Does anyone know what is the bare minimum needed to test the compression of a motor with an official Mazda compression tester? Full block? Short block? What?

I have a long block out of car that I started to disassemble but was told as long as the starter is connected a Mazda compression tester can still test compression.

Anyone have info about this?

Thank you!

 

It's supposed to be performed on a warm engine, so long block really. If you don't care about super official numbers, I imagine you could compression test a short block if you could spin it with a starter.

 

If you have a short block, it just needs a transmission bellhousing and a starter hooked up to crank the motor over. And a flywheel for the starter to engage. Clutch doesn't need to be on.

With a cold engine, all you can really learn from that test is if you're getting good compression pulses. The quality of compression (how tight the motor is) really only shows up with a warm engine, but you should be able to get in the ballpark. If the pulses sound good and strong when you're cranking you'll probably be looking at a good engine.

Dale

 

Just to fill everyone is. Hooked up the shortblock to the bell housing and connected a remote, push button starter and the Mazda Compression Tester.

As this was a shortblock, the engine was cold of course. I ran about 20 runs (10 each) on the top or trailing plug for each housing. The cold engine certainly makes a difference in compression as both sides were between 9.5-10 on all tests. A couple of the later tests dropped down to 8.5-9.2.

Since this is like 130psi and I was told this engine was built with used parts by the builder and it now has 20k miles on it I suspect the actual numbers are probably closer to 6.5-7.5. Who knows however, it was running strong before I went off-roading.

Will be putting the shortblock up for sale tomorrow.

 

Pics of the compression tests.

 

Here is a video i fought this morning. Coincidentally they were using a compression tester but the video is japanese and i cant understand what they're saying!!! Also they were using some sort of protek-r bottle lubricant in the gas tank before the test. What was that for??

http://www.youtube.com/watch?v=Sfmlc...a8FAAAAAAAACAA

 

A warmer engine typically has WORSE compression, so if you're getting good cold numbers you'll likely be fine. The big thing is the quality of the bumps and the evenness of the compression and that looks good. Any low spots mean a sticking or not properly fitted side seal, damaged apex seal, any number of things.

Dale

 

Qwik - You can "fudge" the numbers on compression a variety of ways from what I understand (not if it is blown of course) by adding oil/transfluid/etc to the exhaust ports or via spark plug holes. I'm not saying that is what they are doing there but it can be done.

Edit: After watching the video it looks like they are trying to sell some product that "increases" compression. My guess it is the same as fudging compression and is very temporary. I may be absolutely wrong.

Edit 2: Dale, perhaps I've been looking at old info but on multiple sites it seems to say that cold compression tests give much better results than a properly warmed up engine. So I can further educate myself and reach an informed decision, why is your opinion the opposite?

 

That's what I said - a warm engine has lower compression than a cold engine. Wording was a little obtuse.

All I know is you need that **** running by DGRR '12, ATTACK OF THE TALL DOODZ

Dale