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  #211  
Old 08-09-2018, 02:24 AM
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I remember the lower nuts on my om621 were kinda soft(same part# btw)..two were almost rounded so I ended up buying a set of 8 and I was glad I did so.The color was different too. The new ones felt somehow more solid. I do not know what hardness the old ones had but they felt kinda strange.I do not remember whether I measured the height of new and old ones...but if I don't remeber they must have been the same height....
I had the same problem on the exhaust valve on cyl.1 (zero tolerance) but luckily managed to set it to spec.

On the recessed valve seat concern etc...well , it is not just it ...after so many miles one cannot expect the cam lobe height and the rocker arm geometry and the top nut height to be "as new".If I were you I'd just file off some material from the bottom nut and that's it.
Something else I've noticed that might be of use-the length of the V-shaped channel(groove) that is ground in the threaded valve stem portion (the notch in the retainer would engage the channel)had different length on some of the valves. If it is too short,it would prevent the retainer go deep enough when you are trying to adjust the valve(I don't say this is necessarily the case here...just a possibility or a combination of factors). Or if it is cut waay too deep it would eat material from the valve stem seal...
So I would just remove the rocker arm tower,remove the two nuts (piston TDC'd, of course),remove retainer and inspect the threaded portion of the valve...reinstall the retainer ...then the top nut only and try to bottom it out thus making sure I will be able to obtain the necessary valve clearance. Then I would file off some material from the lower nut (and/or valve retainer top) and reinstall everything back.
I had the complete set Hazets at hand..had to use the 30mm only on two of the valves.

Always clean the rocker arms brackets bolt holes from collected oil before reinstall.

exhaust valve will not adjust.
New valve stem seals installed
Replaced Valve Stem Seals - My experience
OM617 manifold oil = broken valve guide

I'd check the clearance again after some low miles...


Last edited by vox_incognita; 08-09-2018 at 05:34 AM. Reason: clarif.
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  #212  
Old 08-09-2018, 03:42 PM
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Posts: 233
thanks,
i’m not following everything you are saying, but i think most of it.

the bottom nut is not what is preventing me from getting the correct clearance. the bottom but can go much further down than needed. the top nut can only go down so much before it sticks and spins the entire valve, spring and all. i tried to spread the 2 nuts as far as possible to see stripped threads, but did not see any, there is maybe small chance it is stripped where i could not see, but more likely i think the top nut is going as deep as it can, hitting the valve, i think that’s what people are calling bottoming out.

also to consider is that the valve was not staying in locked position for many miles, even when it could get to spec, and would end up too tight prematurely.

maybe the valve was hitting something and getting pushed up?

also i'm trying to visualize what shaving down the threads would do, using attached image, but still get confused...

when everything is working as should, does adjusting the top not effectively lengthen or shorten the valve in terms of length to the rocker arm and lobe?

or would shaving down a few threads change the valve length, so that it might not push into the combustion chamber as much on the exhaust stroke...?
or maybe not pull all the way to get a proper seal on the combustion chamber...?
Attached Thumbnails
valve job?-valve-diagram-02.jpg  
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1985 300D turbo sept 2015 - present
1985 300TD turbo oct 2023 - present
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  #213  
Old 08-09-2018, 05:14 PM
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Posts: 484
Oh I see...I misinterpreted .

First -find a way to hold the valve spring retainer in place ! You may be lucky enough to get some more clearance.

Here's what I would do- remove both nuts and visually inspect the threads. Clean the inside of the top nut. Swap it for another top nut and see if I am able to reach the desired gap(might get lucky here). Measure the valve dive before it hits the piston at TDC and compare with another cylinder(need dial indicator...).
Yes,altering the position of the top nut alters the overall length of the valve.
Exh.valves are sodium filled. I don't know the cavity looks like and if filing the tip is a good idea.

