Thoughts on timing chain - PeachParts Mercedes-Benz Forum

yuke · #1 11-11-2014, 09:39 AM

I have showing 263,000 but could be more as odometer was not working when I got it. I did not measure stretch a little confused but think I will figure it out. About 2 yrs. Ago my mechanic said my chain was stretched near its limit and that I should replace chain. Questions are
1.Do you have to release tension when rolling new chain in?
2.Can I put new chain in with out replaceing any of the rails?
3.I know it would best to replace spring on tensioner I guess a new spring is all you would need not the whole tensioner.
4.Can you release tensioner w/o taking thermo housing off?
5.What am I looking at max. And min. Parts trying to get stuff together to do job.
I was thinking of just rolling a new chain in and call it a day did, nt really feel like draining a.f.and taking thermo houseing off to get tensioner out.
Is the chain crimping tool available from this site to do job or can I get away with just peening it or maybe try the H.F. chain breaking tool? All thoughts welcome
85 300 SD

leathermang · #2 11-11-2014, 10:00 AM

Listen to your mechanic.
Yes.
You can but that might be foolish.
depends on the condition of the surface.
I do not know.
The crimping tool is to squeeze the side plate onto the pins.
If you have the legit MB combo tool .. then you can swap the working part around to also peen... but peening is very simple and foolproof if you follow my directions...

Diesel911 · #3 11-11-2014, 11:05 AM

Quote:

Originally Posted by yuke

I have showing 263,000 but could be more as odometer was not working when I got it. I did not measure stretch a little confused but think I will figure it out. About 2 yrs. Ago my mechanic said my chain was stretched near its limit and that I should replace chain. Questions are
1.Do you have to release tension when rolling new chain in?
2.Can I put new chain in with out replaceing any of the rails?
3.I know it would best to replace spring on tensioner I guess a new spring is all you would need not the whole tensioner.
4.Can you release tensioner w/o taking thermo housing off?
5.What am I looking at max. And min. Parts trying to get stuff together to do job.
I was thinking of just rolling a new chain in and call it a day did, nt really feel like draining a.f.and taking thermo houseing off to get tensioner out.
Is the chain crimping tool available from this site to do job or can I get away with just peening it or maybe try the H.F. chain breaking tool? All thoughts welcome
85 300 SD

You are not saying what Engine you would be working on. On the Turbo Diesel 617.952 The Timing Chain Tensioner assembly needs to come comlpetely off of the Engine because even if you remove the Spring the Piston cannot be pushed back in due to a Retcheting device on the Piston.
When you re-inistall the Timing Chain Tensioner Housing the Piston needs to be removed. The Housing re-installed and the Piston goes back in from the outside followed by the Spring and the End cap and a Crush Washer.

I am not sure if it shows up in the Tool Rental area but several Years ago there was 2 Members who said they would loan out their Timing Chain Crimper.

I have read many times that Mercedes has no spec for Timing Chain Replacement. Apparently you are expected to do the 2mm Method to check the Timing Chain Stretch and decide from there.

Mercedes makes at least 3 Offset Woodruff Keys to compensate for Timing Chain Stretch and Timing Gear Wear.
You need 4 degrees of timing Chain stretch to be able to use the first one.

You can get an approximate idea of how much Timing Chain Stretch you have by lining up the Timeing Mark behind the Camshaft Gear and the Front Camshaft Bearing Tower Mark and then looking down at what degrees the Pointer near the Cranshaft Damper Points to.

When the Engine was new it doing that would have showed OT (top dead center). After 20,000 miles the Manual has it may be 2 dgrees.

Turn the Engine in the Direction of rotation and do not turn it back or the reading will be thorwn off. The more perfect you line up the marks the more accurated it is.
You also need to do the best you can to look straight down on at the Pointer and Crank Damper. Looking at an angle throws off the reading.

See pic.

leathermang · #4 11-11-2014, 11:28 AM

The only proper method of measuring is to use the 2mm method ... url in my signature for ease of access.

the reason for not turning the engine backwards is that the SLACK is taken up in one direction on one side...by the rachet mechanism mentioned... on the other side...the IP side... if you turn the engine backwards you risk the chain going slack enough to skip a sprocket... which is really bad...

The ' spec' from the FSM is that when the offset keys will no longer bring the system back to correct condition the chain is to be replaced. Seems pretty obvious ... but they actually say it...

