Author Topic: compression test results (Read 5012 times)

vegfuel · « **on:** March 16, 2008, 03:24:36 pm »

I posted an earlier thread called "Dying Rabbit, Please Help". Well this is the same Rabbit that I am going to try and sell unfortunately as I am in college and need to save money. This car ran last summer but still won't start up. It cranks over but it won't even fire. The timing is way off as I have screwed it all up learning how to to check it and adjust. Something is also wrong with the glow plug relay. I finally did a compression test on it and came up with these numbers respectively from No. 1 cylinder:

140,141,139,140

Fortunately these numbers are consistent. The trouble is I don't know my engine code so I don't know if these numbers are low for an n/a Rabbit. After looking at the table they seem to be fine.

Also I tried to turn the engine over by hand to get it to TDC and it stops and won't go any further no matter how hard I press.

I honestly don't know what's wrong with it. It's turned into a mechanics special. I just wanted to know if anyone here could tell me what I've mentioned might mean as I am down to my last try (costing me money).

I have everything for an engine rebuild and I wanted to do it but I don't have the time.

Vincent Waldon · « **Reply #1 on:** March 16, 2008, 03:36:47 pm »

Regardless of your engine code those numbers are way way way low... the spec is a minimum of 412 psi with no more than 73psi difference between cylinders for all IDI engines.

Now, if your valve timing is really out it could cause low compression... but it's not clear from your post: you can use the starter to turn it over (enough to test compression) but you can't turn it over by hand ??

If you really can't turn it over by hand STOP !!!! Trying to turn it over with the starter in that case is asking for broken bits.

My suggestion would be to make sure the valve timing is bang on... and that it turns over by hand. Then do the compression test.

Or perhaps I'm not understanding the sequence described in your post ??

Vince

vegfuel · « **Reply #2 on:** March 16, 2008, 07:57:56 pm »

I just tested the cylinders normally by cranking the engine over.

When I said "by hand" I meant that when I go to turn it to TDC to check the IP timing it will turn for just a little bit then stop and won't budge.

It cranks over with the starter just fine.

What's the difference between the IP timing and valve timing?

Is valve timing just making sure the No. 1 cam lobes are both up and the flywheel mark on?

Vincent Waldon · « **Reply #3 on:** March 16, 2008, 08:32:47 pm »

Quote from: "vegfuel"

What's the difference between the IP timing and valve timing?

Is valve timing just making sure the No. 1 cam lobes are both up and the flywheel mark on?

You got it... IP timing is about when the fuel is injected, valve timing is about when the valves open and close and is set by locking the cam at TDC with a locking plate while ensuring the engine is also at TDC (mark on the flywheel). If not, you loosen the cam sprocket nut and adjust as required.

If the valve timing is off significantly compression can be impacted and the engine run like crap if at all. As well, if it is off significantly valves will hit pistons.

Might be worth a check before tearing down the motor... the fact that you can't turn it over by hand sounds like valve timing as well.... unfortunately the "valves will hit pistons" part. Hopefully not the issue...

rallydiesel · « **Reply #4 on:** March 16, 2008, 08:47:29 pm »

You should check all the cylinders. I doubt it could run if all cylinders were that low. You should be able to turn the motor by hand if it will turn over using the starter. Is there anything locking it (IP pin, in gear, cam pulley loose on camshaft, anything seized)?

You may want to try priming the IP by sticking a vacuum pump of some kind to the return fuel line that goes into the fuel filter (or just to the IP if you don't have the 4 spout fuel filter). Pump it until you can see diesel being pulled from the IP return fitting.

rabbitman · « **Reply #5 on:** March 19, 2008, 01:23:48 am »

strange that you can't turn it over by hand.....maybe a valve is bumpin' a piston?

PS. with that compression there's no way it'll start. :roll:

vegfuel · « **Reply #6 on:** March 20, 2008, 10:51:47 am »

thanks everyone but I'm selling her. Good new is I've already had three guys that were interested. One guy wants to rebuild the engine and put it into a 71' bus!