I noticed Tom’s request for feedback regarding sound practice for firing up a rebuilt engine for the first time. I am pleased to offer the following summary of what – from the perspective of my own experience – I have come to consider to be the most crucial points of the matter. Perhaps the writeup that follows will prove somehow useful as Tom plots his way forward with his project.
To be fair, I must first qualify my remarks by acknowledging that my experience in this milieu is confined almost entirely to the realm of small and big block V8’s of American manufacture, involving various refurbishment projects of Cadillac, Chevrolet, Buick, Pontiac and Chrysler engines. The projects in which I have been involved entailed the rebuild of engines manufactured in Detroit, occupying an approximate 15-year vintage slice, from 1957 to 1972, all in my personal pursuit of my Detroit Iron hobby, from about 1968, up to the present day. My current project is the total restoration – with some technological upgrades – of a ’57 Eldorado Seville. As for Mercedes, apart from having my head for a half hour or so beneath the hood, gazing with admiration at our mutual friend Rolf Dieter’s exquisite example of the incomparable and iconic Pagoda, I must acknowledge that my experience working on, or around Mercedes engines is precisely zero.
It will be perfectly understandable if some readers consider the above described context insufficiently relevant, and decide to opt out here and now. Those whose interest in the subject leads them to read on anyway, should keep the potential significance of this context in mind - that of a naturally aspirated - single or dual carbs - overhead valve, pushrod V8, with a single, centrally positioned camshaft, operating the intake and exhaust valves by way of hydraulic flat tappet or roller type lifters, through rocker arms of either adjustable, or non-adjustable (as in the case of Cadillac) design. The fuel pump is typically of the mechanical type, driven by the engine by way of an eccentric cam shaft lobe. The ignition source is the conventional arrangement of a distributor – either with non-contacting electronic proximity sensing trigger or actual breaker points and condenser – and a single induction coil of either conventional or MSD (multiple spark discharge) type.
Notwithstanding the peripheral details however, the underlying concerns that motivate normal standard precautions for preparing American V8 engines to run are universal in nature, and are thus applicable to any internal combustion engine rebuild project. The determination of relevance, and further, the means by which each measure discussed in the following paragraphs might be applied to one’s own individual application and circumstances, must necessarily be left up to the reader.
1 – Preparation:
Effective organization – both during reassembly as well as in advance of firing for the first time involves proportionally little time, and minimal effort, yet the results can be significantly beneficial.
The best results can be enabled by an approach that is both positive in expectations of outcome, and thus anticipates the best, but anticipates the worst. Ergo:
Ensure that your surrounds are neat and tidy, tools you anticipate will be needed are neatly arrayed close at hand, and those that won’t be required are stowed away. Cordless lights work best if possible, serving to avoid tripping hazards associated with extension cords. Use of fender skirts or drop sheets to protect the tops of fenders should be considered as being essential.
Charge your car’s battery fully over the previous night, if possible, and/or have a fully charged spare, or a buzz box available, for backup in the event that your 12V source unexpectedly proves inadequate, or runs down early.
Potential difficulties can be avoided later by the precaution of cranking the engine momentarily with a single spark plug wire pulled and its terminal held a fraction of an inch from a ground location (cast iron block or heavy portion of suspension/frame) to confirm that there is spark at the spark plugs. A ¼ inch stud or bolt inserted into the terminal boot to extend the conductor beyond the insulated boot can facilitate this process.
Make a final check that all hose connections (fuel/water/vacuum etc.) to ensure that all clamps are assembled and tight, and that wiring connections are terminated correctly.
If your car’s instrumentation array does not include a visible indication of actual oil pressure, whether analog or digital, consider installing one, even if only on a temporary basis. The cost and effort involved in doing so is miniscule in comparison with the potential impact of suffering a low oil pressure condition that escapes notice.
Preparatory to firing, make one last final check of all fluid levels prior to starting. Engine oil, coolant, and transmission fluid levels should be at normal running levels.
If the desire is to avoid the use of glycol based anti-freeze for any reason, use of plain water on its own should be avoided. For the optimum blend of corrosion protection of critical engine components, and excellent coolant heat conductivity and transfer capability, water mixed with water wetter is an excellent choice. Among the numerous advantages of water wetter over plain water is the fact that, unless and until an ambient temperature at or near freezing becomes a genuine concern, there is no need to change the coolant later, after the runup is successfully concluded. RED LINE Water Wetter is an excellent choice.
