Rattle under load over 4k rpm

BarryJB · 10-28-2011, 11:40 PM

My guru wrench just fixed a bunch of leaks, replaced distributor with low-mileage used unit, we changed from Mobil 1 15W-50 to Brad Penn 20W-50 before I took an 800 mile round-trip up to the Rennsport Reunion last weekend. When I arrived at Leguna Seca I noticed engine was running a little hotter after "spirited" driving than with Mobil 1, and slightly lower pressure, but the main thing was a new rattle/knock from rear of car whenever engine was under load (accelerating &/or going up a hill) - and over 4k rpm. Never on light throttle or coast, or at lower rpm. It didn't get any worse, I repeated it cautiously a few times but I basically drove back home in 5th keeping load and rpms down just in case and took car back to shop. No metal in oil, engine very clean inside, no valve train issues, but on pulling chain covers, one tensioner was bad, so chain rattle considered culprit, so we agreed to change both out (after having to replace one twice, the bad-from-factory tensioner issue again) and put in new feed lines, one of those may have been cracked and was leaking too. My wrench said both chains and sprockets very clean and good, no appearance of excessive wear. I test drove after this work and thought I could still hear it... but I wasn't sure if I'd become oversensitized to noises... we decided to just see what happens. He said he'd wondered if it was pinging but checked timing, but all was OK. I essentially have used almost nothing but Chevron or Shell 91 octane in this car.

Well after driving around all day, the rattle under load/throttle/over 4krpm is still there. It doesn't seem to be any worse, but it is still doing it, it is repeatable, and consistent. Car is pulling well as ever... Is posting a recording helpful here? I think I can set up an electronic stethoscope and monitor/record the engine in various places while driving it around. Certainly it seems to fit pinging scenario... would/could seized weights in the "new" distributor overcome the electronic timing such as to create too much advance, or does anyone know of something "completely else" with these symptoms?

And just as everything was going so well...

DRACO A5OG · DRACO A5OG's Garage

I can think of only two things:

Do you have the old dizzy? if so swap it back to see if the rattle goes away. The new used izzy may have low miles but did you check it to see if it is not too loose? It should have some resistance from the inner snap in bearings and almost no play at all.

Hotter? hmmm strange, BP should have lowered the temps, not for nothing but after you isolate the rattle issue try switching back to the M1 to see if temps go down.

Jim

BarryJB · 10-29-2011, 12:26 AM

Thanks Jim (and what are you doing up at 1am Sat on the Pelican forums ;-)
I'm afraid old dizzy est kaputen - it was almost seized, hard to turn by hand. He also replaced cap and rotor... but yes that makes sense, we'll investigate timing issues more as that indeed seems likely, if I haven't already blown chunks off my pistons, etc., seeing if it's still making "that noise" :-( teach me to post my car on the high-mileage thread "no work on engine" last week... even if it is still true re top and bottom ends...

I believe I've read that on a change from M1 to BP one will see higher temps (15W-50 v. 20W-50 is all it takes apparently), and my wrench also said to expect that. I've used only M1 for the 180k I've put on car (before that the other 150k I don't know what PO used) and only decided to change to BP after car was being rebuilt for almost 5 years (engine excluded) and much reading up on lubes here at Pelican that M1's suitability re appropriate additives (ZDDP content changed without notifying anyone, and not listed in spec sheet), plus my wrench's opinion... he's a hands-on racer/suspension genius, one-man shop with a helper and only works on air-cooled p-cars - so like the leaks (now fixed save one reassuring slow tiny drip from one valve cover) we've been dealing with multiple annoying issues resulting from all that non-use... If temps stay up there after this rattle issue is sorted, Swepco 15W-40 looks like a suitable & thinner oil to try...

I wonder if anyone has posted a sound file of a 3.2 pinging. I tried a search here but no results.

NOLAsc · NOLAsc's Garage

I read here recently that exhaust leaks/bad exhaust gaskets could cause detonation. I don't know if that's true or if that could be your problem.

Shawn

psalt · 10-29-2011, 04:24 AM

Barry,

If you think it is pinging under load, put some unleaded race fuel in it, you will know right away. Pinging is directly related to heat, engine temp, intake air temp, if the noise is there cold and hot, it probably is a mechanical issue.

Paul

BarryJB · 10-29-2011, 10:00 AM

Thank you Shawn and Paul,
I just spoke with my guy and I'm going to his shop tomorrow morning, we'll double check for exhaust/gasket leaks - he R&R'd the manifolds/exhaust while fixing leaks and used new seals/gaskets; and we're going to try a distributor swap.

Meanwhile I'm going to see if I can find any such leaks and see if there's anything obviously amiss with the ignition timing at 4krpm (will research more, but should be in 22-23 degrees range according to my guy, I'm running the original OEM chip) with the car stationary and warm.

I can get racing gas in town here but I just yesterday filled up with Chevron Supreme...

Other than this we're a bit stumped still... I fear it is insensitive to engine hot/cold, it's been 50's to 70's ambient while I was driving yesterday - mechanical issue not good! Although another possibility is that it is ANOTHER bad chain tensioner from the dealer. The relevant thread mentions one shop that only got a good one third time around on one side - and we replaced both sides on mine.

Will post results after whatever we find tomorrow (Sunday) - thanks again, everyone - fingers crossed but breath not held for something simple, harmless and inexpensive!

