Compression test with engine out of vehicle

[ilovewilly]

Looking to do a compression test on a 172 engine which is no longer fitted in the car - therefore is obviously unable to be cranked by key.

From looking on line hand cranking with a breaker bar is highly likely to be a wasted effort.

The gearbox isn't fitted so neither is the starter. Can I get away with holding the starter to the flywheel and cranking it like that connected to a battery or do I have to pop the gearbox back on? I don't want to fry the starter etc, but I imagine it just requires a 12v feed to the copper stud and earthing to the engine. The spade terminal whatsit - will that need power to?

Suggestions from experience welcomed

 

[Paprika123]

No chance you'll be able to hold the starter in place enough for it to turn the engine.

 

[Chip-mk1]

No chance you'll be able to hold the starter in place enough for it to turn the engine.

This ^^^^

you will need to fit the box, or at least the part of one that holds the starter if you have a scrap one you can chop up. (its how they are often run on an engine dyno)


A leak down test can be done though, and is a better test in many ways.

 

[mikeh]

As the others have said - there is no chance without the gearbox fitted - I didn't really consider this when I asked for one.

FWIW, on the starter, the pin is a permanent live, the spade connector activates the solenoid with 12v.

I shall drop you a PM when I get home.

 

[Chip-mk1]

To fire the starter it needs:
-VE by being bolted up to the engine/box (The solenoid is then earthed through the starter itself)
+VE to the main feed into it
+VE to the solenoid to fire it, you can get this just by touching a bit of wire from the +VE to the spade on the solenoid

 

[ilovewilly]

Thanks for the info chaps

 

[Chip-mk1]

Dan@SJM has a leakdown tester of course, and you could probably bribe him with the offer of some vinyl?

 

[Andyman]

Is a leak down test 100% accurate at pin pointing where the leak is coming from or does it just measure a more accurate loss than a compression tester?

 

[Chip-mk1]

Is a leak down test 100% accurate at pin pointing where the leak is coming from or does it just measure a more accurate loss than a compression tester?

Assuming the person who is using it know what they are doing (like if he takes it to Dan@SJM) then yes it will tell you where the leak is coming from, although to say "100% accurate at pin pointing" is probably a bit hopeful as of course if you have a bad leak somewhere then until its fixed you wont find smaller ones!

 

[ilovewilly]

The only reason I ask is because mikeh raised the question in my for sale thread for the engine. If he's genuinely interested and prepared to purchase based on a healthy result I will buy a compression tester and put the time in to fit/remove the gearbox to do a test.

 

[carnuts]

In your ad it said engine had been drained of all fluids is that oil too? (Just checking)

 

[ilovewilly]

That's a point it's had the oil drained!

 

[carnuts]

Thought you might say that I have done the same makes them easier to move when not making an oily mess

 

[Chip-mk1]

If selling to mikeh do bare in mind he will expect a full unconditional 12 month warranty.

 

[mikeh]

Jokes. Where's the roll eyes smiley?