Have a fire extinguisher close by, the operation of with which you are familiar, and that you know is charged and ready.
2 – Assurance of Adequate Lubrication:
If there is a more crucial concern in successfully returning are built engine to operation than the assurance of lubrication prior to and during start-up, I am hard pressed to imagine what that might be. The first three points in the discussion to follow address this concern.
Well before firing, during assembly of the (new) cam and lifters, a typical precaution is to pour a full can (Approximately 8-oz.) of GM EOS (Engine Oil Supplement) over the cam lobes, prior to installing the lifters in their bores. Or- if using an aftermarket cam and lifters, be sure to use all the assembly lube supplied by the cam shaft manufacturer. The intent of the pre-lube is to ensure that the surfaces that will be subjected to the highest pressure wiping forces will be first coated with a film of high strength lubricant, which will permeate the surface of these components and maximize assurance of a successful break-in. Granted, this precaution might be difficult to observe for an engine that has been previously assembled by someone else, but it is reasonable to anticipate that any reputable engine builder would be well aware of this precaution. If in doubt, a call to the engine builder would not be inappropriate, and might render either peace of mind, or cause for partial disassembly to address.
The selection of the optimum oil for the crank case can be vital to the successful operation of any engine, particularly one having just been rebuilt – and even more so if the restart involves the initial operation and break-in of a new camshaft, lifters and other valve train components. A recent development in the formulation of automotive lubricants in North America has been the drastic reduction, and impending elimination of the use of the highly effective extreme pressure friction reducing additive, zinc dithiophosphate (“ZDP”), from any motor oils used in applications that require SAE certification. ZDP was developed during the 1940’s – a cutting edge evolutionary period for the internal combustion engines – involving test mules like the radial engines that powered such beasts as B-29’s and P47 Thunderbolts. ZDP became indispensable as an oil additive due to the significant contribution to properties of extreme high-pressure lubricity, and improved film wetting effects, resulting in enhanced protection of critical engine components against mechanical wear and corrosion effects, not only under the severest of operating conditions, but - and perhaps of equal or greater importance for the classic car enthusiast - during extended periods of inactivity during storage.
Recent technological developments have given rise to such refinements as multi-valve per cylinder combinations, and the elimination of flat tappet cams in favour of ‘roller-ized’ lifters, have culminated in significant reduction in required valve spring preload levels, and thus a proportional reduction in camshaft lobe and lifter/roller interface pressures. As such, the elimination of the beneficial physical properties associated with oils formulated with ZDP has less importance to engines rolling off assembly lines today than for their older, more primordial forebears.
The universal law of probability dictates that one should always avail one’s self of every possible advantage, and it is only logical to pick the low hanging fruit first. SO - if you’re not already using a high ZDP blend of oil, you should give due consideration to changing your oil now, before starting, and refill with a ZDP blend. There are many options . . . but to name a few:
Royal Purple
Joe Gibbs Racing Oil
AMSOIL
While possibly the following may entail considerable innovation for the Mercedes enthusiast to duplicate, in preparation for starting a rebuilt Mercedes engine – the potential benefits of doing so are sufficient to warrant me sharing it here.
Standard practice for Detroit Iron gearheads like me is to prime the engine oil system completely, and bring up to full pressure for several minutes, as late as possible – if not immediately before - firing the engine for the first time after a rebuild. The tooling required to make this happen need only be very rudimentary. For GM V8’s, this entails removal of the distributor vertically upward and out of the block, and the insertion of a shaft (approx. 14 inch long) with a flat ground on the end business end, of a dimension specific to the purpose of engaging the drive slot provided at the top end of the vertical pump drive shaft. The top end of the shaft is held in a drill chuck, with which the pump is driven to circulate oil throughout the engine oiling circuit. (Important that every precaution is taken throughout this process to avoid foreign objects/dirt etc. falling into the engine. Thoroughly flush, blow and clean the drill chuck first.)
Driving the pump shaft at 1500 RPM with a corded electric drill will produce oil pressure equivalent to 3000 engine RPM. This allows the oil pressure to be brought up to the setting of the pump relief valve (typically in the range of 30 – 50 PSI, monitoring with a temporary pressure gauge is always a good idea), allowing the engine oil circuit to be flooded and pressurized, and oil to flow to all points of the system. If done with the valve cover(s) laid in place but not bolted, copious oil flow can be verified visually by alternate momentary removal of either cover. Until a clear sense is developed as to the amount of oil that splashes around inside the valve train under this condition, it is best to avoid actually running the oil pump with either cover off. Being too cavalier about this point can lead to an oil mess at an awkward time and in the wrong place.
