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M103 leakdown test results

10K views 100 replies 10 participants last post by  tuttebenne 
#1 ·
Folks, in the middle of the soft camshaft/rocker replacement as well as upper timing chain cover seal replacement.
While the valve cover is off decided to take some leakdown measurements since I have all that is needed.
The car burns quite a bit of oil because of the soft valve guides as well (most likely). Engine is at 180K miles.
About a year ago compression tests were done and all ranged from 155-170 psi. I believe #5 and #6 was on the lower side but not 100% sure as it was a year ago. I know #1-3 were all higher at 170psi.

I took careful measurements and sometimes repeatedly if results did not make sense. TDC made at 100PSI all others at 80PSI.
Below are the results:

Cycle: Intake compression combustion Exhaust
Position: BDC Midway-up TDC Midway-down BDC
Cyl #1 66/80 79/80 99/100 68/80 67/80
Cyl #2 69/80 79/80 99/100 69/80 68/80
Cyl #3 68/80 79/80 99/100 67/80 69/80
Cyl #4 67/80 79/80 99/100 69/80 67/80
Cyl #5 64/80 64/80 80/100 76/80 not taken
Cyl #6 66/80 79/80 83/100 68/80 not taken

Looks like all cylinders can hold pressure in some position but #5 and #6 do not at TDC. I repeated these measurements many times.
It was also difficult to keep the pistons in TDC for #5 and #6. It would sometimes move to the next position where the pressure was held.

Cyl #1- 4 look normal to me. #5 and #6 look odd. Hissing sound at TDC appear to come from exhaust but not sure.

Comments and advice would be very welcome.
 
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#2 ·
Did the engine run fine before. I think that you have no reading on 5 -6 is because the head gasket may have blown though , that parts 5 and 6 cylinders and is leaking compresion ,out of cylinder 5 in to cylinder 6 . and again when 6 is at tdc compresion then goes to cylinder 5 . I do hope i am wrong ..
 
#3 ·
Thanks Trevor. To test out that theory, I had plugged the spark plugs on #4 and #6 and retook the measurement on #5 and I made sure that #6 valves were closed when I took repeated the #5 measurement. I still could not get a good reading with all #5 and #6 valves closed but I'm not sure what position the piston was when I took that measurement. Probably not at TDC, so that could be an issue as BDC for example shows leakage anyway.

The car runs fine, quite well actually.

No oil leakage from the Head gasket (original) outside or no oil and coolant mixing at all.

Not sure how common it is to have a cylinder to cylinder leak on an M103 but that is still the most likely scenario.

If so, it is not disastrous, the head has to come off very soon anyway to replace the valve guides as I'm starting burn way too much oil (~500-mi/quart).

I just want to make sure I do not have a bottom end problem that could be causing oil consumption or compression issues.

First things first though. I'll finish replacing the CAM, the original is starting to look really bad. #1 intake is worn 1.5mm to 2 mm now. I can only measure when I take it out.
 
#4 ·
BTW, can I replace the CAM without messing with the timing chain tensioner?

I would rather just replace the sprocket etc. carefully and not change tensioner settings as I have not done this before I do not want to mess up the timing chain and tensioner.

Haynes manual suggests loosening the tensioner but it also suggested taking out other things that were not needed (taking out the radiator fan, draining coolant and removing coolant hose, etc, etc)
 
#6 ·
Thanks knapster for your input. Originally I though this needs some adjustment that I do not have the skill for but it seems it does not, so one just loosens it.

I'll proceed to take it out.

Is it taken out completely or just backed out enough to release the tension?
 
#7 ·
OK, took out the timing chain tension-er cover nut and spring. Backed out the Threaded ring 8 turns so it is flush against the surface of the lower timing cover. This loosened the tension-er enough in which I could take the sprocket out.

Given that I'm replacing camshaft/rocker assemblies/sprocket/rotor adapter from a later model 1990 M103 should I:

(1) Use the rocker bolts from my head or use the bolts on the rocker assemblies from the donor car? Does it matter?
(2) How about the rocker contact pads? from donor or original? Do the pads stay with the valves or stay with the rockers?
 
#8 ·
Well, made more progress on this yesterday and finished replacing the cam/rockers/sprocket with the new style M103.

However, it seems my worst nightmare has come true as the car now does not run. I am sure the timing is very close but maybe not exact because when I was putting the timing chain back on it seemed perhaps I'm off by one tooth but I'm not sure.

The car started one time and ran till hot (not that well though as it was missing at times).
After this it does not start and if I push the throttle when I'm cranking it backfires from the intake and a puff of smoke comes out from the MAF plate.

While I had my wife crank, I checked timing with my strobe light and it is showing 20 degree while cranking, so it is not way off.
And there is nothing wrong with the ignition side of things. Should the timing how 10 BTDC while cranking?

Would being one off the sprocket tooth cause all this problem?

