280 engine pic - PeachParts Mercedes-Benz Forum

#1 10-13-2003, 01:20 PM

Dear friends:

Here's what my engine looks like as of saturday; it's ready to go into my brown '74 280.

The base is an Adsit-sourced rebuilt shortblock, the head and valve assembly came from the original engine with 46K on it. The process of transferring the pieces went pretty smoothly. The short block assy. as it arrived looked really good and concientiously assembled.

As I mentioned in my previous post, at this time I'm replacing the Solex with the Weber 38DGAS kit; any comments/guidance as to the vacuum line hookups would be appreciated. In the mean time, thanks for the help/advice you've already given...

Will

Tomguy · #2 10-13-2003, 11:46 PM

Just wondering - why did you have it rebuilt if it had only 46K? Poor maintanance?

#3 10-14-2003, 12:58 PM

Dear TomGuy:
I bought this otherwise gorgeous car for $2500 because it had a seized motor with a telltale nickel-sized hole in the crankcase. I don't really know what really happened; a rod bearing let loose? Anyway, the car was -and is- otherwise so absolutely clean that I was lured into buying, especially when the seller said that he had a badly rusted 280C to throw into the deal that has a good motor. Well, the 280C's motor ended up to be a high-milage smoker, so I couldn't in good conscience put that into an otherwise low-milage, super clean car.

Upon inspection, I found that the damaged motor's top end (camshaft lobes, etc. looked like new, so I was advised to retain those and transfer them to a rebuilt short block.

By the way, Please, for your own sanity, do not ever try to do business with ASAP motors in Houston, TX. In a huge fiasco that lasted several months last year, they sent me two junk 110 motors in a row. What they practice contitutes fraud, and, upon some research, it's not surprising that the Houston area BBB has a big list of complaints about them. I should have checked this place out first.

Yes, this 280 project has been a real learning experience for me- good and bad- and, on a positive note, I am glad to have found this forum along the way. Thanks for your help and interest.

Will

#4 10-22-2003, 06:42 PM

Continuing my saga of my 280/110 engine project, I have a new problem. I ask anyone who has knowledge of this engine to maybe shed some light.

As above, this is a rebuilt shortblock from Adsit + good, low milage head/cam/valves assembly. New gaskets, timing chain, tensioner, proper torques.

Got the whole thing together, and with some predictable kinks/adjustments, got the thing running smoothly, except for a new tapping/knocking noise that rises to a loud, very harsh TAP TAP TAP and then fades for, say 30 seconds, then rises again. I've had two experienced mechanics (although unfamiliar with this engine) listen, and they say they have never heard a sound that comes and goes like that. They eliminated rocker/valve/cam noise, they re-gapped the valve clearances to .004 intake and .010 exhaust. We've confirmed that everybody gets plenty of oil up top. They initially asked if this engine has hydraulic lifters. The sound seems to be eminating from closer to the rear of the engine (close to the firewall)

The noise seems unrelated to rpm. The rate at which it comes and goes seems unchanged at whether at idle or higher. I was told by my helpers (one a shop foreman at a local Honda dealership) that the engine otherwise sounds great. Shifting in to drive makes no change. The oil pressure is reads fine.

Any thoughts on what I should do? Very frustrated after putting so much time and effort into this project. I would be happy and grateful to maybe talk to someone offline about this.

Thanks as always,
Will

ctaylor738 · #5 10-22-2003, 07:08 PM

If it is any comfort, I have sort of the same noise in my 280C, but probably not as loud as yours.

I would describe it as a sort of "nack-nack-nack" sound. I get it only with the engine fully warmed up at idle. You hear it and think "Damn - I need to adjust that valve." And then it goes away. And the valves are fine. I am equally clueless as to what is causing it.

#6 10-22-2003, 07:18 PM

Long shot , but I have to mention it, check the exhaust!
why I say is we have the same noise on that 280 ce we just got last week, and that is the problem with this one.

do hope its a Little thing.

Litton · #7 10-22-2003, 07:49 PM

I have heard this noise before....not am MB but it turned out to be a broken spring in the flex plate. Although in my case, it sorta went away with higher rpm. Similiar to a clutch plate with broken sping(s).

#8 10-23-2003, 05:39 PM

Thank you so much for your input.

Any more thinking about this noise? At its peak, it really sounds harsh, mechanical, and maybe damaging. Is there any chance that something like this will go away? Should I drive the car with nothing to lose?
It's really mystifying because the baseline, so to speak, is a really good sounding engine...

Thanks as always,
Will

#9 10-23-2003, 05:54 PM

Thank you so much for your input.

Any more thinking about this noise? At its peak, it really sounds harsh, mechanical, and maybe damaging. Is there any chance that something like this will go away? Should I drive the car with nothing to lose?
It's really mystifying because the baseline, so to speak, is a really good sounding engine...

Thanks as always,
Will

ctaylor738 · #10 10-23-2003, 05:58 PM

My darkest suspicion has alway been that the rear cam lobes are losing their oil for a brief period. Why don't make a see-through cover out of a junk valve cover and observe the engine while it's idling?

I have also suspected motor mounts.

#11 10-23-2003, 06:21 PM

how about using a stethoscope to listen?

But the idea of seeing the valve train is awesome!

On another board a guy had that noise and it was a bad valve lash apparently he was as happy as a clam after it got shimmed and adjusted correctly..

Please post when you do find out what it is?

#12 10-23-2003, 06:24 PM

When I had my pair of advisors with me the other night, they ran the engine briefly without the cover; apparently they were thinking along the same lines. A bit messy, but educational. We covered the timing chain and surrounding areas (sort of).
No, everybody was getting oil equally. An air gun with a rubber tip was used to blow into oil holes, seeing it shoot out elsewhere. It's actually interesting to see how oil is fed to all critical places. If nothing else, I could make an elaborate oil fountain. ;^)

Couldn't be motor mounts. Not that kind of sound. This is definitely internal and mechanical.

Thanks.

Will

#13 10-23-2003, 06:41 PM

Further thinking- On one exhaust valve (about where the noise seems to be coming from) I did have to adjust the rocker ball much higher (maybe a whole turn) than the others in order to attain the proper .010 gap at the cam. We had some discussion about this, but it was decided that it shouldn't make any difference because:
a) the gap attained makes it operate identically b) there is still plenty of adjustment left.
But, nonetheless, it's interesting because:
a) it is different from the other guys and b) what condition made it that way,
and c) it corresponds with the noise's apparent source.

Will

300SDog · #14 10-23-2003, 08:14 PM

Those are self-torquing valve adjust nuts on the twin cam 6, are they not? You might have a few that have worn loose and need replacing.

#15 10-24-2003, 12:58 AM

Wouldn't it be obvious that the adjuster nut(s) have worn loose when I go to turn them? It seems all of them have needed considerable energy to turn each one...

Will