OM617 manifold oil = broken valve guide - Page 3 - PeachParts Mercedes-Benz Forum

Stretch · #31 11-10-2010, 06:07 AM

That is a bit of a sweeping statement in the title I know but I'm really irritated:-

I've been busy matching and measuring weights of parts of the engine before starting the rebuild and I found loads of gritty swarf all over the upper surface of the head - valve stems - valve seals - rotor caps etc...

Luckily I've got spare set of valve seals so I can clean it all up and replace bits if necessary.

I'm often told that I need to let it go and trust people to do their jobs properly - where's the evidence that that's a smart thing to do?

{Sorry whinge over}

Stretch · #32 12-13-2010, 01:52 PM

Grrrrrrrr - I had a frustrating weekend - can anyone tell me what has gone on here?

(It is OK I know the answer - just a little quiz for you all - I'm trying to make some fun out of a bad situation - remember this is an OM617...)

Doktor Bert · #33 12-13-2010, 02:12 PM

First and foremost, you need a vapor/oil separator....

Stretch · #34 12-14-2010, 03:54 AM

Well I'm gonna pick up the correct valve in a bit - then I finally finish off the lapping...

vstech · #35 12-14-2010, 07:01 AM

hmm. over a mm larger... outside diameter... as long as there is clearance to the head, and the port matches it should be fine. odd, but ok. I doubt MB build a head with mismatched vavles. is it possible some of them got replaced and not others?

Stretch · #36 12-14-2010, 08:35 AM

Quote:

Originally Posted by vstech

hmm. over a mm larger... outside diameter... as long as there is clearance to the head, and the port matches it should be fine. odd, but ok. I doubt MB build a head with mismatched vavles. is it possible some of them got replaced and not others?

I guess this was a case of the organ grinder being so busy he had to let his monkey do the work (also judging by the amount of gritty muck all over the valve springs etc etc). Anyway they've replaced it with the correct 616 numbered valve - the 615 has gone back.

My problem with it was that when I lapped it in - the contact was right on the edge of the valve. It didn't look like it would seal properly - and I guess it could have failed sooner: imagine knocking the edge of a saucer with a spoon as opposed to knocking the saucer a bit further in towards the middle.

So anyway I'm a happy bunny again. Just this last valve to lap in place, remove the new but probably contaminated valve seals, clean everything up and re-assemble with the other new set of valve seals I've got.

vstech · #37 12-14-2010, 08:39 AM

ahhh. too SMALL a valve is certainly an issue! ya gots to have meat above the seat!

mercmad6.3 · #38 04-04-2011, 06:03 PM

The mark left after lapping should only be 1.5-2mm wide. any wider and it says the seat is not ground properly. Wide lapping marks show valves which will overheat in service and wear prematurely.
I have a 617 here right now with the guides loose in the head and exactly the same issues as you describe. But it exhibited a massive amount of blowby. It turned out that the exhaust was being fed directly into the cam cover because of the room around the valve guide. Unless the seals are checked in place by removing the springs,you would never discover a weird fault like this normally.

Stretch · #39 04-05-2011, 03:04 AM

Quote:

Originally Posted by mercmad6.3

The mark left after lapping should only be 1.5-2mm wide. any wider and it says the seat is not ground properly. Wide lapping marks show valves which will overheat in service and wear prematurely.
I have a 617 here right now with the guides loose in the head and exactly the same issues as you describe. But it exhibited a massive amount of blowby. It turned out that the exhaust was being fed directly into the cam cover because of the room around the valve guide. Unless the seals are checked in place by removing the springs,you would never discover a weird fault like this normally.

It is indeed difficult to see - if not impossible - if you don't remove the valve spring...

...strangely I didn't have too much blow by in my case, it manifested itself with leaking oil. I'm sorry to hear that someone else has the same trouble. I thought it was a weird one off happening. I'm pretty much of the opinion that this damaged was caused by heavy handed use of normal spanners when adjusting valves. I can't see how a valve guide would snap otherwise.

2mm sounds like a lot for a lapped width though - If I remember correctly I estimate it to be closer to 1mm - I'll dig out a picture of the finished product to check.

layback40 · #40 04-05-2011, 04:23 AM

Quote:

Originally Posted by Army

It is indeed difficult to see - if not impossible - if you don't remove the valve spring...

...strangely I didn't have too much blow by in my case, it manifested itself with leaking oil. I'm sorry to hear that someone else has the same trouble. I thought it was a weird one off happening. I'm pretty much of the opinion that this damaged was caused by heavy handed use of normal spanners when adjusting valves. I can't see how a valve guide would snap otherwise.

2mm sounds like a lot for a lapped width though - If I remember correctly I estimate it to be closer to 1mm - I'll dig out a picture of the finished product to check.

X2
The narrower the better. The theory is that the narrower the contact surface, the less likely a particle of burning carbon is going to be stuck between the valve & seat & burn it.

vox_incognita · #41 04-05-2011, 06:05 AM

Hi,
Another thing to consider-note the valve spring marking on the pre-repair pic:

...and after:

The markings are on the same side for a given spring type(#),not sure how it is for om617---on om621 for example,the markings happen to be on the bottom side when installed per manual.....so you need to verify the correct orientation of the springs(narrower coils pointing towards the head).Someone did it wrong(either the present or the previous intervenist...)

Stretch · #42 04-05-2011, 08:59 AM

Quote:

Originally Posted by vox_incognita

Hi,
Another thing to consider-note the valve spring marking on the pre-repair pic:

...and after:

The markings are on the same side for a given spring type(#),not sure how it is for om617---on om621 for example,the markings happen to be on the bottom side when installed per manual.....so you need to verify the correct orientation of the springs(narrower coils pointing towards the head).Someone did it wrong(either the present or the previous intervenist...)

Thank you very much for that - chapter 05-250 does indeed specify dots at top - tighter coils down towards the cylinder head... I don't think Haynes mentions it => I'll be checking that on the engine for sure.

Stretch · #43 04-05-2011, 12:46 PM

Quote:

Originally Posted by Army

Thank you very much for that - chapter 05-250 does indeed specify dots at top - tighter coils down towards the cylinder head... I don't think Haynes mentions it => I'll be checking that on the engine for sure.

Sorry Haynes - you do mention it - in two places... I must have forgotten about this bit 'cos from this picture I must have read to do it as the dots are up!

And here's one of the valves after lapping:-

I didn't measure the width of the lapped contact zone but it looks like it is about 1mm (I think so anyway - any one think different?).