I have recived many requests for a detailed explanation of some of my modifications for the 617 engine.

In actuality, I make rather extensive modifications to these engines which is not only overkill in many respects, but difficult and costly to replicate. However, I will mention just a few of the many changes I make to the venerable 617 Turbo Diesel.

Aside from a fully ported and polished intake tract/cylinder head, I use the larger Buick V6 'Grand National' Exhaust Turbine to improve spin-up at lower exhaust gas velocities. This requires extensive modification of the turbocharger housing, but makes a tremendous difference in low rpm throttle response.

All the injektors are fired on a test stand and the springs are shimmed to bring all injektors to within 10 psi of each other. This isn't as costly as it is time consuming, but can yield tremendous benefits in terms of smoothness and overall performance.

I have even experimented with installing the larger intake valves in the exhaust position for increased exhaust flow, but this is again a very expensive and time consuming operation.

Despite all these tricks, probably the greatest performance potential exists in proper camshaft & injektor pump timing.

I have been asked repeatedly for information on how I time the 617 engine. This post is in response to those requests.

Consider first the two different camshafts available for the 617 engine. The early versions (617.950) used a camshaft marked '00' that had the following timing figures at 2mm valve lift:

Intake Opens 13.5° ATDC Exhaust Opens 19° BBDC

Intake Closes 15.5° ABDC Exhaust Closes 17° BTDC

I prefer the lengthened valve timing of the later (617.951/952) camshaft marked '05' and use it in all 617 engines I work with. The valve events at 2mm valve lift are as follows:

Intake Opens 9° ATDC Exhaust Opens 27° BBDC

Intake Closes 15° ABDC Exhaust Closes 16° BTDC

Mercedes gives these specifications when a new timing chain is used and offeres the following valve timing figures for engines with 20,000 km or more:

Intake Opens 11° ATDC Exhaust Opens 29° BBDC

Intake Closes 17° ABDC Exhaust Closes 14° BTDC

Based on these figures, it is clear that Mercedes wants about 2° of initial advance on the camshaft to account for the eventual stretch/wear of the timing chain.

On my engines (and those of customers) I advance the camshaft timing a full 4° to the following specifications:

Intake Opens 7° ATDC Exhaust Opens 25° BBDC

Intake Closes 13° ABDC Exhaust Closes 12° BTDC

If you consider the theory that the timing will retard approximately 2° after 20,000 km of operation, 4° of advance would cause the engine to 'wear into' the original specification instead of wearing out of specification.

Mercedes offers offset camshaft wooddruff keys ranging from 2° all the way to 10° of correction. I will post the part numbers later this weekend for reference, although they are easy to find at around $7.00 (USD) each.

The important thing to keep in mind when advancing the camshaft timing is to advance injektor pump timing the same amount in camshaft degrees.

Advancing the pump timing 4° from its recommended setting of 24° BTDC would result in a static setting of 28° BTDC overall.

However, after about 20,000 km of operation and a loss of approximately 2° of timing overall, the pump timing would retard to around 26° BTDC.

Keep in mind that Mercedes allows + or - 1° on injektion pump timing making 26° approximately 1° advanced above specification.

The slight amount of advance definitely improves low rpm throttle response and overall smoothness of engine operation, although it does increase the noise of the combustion process slightly at idle.

You would be amazed to see and hear how these engines run when the time is taken to ensure everything is set to an exacting specification.

I hope this information is helpful...Bert

Bert,
That was an exceptional read - THANKS!!!
I had recently advanced my injection pump timing 2 degrees and realized the exact benefits, and slightly higher idle noise, that you commented on. Also, my cold idle seems really low now where before it wasn't. Cold starting is still on the money even at the few 15 degree days we have had.
Is there increased risk to the head gasket as well.
Thanks for your expert advice!
Adam Bush

Bert.........many thanks for that post...........I am printing that out to slip into my service manuals..................When it gets warmer out I am going to try to do exactly as you describe.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Bert,
Do you feel it is realistic to attmempt such modifications on a engine with 250,000 miles on it? or is it best to save for a rebuild, and then go for the porting/super tune up which you have described?
I am excited by the idea of fattening the touque curve in the low end...
Jason

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46 WDX Power Wagon

84 300TDT daily driver

I would honestly have to say that the porting & polishing probably is overkill in this application. However, since I have done it for years on competition engines, I just went ahead and did the same thing to this engine.

