Setting injection timing - accounting for timing chain wear

[JHZR2]

I’m going to reinstall a diesel injection pump in my 1991 MB 350SD soon.

MB provides a convenient way to measure timing chain wear/stretch by lining up marks on the cam tower and measuring the degrees on the harmonic balancer.

2 degrees of west/“stretch” in 206k miles.

However, when I was going to pull my injection pump, the instruction is to turn engine to 14 degrees ATDC, then insert a locking pin to engage a tan on the IP.

The first time I tried to engage the lock tool I had the engine at 14 ATDC. But it didn’t engage. So I turned the engine 360 degrees, twice, and crept up on it. Turns out it was more like 17 ATDC.

So, my chain is stretched about 2 degrees, my pump was mistimed about 2-3 degrees. What should I set the engine to (I’ll turn it over 360 degrees, twice) to account for chain stretch?

Because when the cam marks are lined up, and there is a timing offset, the engine isn’t truly at TDC anymore, right? The cam is set so the valves are in the right position for the engine to be TDC, but the pistons are a few degrees off, right?

That almost makes me think that I should set the engine at 12ATDC so that with two degrees stretch, it will account for two degrees of wear. Or am I thinking of that backwards?

Or is it moot because since the balancer hasn’t moved/shifted, it is absolute relative to the piston location, and I’m thinking about it all wrong?

And if that’s the case, doesn’t valve position matter too?

Thanks!

 

[brages]

Isn't there a MB diesel group that would be a lot more likely to have the answer to this?

I remember needing a special tool with a dial indicator for the timing belt job on my old VW diesel... I think that car also didn't have a key on the camshaft - you locked the cam and set the timing right on the crank and pump and then you torqued down the cam pulley. Crazy design.

 

[Chris142]

A loose chain will allow the pump to move which will effect the timing. One time it may be advanced and next time retarded.

You can't adjust the timing thinking you will make up for a loose chain.

Put the timing where is is supposed to be.

 

[JHZR2]

Isn't there a MB diesel group that would be a lot more likely to have the answer to this?

I remember needing a special tool with a dial indicator for the timing belt job on my old VW diesel... I think that car also didn't have a key on the camshaft - you locked the cam and set the timing right on the crank and pump and then you torqued down the cam pulley. Crazy design.

Yes and no. A lot of the folks on the MB diesel forums are dying off. And wvo and rust killed many of the cars off. Even though they’re collectively probably the longest lasting cars on the planet, old diesels with 300k+ still hot their end.


And setting timing and accounting for timing chain wear seems like a ubiquitous consideration for anyone in the know. Plenty of vehicles have chains and need to consider at least cam timing and wear. Not as many have injection timing based upon it, granted…

 

[JHZR2]

A loose chain will allow the pump to move which will effect the timing. One time it may be advanced and next time retarded.

You can't adjust the timing thinking you will make up for a loose chain.

Put the timing where is is supposed to be.

Not taking a loose chain though. Timing chains are highly tensioned and the timing device will repeatedly verify timing of the engine. Wear in the chain simply retards timing a bit, and there is an adjuster built into the engine to help get it perfect.

Since I had to remove my IP, I can set the engine where I want it before re-installing. Slightly earlier injection I think is beneficial, I’m not trying to “tune it” just get it back to spec accounting for the TC wear.

 

[Chris142]

Not taking a loose chain though. Timing chains are highly tensioned and the timing device will repeatedly verify timing of the engine. Wear in the chain simply retards timing a bit, and there is an adjuster built into the engine to help get it perfect. Since I had to remove my IP, I can set the engine where I want it before re-installing. Slightly earlier injection I think is beneficial, I’m not trying to “tune it” just get it back to spec accounting for the TC wear.

Generally advancing the timing in any engine a couple degrees will improve performance and mpg. I'd try a couple degrees advanced more than the specs call for

 

[Trav]

Make sure #1 is on its compression stroke at TDC then check there is clearance in both of the valves to verify. Rotate the engine clockwise to 15 degrees ATDC (whatever it is for this specific engine). With the pump removed lock the pump with the tool with the pump timing marks aligned and install the pump. You can compensate for chain wear by adjusting the pump.
The last one I did on a W123 was a 240d so it is not quite the same but similar.

 

[JHZR2]

Make sure #1 is on its compression stroke at TDC then check there is clearance in both of the valves to verify. Rotate the engine clockwise to 15 degrees ATDC (whatever it is for this specific engine). With the pump removed lock the pump with the tool with the pump timing marks aligned and install the pump. You can compensate for chain wear by adjusting the pump.
The last one I did on a W123 was a 240d so it is not quite the same but similar.

