1986 420SEL Maintenance Questions
 

Hi all,

Plan to do some maintenance on my car next week. Vehicle has 90,000 miles. The car runs okay. Just trying to prevent major problems. Plan on replacing s. plugs, timing chain or guides or tensioner, Drive shaft flex joints, belts, front and rear brakes. Have some questions:

• Timing Chain: Do I just replace the upper guides or do I need to also change the tensioner and chain?
• What are the best plugs. Platinum or nickel?
• Best source for quality parts?

Thanks, and have a great holiday season

Joe

I would replace the chain, guides and the tensioner.
Ibuy all my parts from Phil found on this site.

The best plugs are, Bosch copper non resister.

Chain, tensioner, all upper rails (4 in total). Oil tube clips and VC'er gaskets.
Contitechs for belts is all I use.
Platinum is a big NO. Copper is what you want, and the BIGGEST concern is that the are non resistor! Beru and NGk are you best bet for NR plugs @ this point, you can basically write Bosch off now.
I'd also look at your dist. cap and rotor. I'd also test all your wires, make sure none have more then 1.1-1.3 Kohms resistance.

There are many places to get parts, just be sure who ever you are buying from has experience working with/on your style car.

Jonathan

Why is platinum a big no and Bosch no good
 

Why is platinum a big no and bosch no good? What is the 4th rail. I am aware of 3 near the top. Is the 4th at the chain tensioner?

Thanks

Joe

All the platinum plugs are resistor which MB states in their literature as NG. Also, the plat. plugs have Very small electrodes thus the can become contaminated quite easily. The resistor plugs also cut down on spark output/energy.
Bosch has stopped making non resistor plugs for our cars...

Yes, the 4th rail is @ the tensioner.

Jonathan

Confused about Resistor/Non Resistor
 

What happens if you run resistor plugs in the car? My mechanic and parts guys say resistor plugs are only needed to reduce electrical system noise that can interfere with radio reception, etc. on that advice, i'm running resistor copper bosch plugs in my 91 560SEL with no problems. PO had Bosch Platinums installed, and I can vouch they are terrible.

Check out this thread:
Bosch Platinum +4 Spark Plug Experienced..?

Sorry the search engine here didn't turn up the title??!! Search on the author: J Irwan

That got me back there.

In your engine, the resistance is in the spark plug wire boot, not the spark plug itself.

If you use a resistor plug (all platinums are resistor plugs), you are doubling the resistance, which is hurting the spark.

Just install regular copper core non-resistor plugs. They are cheap. Your car will run perfectly, and you need to change them every 30,000 miles.

Some time ago a Mercedes-Benz service bulletin recommended against using fine single-wire platinum electrode spark plugs in their engines. The electrode on these plugs was so thin that the spark could be blown off the plug, causing misfires. Thin-wire plugs could cause poor idle quality and misfires at high rpm under full throttle.

Also a lot of good info in this thread:

http://www.peachparts.com/shopforum/tech-help/128120-replaced-spark-plugs-wow-what-difference.html?highlight=star+magazine+plugs

Thanks
 

Thanks all for the help.

I have a box full of parts and will be working on the car the week after Christmas. I don't have to go back to work until Jan 3rd. So will be taking my time, not having time pressure. Should be enjoyable.

Joe

Do you know where to find replacements for Bosch non-resistor plugs? Like the W9DC/w9DC0? TIA.

You can try Phil here at ShopForum. Click on the Buy Parts link at the top of the page.