1991 420SEL won't start - resumed thread

Friends,
I am still troubleshooting my 1991 420SEL. My brother is helping me as I am not mechanically inclined, so please forgive me if I misstate anything.
Here is the list of things I have done so far.
1. Replaced fuel pump relay, overload relay 2. Replaced distributor cap/rotor 3. Replaced fuel/air filters 4. Temporarily replaced fuel distributor 5. Replaced battery 6. Checked fuses in the engine compartment 7. Temporarily replaced ignition box near driver side wheel
It seems to get fuel through the fuel distributor. The fuel pump sounds like it's working when I turn the key. No leaks, no smoke. We get spark at the cylinder. Timing seems to be in synch. Gas tank is 3/8 full. Never any backfiring or hesitation in the past. Starter seems to be working fine; engine tries to turn. *Sometimes was hard to start (before new battery). *Cruise control never worked for me. *When we try to start it, sometimes it makes loud knocking but doesn't start. *Initially stopped on the road after I floored it at 15 or 20 miles an hour to enter a residential street, no hot-rodding. Has sat in my driveway for one year, unable to start.
Thanks, Ron in Salem OR
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Tell me what the compression is on all 8 cylinders.

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You wrote: Starter seems to be working fine; engine tries to turn.
Tries to turn?? It doesn't turn??
If it doesn't turn I suspect the timing chains broke (they last about 125 - 150K miles) allowing some valves to be smashed by their pistons, broken cam(s) rockers etc. -- Major $$ if that's what happened. R.I.P.
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You wrote: *When we try to start it, sometimes it makes loud knocking but doesn't start.
You need to determine if the cams are turning when the engine is cranked. Open the oil filler and watch the cam while someone cranks the engine with the starter - even briefly. The cam should turn, if not, the chain broke. That's why it knocks.
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Yes, we did this; and, yes, the cam turned. Thanks for clarifying. That's why I mentioned the timing seemed to be okay.
Ron
On 4/8/07 6:05 PM, in article 5rWdnQqHTbvxDITbnZ2dnUVZ snipped-for-privacy@comcast.com, "-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote:

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Good, then do the compression test suggested by Karl.
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I'd probably suspect the timing chain has jumped... setting the timing all wrong. Compression test will reveal if this is the case.
Very easy to do, take out all plugs, pull out OVP and fuel pump relay.
Install one compression tester and have someone crank unitl you see the third jump. Repeat on all cylinders.
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Thanks again.
I did read somewhere that I would need an OEM compression tester. Is that accurate? Or can I use any generic brand?
Ron
On 4/8/07 9:47 PM, in article 3zjSh.287$ snipped-for-privacy@newsfe12.lga, "Tiger"

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Any will, including a Harbor Fright one.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber9224
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Yes, as Karl said... any brand will do. The one with a quick disconnect is much easier to use.
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Awesome. Thank you. I happen to have a Harbor Freight store right around the corner from my house. I'll go there right now.
Ron
On 4/9/07 2:44 PM, in article
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