OM617 rocker arm problem? - PeachParts Mercedes-Benz Forum

Stretch · #1 01-25-2011, 05:36 AM

G'day All,

The end is nigh - or so I thought. My OM617 engine rebuild rolls on at the speed of a lazy snail until it hits the next technical hitch...

I've got a new camshaft, new rockers, and new rocker spindles as the old ones were deeply scored and some of the old rockers were wedged on the old spindles good and proper.

When adjusting the valves on the back rockers - the set of four rockers on the shorter spindle over cylinders 4 and 5 - I got the impression that the spindle was curved as the cam lobe did not align nicely with the rocker.

This rocker set was a tight little bugger to fit and previously there had been some damage to the underside of the last rocker "tower".

I am now trying to source replacement towers for this back rocker set => p/n is 616 055 00 10

So my question is:-

Has anyone come across this problem before? Has anyone ever made a fix that didn't involve replacement of the slightly knackered tower?

PS:-

I've found loads of threads concerning rocker problems on petrol engines on this forum but few for the diesels...

layback40 · #2 01-25-2011, 07:43 AM

Is it a tower problem or a bent shaft?
Some small Isuzu diesels with belt drive OHC have weak tower bolts so that if the belt fails the bolts fail before the pistons & valves are damaged. If the motor has had a problem at some stage in the past, it may have something a little out of shape.

Stretch · #3 01-25-2011, 07:56 AM

Quote:

Originally Posted by layback40

Is it a tower problem or a bent shaft?
Some small Isuzu diesels with belt drive OHC have weak tower bolts so that if the belt fails the bolts fail before the pistons & valves are damaged. If the motor has had a problem at some stage in the past, it may have something a little out of shape.

Hi layback40 thanks for the reply. I'm quite sure it is a tower problem as I've just replaced the shaft (I called it spindle in post #1 - I often pick the wrong word!). Also the tower at the back is the one with a knackered fitting - so I guess replacement is the safest way.

The upper surface of the head could be slightly out of whack - but I think that it is more likely that the between the mounting holes on the head is slightly shorter than the distance of the mounting bolts in the towers. I'm about to measure this to check. (To be updated)

Stretch · #4 01-25-2011, 08:31 AM

Update:-

The distance between the mounting holes on the head and the holes on the underside of the towers is difficult to measure but they seem similar - they are both about 90.8mm (that's the best measurement I could make with my vernier caliper).

Stretch · #5 01-25-2011, 12:50 PM

Holy cow - the cost of a new tower (at the dealer) is 169.28 euros plus 19% sales tax... me thinks I'll be visiting the scrappy...

Stretch · #6 02-03-2011, 09:45 AM

I bought some second hand rocker towers for 10 euros a piece and I set to putting the rocker arms into position.

The replacement towers are sitting in front of the old ones in this picture - you can see that the locating holes are not oval!

When fitted to the engine I got the old problem again - the shaft was bending and I could see that the rockers were not nicely in line with the camshaft. The gaps on the replacement rocker towers were larger than with the original rocker towers:- 0.7mm above cylinder 5 and 0.6mm above cylinder 4.

There was only a gap under the towers where you can see the feeler gauges.

Looking at the position of the rocker arms and the cam you get this for cylinder 5:-

And the problem above cylinder 4 is here:-

Here you can see that when the rocker tower is located correctly over the locating ring on the head that the rockers don't line up.

Bugger!

I think the holes have been drilled slightly incorrectly in this head.

Has anybody seen this before?

Yak · #7 02-03-2011, 09:54 PM

A few ideas/observations:

It looks like the replacement towers have a slightly uneven surface or flat surface. On the far right of the pic you can see a different reflectivity. Do you have the tools or a table to check the flatness of the tower? A pane of glass or a lapping surface, perhaps?

If it's flat, is also square with the holes?

Also, have you checked the bolts for trueness? And/or the holes in the head for thread size and cut?

Your last two pics are taken without the bolts in place, correct? If so, I don't think the problem is with the holes in the head, since they're not involved in that picture. That would leave the shaft, the rockers, or the cam as variables, wouldn't it?

