I took the 928 plunge. Always liked these the cars. Got to know and love p-cars after restoring a 71 911. So here is my story. Bought a local 1988 S4 928 that someone was going to part out but decided it could be restored so he sold it whole. The car is in decent shape, but I don’t know much about the history. It sat for about 10 years in a barn. Title was good and miles were in line with title history. So the 108,000 on the odometer is about right.

When I bought the car, it would start no problem, drove it on the trailer, and off the trailer into the garage. Given the time it sat, my initial idea was to replace the timing belt and tensors pronto. Good thing too, belt was slack. Lined the timing marks up and all looks good there, so no slippage.

Here is my issue now that you know my story. When the car was running, the driver’s side had a distinct rattle under the value cover. Easy diagnosis, loose cam chain. The sound was pretty distinct. A clear rattle, not a tick. I searched this board, and learned a good bit. I have an oil pressure issue at that tensioner, a worn guide, a worn out chain, or a broken cam.

I have the valve cover off, now that was fun. Every thing looks good in there. I have not inspected the cam plugs for warping, but they are all in place.
For those of you who have been here before, how should I proceed? I plan on measuring the chain length, I found out how to do that. The pads look good with little ware, so I believe I have an oil pressure issue. Unfortunately I don’t have the key piece of info, and I do not know if the rattle goes away at higher idles. Wanted to get the belt done first.

 

I'd be tempted to pull the intake manifolds and inspect/magnet/vaccum each hole. Just in case there is foreign matter in the path of the valves. A nut, washer, acorn, something. You will be able to see inside if you do that.

The starter will rattle on them too, BTW. Lay underneath and hit it with the heal of your hand and you'll see what I mean. Maybe not a valve train noise? I've noticed that noises antenuate on these cars and sometimes point me in the wrong direction.

 

i am in the process of pulling the intake. will check for crapola...

 

Isn't the cam chain tensioner hydraulic?
Is that tensioner working right? Getting good oil pressure to the tensioner?
Sitting for 10 years may not have done the tensioner much good.

 

Most of these cars are using original cam chains. At 108K miles I'm not inclined to think yours are so loose as to warrant replacement. With the proper weight oil, while cold, your oil pressure should be around 5bar. That's about 70-75PSI. You shouldn't have an oil pressure issue at the tensioner either. Anything small enough to get into the oil passage and cause a problem for the tensioner is going to get forced through by the pressure of the oil.

The real question is why did someone park a 12 year old car in a barn and leave it there for ten years? If the car has a mechanical issue that is causing this noise, I would bet that's the reason it was parked.

How long did you run the car? How old is the oil? What weight is the oil?

At the same time, you have to keep in mind that this car sat for 10 years. Ten years is a long time. Noisy lifters aren't uncommon on a lot of engines. You drive a 911, you should know that.

My first suggestion is to change the timing belt and water pump. Step into the 21st century with Porken's timing belt tensioner setup. I would not put any faith in a timing belt that is a minimum of 10 years old and has been stationary for most of those 10 years. In addition to the belt deteriorating, the rollers, pulleys can seize as well depending on their age. The factory belt tensioner is probably bone dry at this point.

Change the coolant. Make sure you pull the drain plugs on the block as well. Change the engine oil. In SC use 15w-50 and new Porsche oil filter.

Is the car an auto? If so, get under it and check the flexplate tension.

Remove the belt to the smog pump. Smog pumps make a lot of peculiar noises when they go bad.

Stop tearing apart the intake. Chances are, it's never been off the car and I doubt something is loose inside. Randomly tearing things apart is a sure fire way to find yourself overwhelmed and discouraged.

 

The cam chains out of both of mine were perfect, my 87 with 135+ miles on it had zero wear on the link pins, they were tighter than the OEM chain I got to replace them.

Unless a guide has gone or there is another problem, I doubt the chain is going to have worn to the amount you can even measure.