I think the 616 you set to 24 degrees BTDC; this is on a w126 with the 3.5L 603, which has an offset which is why you set it to 14-15. Maybe I’m not recalling the 616/617 procedure correct. But you’ve got it. Set to 14ish, use the locking pin, etc.

So I’ve done all that. Thing is, to lock the IP, I had to turn the engine up to around 17ATDC. Thus my question. Do I just turn it over twice so the stroke is correct and install it at 14, or do I compensate for the wear by actually setting the crank at some different value?

 

[CleanSump]

It's been close to 20 years, but I recall doing what @Trav said.
Set the engine where specified by the book.
Lock the pump with the tool.
Install the pump.
Adjust the pump.

The pump is much easier to adjust with the lines to the injectors disconnected. Then adjust the lines to the pump again.

I recall some people on the old boards were eyeballing the wedge/locking tooth in the pump instead of buying the tool.
I still have the tool in my box. Expensive for how simple it is.

Just an afterthought. Do you have the multi-splined tool for the valves? The valves on the pump, not the head.

 

[JHZR2]

It's been close to 20 years, but I recall doing what @Trav said.
Set the engine where specified by the book.
Lock the pump with the tool.
Install the pump.
Adjust the pump.

The pump is much easier to adjust with the lines to the injectors disconnected. Then adjust the lines to the pump again.

I recall some people on the old boards were eyeballing the wedge/locking tooth in the pump instead of buying the tool.
I still have the tool in my box. Expensive for how simple it is.

Just an afterthought. Do you have the multi-splined tool for the valves? The valves on the pump, not the head.

Yeah it’s a real optical illusion. Eyeballing is no good. I put the engine at 14, saw the tang in the port, but my tool wouldn’t engage. Took a few more degrees. That’s a lot!

I don’t have the multi spline tool for the delivery valves. I’ve not had to replace delivery valve seals/washers yet.

 

[Trav]

I am missing something, you cant set the pump off the engine so it mounts in time?

 

[JHZR2]

I am missing something, you cant set the pump off the engine so it mounts in time?

My pump is locked properly. The engine is currently at around 17ATDC. Maybe I’m overthinking it but my basic premise is if I should turn the engine again (twice so the cam and crank are phased properly, and just set it to -4, or if I should somehow adjust for the two degrees of stretch in the chain by setting it to something different.

 

[Trav]

I get the pump is properly locked but you cannot install it in that position with the engine at 15 degrees?
It ran good before correct? Does this use a drip tube to set the pump?

 

[JHZR2]

I get the pump is properly locked but you cannot install it in that position with the engine at 15 degrees?
It ran good before correct? Does this use a drip tube to set the pump?

No drip tube on the 603. I can install it wherever. FSM says the right timing is 15 for older engines and 14 for post 1990.

What it doesn’t say is if the number should be adjusted to account for roughly chain stretch. That’s all. Certainly can install for 14 or 15 deg.

 

[Trav]

I would set it at the spec setting and don't worry about compensating for the chain wear that way only by adjusting the pump.

 

[dumkid]

install it at 14 degrees and you will have already accounted for the chain stretch. consider replacing the timing chain someday (next time you're in there?)

 

[JHZR2]

install it at 14 degrees and you will have already accounted for the chain stretch. consider replacing the timing chain someday (next time you're in there?)

Condemnation for chains is six or more degrees. The older engines have OE woodruff offset keys that can be used to compensate. Two or so degrees is normal per the FSM.

The thing with setting at 14 is that because of the stretch either the cam or crank has to be off, fwiw…

 

[dumkid]

being off a degree or two from the cam or the crank won't immediately damage anything. earlier injection timing (relative to the crankshaft) will get better throttle response and mpg, but can cause more wear on rod bearings. later injection timing will have slightly higher EGTs (i think) less power by a small amount, less mpg, but the engine will be quieter (less diesel rattle) and your rod bearings may last longer (as if they were to ever wear out on a well maintained engine).

 

[Trav]

AFAIK the pump has an adjustment for that once installed. At least on the old 4 cy you could use a drip tube to time the injection point.

 

[JHZR2]

AFAIK the pump has an adjustment for that once installed. At least on the old 4 cy you could use a drip tube to time the injection point.

Yes there’s a little8mm bolt that tilts the pump towards or away from the block which advances or retards timing. There’s around 5 degrees total adjustment