Bench Compression Test

[Gilly]

ever gone to buy a used engine and had that feeling of uncertainty as to its health?

heres a easy way to test it even though its not running.

Bench compression test (well tyre mounted comp test at least :lol: )

http://www.ae86drivingclub.com.au/dcimages/4/8/4/3/168711.jpg

basically we will build a start circuit so we can see each cylinders compression reading

you will need

engine :P + starter motor
battery (healthy battery)
switch
2x heavy gauge cables with terminals suitable for battery use (2 battery earth straps work)
2x lengths of normal size insulated wire

first bolt the starter up to the engine using 2 short 14mm bolts, install 2 more 17mm short bolts into the sandwich plate to ensure the starter has a good solid mounting. you can see what i mean in the pic below

http://www.ae86drivingclub.com.au/dcimages/4/8/4/3/168712.jpg

now the stater is connected we need to build the start circuit

1. bolt the earth strap to the block/head
2. using a female spade terminal join one of the two thin wires to the starter solenoid spade terminal
3. join the other end to one terminal of your switch (i used a push button switch)
4. attach the other thin gauge wire to the remaining switch terminal
5. attach the heavy gauge positive cable to the large fitting on the starter
6. now attach both the positive and negative cables to the battery and touch the thin wire on to the positive terminal (to ensure the switch is not already on)

should look like this (ish)

http://www.ae86drivingclub.com.au/dcimages/4/8/4/3/168713.jpg

now you can test the circuit

i braced the engine with one hand and pressed the starter button with the other, pressing the switch causes power to trigger the starter solenoid which will the close the start circuit allowing battery voltage to travel to the starter and turn over the engine.

if that is working as it should you can now fit the compression tester and test each cylinder!!

remember to remove all spark plugs and hold the throttle wide open to get an accurate reading.

:)

[rthy]

damn I didnt think that would work going just off a barrier plate, does it squirm around much?


I will keep this in mind for the future

[Nikkojoe]

Had my current ge tested exactly like this too, works like a charm. The sandwich plate does not flex at all really onces it's cranking :)

[patience]

Nice tech article
A friend has been through 3 1JZs from BMI, they refused warranty on the last 2.
Their compression test on all their engines always read well, I would never trust theirs though.

[rthy]

yeah ok thanks guys.

Also one other thing Gilly, those "17mm bolts" thats the head diameter across the flats yeah?

[Matt-AE86]

I actually bench "started" and engine like this. tight the engine down to the tyre via a jarrah work bench and such, worked good :P