Shooting Ducks

ededoad@hotmail · 05-18-2011, 07:44 PM

Reinstalled my 2.7 CIS after a bit of freshening up and it seems to be running on the left bank only. It backfires continuously at lower rpm but the new pop off valve seems to work quite nicely.

The spark plugs were wet on the right hand bank with some soot as if they were firing at times. The left hand plugs look normal.

I rechecked cam timing and found the left hand cam was out of limits by .001 (.015). The right hand cam was at .020. Reset the LH cam to .020.

I did not have shielded ignition wires, could this cause the problem?

The distributer cap was not the Bosh but the other one our benefactor sells. It never seemed to fit right but it ran the same when I put the old cap back on.

Changed from points to Petronix and back to points and back to petronex no change.

If the CIS pistons are installed wrong on the right side could this cause it not to fire on that side? This is about the only thing that I can not easily check.

I do not want to reinstall if I can't find some reason why it will not run on both banks.

Any theory?

Flat6pac · 05-19-2011, 04:18 AM

Easiest check is turn the distributor 180 degrees. If the engine runs on the other side, youre cam is 180 out of sinc. You missed the cam set instructions.
The CIS pocket in the piston always is on the side of the sparkplug, the right.
Bruce

ededoad@hotmail · 05-19-2011, 06:38 AM

The rocker arms all follow the firing order so I don't think the cams are 180 out. Trying to find a way to check piston orientation without complete dis assembly.

ededoad@hotmail · 05-19-2011, 07:42 AM

I put a 3/8 extension down the hole on #2 at TDC and then down #5 at TDC, counting the ticks by the firing order. I measured the distance using a screwdriver on the flat of the spark plug hole compared to the extension resting on the piston and the distance is the same so I assume the low part of the piston is in the same orientation. I use a 3/8 extension so it would be parallel with the sides of the spark plug hole. If the piston was low part to the right on the 456 bank then it should be about 1/2 inch different.
I think. I will continue to check until satisfaction then move on.

ededoad@hotmail · 05-19-2011, 08:44 AM

O>K> I think I lied. The pistons may be backwards on the 123 side. I'm going to the store room for my engine stand and cherry picker.

Flat6pac · 05-19-2011, 09:59 AM

Before I would pull the engine I would flip the distributor because you exhaust valve woud hit the high side of the piston. The highside of the piston is to the top and the intake stroke the valve follows the piston. The exhaust is open when the piston comes up so they would hit.
Bruce

ededoad@hotmail · 05-19-2011, 03:31 PM

The engine was already pulled. The 123 bank pistons were all back wards. Pistons still look good will look at the valves tomorrow. I'm thinking it was popping so bad that the right side could not get enough air . May be a dumb theory. Lots of time to play with it waiting for gaskets.

hcoles · 05-20-2011, 05:51 AM

as mentioned, check for one of the cams being 180 out, it happened to me

Walt Fricke · 05-20-2011, 08:03 PM

For what it is worth, I blame my engine stand for putting in the pistons on one bank upside down. I was working from one side, got one done, flipped the engine, started on the other, like a robot.

Luckily for me, though, this was a race motor which depended on big valve pockets for the intake valves to clear. As soon as I started timing the misassembled side I knew what I had done. At least it was still on the stand, no oil, etc. Not a big deal.

ededoad@hotmail · 05-21-2011, 08:56 AM

I will attribute my mistake as brain fade. I am at that age where that can be used as an excuse. I have seen a lot about the valves hitting the pistons when they are installed back wards but I have had no piston to valve contact. Perhaps some of the CIS pistons have more of a top to bottom orientation. Mine seem to be mostly left to right. Anyway I got away without any damage.

ededoad@hotmail · 06-16-2011, 11:51 AM

Got this thing back together and no continuous backfire. Seems to idle like my old corvette. Is it supposed to? Any sound bite of a 76 911S at idle? Seems to have power and smooths out at 2000 rpm. Maybe I just need to run it longer or fuel injector cleaner?

Walt Fricke · 06-16-2011, 04:04 PM

Welcome to the world of CIS. A stock CIS motor should purr like a kitten at idle. Various things can cause it not to do this, with air leaks being one of many common possible causes. Jim Williams has a website with a copy of the Bosch/Porsche CIS handbook, complete with diagnostic tree on it. All you could possibly want to know about CIS is probably on that site.

You need to do a search for something like CIS Idle Problem to find more information than you can absorb right here already on Pelican. Best not to do it via this discussion about the goofs we sometimes make, and their fixes. The CIS is its own separate subject.

But you will eventually find what is leaking or out of spec or not working, and cure it.

ededoad@hotmail · 06-17-2011, 07:52 PM

I found a dead plug, replaced and it idles fairly smooth with a little "pong" every once in a while. Seems the web site you mention is no longer there.
Thanks though, Ed

ededoad@hotmail · 06-30-2011, 06:21 PM

The little pong turned out to be another bad plug. The engine now runs smooth, no leaks and no pops.