911Freak · 10-29-2011, 12:18 PM

Could possibly be broken/loose head studs. During the recent refresh were they checked for proper torque? Maybe check those while you're under the engine checking the exhaust... Fingers crossed it isn't the HS, probably ignition/detonation related...

Flieger · Flieger's Garage

Is Elfin Forest by Los Osos?

BarryJB · 10-29-2011, 01:49 PM

Hi 911Freak, my guy said he checked all that and the valve train, all looked good ... just been under car looking for exhaust leaks, nothing I can find... I'll check HS again though.

My guy just emailed me... wrist pin is now a suspect. This car dodged the valve-guide job at 150k, so I can't grumble.. now some big decisions about how to move forward, like top-end job both sides, or it's time to pony up for a complete case-split rebuild or that 3.6 conversion that I've been dreaming about

BarryJB · 10-29-2011, 02:01 PM

Quote:

Originally Posted by Flieger

Is Elfin Forest by Los Osos?

Hi Max,
No it's an unincorporated still-rural community in the middle of the coastal half of San Diego North County (92029), I can see the giant red Google balloon on the map from my home ;-).

There's a recreational reserve of the same name (sort of across the street, along with a year-round running river). It's chaparral country, "elfin forest" another name for that. Nice twisty roads too ;-)
vbr
Barry

911Freak · 10-29-2011, 02:09 PM

Quote:

Originally Posted by BarryJB

Hi 911Freak, my guy said he checked all that and the valve train, all looked good ... just been under car looking for exhaust leaks, nothing I can find... I'll check HS again though.

My guy just emailed me... wrist pin is now a suspect. This car dodged the valve-guide job at 150k, so I can't grumble.. now some big decisions about how to move forward, like top-end job both sides, or it's time to pony up for a complete case-split rebuild or that 3.6 conversion that I've been dreaming about

If it were me I'd be looking/preparing for a 3.6 before I rebuilt a 3/3.2!

Opportunity knocks

Flieger · Flieger's Garage

Quote:

Originally Posted by BarryJB

Hi Max,
No it's an unincorporated still-rural community in the middle of the coastal half of San Diego North County (92029), I can see the giant red Google balloon on the map from my home ;-).

There's a recreational reserve of the same name (sort of across the street, along with a year-round running river). It's chaparral country, "elfin forest" another name for that. Nice twisty roads too ;-)
vbr
Barry

OK, there is an Elfin Forest, near Morro Bay and Los Osos, which is like a bunch of dwarf cyprus trees near the estuary and bay or something. I go to school in SLO and there is a good mechanic in Morro Bay, so just wondering if you were in the neighborhood.

BarryJB · 10-29-2011, 02:28 PM

Quote:

Originally Posted by 911Freak

If it were me I'd be looking/preparing for a 3.6 before I rebuilt a 3/3.2!

Opportunity knocks

I'm with you on that

An easy 300hp instead of an expensive 250hp on a non-twin-plug 3.4.
I've been discussing it with my guy for the last year, he's done quite a few of these for others so no unaddressed issues to solve, the plan is exactly that, to get a '95 ready, Sachs clutch, etc., keep the 915 and do the swap when this one bites the dust. I wasn't expecting the demise quite this early... but then who does?!

BarryJB · 10-29-2011, 02:43 PM

Quote:

Originally Posted by Flieger

OK, there is an Elfin Forest, near Morro Bay and Los Osos, which is like a bunch of dwarf cyprus trees near the estuary and bay or something. I go to school in SLO and there is a good mechanic in Morro Bay, so just wondering if you were in the neighborhood.

Yes, noticed the name while on my trip back from the Rennsport Reunion last weekend, as I ran the coast down from Carmel to Morro on Monday - had a flash of getting stranded in the wrong Elfin Forest so decided to jam it in 5th and cruise the highway home, staying away from the rattling noise as much as possible.

I imagine moving up to central California - really like it there.

I often head up to the Bay area on biz (via p-car, so the long way going, coming or both) - would you be OK sharing the mechanic's contact info (PM?). Nice to have recommended Porsche shops scattered about with these old cars.

Flieger · Flieger's Garage

Its no real secret. It is Clint from Rebel Racing's Dad Craig. His operation is just out of his garage but he still manages to do a fair amount of work. His Dad is a 356 guy and has a Carrera, he also builds and sells Polopolos motors. Then there is Clint and all the high-performance parts he makes at Rebel Racing. Check 'em out.

Rebel S Racing Products
Clint Smith
404 Tulare Avenue
Morro Bay, CA 93442
USA

(805) 440-9849
clint@rebelracingproducts.com

BarryJB · 10-29-2011, 07:29 PM

Quote:

Originally Posted by Flieger

Its no real secret. It is Clint from Rebel Racing's Dad Craig. His operation is just out of his garage but he still manages to do a fair amount of work. His Dad is a 356 guy and has a Carrera, he also builds and sells Polopolos motors. Then there is Clint and all the high-performance parts he makes at Rebel Racing. Check 'em out.

Rebel S Racing Products
Clint Smith
404 Tulare Avenue
Morro Bay, CA 93442
USA

(805) 440-9849
clint@rebelracingproducts.com

I will, thank you! Didn't mean to make it sound clandestine, just erring on the side of discretion was all! I've just checked the driver side head studs, all good... break for sustenance then onto the other side...

BarryJB · 10-30-2011, 11:36 AM

Well, all the head studs are definitely good, and no sign of exhaust manifold leaks under car at idle anyway, valve train seems ok. Getting deeper... Will try running output of an acoustic sensor into cockpit to see if I can localize source while driving.