How To Test Engine Compression
How To Test Engine Compression On A Yanmar Engine
You will need a diesel compression tester to test the compression on a Yanmar diesel engine. Compression testers for gas engines will not be rated for the higher pressure of a diesel engine. You can find our compression tester IN THIS LINK
- Remove the steel injector line from injector & loosen the line from the pump side so it can swing out of the way. Avoid getting any dirt in the line by taping over the end.
- Remove the two retaining nuts and the retainer (D & C).
- Remove the injector (B) (soaking overnight in something like WD40 will make it easier to remove. The injector just pulls out but might be stuck.
- Remove the sealing insulator (A) from injector or down in the head using a small pick. Do not attempt to remove any of the other pieces under the injector. If you disrupt these pieces then they will need to be removed and new sealing washers installed.
- Replace the old insulator with new insulator included in our kit.
- Install the tester adapter in place of the old injector. The adapter will NOT fit tight in the hole. You will just center the adapter roughly in the center of the injector hole. The sealing is all done at the bottom.
- Reinstall the retainer & two nuts and tighten. No need to overtighten- just snug.
- Attach compression gauge using the quick disconnect coupler.
- Close bleeder screw on compression tester (turn clockwise just like a water valve).
- Put throttle in 'stop' position or pull the fuel cutoff so engine will not start.
- Be sure the decompression is released (not de-compressing).
- Crank engine over for a few seconds but do not start engine.
- The gauge will hold the maximum pressure created in the cylinder.
- A pressure below 400psi will usually be hard to start. A new engine will be around 500psi - 600psi
- Open bleeder valve (counter-clockwise) to vent out pressure.
- Uncouple the quick disconnect fitting to remove the gauge.
- Remove adapter and re-install injector using a new insulator washer.
- Repeat process for the remaining cylinders.