BLOWN HEAD GASKET

[Scott Sislane]

'76 2002: I've had a set of DCOE 40's that were/are like new, on a fairly fresh 77 head+block (from a 320i) for about 1 month, with practically new or rebuilt everything, from the radiator back to the tail-pipe. Lots of idle & driveway time, testing out the cooling system... & anything else. Temp always perfect, idle perfect, accelerated fine. Did the short drives, and all GREAT. (I never expected to see it run so well)

On my first major drive (with all my tools in the trunk!), about 1 hour into the drive, I had a loud blatting sound & major loss of power. Pulled it over, did some checks & couldn't find the problem. The noise was coming from the intake on cylinder #4. Limped home & parked it.

After looking everything over, I found that I had left a loose bolt where the fuel feeds into 1 carb, where it swivels, and fuel was trickling out. Also saw drips of fuel (not major) from the intake.

Tightened up the bolt, and then checked EVERYTHING, like distributor, plugs, wires, oil, coolant... Although it is far better than what it ran like previously, upon acceleration, the same intake blatts & still no power. It appears this cylinder is not firing properly.

I opened the top of the carb, pulled the jets out, blew into them to make sure they were clear, and they appear to be ok. The bowl has the same level of fuel as the 2nd bowl, and the float does not stick.

There is NO smoke, no loss of oil and no coolant loss. At idle, the temp stays at 40% or so, and I can have it idling for 20 minutes, and stays perfect. Still a little grumbling, but it does idle.

I replaced the plug and wire for that cylinder, just to make sure that it had good spark. The other 3 cylinders seem to be perfect.

I guess I need to do a compression test next? I am certain it's cylinder #4, as the sound is quite obvious, combined w/ a extremely light puff on quick acceleration. (from the intake)

I have a fuel regulator, and no matter what I do w/ it, it doesn't change the over-all problem.

Any advise to help me from here would be appreciated. I have no idea what damage I could have caused, in the head, piston...???

Thanks!

Scott

[MrNvgtr]

Do you have air filters? Hmmmm.

[c.d.iesel]

compression test , YEAuh - FIRST !

valve adjustment ?

loose/broken rocker arm ?

broken valve spring ?

ignition timing set HOW ? What Method ?

[Scott Sislane]

no air filters yet, just getting it on the road after 9 mo's of garage time. I will put those on very soon. Tx.

[Scott Sislane]

rocker arms are good, no apparent broken springs. gaps could be checked, but I have a mechanic/friend who inspected that, and it appears that's ok.

Timing was set by ear, yes not a light yet, as it hasn't been out of the garage to get to a shop, although it was running perfectly, idle + acceleration... if the timing was slightly off, would that cause a sudden problem like I experienced?

I'll do a compression test tomorrow. I need a 2nd person to help w/ that, which I have not had since Sunday when I had the problem...

Thanks for the quick input.

Scott

[bigjim5551212]

the bolt for the auxilliary venturi has backed out and the venturi is now spinning around not giving any fuel

[Scott Sislane]

wow, is that bolt ctr loaded, so I can access from the air horn?

I'll check this the second I get home.

Thank you for the help!

Scott Sislane

[bigjim5551212]

well, there is a bolt with a nut lock on it on the outside. It may be gone. since it is a 40 there is not the biggest chance of that, but, if you have no gas in that hole, then make sure some part is not broken, loose, or missing

[Scott Sislane]

I do have fuel in the horn, and it doesn't appear to be getting drawn in. I'll check it all out in about 4 hours & will let you know what I find.

Thanks - Thanks

Scott

[bigjim5551212]

here is a picture

[/img]

[Scott Sislane]

now I see what you are referring to. (thanks for the nice pic) I think I actually checked all of those, and they were all tight... I'll have to double check as that would be the closest to the firwall and possibly I missed it. I can also check to see if the venturi is loose.

[TobyB]

Uhh, all my 40's don't lock the venturis with bolts-

that's the 45's.

The whole 'hissing out of the intake'

sounds like a timing issue... or valve seal.

Life without a timing light isn't good. You can hurt your motor...

likewise, learning to read plugs is a good skill to have with sidedrafts...

there are quite a few faults that can cause one lean barrel, with unfortunate

effects.

t

[Scott Sislane]

I do have the nuts / bolts as pictured, and the nut WAS loose on the carb. But it did not solve the problem.

I'm in the middle of checking things out right now. Making sure everything is secured, no leaks... Need to do a compression test, I know. IF i had an 8' arm, I'd be all set right now. (just me)

As far as timing, while the car is idling, there's about a 5 MM window where it is smoothest, counter-clockwise 2-3 mm and it starts to get clunky, clockwise 2-3 mm and it starts getting sluggish. I lined up the cam lobes TDC and then inserted the dist w/ the rotor ptg at the mark on the dist, then made an external mark so I could see where that originated while running the motor. The spot that I find to be smoothest, is within 2-3MM of that external mark. With this said, am I at risk of damaging the motor due to timing?

Scott

[dapbmw]

you carbs are brand new? were they jetted properly, post your jet specs. loss of power may be timing related, distributor new or old? idle jet may be too small?

another cause might be your throttle is not opening up fully check linkage movement and see if all is opening up when pedal is depressed fully.

you did say in your post idle is ok, so is your sync right on, have you checked all 4 fuel mixture screws if they are all in sync (turn screws either way find the highest idle and leave it there and move on to the other 3 screws)?

cheers,

dave

[Scott Sislane]

1) your carbs are brand new?: like new, but not new. They are in extremely good condition, new gaskets... very clean & fresh.

2) were they jetted properly, post your jet specs: I do not believe they were jetted correctly, but they worked beautifully for a few hours total. Tuning, up & down the hill... then the 1 hour drive. Acceleration was amazing, tight & quick. (it was awesome)

3) loss of power may be timing related, distributor new or old?: Re-Manufactured distributor. Tip-Top condition. Dist works great.

4) idle jet may be too small?: Possibly, but again, all worked great. Just 1 cylinder gone nutz after what appeared to be clean running.

5) another cause might be your throttle is not opening up fully check linkage movement and see if all is opening up when pedal is depressed fully. : The linkage (TWM) is in sinc, and all mechanics are working perfectly.

6) you did say in your post idle is ok, so is your sync right on, have you checked all 4 fuel mixture screws if they are all in sync (turn screws either way find the highest idle and leave it there and move on to the other 3 screws)?: Yup, again, it was all balanced and appearing to be all in sinc.

After all the input today, I think I may have a valve problem or something of that nature. It seems like something went terribly wrong, in a quick fashion. I wasn't being aggressive w/ the drive by any means.

I need to do a compression test tomorrow and will post the #'s. I do have a spare head on the shelf that came off a running/totaled car. New head gasket maybe...

Scott