Replace Timing Chain?? When??
 

We have two 84 300d's, my wife 300td has 210k and mine has 176k. Both engines are very strong and start up in the coldest of weather(60+!!) here in San Diego. I have changed the oil every 3k and valves adj. every 15k. The previous owners took good care of these beauties but....given the milage, when should I have the timing chains replaced?? My mech said they look fine with not much stretch in them?? Can this check be done during the valve adj.? He gave me a price of close to $600.(each!!!) to have it done, which includes replacing the guides etc.. Both engines sound very tight etc... Thanks for your help:cool:

I just had the timing chain replaced in my 85 300d. My tech suggests to replace the chain @ about 200K. I have 229k (only 229k) now so it was about time. He also said that the 123's don't tend to have any timing chain problems but the chain is much cheaper than a replacement engine. My cost was $370. 4 hours labor to replace the chain & do a valve adjustment. The chain part was $138. $600 is a bit steep for one car.

That other $3-$400 if for the guides. That sounds about right if that included the parts.

You check timing chain stretch using the following procedure (for a non-turbo 300D, you'll need to get the specs for you turbo):

1. remove valve cover
2. adjust #1 intake valve to 0/zero clearance
3. mount a dial gauge so it contacts the valve spring cap at a
perpendicular angle (or as close as you can with a
preload of greater than 2mm, 3-4mm is best)
4. turn engine to TDC #1 cylinder
5. carefully continue to turn engine until #1 intake valve opens
2mm
6. read the degree marks on the harmonic balancer

On the non-turbo 300D a new timing chain will show 11.5 degrees ATDC (after top dead center)

A chain with 20,000 km or more will show 13.5 degrees ATDC

M-B uses/sells offset woodruff keys to adjust cam timing for used timing chains in good condition, offset woodruff keys come in 4, 6 1/2, 8, and 10 degrees of cam timing (cam turns at 1/2 speed of the crankshaft)

You cannot use the notch in the cam washer and the timing mark on the cam support/bearing to determine how much chain stretch you have. These marks are used to assemble and time the engine when assembling it and/or replacing components and the crankshaft, cam, injection pump or the IP timing device have been moved and everything needs to be re-timed.

Your turbo 300D uses a similar method to determine timing chain stretch (and from what I've read in the Tech Forum and at the library a lot of the M-B gas engines also use the above procedure to check chain stretch). What I do not have is the degrees ATDC specs. for your engine. Perhaps one of the other members has this info and will share it with you.

Good Luck!
Tom

I replaced the chain on my 82 300SD at about 200K. It has not had the oil changed as often as it should have, therefore premature wear.

You did not say if the $600 included a new tensioner. I have been told that is should be replaced with the chain. There are several different one for the early 80's 300SDs, of course mine hadto be a more expensive one at $240. I payed around $140 for the chain, about the say as stated in a early post.

I inspected the guides and could not see any wear and opted not to replace them.

I used the method of using the notch in the cam washer and the timing mark on the cam support/bearing to determine how much chain stretch I had. The old chain showed 10 degrees, the new chain 2 degrees. Tom states that this is not the proper method, but I think will show the differences in the chains.

The differnces I saw in performance was :
1. Much less smoke
2. Smoother idle
3. Better acceration

This was the only work I did on the engine which would affect performance.

My odometer is broken, so I can't check mileage.

Wayne

82 300SD
98 ML320

The method I wrote about for checking timing chain stretch came form the official M-B engine service manual. Both my print M-B engine manual and my M-B CD-ROM engine service manual state that for both the non-turbo and turbo engines that the timing marks on the camshaft washer and cam bearing tower are used to assemble the engine. M-B goes on to say that in "special cases, e.g. complaints about poor performance, it is neccessary to check and adjust as follows" and the manual goes into detail about the method I covered in my first reply (using the dial gauge, etc.). You can read other, older threads written by members with a lot of professional experience with M-B diesel engines saying to use the dial gauge method.

