OM617.952 valve adjustment. How tight is too tight where the engine will not run? - PeachParts Mercedes-Benz Forum

charmalu · #1 03-12-2011, 04:47 AM

I have this 84 300TD that was brought to me, to do my magical, mystic massaging to it to bring it back from the dead. (almost) Iam really surprised it made it from it`s home base to our front yard, some 40 + miles.

Iam told they know that Diesels aren`t really fast, but this one really has no fast get up and go, no acceleration, even though it is a Turbo. I ask simple questions, like when were the valves adjusted, oil changes, any sort of records, how long have you owned it, have you been using Vegitable oil etc....??? I was told it was run on WVO Blend for a period of time, but is on diesel now. and as far as any records, or maintenance

we open the hood and there is this grease ball of an engine in there. we start her up, and I thought the engine was going to jump out from under the hood. It was rocking back and forth, harder to the right, and sounded like it was barely able to run. out the tail pipe I could hear it a put put put sound. not the usual 617 sound. Iam surprised there aren`t dents in the hood from all the rocking.

They leave, and my wife and I take it for a run.It`s 3 miles down hill to Soquel (so-kill) and the go light turns red. the whole car is rocking back and fourth, just amazing it still ran. go up the ramp on the freeway and is doggy until I really put my foot into it, but don`t feel the kick down. go as far as the next off ramp and head for home. Well we make it home

. this thing is bad. and going back up the 3 miles to home, had to really bury my foot into the Injection pump.

Next morning I adjust the valves. now on our cars when I do an adjustment, a little turn on the nuts and we are back into spec. if they are out. I couldn`t get any feeler gauge of any size to fit, I don`t think one is made that thin. I backed off the lock nuts several turns, and I bet about all the cap nuts except for one, I turned MORE than 360 deg + to get the feeler in. I kept turning & turning & turning, was beginning to think I was doing something wrong. 3rd from the end, had to jam in a pry bar to keep the valve from turning (no 3rd wrench) and the usually most difficult last one was the easiest and closest to spec.
I left them a little on the loose side.

So, whow many of you out there in MB land has had an engine with the most tight valves and still lived?

I swapped out the Injectors with a used set I have, blew out the plugged up IM banjo bolt and line. today got it all buttoned back up and finally started. WOW, what a beautiful smooth sound a 617 engine has when things are adjusted and cleaned. this thing is so smooth, not a hint of the shakes. took her for a run, and still lacking any boost or real acceleration. HMMMM

someone had messed with the ALDA, so replaced it with a virgin one I pulled at PNP. the old one had a rattle when I shook it, so probably some strong arm cranked down on it.
another thing I need to check is the Waste Gate hose, and maybe bypass the Switch-over valve. I did blow out the boost line to the SOV, but not to the ALDA. I did notice it`s Banjo bolt pretty Sooted up. so in the morning will do it.
I changed the engine oil and filter. the oil has a strange smell to it. Fuel dilution? maybe something from the WVO use? have no idea how long it has been since the last oil change.

Have a filter and ATF for a trans change, no record of it being serviced.

overall a nice car, but not worth the $4000 + they think it is worth, plus a long list of other fix it items I made a list of. big one, broked down drivers seat, like sitting on the floor. seat Bolster tore up etc... and drivers door check door post mount broken.

Charlie

layback40 · #2 03-12-2011, 05:28 AM

I got my 84 from a dealer. It was a trade in in late summer. I looked at it mid winter after their "mechanic' couldnt get it to start. I bought it, borrowed a couple wrenches from their service dept. No valve had a gap. most took 2 turns till they started to have a gap. As I had no feeler gauges I just set them all so they had a gap. Replaced 3 GP's after removing them all & testing on the new battery they had fitted. It started right up & as smooth as a sewing machine. You should have seen the mechanics face!!! He had been trying to get it going for 2 months!!
As these motors get colder the gap decreases. They need to be set cold mid winter.

vstech · #3 03-12-2011, 09:37 AM

most sellers are amazed when I can work magic on the cars, and get them running, when "mechanics" have been working on them forever and unable to start them.

leathermang · #4 03-12-2011, 11:31 AM

The real danger is an engine with the valves set in ' the twilight zone'...
At least half the cooling to a valve comes from being in contact with the head...
that is why the minimum valve ' margin' is specified by the factory ... the length of the seating surface on the valve rim... and the valve setting specs are enough so that a valve which is getting longer due to heat still firmly contacts the head when running...

The worst situation is a valve setting which will allow the car to run... and keep running... but allow heat to build up in that valve due to lack of strong contact with the head to convey ( through convection ) enough heat to keep from burning the valve...

For those who can not wait until their engine is cold in mid winter.... at least let it cool over night and set it cold in the morning.