Any Help would be greatly appreciated on this.....
 
#9 ·
Counting the teeth on the spare sprocket I see there are 39 of them. So each tooth is 9.2 degrees. And the way it was it seemed if anything went wrong it would have been advanced by one tooth (so 19.2 degrees instead of 10 degree BTDC).

Will being just 9 degree too early cause the car not to even start?
 
#12 ·
The timing must be set correctly or your in for a world of hurt. You're dealing with an interference motor. Hopefully you haven't bent a bunch of valves and or knocked a hole or two in the Pistons.

Sent from my XT1080 using Tapatalk
If I'm off, I'm off by one tooth, so 9.2 degrees advanced (BTDC). I think I'm OK on the mechanical damage side of things (for now).
I'll check my hand sketched timing drawings to make sure. Since it started once and ran, with only slight mis-fire issues I'm not that concerned on that front.

I would like to make sure though that when I move by one tooth, I'm not going in the wrong direction. That could be disastrous as you say Jayare. Need to be careful next time.

Any additional tips on the timing chain installation would be more than welcome.
 
#13 ·
Well, I think I'm definitely off by one tooth, but maybe even two. I have read in some posts that the dot is not exactly lined up at TDC. I thought mine was also a little off but not this much. Perhaps I'll move it one notch at a time.

Picture below. The one that is exactly lined up shows 20 BTDC. When it is off, I see O/T.

It is definitely very "touchy", so perhaps I'll go one tooth at a time.

Comments?

First set it OT and its Misalignment

Second set at 20 BTDC and it's perfectly lined up.
 

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#14 ·
I hate unfinished threads, so here goes this one:

Mystery solved. Had nothing to do with timing after all. I might have to fine tune the timing by 3 degrees or so which is done with the sprocket positioning but that will have to wait for the valve job.

It was the damn distributor cap. When I was putting it back in, the HV connection (spring loaded thingy) in the middle got jammed in and stayed there.
Actually it fell out as I was taking distributor cap off. Anyway I put it in the old cap from a year ago that I had saved for some unknown reason and it started in one crank. Too bad the new cap only had 4-5K miles on it.

Thank you everyone for helping.

Now we have to observe and see if the timing cover seal leak is fixed.......

I'll be shocked if I got that right in the first try....

And now I do not have to worry about the worn out CAM.

Also, the 20 degree BTDC issue. It seems while cranking the timing is approximately at 20 degrees. That threw me off. It gets to 10 degree BTDC at idle and around 30 degree BTDC at 3000RPM (I checked with the strobe light and the Haynes manual also suggests this).

And the dot alignment marker is not an exact science, it needs to be in the ball park and later fine tuned with the sprocket rotation per the service manual. So in my case, the dot is not perfectly aligned but the timing is "near" correct.

And the leak down test is still not 100% understood, though the theory is that there is a bit of a leakage between #5 and #6. It does not show in the compression test results. I repeated those and got the following in order (1-6): 150-145-145-150-145-160. So #6 is higher than the rest by 10-15 psi but #5 does not show low compression. So there is something there that I will keep an eye on. The head has to come off for a valve job anyway in the next 6 months.

- Cheers!
 
#15 ·
This is not your problem, but unfortunately, there is an early diagram of a M103 motor that shows using the bar instead of the dot to time your camshaft. My machinist proudly told me he used that diagram when finishing my head. Car wouldn't start and finally, Clark came to my rescue with the proper diagram (the dot). Don't know if I did any damage, but the car has been fine since....this was a long time ago. My timing was 180 degrees off essentially.

Glad you resolved your problem. Most of the time it isn't a tooth issue, but a worn chain that has too much slack (even with the tensioner) to allow perfect timing. Or a worn tensioner, for that matter.

Kevin
 
#16 ·
I'm pretty well versed now in adjusting timing, thanks for all the forum users help and some research. So emboldened that I may even tackle the head removal to sent to a machine shop when the time comes in late fall. Would save me perhaps $1500 around here. When that time arrives I will probably change the timing chain / tensioner as well.

Being 180 degree off should not damage anything mechanically. And since the engine can not start it would never run anyway.
Basically for anyone in doubt you have to make sure the lobes in #1 cylinder need to point down and the dot has to more or less line up with the notch. That's it. And the sprocket has 3 positions for installation to retard or advance the timing by 3 degrees for fine tuning. When you line up the sprocket if you use the elongated 0 shaped hole in the sprocket that is the neutral setting (0 degree fine adjustment). The other two that are round and are for +3 and -3 degrees.

Question:
Can one just buy an OEM timing chain that does not need any tinkering with chain links? Basically just purchase and replace? I would hate to mess up that part as that is pretty much a disaster if the chain breaks.
 