Keep in mind that seldom will a single modification give you a measureable benefit. It often takes a number of small modifications, carefully chosen to work togther, to realize the full benefit in terms of performance.

On an engine with 250,000 miles, I would suggest timing chain and rail replacement along with a new tensioner before making performance modifications.

While you are at it, make sure injektor and camshaft timing are set correctly.

Correct boost pressure (within specification) will do a lot for your performance. Keep in mind that 99% of these engines on the road have badly worn turbochargers.

I have seen some worn so badly the intake turbine actually sawed a hole in the housing. This sprayed aluminum flakes into the engine which casued other damage.

Adam:

The low idle speed cold shouldn't be an issue with only 2° of advance. The opposite should be true when you employ an advanced delivery setting over one that is retarded. The question is, just where is your total injektor pump timing???

Considering the specification non the 617.950 engine is 24° BTDC and these engines will accept settings as high as 28° with no problem, I have seen amny people advance the timing as high as 30° and wonder why the engine isn't running correctly.

I set initial injektion timing with the 'drip' method, as outlined in the 617.950 Shop Manual, but I ALWAYS verify it with a timing light and impulse adapter to be absolutely sure.

I believe what you might be recognizing as a low 'cold' idle speed is the fluid friction of the oil and the resulting resistance to being pumped through the engine.

As far as head gasket life is concerned, I don't see any risk at normal operating temperatures. I use a 70°C thermostat in all my Diesels, which I feel is optimum under most all conditions.

The biggest risk to the head gasket comes from the use of too much boost pressure and the old style (617.950) 'straight-shank' head bolts. These are the ones with the allen heads, not the 'torque-to-yield' bolts with the 12mm 12-point head.


JDMills:

As previously stated, chains, rails, tensioner and timing would be a good start on your engine. Ensuring you have a properly functioning turbo and adequate boost pressure would be the next step. Finally, adjusting the ADLA slightly could very well give you the flatter torque curve you are looking for.

I hope this information is helpful...Bert

Doktor Burt,

I got a much better Idea now about where and how to proceed. Thank You

I have a spare motor, which I hope to use as the base for my 'performance upgrade' I am trying to plan it out befour hand so that it turns out to be balanced improvements with each one being complemantary to the next . I am suprised that you think porting is overkill, but you have much more experince than I. I was under the impression that porting would be necessary as one reaches the limits of the stock injection pump.... overzelous on my part. Thank you for shairing your knowlage and insight.

Jason

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46 WDX Power Wagon

84 300TDT daily driver

Porting & polishing are much less of an issue in a turbocharged application since the intake tract is pressurized.

On a gasoline engine, where the intake tract is under vacuum, any reduction to airflow resistance is most helpful.

I am not saying porting & polishing gives no benefit, but don't expect it to make your 300SD run like a 560SEL.

Just keep the modifications and their benefits in the correct perspective...Bert

Doktor Bert, Danke for the great post, this has awakened my thoughts about the performance of my '85 engine (transplant into '79 300TD). I have been attempting to solve the high idle speed it has, it idles around 750 maybe a tad over that as read on the tach in the instrument cluster and the car creeps more than it should with the brakes off. I have been living with this for almost 2 years since the engine was rebuilt by shifting to N at stop lights. I have driven it cross country and it runs fine after it gets up, the turbo was also rebuilt and spools up (I read boost pressure in the cabin) but the acceleration seems to be lacking. I tweaked the ALDA two turns out and it gets up off the line but still I think its missing a little oomph, the torque curve seems a little steep or something, maybe that isn't the right description.

Everything topside is new with first oversize pistons. Rebuilt IP by Pacific FI and matched injectors.

After reading this thread, I now wonder if my timing might be retarded?
The engine starts perfectly with a twitch of the starter switch and has no nailing cold. If advancing the timing will reduce idle speed then I am for that, I have loosened the idle set screw completely out and never able to drop the speed below 750. The possibility is that IP was set up wrong, but I want to dismiss that because Gus is very thorough and I hope would not deliver something with a problem. I have seen the internal rack, and the rotating wedge that controls flow of fuel as the linkage is operated, its an amazing Bosch design that goes back some 50 years.

