jeff spahn

In inspection of my engine with the heads off there are several very slight, as in feel with your finger nail, scores in one of the cylinders.


So, do I leave them be? Compression check out as pretty darn good when Greg Brown did the PPI 2 years ago.

Pistons are covered with carbon. Gonna brush that off with brass brush and sea foam then shop vac out. You can see it at the bottom that I scratched off with fingernail.

This is the cylinder bank that didn't have the blown head gasket but did have a gasket that was gonna blow.

Suggestions?

Mrmerlin

The cylinder will fine the way it is,
when you clean it out,
dont use aggressive chemicals on the pistons as they could damage the cylinders,
put in new HGs and run it.
to clean the head gasket surfaces use a fresh razor blade held perpendicular to the surface this will neatly scrape off the old materials without damage to the mating surfaces

jeff spahn

Thanks. MrMerlin. I appreciate the advice.
On a side note. Why do you think all the carbon?

Mrmerlin

probably a leaking injector or damper or FPR or a bad O2 sensor or MAF or combination of all of the above and not driving it like you stole it

Lizard928

Just to add to this.

The razor will not damage the surface of the block due to the high silicone content.

However I did have a cam tower gasket on a car that I just did that took HOURS to get off as it had to be scraped off in layers. It was like someone used superglue that permeated the gasket too..... bloody PITA!

jeff spahn

How do I check and see if the damper or FPR's are bad, just put a vac on them and see if it holds. Have them out of the car right now.

I am doing a new 02 sensor and the MAF was replaced in 2000 or so by Porsche. Nothing showed on the hammer last June when Sean hooked it up. Would that show on the MAF. Just put rebuilt injectors in.

Speedtoys

Jeff:

Id just replace them, as cheap as they are...if you dont know when they were last replaced.

Lizard928

Pull a vacuum on them. Say 25" Hg, if it holds it overnight, they are fine.

Maleficio

Bad regulators will leak fuel out of the vacuum port, but you'd have to have them installed and pressurized to see this.

jeff spahn

yeah, no fuel leaking out of port. I'll pull a vac on them and see what happens overnight.

jeff spahn

Apparently sometime in the past this engine ate something. That would explain the scoring and dings in the cylinder wall. The top of the piston is beat to hell also. Was hidden under all the carbon.

Goes to show you these are tough engines.

Mrmerlin

look carefully at the cylinder walls for cracks,

though with all the carbon if it was leaking coolant into the cylinder the piston would have been steam cleaned

GregBBRD

Yes, you can see the small dings around the top of the cylinder, from the foreign object. I'd pull that piston and look at it carefully....no, I'd find one that was the same size and the same weight and replace it. There are "standard" pistons for these engines sitting everywhere...why mess with it?

Podguy

Small scratches will not be a problem. But that piston looks like crap. It might not be for damage but from being fried. Over heating can do that. Be sure to check the deck.

Porsche makes over sized pistons that can be replaced individually. The bigger piston is engineered so you can bore out imperfections and not increase the displacement or compression ratio.

jeff spahn

Engine is still in the car. How big a deal is it now to pull the engine block and replace that piston? Just put the heads back on and lift out. Pistons are stamped with a number 1 on them. do I need to bore that out or just put in new piston and rings and call it good? I am assuming this 90 S4 has 100mm pistons.

If I am gonna do that, I might as well do the silicone pan gasket and stud kit.

Waiting for your reply