Rebuilding a 1966 230S, (M180 motor) any tips or tricks?

[Heckflosse]

I'll try this on this page, considering my car is a W111 and the motor I'm building is naturally aspirated.

My M129 in my 66 230S is pretty much toast. Nothing I've done has improved the idle problem it still does what it does no matter where anything is set at. So I'm going to concede that the engine is "done". The compression is down, it doesn't build any vacuum until about 1200 RPM, and yet the carbs are perfectly dialed in. It starts on the first crack, builds power, but it either has a huge vacuum leak I can't find or it's shot.

So I picked up a 230S motor, a M180 from 1966, the original block to my car. It's a burner, as I understand a lot of these were. But it ran and had compression. I want to overhaul it and obviously make it run cleaner.

I've rebuilt a lot of engines in the past, primarily Buick and Oldsmobile, plus probably about 100 SB Chevys. So I do know a few things. But I've never done a vintage Mercedes 6 before, and from what I've seen so far with these things, they appear to be fragile and finicky, and like most European things, interchangeable parts, - don't, it's a nice suggestion.

Some questions for those of you who've rebuilt these things.
First off, and most importantly, can it be hung on a conventional engine stand? I took off the clutch, flywheel and the transmission adapter bracket, it appears there's 4 small M10 bolts, will they hold the weight? What does this thing weigh?

1) Can it be bored to oversize? What oversizes are available?
    If there are no oversize pistons available, can it be sleeved?
2) Can the cam be built up?
3) How easy are the heads to work with? Are guides removeable, are there valve seals available?
4) Since this is an alloy head, do the valve seats need to be replaced?
5) how much can the crank be cut down?
6) Is there a good source for parts, ie valves, springs, rockers, gears, pistons, rings and bearings?
7) What's a good parts source for a clutch?

Are there any tricks to these things that have to be known? Such as, how to get the chain taken apart? Any pitfalls, newbie mistakes, things not to do?
Is the engine something that an average machine shop can tackle, or is there something that is very specialized going on?

I realize this is a long list, but I'd only ever like to do this job once, and I realize it's not going to be cheap either. Forewarned is forearmed....

Thanks!

[Vander]

I'm curious, what are your hot compression readings on the motor you believe is shot?

[ja17]

You might just want to have the head redone on the 230 engine. That usually will fix most oil burning issues. Also, you might have a balance problem unless you can keep the front dampner, crankshaft and flywheel together. They cannot be split up on the M180 engine.

Parts are expensive for engine these days. Price them before you take the plunge. You may end up with between $200 to $300 ea. for factory pistons with rings. Four oversizes are available. Plan on spending another $400 to $500 on gaskets and seals. You'll have another $750 or more in reconditioning the cylinder head if you take it to a shop. Crankshaft bearings another $400 ( the crank can be cut to four undersizes. Now you have machine work to do on the block and crankshaft and another $500 to $750 depending on what the engine needs. Oil pump, timing chain with guides and sprockets probably around $700. Cluch assembly add another $700. Hope your cam and rockers are good! Water pump, thermostat, hoses, filters and fluids etc. etc. etc. might be cheaper to just find a good car that does not need all the work! Shop manuals, so you don't have to do it twice, and another $300.00.   I still think your carburetors are the problem.

[Heckflosse]

Compression on the M129 was 120, 125, 110, 135, 130, 125 with the lash done and the cam changed. No real improvement from the original cam was in. The car starts brilliantly, first crank, but max vacuum is 15, it goes no higher, it does have a steady needle, so valves aren't the big issue. It doesn't backfire or sputter anymore and it builds some power at high RPMs. Vacuum holds at about 12-13 at 1200 rpm, try to knock the idle down, it's like someone shut off the key. Carbs are dialed in, they are pulling uniform now. Idle tubes are clear. Cover 1 (either) carb, and the revs climb; (Weird) - cover them both, it dies. The floats have been reset now 3 times; - first to spec, then high, then low, and now back to factory, no difference at all. Throttle response is instantaneous, and good; - no flat spot anymore. Take it for a drive, and it pulls pretty good; loping along in 3rd gear it surges a bit, which matches the miss in the exhaust, so I think there's at least one burnt valve.

