924Board.org

[bgammie1]

Recently had my head rebuilt, new guides, seals, reground existing valves and seats, etc...cam shaft has no flat lobes and timing belt is not overtightened.
I have checked and adjusted valve clearance according to hot and cold specs.
Ran the car for 1000 miles and the last adjustment I made was cold (.004 and .016") all were quite close to spec and I only adjusted 2 intakes that were up to .006.
I still have 1 or maybe 2 valves tapping.

How can I identify exactly which valve is making the noise?
Are exhaust or intake more prone to tap?
If specific valve is identified will reducing the clearance of the valve below spec by one turn of the screw (.002") a good or bad idea.
My Porsche mechanic said the cars are notorious for having some valve noise because of the inherent design.

Tapping is annoying to me and I've tried my best to make it go away.
Sure would like some help and advice.

btw it doesn't tap at while idling (~900 rpm) but it does for a few seconds 15 at most when it first starts up cold.
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BFG
1982 Porsche 924 NA

[fiat22turbo]

Use a screwdriver next to your ear and place it on the valve cover in different places and you should hear where the tapping is loudest.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[ideola]

The inherent design of the lifters means you will never get the tapping to go away completely, it's just the nature of the beast. The pronounced tapping you hear on startup is due to lack of oil pressure at initial startup, i.e. the entire engine is essentially unlubricated at that point (except for whatever residue remains on the surfaces since the last time the car was running). You could conceivably eliminate this by running a pre-luber for 10-15 seconds before startup, if you really wanted to go to that trouble. Synthetic oils theoretically minimize the damage of dry cranking.

What oil are you running? (brand and viscosity please)
Did you replace the cam oiler elbow?
Did you replace or clean the cam oiler tube?
Have you confirmed that the cam oiler tube is not clogged?
I know you have a good cam (presuming this is the one you bought from me), but what condition are the lifters?
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erstwhile owner of just about every 924 variant ever made

[bgammie1]

Using valvoline VR1 20W - 50
Using cam and buckets that I bought.
New elbow and cleaned out oil tube with carb cleaner to insure non of the tiny holes were stopped up.
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BFG
1982 Porsche 924 NA

[bgammie1]

Dan,
You raised another question for me.
The cam oil tube has several small holes in it, the ones towards the beginning of the tube are smaller than the ones on the end.
Should they all be the same size?
Tap noise seems be coming from 1 and/or 2 cylinder valves.
Would making the begginning holes larger, the same size as the rest of them help?
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BFG
1982 Porsche 924 NA

[Ian89C4]

I think if all of the holes were the same size, most of oil pressure in the tube would be gone by the time it reached the fourth cylinder and the cam would go dry at that end.

I would think the tube is designed to maintain pressure at the end of the tube.

Cheers,
Ian
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Ian Edgerly
North Carolina

Current:
1981 924 SCCA/ChampCar Weissach Race Car ("Serenity")
1987 924S ChampCar Endurance Car ("Der Weg")
1980 924 Euro ("Wahala")

[ideola]

NOOOOO! Do not tamper with the cam oiler tube! I presume the larger holes at the end are due to the fact that they are further from the inlet, and the larger size is required to deliver proper oiling to the rearward portion of the cam/lifter assembly. If you have flushed and pressurized the cam oiler tube and are getting good spray out of all of the orifices, leave it alone!

While I haven't heard your engine, I think you're overly concerned about the noise. The lifters are referred to as tappets for good reason
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erstwhile owner of just about every 924 variant ever made

[bgammie1]

OK, hole size and makes sense due to pressure drop across the tube.
But the question still remains.
I would expect the tap nosie to remain equal and constant from all of the tappets and not be more pronounced for one over another. I am trying to get them all to sound the same, is that possible?
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BFG
1982 Porsche 924 NA

[ideola]

You should be able to get it close, but it's not an exact science because the tappets, adjusting screws, valve tips, valve seats, etc. will all wear at slightly different rates. To put it another way, your adjuster screws are not all going to be at exactly the same position from one lifter to the next...in fact, that's the whole reason they're there is to account for variability from one valve assembly to the next.

What you should be attempting to do is get the valves as close as possible to the OEM specification clearances. From memory, I believe the hot specs are .20mm on intake and .45mm on exhaust (.10 / .40 respectively for cold lash). What you will find is that you will not be able to get *exactly* .20mm of clearance, for example, one turn of the adjusting screw may put you at .18 or .23 due to variances in the valve assembly. In this case, you should adjust for the largest clearance (i.e. in the example above, choose the .23mm clearance over the .18mm clearance). Looser clearances will result in a noisier engine, so it is inevitable that you will have some valves noisier than others just due to the variance across the valve train components.

As I've mentioned before, in my experience, once you have adjusted all of the valves, I strongly recommend rotating the cam by hand two complete revolutions, and then re-check the clearances. In my experience, you usually have a few valves that need to be re-adjusted. Keep doing this until you can complete two revolutions of the cam and measure all valves within spec. Then button everything up and stop worrying about it. Keep an eye on the oil, and double check clearances after about 1000 miles. Then check it again after 5000 miles.
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erstwhile owner of just about every 924 variant ever made

[bgammie1]

I was not doing the 2 revolution thing, I will try this and take your advise.
Thanks for the help.

"Keep doing this until you can complete two revolutions of the cam and measure all valves within spec. Then button everything up and stop worrying about it."
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BFG
1982 Porsche 924 NA

[emoore924]

Just an additional point, NEVER tighten the clearances on the exhaust valves beyond spec. Doing so will reduce the time the valve is in contact with the head thereby reducing the amount of cooling/heat transfer time the valve has while in contact with the head. This can lead to valve failure from overheating of the valve. It may be quieter --- but only for a little while. Then there will be a bang or perhaps several bangs and then you'll let all the smoke out of the engine and everyone knows engines won't run when you let all the smoke out.

Also, that oiler tube is an engineered marvel. Do NOT mess with the holes other than being sure they're all clear and delivering oil over the length of the cam. They're that way for a reason -- to properly distribute the oil. (Yes, check that the elbow isn't leaking either).

[bgammie1]

Is it possible to check oil tube and elbow without taking the valve cover off?
If the valve cover has to come off to check how / what do you do to keep oil from slinging all over the place?
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BFG
1982 Porsche 924 NA

[ideola]

You can minimize the mess by simply removing the oil filler cap and watching the cam oiler elbow with the engine running. You'll probably want a highly directional flashlight to help see what's going on. You have a new elbow in there, so I wouldn't be overly concerned about it.

As for the oiler tube itself, it should not be hard to find some means of rigging up a feed line and small clamp once it's been removed from the head and had the oiler elbow removed. You will then need a way to slightly pressurize the tube with a solvent or oil to see what's going on with the lubrication holes, maybe something as simple as a hand pump like the one I use to fill my transaxles.
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erstwhile owner of just about every 924 variant ever made

[fiat22turbo]

I used some good brake/carb cleaner with a pipe cleaner to clean out my oil tube. Then a small pick to gently check that the holes were cleaned.

Rinsed, repeated.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[Cedric]

Adding under bonnet insulation (if its rotten away) made my valve train alot less noisy Even with correct spec(valve settings, new elbow, cleaned tube etc) its a bit rough, but on the other hand I havent heard a quiet 924 engine yet, my n/a seems worse than the 931 though, dont know why.
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1980 924 Turbo
www.instagram.com/garagecedric/