Barry Johnson

Hey guys!
The new addition to the 'fleet' has been annoying me lately...
I have this noise that sounds like a heat shield rattling away at around 3-3500 rpms and is quiet before that and after that... Its coming from the middle of the head, and seems right where the VarioCam is. Sounds like the chain buzzing up against the valve cover, and scares the $#!* outta me!

Car has 40k on it (1992) and had been sitting in storage since 1996. No joke, I'll post a separate topic just on the car itself, so don't drool yet

I've replaced all fluids, belts, rollers, water pump, and flushed the (brown and varnished) gas, cleaned the injectors, and threw a little seafoam in the mobil1 to clean up the gunk (worked awesome, I think, ha!).

Car runs like a top, but this noise is scary...


Any thoughts? Sounds a super loose chain, but if it were really that loose I'd imagine I'd have a dead engine from broken cam teeth and total engine failure.
Maybe a frozen valve spring? Clogged up VarioCam piston? I'm pretty stumped...

I haven't disconnected the VC plug, but wouldn't it act the same just as it would if it were gummed up from junk anyway? ie. oil blockage to the piston?

Thanks guys!

Stephenwz968

Just to be sure, you did change the cam chain and pads, and checked all the teeth on the cams, right? If not, make sure to pull the valve cover and get a good look at those parts.

Steve

rob76turbo

There are several posting on this board that show the condition of both the pads and cam teeth to give you an idea of what to look for. There are also detailed DIY's on the procedure to pull the valve cover off. It is quite easy, but you should look into replacing both the valve cover gasket and the spark plug gaskets too.

RajDatta

1st off, congrats on a rare find!
You definitely need to remove the valve cover to inspect. You could be very close to catastrophic damage. I would not start the car if I was you. Its very easy to do. Chance are, either the grooves on the tensioner pads are too deep or one of the pads has actually broken.
I would not be surprised because the car was sitting for so long and when they started the car, something got caught up due to lack of lubrication.
Remove the vanity cover and the 15 or so hex head bolts to remove the valve cover. You should be able to turn the engine using a 24mm socket on the main crank to check for teeth damage.
Good luck and let us know if we can help in any way.
Raj

968rz

+1 on inspecting your cams and chain, also look at the heat shied by the header, mine cracked at a bolt near #1 cyl and would rattle at certain RPMs.

Barry Johnson

Ok, so I've got some pics for you pros to look at. I can't see any damage to the cams (the inside of the heads look great) nor anything wrong with the pads or the chain.

What i was curious about is the position of the piston that moves the top pad. Is that supposed to be lowered all the way with the car off and under a certain amount of revs? I also yanked on the heat shield by the exhaust and couldn't feel any give on it, so it at least seems tight.







Ideas? Thoughts on the pad position? If its not supposed to be pushed out like that, possible a clogged tensioner piston? If so, why would that cause the mini-chainsaw noise I hear?

PorscheDude1

Here is some good info including inspection and how it works.
Scroll down the threads, there are PDF's for download.

http://www.968forums.com/index.php?s...cam+inspection

http://www.968forums.com/index.php?s...cam+inspection

RajDatta

A little history on how variocam works.
Below 1500 rpm, VarioCam allowed only a small amount of valve overlap for a smooth idle and low emissions. Between 1,500 and 5,500 rpm it retarded timing to promote better cylinder filling for more torque. Above 5,500, timing was advanced for maximum power.

Here is an excellent read up on a site that does not require membership to read content.

http://porsche968uk.co.uk/technical_...-timing-01.htm

Unfortunately I can't view your pictures until I get home.

Good luck.
Raj

FRporscheman

The variocam activates at 1500rpm and deactivates at 5500... I don't see why it would make a noise at 3200. Try using a mechanic's stethoscope to be sure where the noise is coming from. Also, try disconnecting the variocam electrical plug and see if the noise still occurs.

good luck

EDIT seems Raj is a quicker draw than I.

968workaholic

Raj, you have the operation wrong. The cams are retarded at idle to around 1500, then ADVANCE until around 5000, when the vario cam deactivates and the timing is RETARDED to achieve top end power. Anyone will tell you reatarded cam timing will produce more top end power, while advancing the cam timing will give you better midrange power.

Barry, you cams look good as well as the pads. A stethoscope would be good for pinpointing the noise as mentioned above.

RajDatta

Maxwell, there is a lot of contradictory information on this, as you can see..

http://auto.howstuffworks.com/porsche-924-history13.htm
Quote, " Below 1500 rpm, VarioCam allowed only a small amount of valve overlap for a smooth idle and low emissions. Between 1,500 and 5,500 rpm it retarded timing to promote better cylinder filling for more torque. Above 5,500, timing was advanced for maximum power. With all this, the 3.0 muscled up to 236 horsepower at 6,200 rpm in U.S. trim and 225 pounds/feet of torque peaking at 4,100 -- the highest torque output in the world for a non-turbo engine of this size."

http://www.cannell.co.uk/968_Worksho...0Camshafts.pdf

Quote, "Below 1500 rpm, the DME unit (main control computer) energises the solenoid, moving the position of the hydraulic shuttle valve in the Variocam, thereby directing oil to lift the pistons. As the pistons lift, so the plastic pad on the rising top piston pushes upwards on the upper run of the chain,
causing it to extend. At the same time, the rising lower piston allows the lower chain run to be shortened. The overall effect is that the intake camshaft is rotated anticlockwise in relation to the exhaust camshaft, thereby retarding the intake timing back to its nominal setting. Above 1500 rpm, the DME de-energises the Variocam solenoid, causing the shuttle valve to move to a different position. Engine oil pressure is then redirected to lower the pistons, extending the lower chain run and shortening the upper chain run. This causes the intake camshaft to rotate clockwise in relation to the exhaust camshaft, advancing the intake timing by 15 degrees. Above 5500 rpm, the solenoid is again energized, and the intake cam is retarded back to its nominal position.
"

http://books.google.com/books?id=it1...esult#PPA60,M1

Not sure who is right and who is wrong.

Raj

968workaholic

Just comon knowledge from engine tuning and building is that advanced cam timing gives the engine a better midrange, while retarded cam timing gives an engine better top end.

FRporscheman

How stuff works is wrong. I'm no tuner, nor an expert on the VC system. But at 1500 rpm the intake cam phases clockwise, we can all agree on that, because at 1500 the tensioner moves down. If a cam moves further clockwise that is known as advancing (because the crank turns clockwise, and the cam is now ahead of the crank).

Barry Johnson

FIXED!!!!

My original hunch was right - stupid heat shield... There was a tiiiiiny part of the heat shield around the bottom of the header that sits right next to a drain plug (or similar) on the bottom of the head, and it would baaarely rub against it.

So, to fix it, I placed a large flathead on it, and whacked it with a hammer Done!



Thank you all for all your willing help and good ideas. I'm glad it wasn't anything valvetrain related!

FRporscheman