Weird Engine Noises After Road Trip

[Bob Butler]

OK, Just got back in town after taking the SC on a ~3K mile romp zig-zagging up and down the east coast. Upon return, just as I unloaded my friend's luggage and drove around the block to my house, I noticed the noise. It could have been there all along buried under the luggage, but I don't think so. It sounds kind of like a sewing machine sometimes and a chainsaw at others. Doesn't really sound like a knock or a tick or valve train or anything. I took it to my local wrench who replaced the starter (which died about 400miles into the trip) and the alternator which he thought was causing the noise, and we both verified the bearings in it were gone with a stethascope. As soon as I picked up the car my son pointed out that it sounded different, and once the engine got warmed up, it was clear that we still had a problem. One other thing, as the engine hunts at idle (buggy CIS) the sound will come and go. Once it gets warm, its always there. Its going back to the shop on Monday, but in the meantime I thought I'd fish for ideas. I don't really know what a bad chain tensioner sounds like (I do a lot more work on bugs than 911s) but I asked my mechanic about them and he said they were fine. I'll try to post a sound clip tomorrow, but in the meantime, anyone got any ideas?

--Bob

[burgermeister]

Complete shot in the dark:
Fan rubbing on housing due to cracked support ribs?

[Bob Butler]

I guess its possible, but you'd think he would have found that while swapping out the alternator. This guys does nothing but 911s, but we're all human. Where are these support ribs at?

[burgermeister]

The thing the alternator bolts to is like a rim with 4 ribs and the alternator bolt-up plate in the middle. Like I said, shot in the dark - I have no clue, but you asked for suggestions Should be easy to tell if the fan is rubbing around its perimeter or not, no need to check the ribs...

[vash]

is the belt tight/loose?

if the guy doesnt work on 911's then maybe he installed the belt incorrectly. is there evidence of the fan rubbing anywhere? should be obvious.

i would turn the motor over by hand. if the alt nuts in back are not tightened down evenly, the alt will sit skewed. strange how you did a roadtrip and the noise never came up. perplexing.

[kilodawg]

Just FYI when I had a chain tensioner fail the sound was like shaking a bunch of bolts in a can. Not something you would drive around with....

[Bob Butler]

The guy is a 911 guru. Lots of experience. I find it hard to believe that he installed it wrong, but anything's possible. I just don't get why it only shows up after the car warms up. I'll get audio in the morning. The wait until Monday is killing me.

[al lkosmal]

Bob,
Check and see if the fan housing has moved outward (towards the fan belt) and is making contact with the belt. Wild *ss guess, but i just fixed mine today after chasing a strange whirring noise. Loosened the strap, moved the housing assembly back .10" or so and it went away.

regards,

al

[SCWDP911]

What Bob is not telling on himself is the new hobby he started during this trip... Now let me see if I can find a clue here... hmmm.............. :smiley

[Bob Butler]

Yes, its true, there could be a slight amount of red clay up in there. We did a little off roading a couple of times during the trip.

[Bob Butler]

Update:
Drove the car to work this morning. Noise is still there, but seems to be much less prominent than before. I also noticed it most when letting off the gas. Almost sounds like its in the exhaust now. Bad Valve?

[Bob Butler]

As for the mud, imagine an SC in this photo and you get the idea.



The driveway into the old family farm is two miles long, all clay, and they had a lot of rain before we got there. You hit the wet spots fast and straight, or its a long walk back to somewhere you can get cell phone coverage to call for a tow. Pretty spectacular, but nothing that won't wash off. We also did some offroading on a few mountain trails in WV, but that's just because one of us on the trip trusted the GPS a little too much.



Less spectacular, but if we broke anything offroading, I'd guess that was when.

[burgermeister]

Damaged exhaust system or disintegrating exhaust gaskets?

[bell]

just to check......the alt housing needs to sit on a small tab to be lined up properly, if it doesn't seat properly the fan housing will move out and scrape on the crank pulley and make weird noises.

[Bob Butler]

I got under the hood at lunch and I think it is coming from the fan or shroud. Called my mechanic and he also suggested a messed up housing or possibly a small crack in the fan (though he looked for both when he was swapping the alt. and didn't see either) It could still something in the exhaust, but I'm leaning back the other way now. It goes back under the knife on Thursday.

Anyone got an old fan or shroud lying around? (930 style)

--Bob

[defcon65]

Try to isolate the sound by removing the fan belt and running the engine to see if it goes away. You can run the engine for a short while in your driveway without it overheating, but don't take it on the road.

[Bob Butler]

Good idea. I'll give it a shot. Need to get the car warmed up first though. It doesn't do it when its cold for some reason. (which I think is odd, but not inconceivable)

[defcon65]

It could be the magnesium housing or fan is thermally expanding to cause the rubbing problem. If that's the case, you may be able to grind down the ends of the fan blades to create more clearance.
BTW, my engine also makes funny fan/housing noises when warm and I've seen/heard others that do it too. And I went through the whole thing until I was SURE it would go away. It didn't. It could just be one of those weird Porsche things, like the clicking sound that comes from the dashboard occasionally.

[Bob Butler]

Thought about that. Any problems with fan balance, or should I just stick to filing the shroud out some?

[defcon65]

I would just file the ends of the blades, no need to worry too much about balance - the magnesium isn't that heavy, doesn't spin that fast and I've seen plenty of pics of fans missing part of a blade that spin just fine.