While a cordless drill might work well here also, there needs to be adequate battery life in reserve to maintain oil pressure for 5-10 minutes.
Among the advantages of achieving full system oil pressure in the manner, for any extended period of time, is the opportunity thus afforded to make a visual check of the entire oil system for external leaks, and to flood a new oil filter, which if only recently installed, may well contain a slug of air of significant volume. This is simply not possible by means of circulating oil by cranking the engine on the starter.
Recheck oil level at the conclusion of this process, and replenish if required.
3) Initial Setting of Ignition Timing:
The final setting of the ignition timing requires the use of a dedicated timing light, while the engine is running at idle speed. (Vacuum advance to distributor disconnected and plugged.) The first few moments of running a rebuilt engine is NOT the ideal opportunity for this, but rather, is best left until after the initial valve train run in that should be performed immediately upon start up.
Potential difficulties can be avoided if the initial clocking of the distributor is done such that when the engine is fired, it will be necessary to retard, rather than to advance the ignition timing to achieve a setting at which the engine runs smoothly during the valve train run in period. (20 minutes or so). The reasoning for this precaution is simply that, when an engine runs with abnormally retarded timing, regardless of RPM, the relatively late spark event results in an artificially shortened duration firing stroke, and correspondingly elevated exhaust gas temperature. In my own experience, running an engine under conditions of no mechanical load, (i.e. transmission in neutral) and with significantly retarded ignition timing – even for a minute or two – can produce sufficiently elevated exhaust temperatures to get headers, or even cast-iron exhaust manifolds glowing red hot. The preferable scenario therefore is to fire the engine with an abnormal degree of advanced timing, and then approach the ideal timing window by rotating the distributor in the “timing retard” direction while cranking the engine to start. (One person can perform this if necessary, by way of a remote start switch, temporarily wired to the starter terminals, and cranking from beneath the hood with the ignition key left in the ON or RUN position.)
4) Initial RPM Range after Starting;
Avoid running the engine at low RPM, near idle, for the first 20 minutes or so after initial firing. This precaution is primarily for protection of new valve train components during the initial break in period, during which the maintenance of adequate lubrication is crucial to success. As the quantity of oil available to lubricate valve train components during operation is always a function of oil pressure, and oil pressure is proportional to engine RPM, operation in the 2000 – 2500 RPM range immediately after initial firing will help to ensure adequate oil flow to lubricate cam lobes, lifter faces and rollers, push rod and rocker arm tips at what is a crucial stage in the break in process.
This initial run in period presents an ideal opportunity to make a visual and audible examination of the engine all over, for abnormal conditions such as, low oil pressure, high coolant temperature, unusual valve train noises, or evidence of fuel, oil water or vacuum leaks. This is also an opportunity to look at ignition timing with the timing light, but any adjustments must be made judiciously at this point, solely with the objective of smooth running and control of exhaust gas temperature in mind. The distributor mechanical advance curve will dictate that the appropriate ignition timing will be significantly BTDC (before top dead center) than the ignition timing specified in the book, perhaps as much as 20 degrees or more.
Unless Mercedes’ philosophy differs from that to which I am accustomed, the final setting of ignition timing will need to be made at idle, later, subsequent to the completion of the initial run, at which RPM the initial timing is typically specified. (Usually with vacuum advance disconnected and plugged.)
5) Final Wrap Up:
Once the initial twenty-minute run has been successfully completed, with no fluid leakage, abnormal noises or overheating issues arising, the engine RPM can be reduced to idle. On our typical V8 breathing through carbs, the idle set screw in the throttle linkage is set to achieve the desired RPM, initial ignition timing setting is finalized, distributor vacuum line is connected and the idle circuit mixture screws are adjusted, to give the desired throttle response.
The engine can then be shut down and restarted a time or two to ensure ease of starting, then a final check of fluid levels to ensure that all are normal.
Next step is to take a few minutes to catch your breath, bask in the warm reflected glow of your accomplishments thus far, while enjoying a bottle of water, or a coffee, a beer of whatever. Then, after tidying up, and aligning and bolting the hood into place, it’s time to open the garage door and let the games begin!
All best,
Robert
“The Coquihalla Kid”
Edit: I have cleaned up a few embarrassing typos, errors in syntax,
