Cracked Manifolds on 450-Way of Life? - PeachParts Mercedes-Benz Forum

rix116 · #1 03-28-2004, 08:04 PM

I bottomed out my 74 450 SEL last week (as you may know if you read my posts last wk. about interchangeability). True- my car was sitting too low. But I broke both exh manifolds. First I thought it was only the rt. side. Went to the jkyd- got another.
Found a77 to go on my 74- header pipe didn't line up right-towed to a muffler place to have them cut and realign header pipe.
This is not a Mercdes place, but they had a 450 SL car there with the same problem- rt. exh man broken in the same place.
They did this- started car and found that the left exh man was cracked badly too. Went to jkyd again- 2 cars available- first one had a cracked left exh man- couldn't believe it- grabbed the other one which wasn't cracked.
I'm sure I'll get this thing back on the road soon, but is this a common problem with 450's? Have any of you built in any "stress
relief" into the header pipes somehow.
As a by product of this nightmare, I've become somewhat of an expert of the different designs over the 73-80 period if anyone
needs help with putting other exh manifolds on their cars other than stock. The Mercedes oriented jkys charge about $150 each, while the self service yds. are about $20 ea. Part of this discrepency is that it takes about 2 hrs. to take them off!

300SDog · #2 03-28-2004, 10:13 PM

C'mon admit it..... seeing other 116's had the same problem as your car made you less angry at the automobile and this made you feel exactly in touch with the rest of the family of past and present 116 owners, didnt it??

Should 116 exhaust mannies be put on "collectible and endangered parts list" along with 115 gasoline engine 4 cyl heads, all Zenith carburetors and 114 6 cyl 280 twincamshafts?? ..... probably so, and it sounds like you've identified chronic problem that typically becomes an issue at/near 200k miles or 30 yrs - long after ordinary cars have run their course.

In defense of Benz, I've gotta say that mid to late '70s were full-tilt boogie yrs for German steel workers' strike that shut down Ruhr Valley steel works, causing MB to import crappy steel from Russia and Italy...... and itsa cynch the *****iest steel of all was used in 'pig-iron' products like exhaust manifolds.

rix116 · #3 03-29-2004, 11:42 AM

Great reply dieseldog.
Of the 73-80 years, are there any years when MB might have put good iron into exhaust manifolds, in other words when there were no strikes?

psfred · #4 03-29-2004, 10:43 PM

280 4.5 manifolds are known for splitting down the "y" on the left side, too, so the steelworker's strike is only part of the issue.

Several things here -- first, hitting ANYTHING with the exhaust is bad news for an old exhaust manifold -- they get nice and hot and have plenty of carbon inside, so I expect that they get brittle with age and use. All cast iron will.

Also, these cars tend to run rich if anything is off with the FI, and the manifolds will then run red hot AND have extra carbon, making the whole problem worse.

Finally, a red hot manifold (from bad mixture control or an ignition miss -- another common problem by this age) and WATER from splash on wet roads will ALWAYS result in a cracked manifold eventually. Typical cracks in the 280 SE 4.5 are on the left side below the Y -- the entire surface gets checked, then some of the cracks propagate into the exhaust stream and the crack will "fold" out and extend up both branches. Usually form running too hot and getting water splaxhed on it from the left wheel. Right side is a double manifold, never seems to crack.

I'd find a good manifold, make absolutely certain my ignition and FI were in good shape, and watch out for anything likely to smash into the exhaust. MBs sit pretty low, pays to be careful.

Peter

rix116 · #5 03-30-2004, 10:40 PM

Yes Peter- that left side crack happens in the Y. And a junkyd. one I inspected was cracked there too.
I did crack- actually break clean -a right side manifold near the rear because the car was loaded with too much weight and it got hung up on a bump forcing all the pressure up into the manifold. But like I said I was surprised when the small muffler shop that repaired my header pipe had a 450 SL there that had the same exact break on the right side manifold.
As much of a pain to remove them (takes me 1 1/2 to 2 hours in the jkyd., I think I will be looking for an extra spare for each side,
just in case it happens again.

psfred · #6 03-31-2004, 12:01 AM

yeah, it's a pain in the sitting part...

I plan to take a nut splitter to all the nuts on mine -- it appears to be original, and the nuts are eroded to the point a 12mm six point socket won't grab very well. Figure split the ones I can reach and heat the rest then use vise grips if I have to....

It will be nice to drive without the roar, though.

The W108 V8 left manifold is worse than the 450SEL one, though -- instead of being somewhat linear, it has a big Y right in the middle, with a straight down section that curves back to the header (to clear the steering box). Way too much thermal stress. No way to reach some of the bottom nuts, either, and two long studs on top, too, making it a pain to remove once loose.

Peter

Peter

Tomguy · #7 03-31-2004, 12:24 AM

Peter: The 116 and 108 have different left manifolds? Pardon me while I curse a bit...

I assume the 116's will not fit on a 108... oh well, I had to remove it from the head to yank it (the head) anyway, but was hoping to grab it as a spare, since mine looks like it's starting to crack... *sigh*

psfred · #8 03-31-2004, 12:34 AM

Tom:

On the 450s I've seen, the manifold goes straight back, then down. On the W108 the downpipe is in the middle.

Various configurations may exist, and the W107 manifold may be different again.

Peter

Tomguy · #9 03-31-2004, 08:56 AM

Peter: To me, the 116 in the junkyard's manifold (driver's) looked the same as mine, as far as I could tell. No measurements or anything but in refference to the "Y". Cyls 5+6 merge with cyls 7+8 in a "Y" at the middle. The right side has a more complex manifold which I am thinking of grabbing for my own car as well (To replace the dual manifold setup on that side and thus make an exhaust change easier in the future)

edit: If I remember the right side right, cyl 1 went "around" and merged into the back of the manifold, and there was a (VERY) small opening to remove the nut on the bottom of cyl 2's port between that pipe and the rest of the manifold

psfred · #10 03-31-2004, 07:44 PM

Tom:

The one I looked at was an '80 model, with K-Jet. If it looks the same, it probably is.

The original setup on the W108 had a single manifold on the right side, but was replaced by the dealer during early service, I would guess because it cracked in service or caused some other problem. May never have been installed on the 4.5 anyway.

The only problem you would get by swapping the right manifold would be the requirement for a custom header pipe to the muffler, none of the factory ones would fit as they are all dual to single pipe.

Peter

rix116 · #11 04-01-2004, 01:54 PM

All the 116 driver's side manifolds I found in the jkyds had the down section in the middle. Don't know the 108's but sounds similar.

psfred · #12 04-01-2004, 08:21 PM

That's the W108 configuration, although I don't know if they are identical. The W107 may have the straight back pipe.

Peter