Benz Dr. · #5 03-12-2011, 12:35 PM

I've noticed that gas engines seem to wear loose while these ones seem to wear tight.
Sounds like these ones were never adjusted almost from new. If you can get them to start they will continue to run. That's a big IF when it's cold out.

leathermang · #6 03-12-2011, 01:04 PM

Quote:

Originally Posted by Benz Dr.

I've noticed that gas engines seem to wear loose while these ones seem to wear tight. .....

It is based on the design of the engine ....not on the type of fuel or the compression ratio... so that generalization would not be proper to make.

charmalu · #7 03-12-2011, 01:11 PM

So most likely the lack of OOMPF this engine is lacking now, could be (from a lack of proper adjustments) burnt valves. so a compression test and/or leak down test.

I`ll get back to this after I get back from South San Francisco this afternoon.

Charlie

leathermang · #8 03-12-2011, 01:24 PM

A leak down test is more informative... since if a problem exists it will also point in the general direction ( up or down ) of the problem...

Stretch · #9 03-12-2011, 01:30 PM

Quote:

Originally Posted by leathermang

It is based on the design of the engine ....not on the type of fuel or the compression ratio... so that generalization would not be proper to make.

So Greg - Is it the rotor washers under the valve springs that promote the tightening?

leathermang · #10 03-12-2011, 01:34 PM

Not sure what you mean by ' rotor washers'....
but it is usually a difference between overhead camshaft and ' not'...

the rotators at the bottom of the valves inside the head are to promote turning of the valve so as to wear evenly. ( and ' roundly' ) ...

Stretch · #11 03-12-2011, 01:42 PM

Quote:

Originally Posted by leathermang

Not sure what you mean by ' rotor washers'....
but it is usually a difference between overhead camshaft and ' not'...

the rotators at the bottom of the valves inside the head are to promote turning of the valve so as to wear evenly. ( and ' roundly' ) ...

Interesting: camshaft configuration - really? Have you got a reference for that? (Please don't think I'm being rude - I just don't see how that would make a difference)

{Rotators == rotor washers}

leathermang · #12 03-12-2011, 03:19 PM

Army, are you referencing a different post where I mention the camshaft configuration affecting the torque and horsepower curves ?

On a diesel engine... due to the almost complete lack of overlap in the valves available due to the overall design.... the max rpms are affected little by camshaft changes.. but the placement in the rpm range of the max torque and horsepower....and the shape of those curves..... can be affected by lobe changes and relationships. The height and shape of the lobes are about all you have to work with on a diesel engine.

The rotators are there for even round wear on the face of the valves... on some of our engines they are provided stock only on the exhaust valves.. but are able to be retrofitted simply by dropping them into place... on the turbo engines they come stock with them on intake and exhaust...

barry123400 · #13 03-12-2011, 06:41 PM

I believe the occassional adjustment is to compensate for wear of the seat and the face of the valve. On the old mercededs six cylinder gas engines sometimes the seats were really back in. Part of this was from cutting the seat enough to clear any damage from the seat.

Result of burning valves from no periodic adjustment and the fact that the adjustments did not hold as well back then. Mercedes really stiffened up the adjusters about 1970 on their gas engines to lessen the problem. The tendency to reduce the clearances with wear is just a result of valve train design. Even way before that some mercedes mechanics could find no good reason that they had not installed hydralic lifters.

layback40 · #14 03-12-2011, 08:09 PM

Quote:

Originally Posted by vstech

most sellers are amazed when I can work magic on the cars, and get them running, when "mechanics" have been working on them forever and unable to start them.

As many will say "there are very few good MB diesel mechanics, even less qualified ones"
Having a good feel for these motors is much more important than a trade certificate.
After all there is an old saying, first year apprentices spend their time sweeping the floor & making coffee for the mechanics. Second years get to watch. third years hand the mechanic his wrenches, forth years are considered to know everything & are let loose on cars unsupervised.

layback40 · #15 03-12-2011, 08:16 PM

Quote:

Originally Posted by leathermang

The real danger is an engine with the valves set in ' the twilight zone'...
At least half the cooling to a valve comes from being in contact with the head...
that is why the minimum valve ' margin' is specified by the factory ... the length of the seating surface on the valve rim... and the valve setting specs are enough so that a valve which is getting longer due to heat still firmly contacts the head when running...

The worst situation is a valve setting which will allow the car to run... and keep running... but allow heat to build up in that valve due to lack of strong contact with the head to convey ( through convection ) enough heat to keep from burning the valve...

For those who can not wait until their engine is cold in mid winter.... at least let it cool over night and set it cold in the morning.

This is excellent advice !!! Could not have put it better!

If you want your indi to do your valves, best drop the car off the night before. The results will be better!!

Charlie,
You will probably need to do those valves again in a couple of hundred miles when the seats have had time to clean.