Took a chance on a W126 rod bender 350SD - PeachParts Mercedes-Benz Forum

JHZR2 · #1 10-01-2018, 11:00 PM

Decided to pull the trigger on a decent 1991 350SD. 113k documented miles. Primarily a FL car. Absolutely solid body, paint is 75% (a few spots with clearcoat funnniness, similar to my old 1991 bmw).

Looks like an original block. There is a computer printed sticker on valve cover and trans. Think it’s just clean original. Absolutely no blow by when oil cap is removed after 75 mile highway drive. ATF is nice pink, though brake fluid will need a swap soon. Ball bearing in EGR line (shhhh).

R-12 ac blows cold, though there's a few bubbles in the sight glass.

Body rolls somewhat on rough or bumps at highway speed. The only other vehicle I’ve experienced that on is an unloaded full size 3/4 ton pickup. I’m guessing shocks? There’s also a sporadic vibration in the floor/seat (not the steering wheel really) at 62-75. Haven’t taken it faster than that. Not sure if the two are related, or if it’s just an unbalanced tire and bad shocks or what. Rear tires are from late 2017 but given no steering wheel shake I’d hage to suspect the rear.

Also, on some roads it will track with the steering wheel angled, while others it tracks straight and true. Standard 1” wheel play I’m used to from my W123s. Jacked up, the only motion I observe when holding the tire and checking for play test is actual play/movement observed in the steering wheel.

Intake gasket is seeping oil at the front two cylinders. Haven’t driven enough to track oil consumption. Believe it has the original block due to machined numbers. Car runs nicely at 85C-ish (needle right through the 80) under all conditions. Doesn’t really have a lot of pressure in the hose even after high speed driving. Was very cognizant of that after reading about 3.0L woes.

Needs shifter bushings and a new windshield gasket. I can tell water is trapped though no rust yet. May spray fluid film in there in the meantime to displace moisture. Wheels need a repaint. Bumpers in great shape but need a very minor few touch up spots. Only 2-3 dime size dents needs to be pulled. Also have some diesel smell in trunk, but not cabin. Figure something is not quite right with filler neck.

Sound system is particularly good sounding with a cassette adapter. Fairly impressed. Original Becker 1432. Will probably send to them for the $100 Bluetooth mod.

Currently over 250 miles in less than half a tank. Lights are ok low, surprisingly good on high. Not a single dash crack, all dash wood looks great. Console wood needs work.

So that’s the deal. Thinking to preemptively do a HG. Never done one before myself, not sure if this is an engine to learn on. Ive already costed in putting a 3.0L on the 3.5 head of need be. Would prefer to not, but counting on ultimately needing to do so at minimum.

sixto · #2 10-02-2018, 12:16 AM

Nice!

Check the data card to confirm the engine is original to the car.

I’m not familiar with the 603.970. The 126 693.961 has a fixed center stem in the oil filter cover vs the 124 603.960 with a removable stem since it’s closer to the bulkhead. I guess it was easier to use one cover for all later engines.

Sixto
98 E320s sedan and wagon
02 C320 wagon

JHZR2 · #3 10-02-2018, 12:47 AM

Definitely a removable stem. No need, IMO.

t walgamuth · #4 10-02-2018, 07:43 AM

Looks nice. I could'nt follow your thoughts about the head quote though. Could you repeat with words please? Also what is an HG?

Dubyagee · #5 10-02-2018, 08:28 AM

Hg is head gasket

MTUpower · #6 10-02-2018, 08:47 AM

If it hasn't given problems then it's most likely not going to. YMMV.

JHZR2 · #7 10-02-2018, 09:37 AM

Quote:

Originally Posted by t walgamuth

Looks nice. I could'nt follow your thoughts about the head quote though. Could you repeat with words please? Also what is an HG?

Lol there were a few typos; sorry to not proofread.

HG = head gasket.

Read lots on the 3.5. Seems that hg may play in to some rod bend theories. Jury will be out forever.

As noted, if there’s any issues long term with the 3.5, frankly I’m expecting and costed it in to the overall economics of the purchase.

Doing a HG I see as a learning opportunity that may pay dividends.... if I diy for relative low cost and learn a ton.

Diseasel300 · #8 10-02-2018, 09:42 AM

I think you did well on this purchase! Car looks great, has a solid core, and an engine that's presently running correctly. Changing the HG isn't a terrible experience, just time consuming. The wallow/weave on the highway is probably shocks. Don't be surprised if the rest of the suspension isn't far behind. My SDL is still running on the stock suspension (minus rear springs and Bilstein HD shocks on all 4 corners) and it's pretty well done front and rear.

