OM617 rocker arm problem? - Page 5 - PeachParts Mercedes-Benz Forum

Yak · #1 02-11-2011, 07:56 PM

Quote:

Originally Posted by Army

Thanks Yak,

I found that one - but I'm missing the tolerance (if there is one) for the width / thickness of the first camshaft bearing tower.

I can't find it in the FSM - in chapter 05-220 "Removal and installation of camshaft" they call it the "camshaft bearing cranking end". It is part 11 in the figure on the last page (page 11) of the chapter...

Haynes also doesn't specify it - despite a surprisingly OK chapter on the engine - well I say OK, OK compared with the rest of that pathetic book!

I'm off to see the engine shop next week. So hopefully he'll have the specifications.

Sorry. I misunderstood which spec you were looking for.

Along the same lines of inspecting the alignment rings in the towers, the camshaft bearings and "bearing crank end" all have dowel pins (cylindrical pins - #16 in the assembly pic in 05-220). Have you done the same sort of inspection on the bearings that you did on the rocker towers? All holes round, good snug fit, pins/dowels in good shape?

Another thought: are you checking alignment too early in the rebuild? (Excuse my ignorance here, I've never rebuilt a head/camshaft). I presume you haven't installed the sprocket. With the "compensating washer" and the sprocket (and chain, maybe?) installed, would that push the camshaft in the direction you need it to move for better alignment?

I'm basing the question on the supposition that bearing #1 may be "too thin" so the camshaft might be a bit "too far forward."

jt20 · #2 02-10-2011, 03:37 PM

Thank you bringing me up to speed and clarifying.

I am unsure of how much discrepancy in this direction is acceptable, but I have never seen it mentioned in the FSM. I am going to wager that yours is permissible, but I will supply data.

I have a rebuilt head coming way and a beautiful set of unscathed rockers to mock up for you. That, and pictures of my engine.

Keep in mind these engines were probably designed in the 60's, and the rocker towers do not use the most precise means of locating themselves in relation to the cam.

I mentioned that the towers might be deformed due to the bending of the mounting dowels... perhaps you should roll one of the dowels on a flat surface?

good luck, hang in there.

layback40 · #3 02-15-2011, 06:42 AM

What are you going to do if you leave it how it is? in a few hundred k miles you will have rockers & cam lobes that have un-worn high ridges on the edges. I guess you could then get the engine rebuilder to grind them down.

Stretch · #4 02-15-2011, 01:41 PM

Quote:

Originally Posted by layback40

What are you going to do if you leave it how it is? in a few hundred k miles you will have rockers & cam lobes that have un-worn high ridges on the edges. I guess you could then get the engine rebuilder to grind them down.

Yeah it is pants - I'm still deciding. After butchering the short axle shaft / spindle for the rocker arms - trying to get it to fit over cylinders 4 and 5 (WHICH IS WRONG!!!! <= added for others!) - I've got another one on order.

When I get that I'll be back fiddling again.

Perhaps I should turn this thread into a pole:-

Should I grind metal and add spacers for better fitting rocker arms?

OR

Should I leave it alone?

Stretch · #5 03-09-2011, 09:08 AM

Well it has been a long time but I've now got my ducks all nicely lined up.

I took the rocker arm towers (all five of them) to a machine shop and got them to mill off 0.5mm off of the back surface of the tower where the rear most rocker arms sit.

You can see this surface here in the picture below.

I then got hold of some 0.3mm and 0.2mm steel shims so that I could "add metal" to the other side of the rocker arm towers and position the forwards / front rockers.

If you didn't know the shims were there - I think most mechanics would miss them:-

I'm now one happy bunny. The rocker arms sit nicely under the cam lobes - I can now (finally) adjust the valves!

Small print:-

This is not an authorised modification - so if you don't see shims between your rocker arms and the rocker arm towers; that is OK, that is how it is meant to be!

I'll keep you all posted on how I get on with this.