450sl noisy start up

[erubin]

There is tons of info on timing chains but maybe someone can give me a good plan of attach. My 1972 450SL has 100k miles since i rebuilt it. During that rebuild I changed the chain, rails, tensioner and sprockets. It's been 18 years since that rebuild so I don't remember if the rails were plastic or metal and if the parts were OE or aftermarket, i suspect the latter.

Just recently the engine makes a chattering sound for a second or two on start up (when oil is hot but engine has been at rest for 10 minutes or more). I suspect a timing chain related problem. I use the car every day so i have to have a plan before attaching.

Should i take one or both valve covers off to see what's up? Should I measure chain stretch and look at the rails for wear? If the rails, tensioner and chain all contribute to excessive stretch how do i identify which is/are the culprit? Is it obvious from inspection whether or not the lower rail needs replacing, I don't want this to turn into a huge job in time and part$.

I've given the engine excellent maintenance since the rebuild so it's not like the oil was never changed.

the car has 250k on it and i never changed the camshafts during the rebuild. I really can't afford new ones but what should I look for regarding their wear limit?

[erubin]

The upper timing guide rails offered are plastic and made by SWAG. Is this a bad choice? Not even the dealer has metal backed ones. Are metal backed ones better and are they available. Which timing chain tensioner: FEBI or LASO (cheaper) is better?

Can the rails that are typically changed at 100K miles be done without taking off the timing cover? My understanding is that the cover only needs to come off to remove the bottom two rails. I don't want to change the lower rails if it reduces the work needed alot. I read a couple of posts that say they dont wear much.

I plan on buying the timing chain, 4 rails (the 2 top inner left and right, one top outer left and tensioner rail), tensioner, cam oiler kit, valve cover gasket. Am I missing anything?

The shop manual says the right hand camshaft sproket must be removed to change the tensioning rail. If so should i change the sprockets (left and right) while I'm there. The shop manual says i need to take off all the right side rockers to change the chain, is this true? Also says the distributor must come out for the side rails.

Should I order new rail guide pins? What about a chain installation guide tool @ $49 is it really useful (I'll be doing the job by myself).

Sorry for all the questions but I want to be prepared with parts and knowledge before digging in. Any part i have to buy once I start will be from the very pricey local MB dealer. Anything bought in advance can go mail order at much better price.

[kip Foss]

I just had the chain, tensioner, and guides changed in my 1977 450slc at about 130k. I use the chief MB mechanic in Corpus Christi because not only is he good but he works on the side for less than half what the dealer charges. He only charged me $180 labor; I bought the parts. I can make $250 a day at work so the economics are really for letting his do it. Plus he did all the front end bushings, ball joints, upper A arms, etc. for $200 labor so I gave him both jobs. Too cheap to turn down.

When he was finished he told me that the chain was good and the upper rails were not that bad. He said that he has seen those 450 engines with 250k+ on them with the same chain. I am an industrial mechanic and work around a lot of chains and sprokets and as a rule never change one w/o changing both. I asked my mechanic about this and he said that unless you can see noticeable wear on the sprokets (there is a gauge to measure this) there is no need to change them.

As far as I know you need to remove the driver's side valve cover in order to access the guides on that side. The chain is fed in through the pass. side and there are guides there too so you need to remove that side also. The rail guide pins don't really get much wear so I doubt that they need replacing. Again, you are there you might as well.

I made my own small slap hammer for removing the guide pins but ended up not using it. I have a small lathe so it wasn't difficult. I think that you could just screw a 6mm (I think that that is the size) bolt into the guide pins and pry it out.

I think that the quality of either chain tensioner is about equal. I can't remember which one I bought but there can't be much difference in either one.

I think getting the chain installation guide would be worth the effort if you are doing this job by yourself. I can't say that I would reccommend doing it by myself since you really need someone to turn the engine over ans someone to feed the chain.

If you change the sprokets (not reccommended with only 100k on the last rebuild) be careful about the timing. You can get a tooth off and bend your valves with no trouble.

I think that I would start out by measuring the play in the system. If you have play but the sproket teeth are not noticeably worn I would look at the guides, tensioner, and the chain. I think all these parts cost me about $150 and if you are going to do one then do them all.

Good luck.

[erubin]

Kip,

Thank you for your info. It helps.

I am starting to rethink how i will deal with my timing system. I think it is a bit hasty to change everything (rails, tensioner and chain) because they have 100K miles on them and I'm starting to hear a bit of chatter on start up. Maybe just the tensioner is bad and is not holding enough pressure before normal oil pressure takes over. Maybe some of the upper rails are worn. From what i have read and heard the double row chains fail when a piece of rail gets caught in it. The chain will stretch from wear and tear but that can be measured and evaluated for out of spec condition.

I will proceed by taking the 2 valve covers off and inspecting the rails. Regardless i'll change the rails and probably the tensioner. Once done i'll measure the chain stretch to see if the chain is really out of spec (I'll also do this before changing the rails and tensioner). I'd like to avoid changing the chain unless necessary (the idea of spending more $ on a new chain, grinding off the old chain, feeding a new one in by myself makes me a bit nervous). The manual also suggests using offset keys on the sprockets to correct for stretch. Anyone have experience with this? I would think that would be very easy to do compared to changing the chain. Some people would say why bother, just change the chain. With that philosophy why not also change all the sprockets as well.

Does my plan make sense?

[txstinger]

It’s very kool hearing about your new mission. I think you can handle it. I don’t know the true condition of my engine so I would investigate it closely first. I use a very bright light and take good inspections while reading the manual.

From my days on domestics, if chain is changed so are the sprockets. However, while working on the SL I notice a tight fit on internals. I’ve read many post on changing chain w/o sprockets. Inspect closely…

I would use the woodruff key to correct stretch. It’s in the manual for this reason.

The biggest thing is you have that ear for the engine. You notice those small sounds that give you time to investigate and make advance purchases. Thumbs up