Another V8 chain and guide question - PeachParts Mercedes-Benz Forum

126nut · #1 03-02-2004, 09:29 AM

I had a chance to pop the valve covers off my 89 420 SEL last night and found a broken upper guide on the driver (left) side. Luckily, I was able to fish the piece out and it looks to be the lower end of the guide which had snapped off right at one of the dowel pins. The piece was just riding between the chain, I guess it was in a position to where it wouldn't get caught up in one of the gears. My records show the chain, tensioner and guides had previously been replaced at 70K (now I'm at 130K) so it looks like this is a common maintenance item.

I was wondering if it is possible to just replace all the upper guides and the tensioner or does the chain need replacement as well? I also have a leaking head gasket to deal with and am thinking I might as well pull the engine and get it all taken care of.

(The wife is gonna freak if she's sees the engine out of her car)

Thanks,

stevebfl · #2 03-02-2004, 10:11 AM

No need to pull the engine to do head gaskets.

Definitely the rails are a maintenance item, and you were real lucky. I advise atleast every 75k or 5 years, but I also advise looking at them at intervals and replacing them as soon as they start to change color. If they are amber they should be replaced. How the car is driven, heat, and oil changes are factors.

dloveless · #3 03-02-2004, 11:30 AM

I am not a tech... just did my 84 V-8... for what its worth as long as you have it that far I would replace the chain... not that expensive of a part... I think mine was $55 or $60 last summer. I also would not remove the motor to remove the heads.

good luck on your project.

peterhardie · #4 03-02-2004, 12:46 PM

I just had my wife's 400 apart for a chain replacement, and its rails were also exploded, INCLUDING the bottom end rails.

The lower ones are not supposed to go bad, according to my tech. Their failure may be related, if your uppers were replaced 60K ago. Failure of the uppers may accelerate failure of the lowers.

I'd at least inspect them, and if you have the time and energy, pull your front cover and replace the rails at the bottom. It's a bit of work, and some might argue against it on that basis. Your call. I'd be curious what your lower rails look like.

dloveless · #5 03-02-2004, 01:13 PM

further comment on the lower rails: I am not sure on your car but on my 84 500 the lower rails were black [the old ones and the new ones] where the uppers were white new and amber/brown old.

Good luck.

jriewer · #6 03-02-2004, 01:15 PM

I just changed the upper guide rails and chain on my 87 420 this weekend. Two of the upper guide rails had broken off at the top, and the chunks were riding between the chain, one on the left and one on the right. I was definately driving on borrowed time.
This was my first time chaining the upper guide rails and tentioner, so It took me a day and a half to pull everything off, deal with stripped 6mm hex nuts, and pull the pins. By contrast, putting the new chain on took only half hour with a helper turning the engine and advancing the channel locks. By all means do the chain if your gonna spend all that time chaining the rails.
www.pindelski.com has a great pictorial on changing the rails and chain and is worth the $30 yearly subscription fee for his site. My indie in San Francisco wanted $1600 to do the job while I did it for $225 in parts and a sore back.

126nut · #7 03-02-2004, 03:40 PM

Thanks fellas,

Definitely happy that I won't have to pull the engine to do the head.

Another question though please,,,

It is the left head gasket that is leaking at this point, should I go ahead and do the right head gasket as well? Is it a pita to do either one in particular with the engine installed car and would doing both warrant engine removal?

I have ordered up all the parts, OE stuff which was really not as expensive as I was prepared for. Interesting thoughts on the lower block guides, I will see how energetic I am at that point and who knows, maybe I'll pull the front cover. If I am going to go that far I guess threading a chain is a mute point, I have never done one that way because the last V8 I did, a 380, had catastrophic chain and guide failure so I ended up tearing it all down.

Also, on the 380 someone told me the aluminum blocks head bolt threads would need Helicoiling, somehow they are meant for one-use only. I had to Helicoil all of them, very expensive and time consuming. Is that necessary on the 420 blocks?

dloveless · #8 03-02-2004, 04:31 PM

I would do both heads. Not sure on your car if one side or the other is more difficult to get. On my 84 500, by the time I got the fuel distributor and intake off it was most of the battle. My block is also aluminum and did not require any helicoils. Just lucky maybe. I would second the pindelski site as worth the $30.

Good Luck.

greenacres2 · #9 03-02-2004, 05:45 PM

I only did one head (left was seeping and bent exhaust valves), should have done both since the intake and all were off. If you do both heads, might as well pull the front cover and get the lower rails. With both heads off, the front cover is only a few bolts, and it will make the "banana" rail a piece of cake.

stevebfl · #10 03-02-2004, 06:14 PM

The front cover is a good ten hours more work on a sedan with a subpan. On SLs with solid pans the whole subframe must be removed to remove the pan to disconnect teh oil pump chain which is captive in the cover.

The AC compressor alone is a pain to remove and likeeverything else it is bolted to the cover.

Take a look at this picture, everything that isn't in the picture takes a while. Notice the home made engine support.

lesrrt · #11 03-02-2004, 06:16 PM

I am also in the process of doing head gaskets on my 380 sel after I converted to a dbl chain. When all is removed: heads, intake, front cover, and etc. there isn't much left. If I had to do this all over again, I would have pulled the engine/trans out together. This way, you might as well change the rear main seal and input seals of the trans. too. Iam elimninating my air pump and want to put tapered alum plugs w/ loctite into the holes that feed the exaust ports via the intake side of the heads. Anyone here done that by just tapping and putting bolts in? Or can you get these alum pins as a kit; I read about them in the cd manual.

les

stevebfl · #12 03-02-2004, 06:16 PM

It is supported because to get the SL pan off this has to go:

126nut · #13 03-02-2004, 07:41 PM

Steve,

Now that looks like a ton of work! Why not just pull the engine? To properly remove the front cover one must pull the upper oil pan I guess? I agree they are not easy to pull on the SL's but removing the subframe? Unless maybe it is one of those early crack prone subframes that were supposedly recalled.

Here's a tip, why don't you go ahead and do the engine mounts while you're in there!

stevebfl · #14 03-02-2004, 08:17 PM

And subframe mounts.

We can support the motor and drop the subframe/suspension in a couple hours. Then there is total access. Pulling the motor will waste a lot of time.

greenacres2 · #15 03-02-2004, 08:32 PM

Wow, makes me glad i have an SEL instead of an SL.
Steve, if one were going to pull the heads anyway (on say a 420 or 560 SEL) wouldn't the only additional components be the hydraulic pump (560) and a/c compressor, with no need to loosen the upper oil pan to r/r the timing cover. In shop time that's 3 hours +/- in labor and expensive to your customer, but for me to add 3 hours to a job that took a month and $10 for the lower rails, it would have made sense "while i was in there"--even if i hadn't found part of the lower left rail in the oil pan. I'd prefer never to do it again, but i am glad i did it once and it worked all right.
You are absolutely right about the a/c compressor, and its carrier, what a PITA.