Compression test, compression test!
01-30-12, 11:27 PM
#1
Compression test, compression test!
I have not been in this section of the board for quite some time even though I am a "senior member". 
I see ALOT of posts, is it blown, please tell me its not blown, is my motor blown....
I have found over the years that the first thing is to compression test AND if coolant seals are thought to be bad, pressurize the cooling system.
for the DIY, Harbor Freight has an awesome coolant pressure testing system which has an adaptor that fits the FD filler neck and the AST.
You need a true rotary compression test which shows the health of each face. There is a kit available from rotarydiagnostics.com. Either this kit or the Mazda OEM, if you can find one, I feel is a must have for every rotary powered RX7 owner, with a wideband at close second.
Just my two cents.
I see ALOT of posts, is it blown, please tell me its not blown, is my motor blown....
I have found over the years that the first thing is to compression test AND if coolant seals are thought to be bad, pressurize the cooling system.
for the DIY, Harbor Freight has an awesome coolant pressure testing system which has an adaptor that fits the FD filler neck and the AST.
You need a true rotary compression test which shows the health of each face. There is a kit available from rotarydiagnostics.com. Either this kit or the Mazda OEM, if you can find one, I feel is a must have for every rotary powered RX7 owner, with a wideband at close second.
Just my two cents.
01-31-12, 08:42 AM
#4
RX-7 Bad Ass
iTrader: (55)
One common misconception is you need an expensive compression tester to see if an engine is blown or bad.
THIS IS NOT THE CASE.
Get a basic compression tester. Harbor Freight has one for $10 -
http://www.harborfreight.com/flex-dr...ter-92697.html
Disable fuel and spark, screw the tester into a plug hole on one rotor (I usually do the trailling hole), have a buddy get in the car and floor the gas pedal and crank.
Hold down the release button on the side of the tester and watch the needle. You should see a pattern of 3 even bounces. If you see a high bounce then 2 low bounces, you've got a broken apex seal. If you have 2 high bounces and one low bounce, you've got a bad or stuck side seal.
You can also let go of the button on the tester and let the numbers build up. This will give you a general picture of the "tightness" of the motor.
If you have 3 even bounces on both rotors, the apex seals are OK.
The rotary-specific testers will give exact numbers for each rotor face. That's nice, but it really isn't necessary to determine if a motor is bad or not.
BTW, you can also get plain compression testers at pretty much any auto parts store. The one I have is from Autozone.
This will give you the yes/no answer to "is my engine blown?" If no, start troubleshooting in another direction.
Dale
THIS IS NOT THE CASE.
Get a basic compression tester. Harbor Freight has one for $10 -
http://www.harborfreight.com/flex-dr...ter-92697.html
Disable fuel and spark, screw the tester into a plug hole on one rotor (I usually do the trailling hole), have a buddy get in the car and floor the gas pedal and crank.
Hold down the release button on the side of the tester and watch the needle. You should see a pattern of 3 even bounces. If you see a high bounce then 2 low bounces, you've got a broken apex seal. If you have 2 high bounces and one low bounce, you've got a bad or stuck side seal.
You can also let go of the button on the tester and let the numbers build up. This will give you a general picture of the "tightness" of the motor.
If you have 3 even bounces on both rotors, the apex seals are OK.
The rotary-specific testers will give exact numbers for each rotor face. That's nice, but it really isn't necessary to determine if a motor is bad or not.
BTW, you can also get plain compression testers at pretty much any auto parts store. The one I have is from Autozone.
This will give you the yes/no answer to "is my engine blown?" If no, start troubleshooting in another direction.
Dale
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01-31-12, 10:17 PM
#9
Original Gangster/Rotary!
iTrader: (213)
I've never seen the need for the el cheapo piston compression testers..... my ears work just as good if not better 
I do agree that a rotary-specific compression tester is worth it's weight in gold though.
I do agree that a rotary-specific compression tester is worth it's weight in gold though.
02-01-12, 10:18 AM
#10
^ How can you hear it with all that starter noise?
Either way since we are on this topic, this is blown correct?
Front
http://s133.photobucket.com/albums/q...t=DSCN3417.mp4
Rear
http://s133.photobucket.com/albums/q...t=DSCN3416.mp4
Either way since we are on this topic, this is blown correct?
Front
http://s133.photobucket.com/albums/q...t=DSCN3417.mp4
Rear
http://s133.photobucket.com/albums/q...t=DSCN3416.mp4
02-01-12, 08:47 PM
#16
That scenerio is hard to see with the Needle Bopper Compression Tester.
Take a video of the car idling like Rich said. And if you have a boost gauge that reads vaccum, take vid of that too.
02-01-12, 10:07 PM
#18
Last time it ran was back in September when I took her out for a cruise with some local member, everything was fine till I start her up after we stopped for an hour, that's when she started idling at 500rpm. Boost gauge read about 11-12inHg, both gauge are steady and not bouncing. I was able to start her up again next morning, but that was the last time I was able to turn her over.
02-01-12, 10:31 PM
#19
Here, get this tester. It is bad *** and worth every penny. IMO, most of us have poured a boatload of coin into our cars what's another 400 bones?
http://rotarydiagnostics.com/model_rect-03b.htm
I am in no way affiliated with Rotary Diagnostics. I just own and use this bad boy and it works flawlessly and is extremely accurate.
http://rotarydiagnostics.com/model_rect-03b.htm
I am in no way affiliated with Rotary Diagnostics. I just own and use this bad boy and it works flawlessly and is extremely accurate.
02-10-12, 12:53 PM
#21
Terminal Project
iTrader: (3)
Join Date: Feb 2003
Location: Smyrna, DE and/or Baltimore, MD
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What kind of test can you do on a motor that isn't in a car? Due to a few factors I've neglected the car for many years. I was 50% don't making many modifications including injectors and ignition so it run but I haven't tried in years. I guess I can hook the starter back up to try this test, but is there an equivalent that I can do if I have the motor out of the car to see if I need to rebuild it?
It ran great last time it ran....in 2007. For about 2 years I stupidly left the coolant in it and read that I probably rusted the coolant passage by the iron so I may end up having to replace.
Don't want to rebuild it just to rebuild it, but also don't want to finish it and expect it to crank and be fine when it might not.
I'll take any suggestions.
It ran great last time it ran....in 2007. For about 2 years I stupidly left the coolant in it and read that I probably rusted the coolant passage by the iron so I may end up having to replace.
Don't want to rebuild it just to rebuild it, but also don't want to finish it and expect it to crank and be fine when it might not.
I'll take any suggestions.
02-10-12, 01:32 PM
#22
You can test the motor outside the car. You can buy a remote starter from Harbor Freight for like $15. Hook up your bellhousing and starter to the engine. Use one of the compression testers above...authentic or basic...and follow the steps as normal.
Your compression will test higher on a cold engine outside of a car as compression should be tested on a warm engine.
Your compression will test higher on a cold engine outside of a car as compression should be tested on a warm engine.
