Broken camshaft, what else to replace? - PeachParts Mercedes-Benz Forum

dr.no · #1 11-12-2020, 12:34 AM

I've had a valve tick for a few days, that got better with adjustment (two tight exhaust valves) but didn't go away. In retrospect, this was probably the vacuum pump instead...
While driving I had a sudden loss of power, with dark smoke, then a few blocks later complete cessation of engine action.

When I got the valve cover off, this is what I found.

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Broken just in front of the second tower. All the valves are closed, the engine spins with no clanky-clanky sounds (and it quit with no bad sounds), so I hope there is valve-meets-piston damage. The first tower is sheared off.

This thread on here raises my hopes: http://www.peachparts.com/shopforum/diesel-discussion/312704-broken-camshaft-617-81-sd-how-could-happen.html
So, I'm hoping to replace the cam and towers (and VP), and since I'll have to re-time the whole thing I might as well replace the chain. And as far as I know none of this has been done and there is a little seepage, might as well do the head gasket too. And valve seals.

What else? chain tensioner, guides (didn't seem out of spec on Friday, but...). I'm not exactly looking forward to the timing experience, so have a lot of reading to do. I can set pump timing on VW diesels with my eyes closed, but these are entirely different beasts.

dr.no · #2 11-12-2020, 12:37 AM

Oh, other info: this is a OM617a, turbo, from a 1979 300TD (at least by the numbers), currently residing in a 1986 W460.
On a related note, anybody know a good mechanic in Santa Fe?

BillGrissom · #3 11-12-2020, 10:38 AM

Hopefully pistons didn't crash into valves. That would be most likely on cyl 5, due to the inclination of the camshaft once broken. I don't know, but would expect all diesel engines are interference type, given the high compression ratio. I think you could check all the cylinders for sealing. Remove the camshaft, which closes all the valves and remove all injectors. Install a compression gage and turn over the engine slowly by hand. If you see the pressure rise to ~400 psig and it holds fairly well, you have good sealing. You should also feel the cylinder resist you like an air spring. Repeat on all cylinders. You might see faster leak-down, so might need to crank it over with the starter as you watch the gage. I wouldn't replace the timing chain unless it is quite worn. You can fix a little wear easily by installing an offset key, which you can buy here on P-P.

Your engine may be worn, so allow windage on the readings. My 1985 OM617 got hard to start on 32 F mornings, needing a block heater, showing only 250 psig compression in most cylinders. Within 2 years, the engine failed, making an internal rattling sound, then seized. Inside, I found chunks missing from the pistons at the ring grooves, a few cylinder walls scored, and the #1 piston top beat up from something round bouncing around inside.

Diesel911 · #4 11-12-2020, 12:07 PM

2 Vacuum Pumps destroyed timer Bushing Identified as the problem
http://www.mbca.org/forum/2013-12-29/why-are-these-vacuum-pumps-being-destroyed

However find out if any of your valves are bent first.

Another way to tell if you valves are damaged would be to remove the camshaft and do a leak back test. Or at least pressurize the cylinders with compressed air. If any valves are bent you are going to hear a lot of air hissing into the manifolds.

gottarollwithit · #5 11-14-2020, 12:51 AM

I’d do the half ass leak down like diesel911 says first. If the cylinders still seal, throw a cam in and run it. JY will be your friend here... if not, I got a spare valve train if ya need

More importantly, what caused this failure??

Sugar Bear · #6 11-14-2020, 08:58 AM

Put air in the cylinders as suggested, you'll probably find valves are ok. The valves are not angled toward the pistons and they are robust. I've repaired two 240D broken timing chains, no bent valves on both even with multiple broken cam towers.

Good luck!!!

t walgamuth · #7 11-14-2020, 11:05 AM

Quote:

Originally Posted by Sugar Bear

Put air in the cylinders as suggested, you'll probably find valves are ok. The valves are not angled toward the pistons and they are robust. I've repaired two 240D broken timing chains, no bent valves on both even with multiple broken cam towers.

Good luck!!!

That is amazing but not surprising.

dr.no · #8 11-14-2020, 11:49 AM

The vacuum pump housing is split right off the bolts. I think that might of been the problem...
Luckily I have a spare VP. The spare engine is NA, so I now have a turbo cam and towers in the mail. Junkyards are not essential businesses but ebay is! (Not a criticism! We should have locked down weeks--or months--ago. Thousands more people would still be alive and I wouldn't have been driving last week.)
More pictures to follow when I have time to tear into it this weekend. I now have ridiculous hope that the chain is still set right on all the sprockets and all I have to do is bolt the cam on and check...who's got a favorite article for checking/setting pump timing though?

Sugar Bear · #9 11-14-2020, 02:16 PM

If the chain/sprockets are still in time, you should play every lottery ASAP ��

Seriously though, good luck and check for bent or leaking valves first so you'll have an idea of what you can expect.

gottarollwithit · #10 11-14-2020, 07:03 PM

If the cam/crank/IP are all still in time, buy me some lottery tics too!

Seriously though, the chain and timing issue might not be too big of a deal. If the cam sprocket didn't entirely come off or go haywire, supposedly the chain should still have tension on it.

So... that could mean that the IP and crank are still timed properly, but the cam is out of time. When you have the cam/sprocket out, you'd just artificially provide tension where the cam sprocket would be, then turn the crank to where it needs to be.

Sugar Bear · #11 11-14-2020, 07:16 PM

With the cam out and air at the cylinders, that is the time to consider replacing the valve seals.

Don't sweat whether or not the cam/crank/pump timing is out of sync. Follow the timing procedure step-by-step and double check your work and it will be fine.

Good luck!!!

dr.no · #12 11-17-2020, 03:47 PM

There are lots of writups of each segment of the timing chain:
1. Making sure the crankshaft and camshaft are zero'ed (0° TDC)
2. loosening tensioner to correct #1
3. timing pump by removal and looking for missing spline
4. correcting pump timing with offset woodruff key

But I have yet to find one that combines these for a complete "I am afraid my sprockets are all messed up/I have completely screwed my engine" situation. I remember reading threads about this long ago but can't find one this week.

So, I just want to confirm the order:
1. Dampner at 0°
2. Set camshaft at timing mark
3. turn engine to 24° BTDC
4. remove injection pump and set missing spline to mark
5. reinstall everything and run.

Currently I am a tooth off at the camshaft. Any reason to worry about being 180° off with this procedure?

Usaguy · #13 11-17-2020, 04:26 PM

Quote:

Originally Posted by dr.no

...
3. turn engine to 24° BTDC
...

On compression stroke on #1 cylinder. Because if you set it on exhaust stroke then it will not work.

Easy to check: both #1 cylinder cam lobes point away from the rockers

dr.no · #14 11-17-2020, 05:53 PM

If I trust that it is only one tooth off...my cam is in three pieces! At present they all point away from the head. But the front fragment was attached to the sprocket so it's likely real.

Usaguy · #15 11-17-2020, 09:04 PM

Quote:

Originally Posted by dr.no

...Any reason to worry about being 180° off...

on OM617 your balancer can be installed 180 off.

there are a number of ways to check if it is.

Removing the lower oil pan and looking or pouring a liquid into a prechamber and looking if it goes up or down as you rotate the engine