Checking the crankshaft to camshaft timing using only the marks on the harmonic balancer and camshaft washer/cam bearing does not provide an accurate measurement of one the most critical relationships/adjustments in a diesel engine. If you do not get enough air into the cylinders, then there will not be enough air compressed/heated on the compression stroke to provide complete combustion for the incoming diesel fuel when it is injected into the cylinders. This critical relationship/adjustment is probably higher with a turbo diesel since the turbo is forcing more air into the cylinders coupled with more diesel fuel from the IP through the injection nozzles, and a new camshaft design (beginning in 1980) that has longer duration (opening time) for the valves to take full advantage of the turbo.

I know when I was looking at my timing chain marks the position of where and how I looked at the marks made a difference. Looking at the harmonic balancer and the timing pointer you must have a perpendicular, 90 degree angle to have correct alignment - the vacuum pump housing is almost in the way on my engine. Also, my harmonic balancer and others that I have seen are marked in 5-degree increments - so unless the harmonic balancer is measured and marked for increments of less than 5-degrees any reading is going to be a guess. The cam washer and cam bearing marks must be looked at using a position along the center line of the camshaft using either the parting surface of the block and head or the contact surface of the head and valve cover as a reference point to make sure you are not too high or low from the center line of the camshaft and then looking back into the recessed area where the marks are located. Even using a strong light and correct positioning it is hard to see the cam marks accurately and those marks are large and not precise. A small deviation in alignment when looking at any of these marks will have significant effect on the crankshaft to camshaft positioning in the degrees that are being read/measured.

M-B does not provide a spec saying that if the timing chain is stretched X degrees, then the chain needs to be replaced. What M-B discusses is the use of offset woodruff keys to correct the crankshaft and camshaft tiiming because of timing chain stretch. The offset woodruff keys go up to 10 degrees of camshaft timing correction, which is a lot - a one tooth difference on the camshaft sprocket equals 18 degrees, so a 10 degree offset key is over 1/2 tooth correction. The M-B engine manual goes on stating that if the timing chain needs adjustment to correct the timing relationship between the piston position for cylinder #1 and #1 intake valve (zereo clearance at 2mm opening) then use the offset woodruff key to correct the timing, unless the timing chain is excessively elongated (not defined by M-B), then the chain needs to be replaced. I recall a thread where one member who worked on M-B diesels professionally for over 20 years stated that if the timing chain had not worn grooves and/or was slapping around in the valve cover and the tensioning rail did not have deep grooves in it that the timing is corrected by using offset woodruff keys.

When I replaced the timing chain on my 300D, with over 300,000 miles on it, I did so because the tensioning rail had some pretty deep grooves in it (about half way through the rubber). I measured the new and old chains and found that the new chain was 50 15/16 inches long and the old chain was 51 1/32 inch long, for a total stretch of 3/32 inch (using the dial gauge method, my chain had 17 1/2 to 18 degrees of stretch, 13 1/2 degrees is the M-B spec for a used chain). I cleaned and inspected my old chain and did not find any cracks in the side plates or cracked rollers (I did use a magnifying glass - 10X - to inspect parts of the chain, but not the entire chain). The old chain looked like it was in good condition and still serviceable.

It was written that you can use the cam washer mark and cam bearing mark to determine the timing relationship of the crankshaft and camshaft instead of the dial gauge method recommended by M-B - and then going on to say how good the engine runs, etc., etc. and that the timing marks are now off by only 2 degrees with the new timing chain instead of 10 degrees with the old timing chain. From this info this engine's timing is off and that when the new timing chain stretches (as they all will) the timing will be off even more - meaning this engine will require a 4 degree offset woodruff key (perhaps another woodruff key) to correct the timing and enable this engine to run as well as it can. Compared to the way this engine ran with the old timing chain to the way it runs now with the new timing chain is probably like night and day - and that's great. However, how much better will this engine run if the crankshaft/camshaft timing is properly adjusted using the M-B dial gauge method? But, hey the engine timing is almost correct and it does run better - so, if the owner is satisfied with an engine that is almost timed correctly then I am almost satisfied that his engine almost runs as well as it can. The point of this forum (as I undersatnd it) is to exchange relevant and accurate information to help each other with our respective problems and questions. All I am doing is passing on the the M-B info for timing chains: how to correctly time the crankshaft to the camshaft - a most critical relationship/adjustment in a diesel engine - and timing chain stretch correction using offset woodruff keys.