Frank Reiner · #9 10-02-2018, 10:29 AM

Quote:

Originally Posted by Diseasel300

I think you did well on this purchase! Car looks great, has a solid core, and an engine that's presently running correctly.

Does price ever enter into the determination of "did well"?

sixto · #10 10-02-2018, 10:43 AM

I corrected a 126 rear end having a mind of its own with subframe bushings. The telltale was the salt shaker shaped bracket around the bushing should have an even gap all the way around. When the gap isn’t even, the bushing is done. As a reference, from what I’ve read, it’s not as nasty a job as in a 123.

Is there oil seeping between the block and head by the timing chain tensioner and #1 exhaust runner? If not, I’d put off replacing the head gasket.

One school of thought is EGR soot deposits on the exhaust valves and pistons causing the rods to bend. I’d do what I can to [ahem] prevent that.

Tom, I think he means he’s ready to swap a 3.0 block under the 3.5 head if he finds the rods are bent.

Sixto
98 E320s sedan and wagon
02 C320 wagon

JHZR2 · #11 10-02-2018, 11:48 AM

Quote:

Originally Posted by Frank Reiner

Does price ever enter into the determination of "did well"?

Price isn’t really anybody’s business, but I’ve stated that the economics were favorable even if I had an engine issue. That should suffice.

JHZR2 · #12 10-02-2018, 12:45 PM

Quote:

Originally Posted by sixto

I corrected a 126 rear end having a mind of its own with subframe bushings. The telltale was the salt shaker shaped bracket around the bushing should have an even gap all the way around. When the gap isn’t even, the bushing is done. As a reference, from what I’ve read, it’s not as nasty a job as in a 123.

Is there oil seeping between the block and head by the timing chain tensioner and #1 exhaust runner? If not, I’d put off replacing the head gasket.

One school of thought is EGR soot deposits on the exhaust valves and pistons causing the rods to bend. I’d do what I can to [ahem] prevent that.

Tom, I think he means he’s ready to swap a 3.0 block under the 3.5 head if he finds the rods are bent.

Sixto
98 E320s sedan and wagon
02 C320 wagon

AFAIK the whole block, head, hg is dry on the turbo/exhaust side.

Only notice oil at the forward-most intake runner, seemingly due to bad intake gasket. There is zero blowby smoke even when full hot after a highway run. But the think I’ve noticed is some black oil sheen in the plastic coolant tank. I verified the coolant in the system is a beautiful clear blue. But I suspect there is some seepage some place, under some conditions.

I have ordered the intake gaskets and look forward to cleaning the whole thing off and out. I remember doing that on my father’s NA 606 after around 150k and getting a decent amount of junk out.

I do want to check out the turbo, both boost levels and oil in there, but it’s much more complex to get to than my 617 (initial impression, maybe I’m wrong.

EGR got a ball bearing in the hose as soon as I took possession. Should block vac decently, it was a big ball and firmly planted against the EGR nipple. I get it that they can be stuck open. Priorities first.

Diseasel300 · #13 10-02-2018, 01:27 PM

Quote:

Originally Posted by Frank Reiner

Does price ever enter into the determination of "did well"?

If you're buying one of these cars, price is of concern only to those who care about trying to flip for a profit. If you know anything about these cars, that's just about impossible unless you got it for free and has literally nothing wrong with it. If he had the money and got it for a fair market value, he appears to have gotten a good car. Considering he's talking about factoring in costs such as HG replacement or replacing the engine, I'd say he got it for a pretty fair price.

JHZR2 · #14 10-02-2018, 01:30 PM

Quote:

Originally Posted by Diseasel300

If you're buying one of these cars, price is of concern only to those who care about trying to flip for a profit. If you know anything about these cars, that's just about impossible unless you got it for free and has literally nothing wrong with it. If he had the money and got it for a fair market value, he appears to have gotten a good car. Considering he's talking about factoring in costs such as HG replacement or replacing the engine, I'd say he got it for a pretty fair price.

Precisely. Initially wanted a G1 617 SD with bundts and mb Tex.

Happened upon this one by accident. Deal was right. Did my research to know the bogeymen of the 603/350. I’m comfortablw with the risk (famous last words). Sold by a legit private party.

Time will tell. I like it.

jake12tech · #15 10-02-2018, 02:49 PM

Replacing the head gasket is a total waste of time unless the car is running bad, pouring coolant out the exhaust or coolant mixing with oil or vice vwrsa. You’re putting a lot of work into something that isn’t broke. The saying goes if it ain’t broke don’t fix it.

If it’s got 113k miles on it I doubt anything is wrong with it internally. Just drive it and enjoy it til it blows up or comes close. If the engine bends a rod at some point swap it.