Cylinder Compression Test For The Xu10j4rs

[SurGie 54]

Hi,

 

 

I have been trying to do a compression test for my newly acquired engine that il be converting it to my 205.

I know it is in good condition, but i want to be totally sure its good enough to put in the 205, so i only have to put

this engine in the 205 once.

 

Anyhoo, after trying to do the test exactly as the compresser tester says too it only goes up to 60 psi max, i found

out from Carl (mechanical repairs) that i should turn the engine with the starter motor not by hand.

 

So as the engine is on a pallet, im going to wire up the battery to the starter motor and do it that way.

The problem i have is which starter motor wire connector is the live & the earth.

 

Here are some pics of my uprated starter motor, i believe the larger connector bit in copper is the earth and the smaller is

the live.

 

 

Can any one advise me which is which so i don't damage anything.

 

Cheers

[DrSarty 90 1 Cars]

George, stop, before you kill yourself!!!!

 

The starter earths itself through its casing, into the engine block to the main chassis as its ground.

 

Have you not ever wired up a starter before? One wire comes from the battery, and then comes out from the other terminal to go to the alternator.

 

I'm saying this harshly as battery cranking voltage/amps is NOT something to f*ck about with; you'll get a vicious belt mate.

 

Only use one large terminal (either), and earth the battery to the engine block. The small terminal is the solenoid activation terminal which goes live when you turn the ignition key onto 'crank'.

 

When you get this sorted, plug in your comp tester, open the throttle butterfly (if you have the inlet manifold fitted) and crank and take the readings.

 

You worry me lad.

Edited November 6, 2009 by DrSarty

[Tom Fenton 1,542]

Huh?

 

How can you get a belt from 12V? If this were the case it would be dangerous to hold both terminal posts of a battery. I'll happily sit there for as long as you like holding each battery post in each hand.

[Cameron 16]

Nooooo! It isn't the earth, the starter earths through the body.

 

If you want to start it off the car, do the following:

 

Bolt the starter in place.

Attach the +ve lead (big thick lead) from battery to the large copper stud - the one with the nut on the end in those pics.

Attach the earth lead from battery -ve to the engine.

Attach your signal wire (small wire from battery +ve) to the small silver stud, and it should turn over.

[DrSarty 90 1 Cars]

Huh?

 

How can you get a belt from 12V? If this were the case it would be dangerous to hold both terminal posts of a battery. I'll happily sit there for as long as you like holding each battery post in each hand.

 

Are you just being argumentative? You know EXACTLY what I mean.

 

Take a wire Tom, for me, for us all, and video it please, and join it direct from positive to negative of a car battery. Those sparks you see will be the current I'm on about.

 

Give us a break eh?

Edited November 6, 2009 by DrSarty

[SurGie 54]

Oh yes i have fitted a starter motor before when its on the engine in the car, but its been a while since i last did it, and iv never attempted

to test a starter on its own with just the battery. I remember more about it now, after you told me about the alternator wire attachment.

 

So i though it best to get some good advice to make sure before attempting to do it, as i did not want the battery to blow up or get a bad

shock from it. Also the little bit of advice about doing a compression test on this thread could help someone on here one day.

 

Thanks Rich for the advice, i will do it as you said. So il connect a thick wire to the large copper threaded connection on the starter, then

connect the other end of the wire to the live on the battery.

 

Can you tell me how long i should i run the starter to get the full compression test result ? As the instructions are not very clear cut TBH.

 

Once iv sorted it over the weekend sometime, i will post my results for each cylinder with added pictures

 

Cheers...

 

EDIT> Thanks Cameron but i am a little confused now as two members that know a lot have suggested two different ways of tackling

this, i would prefer the easiest way if it works just as well.

 

Cheers...

Edited November 6, 2009 by SurGie

[Tom Fenton 1,542]

For a start, stop being so condescending to everyone else. Is it special week this week or something?

 

Yes there is a lot of current that can potentially travel THROUGH A CONDUCTOR OF LOW RESISTANCE drive by a potential difference of 12v.

 

However the human body is too high resistance to allow a 12v potential to drive any current through it. Therefore as I said before, you can hold the terminals all day long.

 

In the event above, if he connected the 12v to the small spade, and earth to the large connector, what would happen? Maybe the solenoid would throw out. But that is about it.

 

So no I don't know exactly what you mean.

[jackherer 543]

Huh?