I looked at my CD-ROM engine manual for the turbo 300D engines for the timing chain and crankshaft/camshaft relationship. The specs I wrote in my first reply for the relationship of #1 piston and #1 intake valve are good for 300D turbo diesels up to the 1979 model year with engine 917.950 and camshaft code 00 or 08.

The 1980 model year and newer have a redesigned camshaft and the timing specs are different. These specs apply to the 917.950 engine with cam code 05 (cam made of chilled cast iron) and also the 917.951 and 917.952 engines. Using the M-B dial gauge method (#1 intake at zero clearance and 2mm open on #1 cylinder) the intake valve should be at 9 degrees ATDC (after top dead center) read on the harmonic balancer and a used chain with 20,000+ km has a spec of 11 degrees ATDC.

Good Luck!
Tom

With religious 3,000 mile oil changes in this engine as it has seen. and with its double row timing chain, the chain will outlast the engine, no problem.

Good luck,

A dial gauge with a magnetic stand is available for $75.79 (list $141.62) at this site:

http://robertstool.com:81/central_tools.htm

You will find the Long-Range Indicator Test Set model number 6410 made by Central Tools. This dial gauge measures inches, but a metric gauge may be available for the same price (you'll need to ask). If they will only sell the dial gauge calibrated for inches, then the conversion factor is easy: multiply millimeters by .0394 to get inches, so 2mm of valve lift is the same as .0788 inches of lift (2mm x .0394).

Central Tools makes high quality precision measuring instruments.

You can also buy dial gauges with flexible stands (the kind I own) or magnetic stands made by Central Tools for about $140 and up from OnTools.com.

In addition to measuring the valve lift to time an engine, a dial gauge can also be used for normal maintenance operations such as:

front wheel bearing clearance adjustment
brake rotor runout/warpage
ball joint play

And other precision measurements such as:

crankshaft main bearing runout
crankshaft end play
camshaft bearing runout, lobe measurement
valve guide clearance
gear backlash

Tom

Timing chains for DIY's are $70 from Performance.

What are the symptoms of a stretched chain from an engine performance aspect?

Frank.

My timing chain at 2mm valve opening with 17.5 to 18 degrees ATDC of stretch (13.5 is normal) had these operating characteristics:

started easily
ran smoothly
loss of power up hills
slower than normal acceleration
on a flat road would cruise at 70mph, but slowed down up almost any hill
excessive black smoke out of exhaust on start-up and warm-up
excessive black smoke when the accelerator was opened to full open position or close to
fuel efficiency dropped

Hope this helps!
Tom

Problems of delayed camshaft timing, etc.
 

It is well known among grey-haired old hot rodders like me that retarding the camshaft on a gas-burner will increase top end power but kill low end torque, whereas advancing the cam will increase the bottom end while lowering the top end peak -- lots of us used to have sets of offset Woodruf keys in our tool boxes to adjust the cam timing in various 427 cid super modifieds for varying track conditions.

I'm not sure that checking against the assembly timing marks isn't plenty good enough for keeping a watch on chain stretch, though, provided you know where your motor was at to begin with. Lots of the high end motors that I've worked on with vernier type of adjustable cam sprockets from the factory to allow for compensation for chain stretch (Maserati V8s and classic Lancias, for instance) just specified checking and resetting the cams by the marks at every valve setting -- but they were indeed assuming that they were set up right on to perfection from the beginning. To me, the factors other than chain stretch that would throw off the assembly marks, such as tensioner or sprocket wear, would also throw off the dial indicator method, and in the latter case, you might get fooled by cam and rocker wear if you weren't careful, too. The real key is being perfectly familiar with every individual motor and taking notes from one tune-up to the next.

Fimum, welcome to the board...Greg

Thanks Tom. That last one is what got me. The fuel efficiency. I have this inexplicable poor mileage. After reading the other post about timing and top vs. low end torque, I have a lot of top end torque. I don't know if the low is missing any because if it is it was that way when I got the car. I'm going to check the valve timing and see what comes up.

Frank.