Another engine issue

[BernardoEsteves]

Hi everyone,

I have a Porsche 911 with a freshly built 2.7 engine.

Specs:

2.7L engine, 9.8:1 compression ratio

2.4S original cams

Ø90mm Mahle pistons

Intake valve: Ø47mm

Exhaust valve: Ø40mm

Intake port: Ø37mm

Exhaust port: Ø35mm

Intake valve lift: 10.5mm

MFI system (no solenoid/cold start)

Cold iridium spark plugs

Fully rebuilt from scratch — 0 hours on it

The engine started fine for the first time. Oil pressure isn’t perfect, but I’m getting around 1.5 bar at idle and 5.5 bar under load when warm, which seems acceptable.I think it's importante to mention that the engine was rebuilt in 2019, and was sitted in a dry place for 6 years until now

Now the issue:
When accelerating (around 2000 rpm and above), I can hear a tickling noise coming from the left bank. There’s also a bit of bluish smoke from that side, but not too much.

I checked:

Compression: all six cylinders are OK
Valve clearances (left side only intake): 0.1 mm
Spark plugs: all dry except cylinder #3, which shows a bit of oil
Also check with camera and cylinder looked OK as far as I could see

Any ideas what could be causing this? What would you check next?

Thanks in advance for any insight!

[BernardoEsteves]

Anyone can support me?
Any idea?

[dannobee]

Post a video with the noise.

[917_Langheck]

Possibly the valve is sticking slightly open on that cylinder, creating the clicking, but eventually closes by the time of inspection.

[Henry Schmidt]

You may be dealing with a valve to piston clearance issue.
The Mahle valve pockets are designed with a pretty close perimeter tolerance. The stock intake valve is 46 mm mm and you state that your intake valve is 47mm. I may be experiencing a slight interference on just one or two valves.

2.4S original cams

Ø90mm Mahle pistons

Intake valve: Ø47mm

Exhaust valve: Ø40mm

[BernardoEsteves]

I did insert a boroscope and no damage is seen from inside the chamber

Videos for sound and reference

https://youtu.be/Kpym3LuPdZg?si=xHQQHLHfKI8yg2Cy

https://youtu.be/iCW2t6KjsfE?si=zrvkGVuOCsAoC8UQ

[PeteKz]

Sounds to me like valve noise from a loose valve or two, so recheck the valve clearances and be sure to make the adjustment at TDC on each cylinder. Yes, there is a procedure for adjusting multiple valves at certain points, but do it by the TDC method to be sure.

Next, it also sounds like it could be loose or blown exhaust gaskets. Check those.

While you have the valve covers off, check for broken head studs.

[BernardoEsteves]

I will check those, but the #3 cylinder spark plug oily (not much) has nothing to do with valve clearance I believe. Blown exhaust gasket can lead to this?

[stownsen914]

You mention compression good. You did a compression test? Did you did a leakdown test? Oily sparkplug could suggest some blowby. Could be unrelated to the oil pressure and valve train noise issues.

[BernardoEsteves]

Did a compression test, and when cold around 12bar every cylinder.. Believe its satisfatory
Tried to blow air inside the #3, but don't have proper tools to do it. Couldn't ear air leaving from oil tank (don't know if there is any other way to do it)

[r lane]

Originally Posted by Henry Schmidt

You may be dealing with a valve to piston clearance issue.
The Mahle valve pockets are designed with a pretty close perimeter tolerance. The stock intake valve is 46 mm mm and you state that your intake valve is 47mm. I may be experiencing a slight interference on just one or two valves.

Years ago a rebuilt engine with a substantial clicking noise. We had combined diff pistons, heads etc. Pulled it down and saw nothing, at least at first. We were looking for something glaring due to the noise. What we finally discovered was barely a fingernail shaped crescent shadow on the exhaust valve pocket shoulder. Doesn't take much to make a racket. Bob

[Henry Schmidt]

Originally Posted by r lane

Years ago a rebuilt engine with a substantial clicking noise. We had combined diff pistons, heads etc. Pulled it down and saw nothing, at least at first. We were looking for something glaring due to the noise. What we finally discovered was barely a fingernail shaped crescent shadow on the exhaust valve pocket shoulder. Doesn't take much to make a racket. Bob

Much like the faint trace you can see when a valve diameter is too tight in the valve pocket. Generally, there is only a .040 clearance between the valve and pocket. With a 47 mm valve (as stated) in a piston designed for a 46mm valve the clearance may be too small.

[PeteKz]

If the valve is interfering with the valve pocket you may be able to feel it by checking valve clearance at overlap. Set each cylinder at overlap TDC, then gently screw in the valve adjusters until they bottom or scrape. Count the turns, each turn = 1mm. If you feel something like scraping or increased resistance, that's probably what's happening. If you don't feel anything odd, and the adjuster screws in freely 1mm or more, then it's unlikely that the valve is touching the piston.

Do this before removing the heads and post your findings.