Compression Testing

leeroy_25 · August 31, 2007, 07:34:35 PM

I have a spare engine for my new FD3S at home and want to compression test it before I fit it. I know it ran ok wen it came out of another car but I want to be sure it\'s not about to give up when I fit it!

The best I will be able to do is flick it over on the starter on an engine stand cold. I know this is not ideal! I was thinking of putting a little engine oil into the plug holes to lube up the seals and then doing the compression test.. What should I be looking for a good result on a cold engine? Anything else I should check before I put it in?

Thank you
Lee

Grizzly · September 01, 2007, 01:51:17 AM

The only time i\'ve comp tested a motor out of the car i put the Gear box and starter on it and as you say turn it over that way.

As for the Oil, i would use no more than a tea spoon full in each rotor bath. The best way do making sure you have oil in each bath is shine a flash light down the lower plug hole and get a second person to turn the engine by hand then you watch for the Apex to pass, Once the Apex goes passed get a length of tube and a small funnel and pore 1 tea spoon of oil in each bath. Front and rear housings. Once this is all done spin the motor over a few times before you fit the Comp tester or you will end up with oil in the tester.

From past experiance i found there is not a Massive difference in Comp between Hot and Cold as long as the throttle is fully open, there is some sort of Lube in the bores and the RPM is roughly the same, but in any case i would only use a motor that was seeing 7bar or more on each Bath, TBH its more about constancy than over all Pressure, I would rather see a Motor with a comp of 7.0-7.0-7.0 6.8-6.7-6.9 than something that gave a reading variation of roughly 1 bar.(i.e. 7.1-8.2-7.9 8.1-7.5-8.7)

leeroy_25 · September 02, 2007, 01:20:16 PM

Thank you very much for the info.. I have a mission and a half ahead!

Lee

leeroy_25 · September 19, 2007, 01:42:25 PM

Just a quick one guys before I go for it..

does it matter if you put the compression tester in the top or bottom plug hole? I assume not but thought I would check!

Thank you
Lee

ianelvar · September 21, 2007, 10:34:52 AM

Trailing according to the howto. I\'d test the coolant seals as well if I was fitting another used motor. I made a cooling system tester out of an old filler cap, a footpump, and some fuel line. Can supply pics, or even the actual thing if you want to use it?

leeroy_25 · September 21, 2007, 02:26:47 PM

Hi Ian!

Test the seals? does this not show up on the compression test then?

Let me know roughly how and I am sure I can knock one up..

By trailing plugs I assume you mean top?

At the moment I am hoping to get a lump in the car to see if I like it and can fit after moving the seat and steering!! If not I\'ll have to sell it.. but if I keep it and the engine lets go I can rebuild it later or look for a spare to rebuild in the meantime.

So much to learn about the RX7! thank god for the forum and helpful people! Have you seen the post about my project car?

Cheers
Lee

ianelvar · September 21, 2007, 03:06:10 PM

Hi mate.

Top plugs, yes.

No, it won\'t show on comp test.
To build the tester:

Blank off all coolant hose connections if the engine is not in a car and connected to rad, ast etc. I\'d advise attaching an AST if you can. Explanation later.
Fill engine with water.
Cut the end off the pipe from the footpump.
Find a bolt that fits inside the tube from the pump, and a nut that goes on it. Drill a hole right through the centre of the bolt. 3-4mm will do, doesn\'t matter if it\'s a bit off centre.
Take a spare filler cap, and drill out the centre to the size of the bolt. You\'ll acrtually be drilling though a little springy metal thing under the rubber, as the cap body is already drilled.
Put the drilled bolt through the rubber, springy bit and cap, and tighted the nut up.
Put some silicone on the remaining threads of the bolt, and feed into the rubber tube. Put a hose clip on, and leave to set.
Put cap on car, pump away carefully up to 13psi, and listen for leaking noises / watch for dropping pressure. Might have to leave it some time, mine took a while to go down, even though the seals are clearly completely shot!

If the AST is attached it acts as a safety valve because it will lift and release at it\'s rated pressure. I\'ve caught a couple of faulty caps this way, because they lift before they\'re supposed to. You\'ll hear it gurgle when/if it does lift.
Do be careful though, I\'m sure the seals could be damaged if pushed much beyond 13psi

It\'s just a DIY version of the commercially available cooling system pressure testers really.

Hope that makes sense! Guess it seems like a lot of work, but I\'ve found it\'s a really useful tool, and it would drive me nuts to put a duff motor in after all the work. Let me know if you need anything clarifying, and good luck!

ianelvar · September 21, 2007, 03:07:49 PM

Pics attached:

leeroy_25 · September 21, 2007, 07:18:55 PM

Nice one..

I think I have that..

Not sure what the AST is? I am gonna guess it\'s the grey bottle that sits in the engine bay?
Also judging from your picture the water filler cap is o the engine? that would makes sense as to why I couldn\'t find it in the car!!! Think I might have a spare rad cap if it\'s a standard size.. May try and build a valve into the cap to rule out any leakage via the foot pump. but nifty tool!

Cheers
Lee

leeroy_25 · September 21, 2007, 08:45:24 PM

Ian,
Don\'t suppose you have any aftermarket stuff to sell in amongst your bits!?

performance, Handling, bodykit... etc..

I am always looking!

Cheers
Lee

Rixio · September 21, 2007, 10:43:39 PM

Iv got some go faster bits and bobs...drop me an email lightningdyn@msn.com

ianelvar · September 22, 2007, 12:13:01 AM

Yeah, the AST is the little box that has the second filler cap and generally has NEVER OPEN on the yellow sticker. Sits bolted to the back of the intercooler.
Glad you like the idea for the tool. If it saves you some work I could mail you my ready modified cap. It\'ll fit in a small padder bag easily, and doesn\'t weigh much.
I\'ve got Greddy hard pipes, HKS dump valve, and HKS filters and that\'s it. Could be persuaded to part with them I guess.

leeroy_25 · September 22, 2007, 10:55:43 AM

Ian let me now what you want for te go faster parts?! you have my e-mail right?
Leeroy_25@hotmail.com

I had an idea about your kit.. if the engine is out I guess I can pressure it up via one of the hoses instead of having to drill a cap out? what say you to that?

thanks again

Lee

ianelvar · September 22, 2007, 07:32:45 PM

Yeah, hadn\'t thought of that! :Hammer

Perfect

leeroy_25 · September 22, 2007, 07:56:07 PM

Only problem... finding something to block all the pipes with! need to get some bit bungs or link them together.. Didn\'t have time today in the end.. I Did a compression test that ddin\'t tell me much! was so irratic I couldn\'t say anything for sure.. One minute there was nothing.. then it would shoot up on one, then I would get all three.. then it would drop out again! Think I may have got oil or crap in the tester? lugs were nice and clean and lovely cream/brown colour. Best reading was around low 5\'s something on all I reckon.
I am thinking about just taking the chance?! It was running fine when it came out of the other car!
Lee