an6drew

Bad news this morning:
I went to pick up the car from the shop after getting a little work done (alignment, adjust timing & mixture, replaced leaking distributor vacuum line) following my turbo tie-rod, ball joint, steering rack spacer install last weekend. Was greeted with the news that the car had just backfired when they started it up before I arrived, & sure enough the airbox is split. I had been meaning to install a pop-off valve, but as the car had always started fine everytime without a hint of any problems I put a couple other projects ahead on the list.

Thinking about it it does seem a little unlucky that, after lasting 190 000 miles the airbox would wait until just after this work was done (also following a recent ignition tune-up) to explode! Is it possible that the faulty distributor vacuum hose leak had been providing relief to the system, preventing backfires??

The shop said they typically do a partial engine drop for this, although the Porsche book rate I asked them to look up gives 7 hours labor (which I guess assumes a full engine drop- 7 hours seems alot!) I have to contemplate towing it home & tackling this myself- I doubt its possible without dropping the engine at least a few inches though? Has anyone who's done this have any words of advice? What would a realistic time estimate be for the shop to do this?

Obviously the moral of the story is- fit a pop-off valve if you don't have one!

Any advice appreciated. I guess testing out the renewed steering this weekend

__________________
Andrew
1982 911SC Coupé

wwest

airbox blow ups were determined, finally, to be the result of fuel pooling (from the startup injector)in the bottom of the airbox, and igniting from a backfire.

New airbox design has an internal fuel distribution manifold so the startup injection fuel flows much more evenly to each of the intake ports.

Recent ignition tuneup, MORE, HEATHIER SPARK, and return of vacuum advance, EARLIER SPARK, and a slightly leaking (Cold, slowly closing)intake valve, 190K, would be the most likely causes of the explosion.

IMMHO.

Replaced the airbox in my 78 myself, from the top. Put in a pop-off valve at the same time.

Bill Gregory

Andrew,

There's an article on tech.rennlist.com <a href="http://tech.rennlist.com/911/pdf/911CISairboxreplacement.PDF" target="_blank">here</a> that tells you how to replace your airbox. A partial engine drop will work fine. Install the pop-off valve before you install your new airbox (or you can take your old box and try epoxying it back together - I like JBWeld as it has fairly high temperature resistance). There's also an article under 911 engines on tech.rennlist.com that details how to do a partial engine drop, which is quite easy.

wwest

Having done this job from the top, abet years ago, I can't see how partially dropping the engine would be of any help. Can you enlighten me?

jlkline

If you decide to perform this task with a partial engine drop, it's a good time to consider replacing a couple of things at the rear of the motor / engine comparment such as the notorious leaky O-ring on the oil pressure switch, and the engine compartment noise insulation(unless you prefer the full, unmuffled sound of your fabulous 911 motor.)

Bill Gregory

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by wwest:
<strong>Having done this job from the top, abet years ago, I can't see how partially dropping the engine would be of any help. Can you enlighten me?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">A partial engine drop merely lowers the engine against the transmission mounts, so the end closest to the rear bumper goes down maybe 6"-8". What this does is gain you much better access behind the airbox, and makes the replacement process much easier.

an6drew

Is there any danger in going for a used airbox that looks to be in good condition? It seems like this is not a wear item (either they're exploded or not-exploded) so should be OK?

Also, does anyone know of a good cheap source for these things new?

thanks,
Andrew

jlkline

If you could find a used one with the Pop Off valve already installed properly at a good price, that would be worthwhile IMHO.

I like Partsheaven on the west coast. Good prices and good quality on used parts.

Bill Gregory

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"><strong>I like Partsheaven ... god quality on used parts.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Was this a misspelling or a purposeful play on words? If not, that's quite an endorsement

Bryan Moore

When I went through the same thing on my car about a year ago, I went ahead and bought a new airbox - at $250 or so it didn't seen unreasonable. I was able to do the work myself and did a partial engine drop. It's difficult (tight spaces and sometimes working by feel alone) but can be done. I probably could have done it in one day had I not found a bunch of other things to do at the same time. Replacing the oil pressure switch "gasket" is a given. The crankcase breather gasket, oil thermostat O-ring, and sound pad are probably good ideas as well - I didn't do them and will probably need to do them in the near future. Considering the age of our cars, you may also want to evaluate the fuel injector O-rings "insulators" (the Bakelite sleeves that the injectors fit into.

If you go with a new airbox, here's a caution. There's a plastic fitting (about 1/2 " diameter) that goes into the front (hard to reach, firewall side) of the big rubber boot on top and has a vacuum hose attached to it. My new airbox came with two of these pieces which, except for color (one red, one black) seemed identical. Since the piece I took out was red, I replaced it with the new red one. I went through two weeks of driveability problems until I talked to an expert. I had used the wrong piece - the one that is blocked off inside and doesn't allow any vacuum to pass. I swapped them (not an easy task) and my problems were solved. If you have to make the choice between the two parts, make sure you use the one that matches the original configuration of your car.

Best of luck.

jlkline

Bill, I'm quite satisfied with Partsheaven parts and service, but not to the level that my typo implied.(which has now been corrected)

Thanks for the catch.

an6drew

Alright- think I've found a used airbox w/ pop-off valve for $100 & am going to have a go at replacing it by doing a partial engine drop. A few people claim this cannot be done (or is exceedingly difficult) on an '80-'83 SC so we'll have to see how it goes- the tech article on this site does suggest it is possible?

Andrew