 

While you're in there, get the cam lobe on the heel and check for some play on the lifter underneath. This is almost certainly a lack of oil in the lifters. I would be tempted to run a quart of tranny fluid in the oil for a few hours of running to get them cleaned out and filled well. There is a pressure relief valve near the front of the engine, under the exhaust cam. Taking the exhaust cam off is a mucho hassle due to the stupid triple square bolts used, but it would be of some value to get the ex cam off and pull that relief valve and have it cleaned. If it's stuck open, the lifters on that bank will have a very hard time filling.

Do the belt and WP and prolly change the tensioner as has been mentioned.

And of course, you are required to post pics right away.

 

Its not unheard of for a tooth (or teeth in kiborts case) to break off the cam sprocket, although it is very rare - have you turned the engine and checked for teeth all the way around the cams?

 

To be pedantic it's only a pressure relief valve by accident when the O ring that seals the top starts leaking. When all is in good nick it's a non return valve. However it could still be the cause of the problem.

If the O ring is leaking it will reduce pressure to the oil galleries in the head. which could potentially cause the chain tensioner not to expand far enough. I'ld also expect lifter noise on start up if this is the case - could be masked by rattly chain.

The valve can be removed without removing anything else but the cam covers.

I also wouldn't discount the noise just being a lot of stuck lifters - after a prolonged stand it could take a good hour or so of running to get them all unstuck.

 

Check, as opposed to relief valve. Which will make it nearly impossible for the lifters to fill if it is stuck open. My bad.

 

Nearly - the non return part stops oil leaking from the head galleries back down into the block galleries when the engine isn't running. It's just a spring, ball and seat. Dirt/debris could stop the ball seating properly.

The bit that can leak and reduce pressure to the head galleries is the O ring around the "spring guide" that seals the hole in the head that the ball and spring is mounted in. The spring guide is just a cylindical plug held in place with a set screw through the side of the head. When the O ring dies of old age the oil that should have gone into the head galleries just goes straight into the space under the cam covers (wot I would call the cam box)

Porsche did develop a combined check and pressure relief valve for the racing 944s to prevent too much oil/ pressure going to the lifters at high revs - This can be retrofitted to the 928 heads.

 

since you have the cam cover off i would remove the anti back flow valve the exhaust cam may have to be removed to get to this part, it is held into the head with a 3mm allen screw that is inserted from the outside of the head, once you have the top portion out there is a spring that holds a ball bearing into the lower section inspect the spring for a normal look IE not burned or otherwise deformed, replace the O ring on the plug portion then with a small hook tool see if the lower ball seat is loose its shouldnt be, if it is try to remove it then use some green loctite and reglue it into the head then stake it in a few places to hold it there.
This lower seat can come loose and then oil will push it upwards and then it will cut off the oilflow to the head and quickly seize the cams.
Also take the tensioner apart and clean it out.
and replace the cam bore block off plugs with the new metal rod pins .
replace the cam end plugs and

Use loctite 574 sealant on both of the cam end caps so oil wont leak out (You fit the rubber cam/head) end caps while the cam caps are loose, then a dab of Honda bond on the cap to head area so the rubber gasket wont leak (4 spots per head)
Let us know what you find.

 

Since you have the cam cover off, what is the condition of the chain and tensioner? You say everything "looks good". I saw one 87 where the tensioner piston (top on the passenger or 1-4 side) had locked up and no longer adjusted to keep the chain tensioned properly. You should be able to compress that piston down and it should spring back even without oil in it as it is spring-loaded too.

 

I can compress the cam tensioner, but not sure how springgie it needs to be. i will check when I go by the shop this afternoon, and compare to the other side. I will take pics as well, but they will be from the ipone so mediocre quality at best.

And I don;t get frustrated, I want to give the engine top end a good exam. Since I don't know the history, I can see a few issues, and I will seek advice later on those. Someone local suggested a leak down test, and I think that will be a good idea, and I want to visually inspect the intake valves anyway to make sure nothing is bent.

the PK tensioner is a great idea and I plan to order one.