valve problem?, cylinder 1 not firing Options

[wihlenfeldt]

I have a 2.0 liter Porsche 912e. I discovered a broken intake rocker on cylinder number 1. I have replaced it, set valves, and it worked great--for a while, then started acting up again. I have spark to the cylinder, but notice no difference when removing wire as I do with the others. I did notice unburned gas on the ground below the car under that cylinder. I have reset the valves, tapped the valve stem, and the car works great --for a while. the car did sit for 6 months with ethanol fuel in it (with stabilizer) prior to this. I have since found non-ethanol gas and have also run Marvel Mystery in the gas and oil but to no avail. Suggestions have been a sticking valve, dropped seat, etc. I have checked the pushrod and it is not bent, and the valve train seems to operate properly when viewed with the valve cover off.

I want to make sure that this requires removing the head before I proceed as that will require dropping the engine and is probably beyond my expertise.

any suggestions?

[ChrisFoley]

The next step is to see if the #1 injector is spraying fuel.

[r_towle]

If you are seeing a wet plug, and fuel below that cylinder, you may want to remove both rocker arms on the cylinder in question and then run a compression test or leak down test to see if the valves are really seating.
This can be done without removing the heads.
Its a diagnostic test to see if the cylinder holds the correct amount of air when the valves are closed...or supposedly closed.

a broken rocker arm would lead me to look at why a rocker arm got broken in the first place.
Its a fairly robust part that would not break unless it experienced some stopping force at the wrong moment in time.

A compression test and a leak down test will tell you what is going on.
If you dont have the tools, a hose hooked up to an air source, compressor or hand pump, insterted into the spark plug hole to fill the cylinder to 100PSI
then listen with a hose to your ear at the intake, exhaust and oil filler.
You need to find out where the air is going...that will let you know where the issue may be.

Intake noise...intake valve
Exhause noise, exhaust valve
Oil filler noise, piston ring issue, or piston issue.

If you get no compression due to a holed piston or dropped seat, you may never get that cylinder to fire due to the lack of compression.

Rich

[porschefile2010]

Do the easy checks first. Like Chris said, check that the injector is spraying. It could be something as simple as the flexible fuel line from the rail collapsing and kinking and stopping fuel getting to the injector??

[stugray]

a broken rocker arm would lead me to look at why a rocker arm got broken in the first place.

This very thing happened to my brother in vintage racing (triumph TR4). He was taking me out for a "lunch time track worker's ride" and the car felt like it detonated.
We limped back into the paddock and found a rocker arm hold down bolt had snapped.
We fixed the problem and he continued racing that weekend (this happened years ago), but just this last weekend, I started wondering what had happened since I am about to put my engine together.

Was it abuse by the engine running (too tight gaps) or abuse (over-torquing, etc)?
Those components are not supposed to be the first to fail even in race applications, so I wonder what really happened.
I would expect a valve stem to break before a rocker shaft hold down bolt....

Stu

[Jon H.]

I had the same problems last month with my Westfalia and it ended up being a burnt exhaust valve which lead to zero compression. I diagnosed it as suggested above with an airhose using a compression tester hose with the spark plug end so I could screw it into the spark plug hole. It cost me $165 at the local machine shop to replace the valve and check all the valve guides to see if they were within spec. Pulling and replacing the head wasn't too difficult.

Jon

[luskesq]

You may want to double check that you didn't reverse an ignition wire. It would still run and you'd still get spark but not at the correct time.

Keith

[CG-914]

you can get compression test tools as rental tools in the local parts stores for free with a deposit of course...

But what rich said is where you need to start when you already have a gas puddle!
That is already dangerous for the well being of your baby ah car I mean....

[brant]

compression, leakdown first...

but why did it have a broken rocker in the first place.
I would guess you have a significant issue
compression and leakdown is the starting place

[wihlenfeldt]

Thanks for all the help. Sounds like I have my work cut out for me. The small puddle of gasoline beneath the car only happened once and was about the size of a quarter.
I will report back, and thanks again for the help.
Bill