Pointy gears on a 1988 420 sel?

[Blu 420Sel]

I've recently purchased a 1988 420sel with 165,ooo from a friend of the family in AZ. My friend's uncle was a fastidious owner and always took excellent car of the car before he passed away. Although I don't have any records the car was obviously well loved and immaculate.

I've probably read thousands of posts by now and feeling fairly well informed I took the car to a respected local MB Indy for a full-check-up (especially the timing chain). I had them, pull the valve covers, drive it, throw it in the air and look uderneath, everything.

His report is very positive, both the cylinder heads and transmission look virtually new, the chain has been replaced (has a master-link) along with the rails and tensioner at some point within the last 50k he thinks. The only major thing he finds is that it doesn't look as though the cam gears were not replaced with the chain. He says that they look 'pointy' and aught to be replaced. He is also worried that the lower gears may also be worn and wants to replace them as well. They are guessing that it would be two days labor to pull the front cover and replace everything (I'll get an estimate tomorrow).

What does everyone think? If I hadn't read dozens upon dozens of posts about the timing chain I probably wouldn't worry about it. Since I have however, I'm concerned.

[Blu 420Sel]

I should have mentioned that the chain has about 4 degrees of stretch on it.

[Blu 420Sel]

TTT

Is there a recommended replacement interval for the lower sprockets?

[Robby Ackerman]

If the upper gears are pointy the lower gears are as well. They should be flat, and if worn gears are not replaced when renewing the chain, worn gears will greatly diminish the useful life of a new chain. In other words worn gears will ruin a new chain. If you intend on keeping the car replace all the gears and install a new chain as well.

[Blu 420Sel]

Robby-

Thanks for the reply, I was beginning to lose hope. I've been voraciously reading posts and for all the information on W126 timing chains there is almost nothing on crankshaft sprockets. Its nice to have a second opinion.

I think I'll leave this one to the pros, I was feeling pretty confident about trying the chain and guides but pulling the whole front cover seems like a whole new level of difficulty.

I'll stick to chassis repairs and tune ups for now.

[Robby Ackerman]

Yes, it is just a lot of grunt work. I've changed them a couple times on my old 190SL. I must remove the engine to change its gears, but it only takes four hours to pull the engine. And the engine rolls out from under the car on the front wheels. Ha!

[Blu 420Sel]

That's great, just bolt the driver's seat to the top and you'll have the ultimate convertible! I do wish I had a week off to muddle through this though... seems like a lot of fun.... sigh...

[Blu 420Sel]

Robby,

Thanks again for your advice. I have a long weekend coming up and was thinking of trying to tackle this myself. I've done a lot of smaller repairs and recently a successful head gasket on a '95 Saab. Do you thnk this is a repair I could handle if I take my time and take lots of pictures for reassembly? Its seems pretty straight forward, but maybe I'm being too optimistic.

Thanks!

Tim

[afmcorp]

hello tim,

i'd like to suggest you try to find posts from stevebfl and Thomaspin. there are also some others that i am no doubt forgetting.

my reasoning is that it has been said quite often that the bottom end of these 4.2's can expect a life of 350 to 400k with out replacing the rails. so that mileage would include the lower chain sprocket.

the upper sprockets are very easy to do and you should not have any problem doing these yourself. caution and care on how the sprocket fits in the chain is needed but beyond that it is a fairly simple task.

by looking at the keys you can determine if you need to use an offset key or not. 4 degrees is not that much lash but you could take that up if you choose.

the lower gear i believe sits in an oil bath of sorts is my understanding on the rails life span so i think you could extend that reasoning to the gear as well. also don't forget to replace the valve cover gaskets and the small lock washers on the vlv cover screws.

good luck
tks
craig

[Blu 420Sel]

Hi Craig,

Thanks for taking the time to post. What you say makes a lot of sense. It would certainly explain why I've had no luck finding any posts on the lower end. If nothing else the statistics are on my side.

I have a small leak around my oil level sender that I was planning to replace soon. I think I'll try to get a good look at the crankshaft sprocket when I have the pan off. I'm not positive but I think I should be able to see it fairly well once I'm in there. Just to be safe I'll try to pop off a digital photo to post for more experienced eyes to look at.

[william rogers]

I did a cover off on my Euro 500 SE witch has a Euro 420 engine in it. I replaced all rails oil punp chain tensioner both pan gaskets ect(the gears looked fine).I thought myself compentent enough to do the job with out a manual,VERY BAD MISTAKE could have done job in half the time with a book even then it's no small chore to do a cover off but it sure looks cool when its all apart.......
William Rogers........

[william rogers]

hmmmm, a little more pointy than I remember, but sure is pretty........

[Blu 420Sel]

Wow, that's a great looking shot, it kind of mesmerizes you when you look at it.

How long did the job take? Is it possible to do it without pulling the engine?