#17 ·
OK on the chain.....as with most procedures MB, there is a special joiner tool to fasten the chain back once you've fed it in by rotating the engine slowly by hand. I have a LOT of experience with HS machinery chain and so I peened it myself. As far as 'breaking' the chain, you can make a regular chain break tool work for you. I would NOT recommend peening the chain yourself unless you have considerable experience.

The proper tool might be available @peach parts etc.

Kevin
 
#18 ·
Hmmm, I see Kevin. So one can not buy the correct length chain and just put it on without breaking the loop? Even if the lower timing chain cover is removed? I would be nervous about breaking the chain and peening it back together. If I got that wrong that would be disastrous.
 
#19 ·
I don't know if you can buy a fitted complete loop. Taking the lower timing cover off with the motor in place is a lot of extra work if you don't have a leak.

If I were you, I'd look into renting the proper tool....it will do a perfect job with no guesswork. And yes, interference fit with a chain breaking is usually disastrous.

I will say this; we had a hell of a row in here once about the efficacy of changing the M103 chain in anything but a really high mileage engine. I fall on the side that thinks if the engine has 200,000 miles, replace the chain. On the M104 with the double row chain, probably not. The M103 however, unlike the V-8's is not known to have chain break issues. Still, as you surmised, the chain breaks and your engine is ruined.

Kevin
 
#20 ·
I found a FEBI kit that includes everything (tensioner, guides, unbroken, continuous chain) for $75. Would this do the trick?
For 180K miles on the engine would you guys replace everything with this from AutoHausAZ?

http://www.autohausaz.com/search/pr...s, Seals & Gaskets&gid=11919@Timing Chain Kit

Just preparing for the cyl head removal and valve guide replacement this fall.
Any comments would be appreciated.
 
#21 ·
In the end it will be your decision as to what to do. Here are my data points for our consideration. As Kevin stated, there are some strong opinions on M103 chain life. My experience has been good leaving the original chain alone. I have an '89 300e with over 200k on it and the original chain (did the valve guides at 130k) and my long gone '88 300e had 330k on the original chain (did the valve guides at 234k and the HG again at 248k)
.
I agree with Kevin on the method for changing the chain though. If Mercedes replaces the chain by cranking in a new opened loop chain and they make the tool to join them, that would be good enough for me if I was changing the chain.
 
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#23 · (Edited)
You should consult ps2cho on this as well. He's probably pulled M103 heads more often than any of us, save the pro tech member or two that chime in from time to time. Robert has some valuable info on his site. Check it out if you haven't already done so.

Good luck

Jayare

Sent from my XT1080 using Tapatalk
 
#25 ·
Off topic but related to the reason for talking about specific gaskets; tucked in the back of my grey matter is what I will do the next time I have to pull one of my M103 heads. I have been thinking about developing a channel that can be dropped into the number 6 oil return line. This channel would fit the contours of the casting and protrude at least 5 and maybe 10mm beyond the block deck. Since the oil leak at the rear of the block is from an oil return line, and not under pressure, in theory, if the oil is being channeled past the head/block parting line and not exposed to the gasket, will another leak ever occur?
 
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#28 ·
Back on the timing chain, what is the average and expected minimum life of a timing chain for a gently used manual transmission car?
I mention "manual" because I would say some of the drive train expected life definitely is effected by it. For example the differential gets more torque it seems.
 
#33 · (Edited)
Wrongo. BTW, no need to shout with the all caps either.

Febi Bilstein is part of the Bilstein Group that mainly deals in selling automotive parts supplied by other suppliers. They buy and rebox so much Febi themselves at times don't even know who and/or where it came from. See photo.

bilstein group // Your partner for the Independent Aftermarket //*Brands*

Bilstein, mainly known for suspension components is a division of the ThyssenKrupp Group.

https://www2.bilstein.com/en/

FWIW, ThyssenKrupp is a worldwide manufacturer and supplier to diverse industries.

https://www.thyssenkrupp.com/en/
 

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#35 ·
Febi's fluids are currently manufactured by Fuchs, a very respected manufacturer and also the main fluid supplier to MB.

But, being Febi, that could all change by end of business today when they find "another supplier" who can offer a similar, but not always identical product, for a few pennies less.

Bottom line: Febi, Meyle, URO, Hamburg Technic, Trucktec and the like. It's all the same shite for the same "cheap b@stard crowd"
 
#36 ·
Absolutely! And I consider Meyle (a German company), especially 'evil' because they purport to have German made parts. Their boxes and packing are indeed made in Germany, but their parts are third world et al. They also purport to redesign parts to make them beefier/stronger, like suspension parts. Well, so what if they are still made third world? Talk about smoke & mirrors.

Kevin
 
#37 ·
I'm surprised nobody has gotten confused between Meyle and Miele, or between Smith, Smythe, and Smiths for that matter.

Just because it sounds the same doesn't mean it is the same.

Ain't no such thing as a Rolex made in Romania either.
 
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