So the rotor housings are stacked but have walls inside keeping the chambers separate. In my head when housings were stacked, I envisioned one continuous chamber with the rotors turning adjacent to each other inside. Interesting.

Brigdh wrote:I usually take one spark plug out of the front rotor, run the test, replace the spark plug, then take a spark plug out of the rear rotor and test. However that's generally to prevent me from mixing up sparkplugs or sparkplug wires. Technically there wouldn't be a problem with taking out both leading plugs or whatever at the same time.

I was asking because I've wondered about having one housing's compression pushing back causing a false reading on the rotor being tested.

Shadowden wrote:So the rotor housings are stacked but have walls inside keeping the chambers separate. In my head when housings were stacked, I envisioned one continuous chamber with the rotors turning adjacent to each other inside. Interesting.

It's stacked kind of like a loaf of bread, with five pieces, the first, third and fifth pieces being solid and the second and fourth pieces being hollow and holding the rotor inside. The solid pieces have the intake ports (except for on the RX-8s where the intake and exhaust ports are on the housings), and the housings have the exhaust ports.

http://www.howstuffworks.com/rotary-engine.htm

speedjunkie wrote:I was asking because I've wondered about having one housing's compression pushing back causing a false reading on the rotor being tested.

I've never heard that concern in relation to compression testing rotary or piston engines. Again, the spec for minimum pressure is based on the starter turning the engine at 250 RPM. So, assuming you are testing the front rotor, and the rear rotor's compression stroke is "pushing back" that would result in the starter encountering additional resistance, and spinning the motor slower. However, the test results include the RPM observed, so you then adjust the compression numbers based on the observed RPM vs 250. The FSMs provide a diagram to do so, but generally if you observed RPM is less than 250, the compression numbers are "low" and need to be increased, and if the observed RPM is more than 250, the compression numbers are "high" and need to be decreased to get the "true" compression reading.

Brigdh wrote:......

The tool displays your raw readings. You'll need to normalize them for cranking RPM (the spec assumes the starter will spin at exactly 250 RPM) and altitude (the spec assumes sea level). You can use this online calculator to do the conversion: http://foxed.ca/index.php?page=rotarycalc

That calculator is useful. Last time I checked compression I had the Access Port to view my rpm and in the shop manual looking at the graph it was way off. I figured it was due to the altitude that it was reading below the graph. I looked at my numbers for the 3 faces and figured all was good. They were all within 4psi of each other. Same with the numbers from the back rotor to the front.

Ok gotcha. That's pretty handy.

BrigDH, can you I just let you check mine?

I'm planning on getting this compression tester this month because there is a sale. FINALLY we'll have a legit rotary compression tester to use, and we can do both rotors at once.

http://rotarydiagnostics.com/

Here is the thread on RCC about the sale...

http://rotarycarclub.com/rotary_forum/showthread.php?t=18420

Cool. I'm definitely going to need to try that out on my car.

I'd be interested to know if they improved their software any from when I trialed it 3 years ago. I found having to calculate the RPM off of the provided graph to be an annoyance.

RX-7 Chris wrote:Cool. I'm definitely going to need to try that out on my car.

I was thinking about getting the 4 rotor one so we could use it on any rotary in the area, and I figured it would be handy if I ever opened a shop, but since we don't have a single car around with more than 2 rotors (aside from Cory talking about building one) and I could just buy the 4 rotor one down the road, I decided the 2 rotor one will suffice lol.

Brigdh wrote:I'd be interested to know if they improved their software any from when I trialed it 3 years ago. I found having to calculate the RPM off of the provided graph to be an annoyance.

Was there anything else you didn't like about it?

Brigdh wrote:So, the Twisted Rotors compression testers are back (sort of). The guy behind TR has been making 5 testers a week, and then selling them online for $350 + $20 shipping every Friday at 5pm CST (aka 4pm here). The first 3 rounds of this had the testers selling out within minutes, but the batch that started selling yesterday was not sold out until sometime this afternoon (so almost 24 hours). I managed to snag one, but if anyone else is looking to get one, it seems like you'd probably get one from the batch to be sold on the 1st without too much trouble. Seeing as how the TR guy seems to promise a lot and take forever to execute, I wouldn't wait too long, he might stop doing this 5 every Friday routine if he thinks the demand has vanished.

I did a search on 7club on the Rotary Diagnostics tester to see what people thought of it, and someone had one of the older TR designs. It said the price was $150. I forgot you had posted about this one. How do you like it? I was thinking about maybe getting two so I can do both rotors at the same time, but I guess I could still just do one and just make sure the RPM is the same front and rear while testing.

http://www.twistedrotors.com/

Also, someone else in the thread made this, which would come in really handy for us...

http://foxed.ca/index.php?page=rotarycalc

speedjunkie wrote:Was there anything else you didn't like about it?

Atleast when I evaluated it, my impression was that it was quite powerful, but almost the wrong tool if all you wanted was basic compression numbers. It seemed to me that it was more of a comprehensive diagnostic tool.

At the time, all the system really did was graph the pressure the sensors were reading, over time. You'd get a nice plot of the pressure at any point in the rotor's rotation. You could also click on the graph, and get the time, and pressure reading for any point along the graph.

Looking at it from the basic compression test perspective, I'd have to find the peaks of each face on the graph, get the reading, get the time, and calculate the rpm. Since its a computerized system, it should have been pretty easy to have a function in the software to do that for me.

However, if you were a shop, I could see how it would be useful. If you are good at reading and understanding the graphs, you could easily tell if a side seal was damaged or something.

So for me, the Twisted Rotors system was cheaper and less work.

speedjunkie wrote:I did a search on 7club on the Rotary Diagnostics tester to see what people thought of it, and someone had one of the older TR designs. It said the price was $150. I forgot you had posted about this one. How do you like it? I was thinking about maybe getting two so I can do both rotors at the same time, but I guess I could still just do one and just make sure the RPM is the same front and rear while testing.

http://www.twistedrotors.com/

Also, someone else in the thread made this, which would come in really handy for us...

http://foxed.ca/index.php?page=rotarycalc

I've used one of the old designs as well. The new design is easier to read the output, and looks more "professional" in its construction, but there are still some hand done modifications with a dremel or something that kind of detract from the looks of the rest of the unit. They function identically.

I find it pretty easy to use. Disable spark/fuel (different mechanism for each vehicle but its usually pretty easy - disconnect a sensor or yank a fuse), pull a plug on one rotor, crank for 5-10 seconds, note the output (you get psi on the 3 rotors and RPM), and repeat for the other rotor. I don't think that it matters if the RPM reading is different between the rotors for the raw output, because you have to adjust the readings for RPM and altitude anyways, which is what the calculator your linked to does for you.

I don't use the tool every day, and I can easily test an engine in 10 minutes.

Alright. Maybe I'll get the RD tester just in case I have a shop someday haha, but I'd much rather have one that's easier to use for my own use. I PMd TR about his tester, but I haven't heard anything back yet and his site says sold out.

it doesn't just say sold out, lol. it says "back in stock" and "sold out" haha

Yeah I noticed that too haha.