Question re: timing chain guide rails

[pauldridge]

I'm putting my 280 SL engine back together after its 3 month visit to the machine shop... new guides, pistons, rings, bearings, etc...

While installing the two lower timing chain rails, I ran into a head-scratcher.  The shorter rail, underneath the large chain sprocket that also drives the injection pump, is shown in a third-party manual I have, as being installed with the longer end of the rail pointing UP (i.e., two pin holes at the bottom).  I tried this configuration, but find that the chain binds between the main sprocket and the guide rail.  Then I look at the exploded drawing from the Millers MBZ website, and it shows the the chain rail installed with the two pin mounting holes at the TOP, and the rail extending downward, per this picture (it's part 05-0001 in question:


This will solve my clearance problem, but before proceeding further, I wanted to make sure this is the correct configuration.  Can someone please confirm this?

Thanks
Phil
Austin

[DavidBrough]

Hi Phil,

The Millers diagram is correct have a look here: http://www.sl113.org/forums/index.php?topic=12510.msg84705#msg84705

[ctaylor738]

Presume you are talking about the Haynes book.  I ran into the same thing.  I think Haynes took the diagram from the parts book, which has the rail upside down.

[wwheeler]

I know Phil is assembling his engine, but can you change out the guides w/o disassembling the engine?

[pauldridge]

First, THANKS to David for this quick response.  Thanks to you, I got my basic internal engine together today.  All that is left is refurbing the accessories and hanging them back on.

To the other poster asking about changing guide rails without disassembling the engine:
1)  Are you sure this is an issue in your engine?  These things are pretty hardy... my old guides, in a very tired engine, were very serviceable.. if the new guides weren't so inexpensive, I might have been tempted to just use the old ones.
2)  Are you having problems with chain noise?  It could be that your chain is worn, hence longer length which can't fully be taken up with the tensioner.  I experienced this with another engine, and was able to successfully replace the timing chain without any disassembly of the engine (lots of good advice on this subject on this forum)

If you're certain you need to change the rails... my opinion:
a) The upper rail on top of the head, of course, can be easily changed by just removing the valve/cam cover
b) I do know for sure that you can slip the shorter lower guide (lower right side if facing the engine) in and out of the cavity without removing the chain.  However, to do this, you'd almost certainly need to remove the radiator and the distributor base housing to get to that guide.  Might have to remove the water pump also.  Even with that, you really need to get to the guide from underneath, i.e. by removing the oil pan.  It wouldn't be a pretty job.  Not sure if the longer guide rale on the left would come out with the chain in place.
Hope this helps
Phil/

[wwheeler]

Phil,

I am going to remove the radiator and pretty much everything in the front of the engine for maintenance, detailing and peace of mind. My engine was rebuilt 15 years and 12,000 miles ago, but who really knows what and how well it was done. The receipt shows a new timing chain but not the guides. I am not having any noise problems now, but I don't want to ask for trouble. While I am there, I want to do as much as I can to assure reliability. 

Hopefully, I can remove the lower guide without taking off the oil pan. That is not in my current things to do!

Thank you for your thoughts.

[ja17]

Hello Wallace,

Those lower guides on a fuel injected engine are very difficult to change while the engine is together. The main drive sprocket for the injection pump/distriburtor is in the way and it is not easy to remove. The timing chain must be let completely slack and the distributor housing and big sprocket in the block have to be removed. Once all of this is out of way you can safely work on replacing the lower rails.  Anyway the timing chain does not flop around too much way down there close to the crankshaft drive sprocket. The only time I have seen a lower rail fail is when something from above has fallen on it and jambed.  The lower rail on the other side can be replaced if you remove the chain tensioning sprocket and arm.  Still a bit tedious and most likely not worth the risks. Replace the top one if it is plastic. Check the timing chain and save the major rail replacement to do when the engine is apart.

The risks are........... getting the injection and ignition out of time and dropping parts down into the engine,

If yours are the old aluminum and rubber rails they are less prone to break than the new plastic ones.

[wwheeler]

Those are great thoughts Joe! Thank you for your wisdom.

I am planing on taking out the belt pulleys and such to replace the front seal which is leaking a bit as is the p/s pump. I was going to remove dist/IP gear cover while I am there to clean it up. It sounds like it may be a bit risky. If I index everything and don't move the engine, will those be adequate precautions? I am also going to remove the lower oil pan to remove some dents and creases. So If a part drops in the front part of the upper pan, it should fall into the lower one, right?

Always scary going into places you have never been before. Without help from this site, these expeditions will always be much scarier AND less successful.

[ja17]

Just take some pics along the way and we will help you along!

Just remember, anything dropped, usually does not end up in the pan. It usually gets lodged on the crankshaft sprocket/timing chain area. Where it causes lots of damaged the first time the engine is started. Yes index everything and also double check all timing before start up.  The most difficult part is to keep the injection pump in time while the sprocket is off. You may just want to remove the pump and re-time it also.  Take a good flash light and examine your chain rails first to see what condition they are in and what version they are (plastic or aluminum).

Keep us up to date.