Giantman

After a jolly old pootle in the 83SC this afternoon I noticed when pulling into the garage a new rattle from the engine bay. Investigation revealed it is coming from the left side of engine around the alternator area (see photo).

Rather than try to describe the rattle I have posted a digital recording here ( size is 628k):

http://tinyurl.com/bhdy9

Of course I am worried about imminent tensioner failure but I have also read that failing alternator bearings can make a rattle type of noise.

If you have a minute to listen I would very much appreciate hearing your opinions of the .mp3 sample?

Thanks

PS The tensioners are original, ie NOT oil fed Carrera types.

divezic

I hate new sounds. Very difficult to localize with the bare ear. It might be coming from somewhere else altogether and the acoustics make it sound like it's coming from the alternator. I use a mechanic's stethoscope...it's like a doctor's but it terminates as a simple open metal tube. This should help determine specifically where the sound originates.

Peter Zimmermann

Simon: See what happens when you have full throttle! If you dare start the car, do it after you remove the smog pump belt. Find a long screwdriver with a skinny shaft, place its flat-bladed tip against the chain box cover and press your ear against its handle. Move it around a little, up and down/left and right, to pinpoint the noise. It's most likely a tensioner, which means that you have an upgrade and cam o-ring replacement in your near future. Do not drive the car again until you've determined the source of the noise!
Pete

Giantman

On Pete's advice (Thanks Pete) I disconnected the Air Pump belt to gain better access to the tensioner housing. Started her up and guess what? No more rattle! Ah ha!

Spinning the air pump by hand revealed a nasty grinding sound eminating from the housing so I pulled it out and stripped it down (***** of a job getting those housing bolts out BTW).

Inspection revealed that one of the fan 'guides' (see photo) for lack of a better word, has broken in two and the pieces were floating around inside the pump housing causing the rattling sound.

So, questions:

a) What exactly does the air pump do?

b) Can I drive without it and how is performance affected?

c) If so what do I do with the open hose?

d) If not, can it be rebuilt because the price is just nuts!!!

Many thanks for your interest and advice!

Simon.

DGaunt

WEll, that would seem to be the culprit, alright!

The air pump delivers air to the exhaust port in the head via metal lines. providing 'new' oxygen to burn excess hydrocarbons in the exhaust. It is strictly a pollution thing. You can remove it and get plugs for the heads from many sources. A cheaper plug is a 1/8 pip plug witch fits 'sorta' but not quite. If you go that route (and I have in the past) use brass to prevent damage to the head threads.

If you want/need to replace the pump, I have one from my 1976 911s that I would let go reasonably.

Giantman

Thanks Dave. There is no smog testing in my neck of woods so I think I will just plug the heads. Do Pelican sell the appropriate item and if so by what name do they go by?

Cheers,

Simon.

DGaunt

I'm sure pelican does, but don;t know the right name. They are a custom fastener and look worth the somewhat outrageous cost (about $US 26.00 IIRC)

I knoew PH has them and they are consistently cheaper than Pelican in my experience, but I am sure if you call Pelican and tell them you need plugs for the air injection ports in your 2.7, they will know.

Giantman

Ok thanks again Dave I will check it out!

Simon.

Peter Zimmermann

Simon: Glad it was an easy solution - like the gas pedal "play!" Those air pumps are a pain, and rebuilt units aren't very reliable! Make sure that you keep all the parts that you remove!
Pete

Giantman

Thanks Pete, very much appreciate your help and input on this forum. I have kept all the parts together should any future owner want it reverted for concours events. Sure leaves a large hole there in the engine bay, but less weight and less drag on the engine, however minor, is a good thing I guess.

Question: I have temporarily bloked the air pump hose with a piece of broom handle until such time as I remove all the hoses and block up the air injection ports properly. Will this 'fix' be ok for a while in your opinion?

Also what is the part circled in the picture below and should I remove that too? (I know, I really need to buy Bentley's!).

Cheers,

Simon.

theiceman

there is an air pump on ebay if you are interested... just saw it

Peter Zimmermann

Simon: Circled part is a diverter valve - part of the air pump system. The only negative to leaving the system plugged, but intact, is that the exhaust port injectors will plug up with carbon over an unknown period of time. That's why it's important to get those injectors out and plug the holes - you don't want to have a carbon mound build up in those ports. I can't remember the correct thread size in the exhaust port holes, but I'll try to find out for you later today.
Pete

Peter Zimmermann

Simon: Plugs needed are 10mm x 1.0 thread. Yes, you can use pipe plugs, but they will bugger the threads in the exhaust ports.
Pete

Giantman

Cheers Pete, many thanks for checking that out for me.

On his 911SC site (http://www.adelgigs.com/911engrebuild.shtml) this guy (another Simon) used and I quote:

"I dispensed with the factory air pump and injection system, and plugged the injector holes in the heads with a Mercedes Benz "Torque Converter Sump Plug". This is an Allen keyed plug that fits perfectly."

What do you think of this idea? Any reason not to do the same?

Simon.

Peter Zimmermann

No reason not to. I never knew the origin of the plugs we used a few times at the shop, maybe this is them. When you remove your port air injectors you will find that each has a very thin, almost fragile, copper seal washer on it. We special ordered those washers from Porsche, and they fit the replacement plugs perfectly. The plugs that I used were either a 4mm or 5mm allen drive, and they had a thin head that held the seal washer in place. It's been many years since I've installed one, but I remember the length of the plugs being about 12 or 13 mm.
Pete