Stretch · #8 02-04-2011, 04:44 AM

Quote:

Originally Posted by Yak

A few ideas/observations:

It looks like the replacement towers have a slightly uneven surface or flat surface. On the far right of the pic you can see a different reflectivity. Do you have the tools or a table to check the flatness of the tower? A pane of glass or a lapping surface, perhaps?

If it's flat, is also square with the holes?

Also, have you checked the bolts for trueness? And/or the holes in the head for thread size and cut?

Your last two pics are taken without the bolts in place, correct? If so, I don't think the problem is with the holes in the head, since they're not involved in that picture. That would leave the shaft, the rockers, or the cam as variables, wouldn't it?

I would kill for a surface plate! I am pretty sure the problem is with the position of the holes - well the locating rings set in the holes in the head - but I will check them all out tomorrow. I will check the bolts too. Put it this way I have now used 4 towers and I have got the same / similar result each time...

Thanks for the input Yak

layback40 · #9 02-05-2011, 07:09 AM

Quote:

Originally Posted by Army

I would kill for a surface plate! I am pretty sure the problem is with the position of the holes - well the locating rings set in the holes in the head - but I will check them all out tomorrow. I will check the bolts too. Put it this way I have now used 4 towers and I have got the same / similar result each time...

Thanks for the input Yak

Army,
I have an old WW2 bomber windscreen, its about 3" thick. perfectly flat. It cost me nothing, was on a junk heap. Just as well I am on the other side of the world!! A guy like you should be able to find one !!

vstech · #10 02-04-2011, 10:01 AM

heh. how bad would you like one?
I've got a granite one, and a steel one...

shipping might be a killer though...

rscurtis · #11 02-04-2011, 10:21 AM

How do the stanchions fit if you bolt them down without the shaft? Could something on the shaft be forcing the top of the stanchions apart?

Alastair · #12 02-04-2011, 11:02 AM

Only issues Ive had with these was a set-bolt that was just slightly bent and had a damaged thread...

--Prolly from some muppet in the past. The head thread was fine, so were the towers and follower-shafts.

--It too was on nos. 5/6 pot supports...

Fitted new (S/H) set-bolt and all was fine....

Stretch · #13 02-04-2011, 02:12 PM

Quote:

Originally Posted by rscurtis

How do the stanchions fit if you bolt them down without the shaft? Could something on the shaft be forcing the top of the stanchions apart?

I don't think so - here are some photographs I made ages ago when I was checking out the work done at the machine shop on my head.

The locating ring for the rocker tower above cylinder 5 was all mangled up so I replaced it:-

Just knocked it out with a hammer and punch (as carefully as possible!).

The hole "north" of the mangled locating ring is a hole for a (head) bolt.

Part number for the ring:-

EDIT:-

I've just ordered another locating ring from the dealer and I'm reliably informed that there is a fold in the bit of paper that shows the part number!

The part number is 180 055 01 75

Stretch · #14 02-05-2011, 10:59 AM

Quote:

Originally Posted by vstech

heh. how bad would you like one?
I've got a granite one, and a steel one...

shipping might be a killer though...

Shipping will be the killer - thanks for the offer - besides layback40 reckons WW2 bomber windscreens are the bomb...

...perhaps saying I'd kill for one was a bit misleading...

Stretch · #15 02-05-2011, 11:23 AM

I've got the rocker towers to sit flat on the top of the cylinder head. I adjusted the spindle that runs through the towers to get them to fit:- I filed away some of the cut out on the shaft with a rat's tail file.

The spindle (rocker arm shaft) no longer pushes against the rocker tower bolts - making the distance between the towers at the top greater than at the bottom. So I no longer have the bending spindle effect I tried to demonstrate in my first post.

The rocker surfaces are now in line with the camshaft lobe surfaces.

Unfortunately they are slightly misaligned in the longitudinal direction - along the engine's length. It is most noticeable on cylinder #4:-

It is not so bad for cylinder #5:-

I'm a bit concerned that if I run the engine now I'll eventually get a groove in the cam lobe surfaces due to this misalignment.