Timing marks

[Tom Z]

Good Day all
My 68 280 sl over heated on me I did a compression check all above 150 psi the plugs looked good but I changed them anyway no water in the oil and the coolant reservoir stays full I did find a bad hose clamp and replaced it. She's popping back thru the intake manifold. I think I my have jumped time on the IP or cam due to over revving at no load. I can't seam to find the location of the timing marks anywhere here on this site can someone point me in a direction?

[garymand]

I found the timing marks under http://www.sl113.org/wiki/Electrical/Distributor.  Take the valve cover off and verify TDC on #1.  timing marks are in the usual place on the harmonic balancer but its the inside set of #'s.  Pull the #1 plug and find the physical tdc.

Verify mark on crank is at 0 at TDC with the notch in the spacer ring behind the cam gear lines up w the molded releaf mark on the cam tower.

Its a difficult for me to relate over heating to 150 psi (good compression), no water in oil (gasket leak), and intake valve leaking (timing).  timing and gasket leaks are pinpointed well with a leak down guage set.  You can hear which cylindar is leaking and  if valves are leakin, which ones and measure how much.  If the leak is into the water, you get bubbles in the coolant.

Are you saying it starts and over heats, or it used to start?  Is there dirt on the radiator cap (combustion into water)?

[Tom Z]

She overheated on me, after I filled her back up with water and the temp started to come down I foolishly throtled her up trying to clear what could have ben fowled plugs and then I experanced this popping problem in the intake manafold towed her home. Checked compretion, coolent pressure test all were good so I don't belive I have a bad head or gasket or intake valve.It idles poorly ,I need to raise the throtle to keep running, if I raise it more is when she starts to pop. What is the simplest way to check the IP timing?

[garymand]

Don't worry about the fip.

I think we need more details.   I could assume the motor started but sputtered relentlessly at or near idle.  But we need to go back farther: Do you have a good guess as to why she overheated?
How much water you had to add?  
Where did the coolant go?

1) I can take a stab at steam getting water inside the distributor cap or a spark plug wire is off.  You would hear snapping near the plugs, but the cap will not probably make noise, but the spark happening at the wrong time could be the popping (spark with a valve open), just sending spark to the wrong plugs.  Dry the inside of the cap.  That might fix it.

2) Please explain in more detail the popping sound.  Were you under the hood to know where it was coming from?
3) how high did you rev the engine?  3 or 4 k is not a problem and that is pretty high.
4 coolant pressure test is good, you pressurized to what # and how long did you wait as the pressure stayed up?  You might pull the plugs and pressurize with a stethiscope (hose) in each spark hole to see if you here leakage.  

FIP timing is controlled by the timing chain. oops, I forgot to say in the last message to pull the cap and see where the disty is at tdc.  It should point to #1 spark wire every other TDC.  If so, no FIP problem and if all the marks line up: crank, cam and disty then you timing is ok.  The trick is to line up the cam and disty, then see what the number is on the crank.  That tells you how old your chain is or if its skipped.

[ja17]

Some good thoughts "garymand",

Yes, overheating could have fried something on the ignition like the resistor ends on the wires. Check them with an ohm meter replace andy bad ones.  Install a new set of spark plugs. Check the distributor to make sure the centrificle advance and vacuum is working properly.

[Tom Z]

Thank you for your input ! Yes I was under the hood with a remote start switch. I did rev it quite high @6000 or better in park after the over heat (after I added coolant) and the temp came down. I did find a bad (leaking) hose clamp replaced and pressured to@17psi for @20 min the cap is clean and she will start every time.Just no power and popping thru the intake not the exhaust.Thanks for the link to the distributor sight. Are there any markings for the IP under the distributor drive cover?

[ja17]

Check the ignition wires, ends, replace the park plugs, check the distributor and ignition timing first. Not likely that injection timing is the issue. Not likely the valve timing is an issue but look at it next. Turn the engine to "TDC" (top dead center) "0"  on the crankshaft dampner.  Always turn the engine in the proper direction. Make sure to use the correct scale on your vibration dampner if it has two scales. Remove the valve cover, check the alignment notched washer on the front of the cam (behind the first cam stand). The cast mark on the cam stand should align with the natch in the washer or be slightly in front of the notch in the washer.

Let us know what you find.

[Tom Z]

Thanks again I don't have a lot of time as the car is in a rented garage and I don't want to go back time and time again soThe crank and cam are easy but what about the IP can anyone help me out with a way to aline or check the pump timing?

[garymand]

Forget the ip.  It is driven by the timing chain, check the timing chain.  But theonly way you get popping in the intake manifold is getting spark when the valves are open. :'(

[ja17]

Gary,

The injection timing is not that critical on these engines. Look elsewhere first.

[Tom Z]

I'm guessing that no one can tell me how to check the IP timing?

[66andBlue]

You could buy a DIY book that might tell you everything you ever (never?) wanted to know about these pumps. 
http://911mfi.com/6.html

[ja17]

Hello Tom,

Actually checking the injection timing requires removal of the injection pump.  The engine is set at 20 degrees after TDC compression stroke #1 cylinder. Remove the injection pump and check the alignment marks on the pump. They should be lined up. Check the information on this site to familiarize yourself with the injection pump, its removal and the alignment marks.  Always turn the engine in the normal direction of rotation.

Check everything else first. Removal of the injection pump is a lot of work for nothing, if it turns out to be something else.

Ask questions as needed.

[Tom Z]

Hello all thanks for the feed back. Checked the cam timing,the distributer timing was where it belonged( An easy way to check IP timing) so I assume the IP is O.K., on further checking I found the "popping' in the intake came from #5 cyl (pulling plug wires), the popping went away but a knock occasionally occurred. I'm thinking I have an intermitted stuck intake valve on #5 cly. I'm going to pull the head next chance I get and see if it is indeed a sticky valve. 

[ja17]

Tom,

Check that plug wire with a ohm meter, from the distributor and all the way to the spark plug. You may even want to try a fresh set of plugs.  Make sure you do not have some plug wires switched (1,5,3,6,2,4). Sort of sounds like you have two plug wires swapped.

[garymand]

Tht's possible.  The only way you can get an intake explosion is if the spark hits with the intake valve open.

[Benz Dr.]

You can also get a back fire or popping sound if the fuel mixture is too lean. This would be more pronounced on a cold engine.

[ja17]

Yes, as Dan suggests, a lean mixture will cause a popping or coughing back through the intake. A fuel pressure and volume should be carried to make sure your fuel supply has good pressure and volume.

[garymand]

I knew as soon as I wrote "only" it was a big mistake.    I'm primarily advising against pulling the FIP until he's sure it is nothing else.

[travellerdogs]

Before pulling the head, I would pull the valve cover and check the intake valve spring and see if the valve is moving up and down the same amount as the adjacent intake valve and also by over revving you may have broken a valve spring. Just my 5 cents worth.