Do you find the nuts loosened on this valve every time you check?
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  #214  
Old 08-10-2018, 07:18 AM
t walgamuth's Avatar
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Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 38,613
The sodium cavity does not reach all the way to the top of the valve.
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #215  
Old 08-16-2018, 11:04 PM
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ok, so let's say i changed the top nut and was able to reach the correct clearance, or i still had to shave down the top few threads to change the effective length of the valve to get the correct clearance...

either way, i was able to reach the correct clearance the 1st 3 times. so the other issue now is that it doesn't stay in place, it needs adjusting every couple months, give or take 1500-2000 miles, the nuts on that valve will be loose. would any of that even make the valve stay at spec for the usual amount of time?

i'm not sure, if it weren't for the potential $ savings, i'd just swap the head.
thanks,
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  #216  
Old 08-16-2018, 11:17 PM
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Shaving the valve stem is a band-aid that won't last. The valve face and/or valve seat is worn out. When you get the valve in tolerance it quickly wears down again and goes right back to being tight. Most likely the valve is "tuliped" and just wearing itself in as you adjust it. At a minimum the valve and/or seat needs replaced. Since you have another head, you're time and money ahead to have it fixed up and swap it in.
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  #217  
Old 08-16-2018, 11:22 PM
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thanks, i suspected it would be something along those lines, but needed to hear it from someone who actually knows.
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1985 300D turbo sept 2015 - present
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  #218  
Old 09-04-2018, 02:05 PM
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well, willy who gave me the cylinder head, that I had rebuilt, and was going to do the swap, is ill, and pretty much not able to do it anymore, so now I’m looking for another mechanic close to NYC that is willing and able, all the other ones I had contacted did not really seem like they were willing to.

anyone have any shop recommendations?

thanks.
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1985 300D turbo sept 2015 - present
1985 300TD turbo oct 2023 - present
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  #219  
Old 09-04-2018, 05:48 PM
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well i visited gene german auto in queens, he can do it but his operation is small, so it's like maybe next week, maybe not, call me monday, things can come up. his accent isn't easy to understand, and he rambles on about other vehicles, as some of these mechanics do, and showed me a tool he has to check rebuilt heads before installing.

the machinist also recommended a shop called urban classics in brooklyn, that doesn't do classics anymore, but was willing to help and called 2 other shops to ask around for me.

the 2nd one he called was master mechanix in yonkers, ny. he said there is no one better. i don't think they're specifically classic mercedes specialists but they are confident about doing head swap. they charge $105/hr, and is thinking it's a 12 hour job. just from talking on the phone it seems like a smooth operation, appointment scheduled, and it'll be out in a few days, as opposed to a smaller operation where it's like, it might take me a over a week get to finish it.
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1985 300D turbo sept 2015 - present
1985 300TD turbo oct 2023 - present
looking for biodiesel in nyc

Last edited by allenying; 09-04-2018 at 06:16 PM.
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  #220  
Old 09-21-2018, 04:26 PM
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ok, the neverending saga is maybe nearing the end, of this chapter

master mechanix in yonkers performed the head transplant. the initial drive home seems like the engine is running smooth again. it is a big relief, though i’m being wary for a few months.

he charged 11 hrs at $105/hr, + some coolant and a tensioner gasket that i didn’t provide. i provided the head gasket set and cover gasket.

he said he did not see a burnt valve, but we agreed it could be a guide or something that is not visible until taking it apart.

i hope to sell my head, before rebuilding, or have it rebuilt for $400, and then sell.

it really makes me wonder question the shops that suggested it was the IP, which was quoted at $2000. i did spend quite a bit leading up to the head rebuild and swap, diagnosing and testing all the possible other issues.

i am still getting this, which is a much less significant issue: when fully warm, if i press the throttle and let go suddenly, the pressure gauge dial dips below 1.5. the rpm dial dips lower than what it is at idle as well. so when it dips low enough, the engine stalls. this happens in city driving now and then. i will adjust the rack damper idle adjuster again now that i should be having good compression again.

here is a video of it:
https://drive.google.com/open?id=197CDLquv7RK9wRolKpEB7X25aaEvoGGJ

thanks again to everyone who has given input and suggestions.

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1985 300TD turbo oct 2023 - present
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