M103 cam shaft 3° timing advance

[lsmalley]

I am curious as to the proper method of advancing the cam timing on the m103 engine. The fsm seems pretty ambiguous to me. It shows to line everything up to TDC, then remove the cam sprocket, I'm assuming flip the sprocket over so that the front of the sprocket (side facing the radiator) now faces the windshield...and thats as far as I get. I see it says to mount it so that the locating pin lines up with the sprocket, but should the cam be turned so that the journal in the cam shaft is slightly before the TDC mark on the head while the crankshaft remains stationary? And if so, by how much? I have a spare complete m103 that I've been trying to mock up this cam advance, but following these vague instructions and trying to interpret it the best I can, I cannot get the same results consecutively, so something that I'm doing is wrong.

[duxthe1]

I did the same in my TE quite a few years ago. I don't recall the specific gear mounting to get 3+ and the page you posted isn't clear enough to tell for certain. If I get a chance tmrw, I'll try to pull it up in WIS to see if its clearer instructions there.

[lsmalley]

Thanks

[duxthe1]

The picsture I have access to really isnt any better. It appears though that 3+ does not flip the gear and uses the alternative dowl pin hole

[lsmalley]

I know that doing it the way the manual states is the proper way to get 3° advancement, but alternatively wouldn't just turning the camshaft a bit before the crankshaft also give you an advancement, though you may not be able to say for sure to what degree without testing it? I just replaced my headgasket and I had everything lined up TDC, but upon closer inspection I noticed that the cam was slightly behind the TDC of the crank. So when I lined up the crank to TDC, the cam was maybe 2-3mm behind the TDC mark on the head, so I removed the chain from the cam and turned the cam only to line up TDC, then I put the chain back on. This actually improved my throttle response, but it made me wonder that if I'm at 0° cam advance, then a 3° advance must improve response even more.

[lsmalley]

Ok so I went back out and took apart my timing cover again and I verified that I was lined up with both camshaft and crankshaft at the TDC position. Upon looking at the service manual photo and reading the note, I see that the camshaft for automatic transmissions with the m103 came from the factory modified with a 5 degree retard. I went out and verified whether my camshaft had the 5 degree retard and sure enough, I see the code (53) stamped right on the edge. What I did was manually advance the camshaft a few degrees and verified that there was no interference between the pistons and intake/exhaust valves. What I have now is that the pin hole mark on the camshaft sits right after the post mark on the cylinder head while the crankshaft is at the TDC mark. I took it out for a test drive and there is a big difference accelerating. It only takes about 1/3 of what I would normal depress the accelerator to reach 60 mph. I just filled up a full tank on 91. I'll report back.

[Dave Kost]

Very interested. I have a 2.6 190e automatic California delivered.

[Frank Reiner]

Originally Posted by lsmalley

So when I lined up the crank to TDC, the cam was maybe 2-3mm behind the TDC mark on the head, so I removed the chain from the cam and turned the cam only to line up TDC, then I put the chain back on.

Originally Posted by lsmalley

What I did was manually advance the camshaft a few degrees and verified that there was no interference between the pistons and intake/exhaust valves.

It would appear that in fact you have advanced the camshaft by one tooth of the camshaft sprocket. If the cam sprocket has 40 teeth the crankshaft angle (CA) at which the camshaft is timed has been advanced by 18 degrees. If the cam sprocket has 36 teeth the advance is 20 degrees.
That there is no valve-to-piston interference is testimony to how wimpy those cams are in the first place!

[lsmalley]

So I did some more testing and I'm posting these photos regarding more advancement of the camshaft for the m103. The following photos show the max that the camshaft can advance with the crankshaft at TDC position without any piston to valve interference. There is probably a slight bit more advance to be had since I am testing this without a head gasket. Of course certain factors may play a role in each individual case, like whether or not your head has been resurfaced, etc. But for the most part I have set the crankshaft at the absolute TDC and I would slightly rotate the cam until I got contact between cylinder 1 & 6 piston, with their respective exhaust valves. There is ZERO measurement or calculations on the amount of advance this is since I do not have the proper equipment to verify to what degree advance I am at. Frank Reiner seems to believe that I have advanced my cam anywhere from 18-20 degrees. I think that is an extreme amount, but I couldn't tell you exactly what it is since I am only going based on what physically works. My current situation seems to be consistent with what I experienced when I first made the change and has not deviated: at a fraction of the pedal deflection of what I previously had, the car will accelerate a lot faster. This isn't like the R16 resistor "mod" either, this is something you can actually see on the speedometer and feel. I did notice that I could previously get away with running 89 octane with zero pinging, but now the car definitely pings, especially when taking off from a stop or idle. I may have lost a bit of mpg, before I was at about 20.4 mpg running 89 octane, now at 91 octane I'm at about 19.7 mpg, but that was only on 1 full tank. I will monitor a bit more. I hope this info is useful.

[Frank Reiner]

Piston-to-valve interference does not occur at TDC.
It occurs when the piston is descending on the intake stroke, and the opening inlet valve catches up with the descending piston.
It occurs on the exhaust stroke when the rising piston catches up with the closing exhaust valve.
Intake interference occurs when the cam is either much too advanced, or there is insufficient notch depth in the piston for the valve motion.
Exhaust interference occurs when the cam is much too retarded, or there is too little notch depth.

[lsmalley]

Originally Posted by Frank Reiner

Piston-to-valve interference does not occur at TDC.

Originally Posted by lsmalley

The following photos show the max that the camshaft can advance with the crankshaft at TDC position without any piston to valve interference.

It most certainly does per my method in respect to the crankshaft. Crankshaft is at TDC. As I slowly rotate the cam, I can see the head beginning to lift up due to the valve beginning to contact the #1/#6 piston as the crankshaft still remains in the TDC position. When I rotate the cam counter-clockwise, the head begins to fall back into place on the block. Doing this on my test engine is how I was able to determine that there would be no interference if I did it to my car. Although, I couldn't tell you to what degree the advancement is, if any, being that the camshaft came with 5° of retard from the factory.

[Frank Reiner]

The ghosts of Moliere and Kafka rejoice.

[Dave Kost]

I would not advance the timing more than 6 degrees, wanting to avoid detonation. You could put a timing light on to see what the timing advance at Idle and 4000-6000 rpm. There should be a timing spec in the service manual.*

[lsmalley]

Originally Posted by Dave Kost

I would not advance the timing more than 6 degrees, wanting to avoid detonation. You could put a timing light on to see what the timing advance at Idle and 4000-6000 rpm. There should be a timing spec in the service manual.*

This! So after about a month, there is some detonation that is going on with the advanced can and running on 91. I tested out several configurations with this cam advance:

1. On 91 octane and no R16/1 (open circuit) there is detonation.
2. On 91 octane and 750Ω there is detonation.
3. On 91 octane and 1.3kΩ there is very slight detonation and car feels noticeably slow and will sometimes bog down or acceleration is extremely slow.
4. On 3 gallons of 110 octane and the rest approx 11-12 gallons of 91 and no. R16/1 resistor, car is extremely responsive.

I also did some trials with E85, but I didn't want to mess around with that too much so I didn't track it. I think I will dial the cam back a tiny bit so I don't need to mess around with the fuel ratio, etc. I may decide to build an ignition trimming plug for inside the car so I can toggle between fuels and resistors.