FRporscheman

The machine shop that did my head work decided to "do me a favor" and paint the head silver. For this and other reasons I won't use that shop again. So the car ('84 944) is now running but poorly. It will rev all the way from idle to redline, and it drives ok and revs consistently and smoothly, but it feels weak. It revs slowly. While revving (or just idling) it sounds like it has a minor and constant miss or something.

My first thought was actually a bad spark, so I started by checking the wires, and one of them was bad (20k ohms) so I got new wires and it got slightly better.

Next, I realized that the paint may be making the spark plugs' grounding to the head very poor.

So my questions are:
Would paint cause problems in spark plugs' grounds?
How can I clean the paint off without anything falling into the cylinder?

If I do have to clean off this paint (which I'm pretty sure is indeed the problem) I take it I have to clean the threads as well as the surface where the washer sits.

3rd question: How can I measure or check the strength of spark?

FRporscheman

I just remembered another detail - the oil pressure gauge will go nuts sometimes. It seems to happen most when I'm at partial throttle at cruising rpm. The gauge will just bounce between 0 and 5 really fast, making a fast clicking sound from the needle hitting the peg. I assumed it was electrical, from the spark plug arc or something.

Funn944

Painting the head silver should'nt cause that problem, after all the head is made of metal to start with.

944Ross

The spark plug hole threads should conduct plenty of current, I assume they didn't go to extraordinary lengths to paint them?

Could the oil gauge issues be a ground issue? or a loose connection.

FRporscheman

I will check the connections at the oil pressure sender. Which grounds should I check? I already checked the battery ground and the main engine ground, both clean and tight.

I don't know how much paint got into the threads of the spark plug holes. I'm hoping not a lot? FWIW, the machinist also painted the underside of the head, all inside the combustion chambers. Oh yeah, I just remembered looking at the spark plug holes from underneath and there was some paint in there. Not sure how good the electrical contact is.

Lemming

Arash, what other work did you do while the head was off? Is it possible that your timing belt is off a tooth?

944Ross

Really?? They painted the machined head surface?? So there is paint in oil passages, coolant passages, etc. not to mention the combustion chambers?? What were they thinking???

Did they paint it Ford Blue or Chevy Orange?!

Funn944

Ahhh, paint in the combustion chambers ?? That might cause a problem...fouled plugs after initial firing it up ?

V2Rocket

Sorry to say it, but if there was a chance of paint in the combustion chamber, I would pull the head off ASAP.

pettybird

if there was paint in the combustion chamber it's LOOOOONG gone.

I agree it's something else.

V2Rocket

Not just from the fact of possible paint, but the stupidity of a shop that would do that likely ****ed up something else in the head also.

s14kev

Are you sure they painted the underside of the head also? Surely no one could be that retarded. Head gasket would do an awesome job sealing against paint.....

PorscheDoc

I'm going with a bad ground cable on the block/bellhousing. A loose cable will cause the oil pressure gauge to freak out randomly. I don't see getting paint completely in the threads of the spark plug holes enough to keep it from making any "ground" I think your problem lies elsewhere.

PorscheDoc

I agree, I can't believe they would have done this. I also can't believe anyone would put the head on without cleaning that off first if they did.

JohnKoaWood

Something about birds of a feather... awe crap I cant remember the rest...

IMHO there is little more beutiful than the motor the way it was intended... I have seen TONS of powdercoated / painted engines... but always seem to gravitate to the raw ones...

That having been said, I DO have parts at a coater, but not core engine parts...