 

How can you get a belt from 12V? If this were the case it would be dangerous to hold both terminal posts of a battery. I'll happily sit there for as long as you like holding each battery post in each hand.

 

I'm sure I've had this discussion with Rich before...

 

As Tom says, nobody is going to electrocute themselves with 12V.

 

However you might short something out and see a lot of sparks, possibly start a fire and consequently burn yourself.

 

But the only way you will learn is if you do it yourself anyway, the first time you put a spanner on an alternator or something without disconnecting the battery you will know not to do it again. Rich's comments remind me of the phrase nanny state which I am sure is not what he intended

[SurGie 54]

Sometimes i get an electric shock from the door when getting out of the car when i just slightly touch it, i think the rubber thing

that some people have at the back of the car stops this happening, not sure though.

 

So where does this shock come from if the human body has to high resistance to get 12v shock ?

 

Cheers..

[DrSarty 90 1 Cars]

Thanks Kieran.

 

You see a huge technical diatribe to say what you all know I meant. I'm trying to avoid George the unpleasantness. If you think that's nanny state, any of you, then we'll have to disagree.

 

Cameron just suggested a way to permanently connect the battery to the starter, only triggering it using the small spade connector on the solenoid. Same deal really, but perhaps easier to manage his way if you're on your own.

 

Tom>

Calm down man! This is not an argument. We're trying to help George. It's you who's kicked off.

Edited November 6, 2009 by DrSarty

[Emmy Seize 8]

Hmm - you lot are getting quite eloquent where a simple statement would do: IT HURTS!

 

Ok, having two little girls probably streamlines your language somewhat

[SurGie 54]

Id much rather learn from asking than doing when it comes to electric and safety, saves me getting a shock which could end up

me looking like Mr Bean on a mad un, everything flying everywhere

 

Cheers for the help and il keep you all posted on my results, shock or no shock lol

[Cameron 16]

George the little shock you get when you step out of the car is down to static electricity, rather than the car's electrics. Static electricity is in the hundreds of thousands of volts, but very low current, which is why it doesn't kill you.

 

But yes, what Tom is saying is correct. If you want proof, you know that Current (I) = Voltage (V) / resistance ( R ), right? So if you have an object of high resistance and a low voltage, you have a small number divided by a large number, which equals a very small number. So I = 12V / lots of resistance = f*** all.

Conversely, your nice copper wire has very low resistance, which is why the very large amount of current flows through it and you get the big sparks.

 

Now stop your bitching.

Edited November 6, 2009 by Cameron

[welshpug 1,657]

you do have a gearbox you can bolt to it right?

 

sort that, then attach starter motor, if you hve one to hand connect the main alternator-starter-battery lead, and connect the earth lead to the battery.

 

if you dont have an alternator on there you need to make sure the loose end wont touch anything, wrap the bare end in tape or a rubber glove.

 

fit the compression tester to a cylinder (other plugs out, throttle held wide open if the manifold is still attached)

 

then crank it over, 2 ways to do it, either use a large screwdriver to bridge across from the big bolt to the small spade/ring terminal to activate the solenoid or attach a lenth of wire to the positive terminal (battery or starter, whichever is easiest)

 

good figures would be in the region of 200-220, though dont be worried about a lower reading as long as they are all within 10-15%, unless you have a very expensive accurate well fitting gauge.

[DamirGTI 342]

use a large screwdriver to bridge across from the big bolt to the small spade/ring terminal to activate the solenoid

 

Im doing it like this as well when ever i need to crank the engine on a car with fubared electrics or similar stuff .. it's simple , easy and quick

 

Damir

[GLPoomobile 958]

Can you tell me how long i should i run the starter to get the full compression test result ? As the instructions are not very clear cut TBH.

 

It's usually just a few seconds, or the equivilent of a few engine revolutions.

 

What you should see is that the needle on the tester jumps up in large numbers for the first couple of revolutions and then as it gets to it's max reading, it'll increase in smaller increments. After about 5 or 6 revolutions it'll have probably reached it's max reading, and no amount of cranking on the starter will get it any higher, so you stop at that point.

[SurGie 54]

you do have a gearbox you can bolt to it right?

 

If you have one to hand connect the main "alternator-starter-battery lead", and connect the earth lead to the battery.

 

if you don't have an alternator on there you need to make sure the loose end wont touch anything, wrap the bare end in tape or a rubber glove.

