Freaky Sunday Start Up and a Question

[jkh2cpu]

If you haven't guessed by now, it was a near disaster. I fire up the old 73 911 after a long slumber in Michigan. It fires up, and then after a bit, I realize that it's firing up, as in a carb fire. I haul out the trusty extinguisher that's been in the back seat since the last major rebuild 20 years ago, and extinguish the fire, but the carb is still hot. My dear wife must have heard the explosions of curses that were coming from the garage, so she comes to help. GetTheWater I say as one word, and shortly enough everything is cooled down so that I won't have any flashing over (as in reignition of the gasoline).

I pull the carb and look it over. There is metal from the secondaries on two butterflies, and the butterflies don't close completely. I knock off the metal on the butterflies, and the butterflies now come close to closing. A close call, I think to myself. Now, what to do. Eurometrix comes to mind, as I've seen their adds for over 40 years (I've had the car since new in February 1973) so I shoot them an e-mail. In the meantime, I start thinking about EFI, so I check that out as well: Megasquirt and PMO's throttle barrels.

I hear back from Eurometrix, and Matt tells me enough about what to look for regarding rebuildability that I'm pretty sure that they can be repaired, so I just shipped them off. We won't know for sure until he can examine them. As far as I can see, there is only damage to the secondaries; the barrels look ok / not warped.

Moral: I won't wait so long between rebuilds. These Weber 40IDA-3C's were from PMO back in the early days, and they cost back then around $1140.00

Now for the question. The motor ran for maybe a minute before I figured something was wrong (I could not throttle down to idle -- because of the metal on the butterflies.) I shut it off when I saw the fire, but the fire continued to burn, so I extinguished it and cooled the carbs. I need to determine whether I should tear the engine down to point that the heads are off the engine so I can determine whether there is any damage to the valve train / pistons / cylinders.

Since the original motor has around 130 K on it, it is due tor splitting, machining if necessary, and reassembly. If I do that, I then have to consider whether to rebuild the 2.4 engine (was MFI to start with -- MFI sucked on this particular 911T, so I decided on carbs a long time before I had the bux to do it -- growing family and all) ... or ... put the rebuilding effort into a nice 2.7 short block that I bought years ago for the purpose of replacing the 2.4 engine.

The photo is a closeup of the middle carb barrel. You can tell that the secondary has seen a bit of heat... They were all burned to some degree, but this was the worst.

TIA, John.

[jkh2cpu]

Well, today I thought I'd better see what the heads (inlet ports) looked like from the topside of the engine, and I saw some liquid, so I pulled the manifold on the passenger side (cyls 4-6) and took a look. A bit of water and gas, so I removed it with paper towels. I did not like the looks of port 5: see the photo -- there is a collection of metal dribble on the number five intake port. That dribble is, of course, from the secondaries that could not take the heat and flame of the gas fire.

1) Carbs have been sent off for evaluation and most likely repair.

2) I've checked with Competition Engineering, and they'll look at the 2.7 case / crank, and it they are rebuildable, I'll go for that with the eventual plan of using that as the engine. I've got a pair of Euro CIS-S pistons and cylinders (new) so they'll go on that block... and I think Clewett Engineering spark. Carbs for a bit, but I'm leaning heavily toward EFI for maybe next year.

3) When I get a bit of time, I'll pull the engine and tear down the top end so that I can send the 2.4 heads out for renewal / repair. I don't think that any of the liquid carb metal got as far as the heads, but why take a chance. Head rebuilding is a lot cheaper than repairing an exploded boxer motor.

John.

[jkh2cpu]

It's the middle of August now, and the carbs are back from Eurometrix, and I've just pulled the engine with the help of my son. I'll tear down the right hand side of the engine, pull number five head, and evaluate it.. I'm guessing that I can 'pop' the melted carburetor material from the head and put it back together with out crossing my fingers, and I'll be back on the road. While I'm at it, I'm going to do some serious clean up and repair / replace a few things that need it after 40 years.

I've got a spare 2.7 engine that's been sent out and by and by it will replace the tired 2.4.

John.

Here's the obligatory shot.

[callard]

Do a leakdown before you pull the heads. There may not be any metal or damage inside the # 5 chamber. If all readings are nominal, I'd fire it up again.

[jkh2cpu]

That's a thought, but I imagine there would be a problem with turning the crank at all. Check these shots of ports 4-6. They all have to come off, and then I need to see what the cylinders look like debris wise.

Remember: I had a fire and I used an extinguisher to put it out. Had this been a more perfect world, I would have pulled the engine that day and disassembled the right side of the motor, but alas, as we mostly know these days, the world ain't perfect.

Like I said, CE has my 2.7 case and it's getting some attention. If the 2.4 is a sorry wreck sorely needing a rebuild, I'll put the bux into the 2.7 and at least have a machine that can roar around town in proper style.







As far as I can tell by photo and fingers, I have carb metal in two heads, and debris in all three on the right side. These are some horror shots to look at when you think you've got it bad ;-) It cudda been worse: a real engine bay fire, at which I try to part out the car.

John.

[E Sully]

With the mileage and the carb fire, especialy looking at those last pictures, a rebuild seems like the best route.
At least the damage from the fire was minimal. With a magnesium engine and transmission case things easily could have been a lot worse. At the fire training center I attended years back they demonstrated a magnesium fire. The heat was so intense water would have no effect on it.
I always keep a good fire extinguisher in my '73.5

[callard]

Yep, I agree with Sully. Those shots are worse than the first. On the plus side, rebuilds are fun!

[jkh2cpu]

Well, what I'm going to do is tear down the right side, starting today, and evaluate what I really have. If the heads hold gasoline, then I'll see if I can clean them up... Otherwise it's rebuild time for the heads.

[jkh2cpu]

Over the past several days, I've puttered around with the 73 911 motor. I did tear down the right side of the engine today and I can see the damage that I did with the number four cylinder and head.

The first photo is looking down, the second is looking up, and the third is the cylinder head.

The debris in the cylinder cleaned up fairly well, so I think I'll take the cylinder to a local bike shop and see if they can clean it up by honing. The heads are not in bad condition except for the melted carburetor metal. I'm guessing that the bike shop can also clean this up with bead blasting. The heads are relatively new, having had a rebuilt about 35 K Miles ago.







John.

[jkh2cpu]

Yippie (with Handel's Hallelujah Chorus blaring in the background)

Got curious this AM, and pried off the heat insulator on head number four. Lucky thing: all of that carb metal stuck to the insulator, not to the head. This is getting better by the day :-)

Bike shops tomorrow.

[jkh2cpu]

Argh. I guess I could get the heads and cylinders cleaned up easily enough, but the engine is simply tired: it's about 40 years old now (39-10) and all I've really done to it was renew the heads / valve guides and re-ring it 21 years ago. It's filty dirty on the outside, and I know that I did not keep that 'patina' out of the case, so I'm opting to put the bux into the 2.7 engine and revisit the 2.4 case when I'm on the road again... which will probably be late fall or next spring. The tear down has been a blast.

There's always the 1-3 synchros in that 915 transmission that could always use some help...