Diesel911 · #5 11-11-2014, 04:13 PM

Quote:

Originally Posted by leathermang

The only proper method of measuring is to use the 2mm method ... url in my signature for ease of access.

the reason for not turning the engine backwards is that the SLACK is taken up in one direction on one side...by the rachet mechanism mentioned... on the other side...the IP side... if you turn the engine backwards you risk the chain going slack enough to skip a sprocket... which is really bad...

The ' spec' from the FSM is that when the offset keys will no longer bring the system back to correct condition the chain is to be replaced. Seems pretty obvious ... but they actually say it...

I will remember that. I had not read the Manual that close as My own Engine is not a canidate for that so far as I know.

Many People are used to US Gasser Cars that used to have Timing Chains with no Tensioner on them.
And, then there was those Timing Gear Sets where the large Gear had Nylon (Plastic?) Gear Teeth on them.
There was a recommended mileage when they were supposed to be changed.
Or a kind of common knowlege on when they should be changed developed based on when a lot of People had theirs fail.

leathermang · #6 11-11-2014, 05:24 PM

Quote:

Originally Posted by Diesel911

.......Many People are used to US Gasser Cars that used to have Timing Chains with no Tensioner on them. .....

For people wondering how that worked....
it was on engines where the only things connected were the crank and the camshaft... and it was very short .. with access to both pretty easily from the front of the engine.. you put the chain on both sprockets and put the two sprockets onto the engine at the same time...so the chain started out very tight... and since it was on overhead valve engines... not overhead cams like ours.... the distance was very short... and the lifters and pushrods made up the difference to get to the rocker arms to actuate the valves...

yuke · #7 11-11-2014, 05:28 PM

Another question I just thought of is Do you have to take cam sprocket off to determine if p.o. put offset woodruff key in if so would it be stamped? I imagine the stock key was not offset on the 617 turbo. So I do have to take thermo. houseing off to releash tension on chain. I guess that takes a different gasket then the one that holds the stat in? Is there also a gasket for the tensioner also? Can gaskets be reused with a little silicon on them? I think just the spring itself can be bought and replaced in tensioner to save a little money. Considering everthing might just put new chain in and thats it.

leathermang · #8 11-11-2014, 06:39 PM

You need to find a copy of the FSM to guide you on this project...
because you will never see all the warnings which are in the FSM here on this or any other forum....
and there are some times to be frugal and some not... what usually causes chain failure.... with the associated bending of valves or holes in pistons... is not the chain itself failing.. but the parts which guide it around its path and keep it tight...

Lucas · #9 11-11-2014, 08:09 PM

I'm new to mb but researched this a ton due to its importance.

Like he said, worry about the guides. That's what causes chain failure. And he's right about getting an original FSM. I got an original digital copy off eBay from a seller named "mbmanuals". Pictures suck but it's all there.

You replace the chain when you are out of keys to correct valve timing.

Someone may have replaced the key previously, so if you put a new chain in valve timing may be off.

Two separate gaskets. You already have a head gasket to mix your oil and water. I cut my own for simple stuff like that. I have a big roll of fuel pump gasket material as its the most resilient. I use sockets as templates and a retractable razor knife that you can break off a piece for a new cutting edge. I'm liberal about breaking it off. Experience from the tint industry.

The auto store guy showed me a spray can of "right stuff" gasket material. It's supposed to not spread and get into your motor when you assemble. It was $20 for one can.

Don't loose your water or oil and blow your motor. Been there done that.

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leathermang · #10 11-11-2014, 09:57 PM

Quote:

Originally Posted by Lucas

.... Pictures suck but it's all there. .....

The MB FSM is really required..but it is true that even the paper manuals have iffy picture quality many times... so I have long recommended that one have the Haynes manual IN ADDITION to the MB FSM... still not perfect.. but the more help one has the better...

The FSM is not written in the spirit of ' How to keep your VW alive for the complete idiot'..... I wish it were.....

Lucas · #11 11-11-2014, 10:12 PM

Quote:

Originally Posted by leathermang

The FSM is not written in the spirit of How to keep your VW alive for the complete idiot'..... I wish it were.....

That's what Hondas are for.

I talked to my eBay seller about the manual, and I admitted technology for pictures probably wasn't the best in the 70's. He said they produced the manuals in the late 90's as per a class action lawsuit, and said they were produced at minimum spec."

I find the info helpful, but as a DIY mechanic I have to re-read multiple times. I could probably use the idiot version manual. But I'm keeping my budget super limited until I can go 1000 miles without working on my car.

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