(other plugs out, throttle held wide open if the manifold is still attached)

 

then crank it over, 2 ways to do it, either use a large screwdriver to bridge across from the big bolt to the small spade/ring terminal to activate the solenoid or attach a length of wire to the positive terminal (battery or starter, whichever is easiest)

 

good figures would be in the region of 200-220, though don't be worried about a lower reading as long as they are all within 10-15%, unless you have a very expensive accurate well fitting gauge.

 

 

Yes my engine has the gearbox fitted but not the alternator.

 

Just to be sure,

 

Is the alternator-starter-battery lead the lead from the alternator to the small nut attachment on the starter alone >?

I can easily use the 205 alternator wire from its loom for this.

 

Do i need an earth lead at all with it being attached to the gearbox for the earth ? Or is it best to have an earth lead from the gearbox

to the battery, when starting the starter this way ?

 

I have an alternator spare lying on the floor, so is it worth connecting it to the starter ?

 

I will cover up all the other connections on the starter so it does not cross over.

 

"Other plugs out" if you meant the spark plugs, then its already done.

All the manifolds are fitted and i know i have to open the throttle plate for this test.

 

Iv found a good red power lead meant for boot installs with looped ends il use for the positive starter attachment meant for the positive on

the battery, hands away from the sparks.

 

I have bought myself the compresser tester from Machine Mart about £40. Its a well fitting gauge & iv put a little oil around the seals, like i said i managed to get 60 psi by hand, which iv been told that is quite high and i should of only got around 10-20 psi by hand. Unless its because i have strong arms

 

When i have done it by hand, i noticed that when turning the crank some of it is easy to turn then further in turning it gets a bit stiffer to

turn, is this normal ? Is it something to do with counter weight ?

 

200/220 psi is what iv been told and if the pressure is more than 15% lower amount difference then it could be a head gasket or seals.

 

EDIT> Thanks for that GLP.

 

 

Cheers George

Edited November 6, 2009 by SurGie

[craig_007 1]

Hi All,

 

I might be wrong in saying this but surely this is not complex at all,Is it not a case of - Earth from battery to gearbox(as you would on car) Then take the live from the battery to the live terminal on the starter and the bridge the connections on the starter and then take your readings.I wouldn't worry about the altenator,If your concerned just insulate the live that would go the altenator live terminal.

 

I done this on my 205 to identify a starting problem.

 

The way you describe it turning by hand is perfectly normal,mine is also like this.

 

Compression wise,You won't see 200/220 psi cold,

 

On my engine the compression was 185psi cold and I was told this was very good,I would be thinking 200+psi when up to temp.

Edited November 6, 2009 by craig_007

[hcmini1989 16]

Hi All,

 

I might be wrong in saying this but surely this is not complex at all,Is it not a case of - Earth from battery to gearbox(as you would on car) Then take the live from the battery to the live terminal on the starter and the bridge the connections on the starter and then take your readings.I wouldn't worry about the altenator,If your concerned just insulate the live that would go the altenator live terminal.

 

I done this on my 205 to identify a starting problem.

 

The way you describe it turning by hand is perfectly normal,mine is also like this.

 

Compression wise,You won't see 200/220 psi cold,

 

On my engine the compression was 185psi cold and I was told this was very good,I would be thinking 200+psi when up to temp.

 

yup spot on thats the way i do it .all you need is a set of jump leads.and a bit off wire maybe or a screwdriver to bridge it .do a search on google .on how to bench test a starter motor .if you need more info

Edited November 6, 2009 by hcmini1989

[Cameron 16]

This has all been covered, we're going round in circles!

[EdCherry 34 1 Cars]

When i have done it by hand, i noticed that when turning the crank some of it is easy to turn then further in turning it gets a bit stiffer to

turn, is this normal ? Is it something to do with counter weight ?

 

This is because of compression funnily enough

[SurGie 54]

[DrSarty 90 1 Cars]

Are you happy with the explanations George coz this really isn't complicated?

 

So as people have said:

 

Battery neg>>>>big lead>>>>attached to gearbox or engine block

Battery pos>>>>big lead>>>>attached to one of the two large posts on the solenoid

 

Then to trigger the starter, either bridge (with a plastic handled screwdriver) between your positive cable on the solenoid to the spade connector on the solenoid, OR, take a smaller wire from the positive battery terminal to that spade.

 

Leave the alternator alone; it's not fitted, and it's not needed for this test.

 

Good luck mate.

[Cameron 16]

Bridge the starter terminals by licking them.

[Galifrey 1]

Bridge the starter terminals by licking them.