I am going to go after this issue as weather improves. I think a little effort will make the car run like my other wagon, a stock '85 with 220K miles on it, it has better acceleration than the rebuilt engine discussed above, even with the taller gears in the differential.
My herd:
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 296650 (14K on rebuilt engine)
1983 300D 243280 w/2.88 differential
1985 300TD 223470
1987 300D 262300

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Gus does very good work. He did a few Kuglefischer Mechanical Pumps for me years ago when I was working on Vasek Pollack's 5.4 Litre Flat 12's in the Porsche 917. Very nice man to do business with.

Your ilde speed sounds very good at 750. You might try looking at the linkage to see if it is binding somewhere and causing the idle speed to 'hang' slightly.

It never hurts to check your timing...Bert

Here are the part numbers for the offset woodruff keys:

621 991 04 67 2°

621 991 02 67 3°

621 991 01 67 4°

621 991 00 67 5°

I have found the 621 991 02 67 is the most frequently used key in the series.

On my 617.950 engine with the '05' camshaft, I needed 9° ATDC @ 2mm Valve Lift and with the stock key I had 11° instead.

The addition of the 621 991 02 67 key brought my intake timing to 7° ATDC @ 2mm Valve Lift which is 2° advanced from the camshaft specification sheet.

Since MBZ states the timing after 20,000 km will retard approximately 2° (from 9° to 11°) setting the intake lobe of the '05' (late style) camshaft to 7° ATDC will allow the engine to 'wear into' a near-perfcet state of tune as the timing chain stretches/wears.

I also advance injektor pump timing 2° (from 24° BTDC to 26° BTDC) to keep them both in the same relation to each other.

I hope this information is helpful...Bert

Innnnnteresting....Hmmmmmmmmmm.

I did this kind of thing to a 1984 300D in a 124 chassis...fully ported, heavy valve springs, rebuilt turbo and IP.
Ran sub 10 second zero to 60 when the tires could bite.

I ran it at 112 mph in 96 degree weather with the a/c on for about 4 miles....
until the oe radiator finally could not keep it cool enough and the needle climbed to the peg and I backed off to 70 to 70 cooling it off
That's when I found my manual turbo boost limiter had allowed it to creep up to 35 psi !

One point to note though, and you can debate me on this ...higher turbo boost and fueling is a
candidate for LOWER compression and RETARDED IP timing.
My compression ratio worked out at about 17 to 18 to 1. and still got cranking pressures over 400 psi.

The injectors I set to 170 bar.
I used a Total Seal® ring set too.

Why ? The higher boost/fuel load leads to too much heat for the engine to reject at normal OE spec's.
To get reliable power at this elevated level is to ceramic coat the pistons crowns and the exhaust valve heads.
Reset the IP timing devise to limit advance by 8 degrees at the higher rpm.

Ideally, there needs to be an inter cooler or water injection at least and most importantly a pyrometer BEFORE the turbo.

This car of mine made 35 psi of boost unlimited and was finally restricted to 19 psi.
I know it lived with the new owner for 5 years and he with a silly permanent grin on his face.

As a little prospective here, I have been racing/ repairing/modifying motors of all types for nearly 40 years.

As for your lake of grunt off the line there are various reasons for this...try turning out the ADL boost capsule all the way.
Check your stall speed, should be around 2300 to 2500 rpm warm. DO NOT STALL TEST FOR MORE THAN 5 SECONDS !!!!
If stall is around 1200 to 1800rpm your torque convertor is bad. If it is 2800 to 3000rpm or more the forward clutch is shot or your spinning the rear tires !

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TTT for n00bs.........

maybe x post to the performance section??

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1984 123.193 372,xxx miles, room for Seven.

1999 Dodge Durango Cummins 4BTAA 47RE 5k lb 4x4 getting 25+mpgs, room for Seven.

I'm about to have my mechanic do my timing chain+sprockets+tensioner+guides on my OM616, same thing applies -- advance by 4 degrees?

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231K Miles FOR SALE MAKE OFFER

4° is a good setting. I usually find they lose around 2° by 20,000 miles due to chain wear/stretch...Bert

Howdy Dr. Bert, glad to see your still around!
I've put maybe 20K on my 617 since it was rebuilt, it seems to be getting stronger every time I drive it! I didn't hassle with sleeves, I had it bored first oversize and new pistons.
Reid

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!