It's running better now than it ever did, but it still will not idle. The old cam was wiped, the blowback and spitting through the carb has stopped, as has the backfiring. There's now just a miss, which was there when I got the car.

According to what I've read in the various Zenith troubleshooting guides, if there isn't at least 15 inches of vacuum, the carbs will not function. At engine speeds of less than 1200 rpm, the vacuum falls off instantly. And yes, I did spray it down, checked for leaks, throttle shafts are tight, heat risers are free, spacer plates and heat shields are flat and in good shape, carb bottoms are flat, and intake gaskets were replaced. I cannot find a vacuum leak. Maybe the head gasket is gone, but when the cam was changed, I retorqued the head.

So I'm done with it; - the parts I've pulled off exhibit far more wear than the supposed 70,000 miles. It's more like 170,000 miles. I'd rebuild the M129 but I read that they have head issues and parts are even scarcer for them, so that's why I went to the 230, which coincidently is the original block to the car.

The head on the 230 was redone before it was parked. Of course I would get it gone through again before I put it back together. The compression is apparently no good on this thing either, but it ran smoothly and just smoked like the Titanic. Thanks for confirming that oversizes do exist, from what I've heard, these 230 (M180) engines in 1966 had a taper problem, they cut the taper wrong at the factory and so the rings fail prematurely on them. To correct that will likely need a bore and an oversize. So who sells pistons and rings? I can't find anyone that has them.

Good thing I have the flywheel, clutch and balancer to the 230. I'm just not sure I have the right transmission for it, so will it fit the M129's transmission? They look the same...

Yeah, I knew this was going to get expensive; - but the body on the car is perfect, there is no rust at all on it. If it had any rust, I probably would have cried a little and scrapped it all rather than sinking a ton of money into it.

There are none of these cars around here anymore, they all dissolved back in the 90s. This might be the last one in the Edmonton area. As I said, I'm no stranger to rebuilding engines, I've done dozens of Buicks and Oldsmobiles, (I've been into collectable cars for 40 years now) and they aren't cheap either. (I seem to have a knack for buying them, beautiful body but exhausted mechanicals, it never fails!) They're a lot easier to rebuild though. And the last set of Nailhead pistons I bought were about $150 a hole. So while these are double, there's only 6.

I do have the factory manuals, and yes, I only want to do this once.

[Heckflosse]

Just so that everyone knows what I'm playing with, here's a picture of the car.

[ja17]

Send me a PM and we can talk on the phone. I still think your missing something on the carbs. I know where to look!

[Heckflosse]

PM sent...

[Heckflosse]

So; - to follow up;  the 250 (M129) engine has one dead hole. The #3 is down to < 90 and the #4 is at 100, the rest are between 125-135. So there's potentially a head gasket issue if nothing else. A cam swap made it run a little better, but the original issues haven't changed, so that implies something more than a vacuum leak.
I have it running and "idling" at about 1100 RPM. It's still a bear to start.
So it's toast.
I might strip it down over the winter and see if it is a head gasket, I don't know, and I don't know if it's worth the trouble. From what I've seen so far, this engine is pretty worn out. I might be wasting a lot of time if I did take it apart. If so, why did it fail; - was it a head issue (apparently M129 is famous for that) or is it bottom end? One thing i do know, is that before I got it, it hadn't seen an oil change in decades. The filter was a long out of production thing, and what was in there was very black. 
In the meantime, I'm going to rebuild the 230, hopefully it's easier to find parts for it than the M129. It at least has a completely refurbished head.
I'm just sick and tired of playing with junk; - might as well do what it wants and just rebuild the damn thing and be done with it.