in-situ head gasket replacement?

[denizen224]

Looks like I may have blown the head gasket on the driver's side of my engine during an over-exuberant downshift ('69 S with a 3.2 and Webers). Engine is down on power, runs rough under power, misses and pops, unusually strong smell of raw gas. Passenger side cylinder bank's warm compression is 148-155 psi, driver's side is 131-135 psi.

Other than the popping, the engine isn't making any "expensive noises."

Can I replace the head gasket with the engine in the car, or do I need to resign myself to dropping the engine? I've done in-situ head gasket replacements in aircooled VWs before, but this is obviously a rather different beast.

The engine had a thorough, professional "going-thru" about 10-15k miles ago, so I don't see this as an excuse for looking at freshening the entire engine.

[edmayo]

You're partially in luck, the 3.2 didn't use a head gasket. I'd do a leakdown test and look for bent intake valves.

[denizen224]

Hmm... technically, it's a '78 SC rebuilt with 98mm cylinders to bump it up to 3.2. Receipts from when the PO had the engine refreshed shows "Head Gasket Kit - 911 Carrera" in the parts list. It's a bit hard to tell by looking at pics of that kit on Pelican, but it looks like it includes head-cylinder gaskets.

The fact that three on one side are low and the three on the other side look okay have me hoping I just hoisted that side rather than bent valves; I'd expect to see that on both sides. But yeah, a leakdown test is in order. Also checking valve clearance; if I bent a valve, I would expect its clearance gap to grow.

The more I can try to diagnose before tearing things apart, the better.

[jameshtaylor]

I can't imagine pulling out camshafts and towers, chains, heads with the motor in place. More to the point, why? Takes a rank amateur about 2 hours to pull the motor. Why stand on your head for a week when you can attack it on a bench?

[denizen224]

Why? Mostly "muscle memory" from working on VWs and 356es, where so much more can be done with the engine in place.

This is the first time I'm having to go deep into a 911, brave new world.

[jameshtaylor]

Spend some time gathering info on removing the motor. Lots of threads here and on Pelican. Look for things that have stopped others: the cables to the starter motor, the speedometer cable (if you have one), the shift lever and see what's needed. Build a little plywood cart with wheels and a slot for the jack to move the motor around. Then gather the tools, a good floor jack, a few beers, and have at it. Not that hard.

[savaden]

VW's and 356's don't have head gaskets either... but I'm with Ed, more likely scenario is bent valves. Do a leakdown test.

SV

[denizen224]

[visualizes a 356 head, the last such head I had hands on]

Yep, flycut and direct seal to the cylinders. Oh d@mn, I know what I'm remembering... my BMW R100/7, that's where I've installed a head gasket on a horizontally-opposed aircooled! [facepalm]

http://store.bobsbmw.com/microfiche/...Z&ImageID=1142

And perhaps with some wishful thinking thrown in... Okay, most likely I bent some valves [$igh]. Off to buy a leakdown tester this weekend, and start figuring out the best way to pull the lump.