre-installed, one 12 mm and the other 18 mm. I have no idea how well it works yet as a tester as I did not have a spare month to wait around with my airplane out of service. I let CPS know exactly what the problem was, sending them a photo of the offending part, and they sent a new kit without question or delay. I was surprised to then receive a letter from the post office expressing regret that my package had been damaged during shipment and to please retain the damaged packaging while they investigate.

June 16, 2018

DIFFERENTIAL COMPRESSION TESTER W/ 12MM & 18MM ADAPTERS//Part #: 15-05209: Received email asking to review this product. Process to do so IS NOT user friendly and after some time of trying to figure it out, I clicked SUBMIT and received a message saying it was unable to find the page. After several attempts to do so, I gave up and decided to address this issue via the CONTACT US page. Review is as follows: Received in timely manner. Compression hose defective out of box/leaked air at fitting junction. Had to repair hose in order to use product and check compression. Quality of product was/is definitely sub-standard which is very disappointing coming from a company I believed I could always count on for excellent product quality and integrity.

November 14, 2018

This was on backorder for over 6 months, unacceptable.

Dennis C
November 5, 2020


Please note, Aircraft Spruce's personnel are not certified aircraft mechanics and can only provide general support and ideas, which should not be relied upon or implemented in lieu of consulting an A&P or other qualified technician. Aircraft Spruce assumes no responsibility or liability for any issue or problem which may arise from any repair, modification or other work done from this knowledge base. Any product eligibility information provided here is based on general application guides and we recommend always referring to your specific aircraft parts manual, the parts manufacturer or consulting with a qualified mechanic.

Q: Do these compression testers come calibrated?

Yes, these will come calibrated. It does not come with a calibration certificate but does have a stamp stating that it is calibrated from the manufacturer.

Q: Does this come with the spark plug adapter to test Lycoming engines? If not, do you sell that adapter?

Part number 15-05209 will have both the 12MM and 18MM adapter. The 18MM unit is used on both Lycoming and Continental engines.

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