Timing Chain missed

[scottgoing]

I have an 81SC with original mech. tensioners. While driving the car died and I had it towed home.

After checking fuel, spark, etc. I believe the timing chains may have skipped a tooth on the driveshaft. I did a compression check (by cranking only because it still won't fire) and all cylinders were 135-160 psi, which I thought was OK, but is there a better way to determine if the timing chain has skipped without removing the chain covers?

Scott

[Zeke]

Welcome to the bbs. I have to ask, why do you think the chain(s) jumped? We can go from there.

(Where'd he go?)

[scottgoing]

I am thinking of the timing chain, mainly because I have nowhere else to look. Yesterday, I also got it to sputter by retarding the timing quite bit and removing the vacuum hoses at the distributor. Before messing with the timing, I determined cyl #1 at TDC was on Z1 (static check) and returned it to that point.

This is my project diary that I started keeping (sorry so long). Critical events in red.


--------------------------------

Update: 29Mar07

Background:

May 2006 - took the car out for the first time in a few months. Filled up with gas at Shell station on 66th and Slide. Drove around for 1-2 hours about 20-30 miles without any problems. Car suddenly quit at cruising speed (about 60mph) and has started only once since.


Work and Testing:

June 2006 - replaced fuel filter… no difference. Checked ignition and noted that the CD did not “hum”. Confirmed 12V was being sent to the CD box, but otherwise did not check anything else on the box (e.g. amp draw as described in the Haynes’ Manual). The coil/transformer resistance was outside the specification given in the Haynes’ Manual and it was believed to be an original part. Therefore, a PermaTune box and new Bosch OEM coil/transformer was purchased. Also, confirmed that the fuel pump was pumping by lifting the “air plate” with ignition ON and hearing the injector high-pitched hum, but without using a pressure gauge.

August 2006 - installed new PermaTune box and new coil/transformer. During this time, I also pulled all the plugs to check condition and gap. With the new box in place, spark was also confirmed from coil/transformer, as well as from cylinder #1. Timing was also confirmed. NOTES: spark was brilliant white and very thin, not blue and fat. Cylinders 4,5,6 on the right bank had a noticeably larger amount of carbon build-up than the cylinders on the left bank. Also, checked for vacuum leaks (only visually and held the pop-off valve, completely shut) and the car would turn over, but not fire even using starter fluid. Still the car did not start.

September 2006 - replaced the fuel pump relay as a “just in case” and it was cheap. Also, checked the fuses and replaced one fuse anyway. The car did start, but very, very begrudgingly. Don’t really think the relay had anything to do with the car starting. Moreover, it has not started since. Decided to purchase a CIS tester from JCWhitney to check the pressure.

October 2006 - checked the primary and control pressure with the CIS tester. They appeared OK. However, the residual pressure did not nearly hold at 20psi for 10 minutes minimum (if that is the correct specification). It would only hold above 20psi for maybe 30 seconds and above 18 psi for maybe another minute. As this is normally the cause for a Hot Start (which I experience) issue, I decided to pursue trying to correct it anyway. I suspected the fuel pump check valve or the injectors, so I purchased a new fuel pump with check valve.

January 2007 - replaced the fuel pump, but the car did not behave any differently, nor did the primary or control pressures change. At this time, I also siphoned all but a few gallons from the gas tank in case the cause may be bad gas.

February 2007 - pulled the injectors and checked for leaking injectors, but did not find one. Spray atomization did not look real good, nor were the sprays total even (2 being more than 10% different). Once again, while I didn’t fully expect this as the cause, and being very frustrated I sent them out to be cleaned anyway. I also decided to purchase an inexpensive compression tester and conduct that during my next round of tests.

March 2007 - placed cleaned injectors on the car. I sprayed all 6 into bottles for a short period and noticed a difference immediately in atomization. They also sprayed very evenly. I performed a compression test as good as possible with the car only cranking, not running. I cranked a minimum of 8 turns for each cylinder and got values ranging from 135 psi to 160 psi. NOTE: I did not check cylinder #6, because I got tired and it’s access is difficult. I figured I was looking for a timing skip on one of the cylinder banks anyway, and had enough information to dispel that as a cause. I added 3.5 gallons of fresh gas that likely mixed with a 3-4 gallons of suspect fuel already in the tank. Also, checked the relay for the Lambda system under the passenger seat by jumping the 30-87 pins, but nothing happened any different.

[Zeke]

In my estimation, if you were at cruising speed minding your own business, the chain did not all of a sudden decide to jump. However, stranger things have happened. To put this to rest, purchase a dial indicator (Harbor Freight has one good enough for the purpose for something like 10 bucks) and get or make a z block to use it. Somewhere here in the archives (probably over on the engine rebuilding forum) are the specs to measure the cam timing.

I hope you can find that your chains are OK. You could also do a partial engine drop, remove the exhaust and chain covers and check your ramps and tensioners. Normally, it there were something really wrong in there, you would have heard some noises like an lod Michael Jackson video in a cemetery.

A sudden failure of the engine without catastrophic sounding noises would be an ignition or fuel problem. You are at least half way through the process of checking those systems.

I will let some others come up with their suggestions. There are complete threads about these kind of situations with titles like "SC quit on me." or "Died while driving."

[Gunter]

Failing tensioners make a horrible noise already in idle.
If the chain jumped at 60 MPH, you would have noticed the pistons hitting the exhaust valves.
I suspect the ignition.
Permatune doesn't have a good reputation.
Service your distributor first with my easy instructions; do a search under Gunter.
I would go back to Bosch CDI. Get a good used Bosch 6-pin module or ask a friend with an SC to let you swap it out temporarily. The same for the black Bosch coil. Set the timing back to 5deg TDC and leave the vac. hoses connected.

Fuse for the dome light is the fuse for the Lambda relay. Make sure it has power. Use dielectric grease on the pins. Get a new relay if in doubt.

Forget the Haynes, get the Bentley SC Manual.

[Craig]

Something quick and easy to check is the airbox and pop-off valve. Check to see if airbox is blown, and make sure pop-off valve is still secure. I had a pop-off valve that would occasionally come loose. Probably not the issue, but at least it will eliminate the airbox and pop-off valve as a cause.

Good luck!
Craig

[scottgoing]

Thanks Milt, Gunter, and Craig - that helps a lot. My intuition tells me I still have something with the ignition as the spark doesn't look terrific (but hell how many sparks have I really viewed?). I have one of those cheap spark testers with the pointed tips that is supposed to measure spark intensity. The scale is 10-20-30-40. When the pointed tips are gapped to the 20, it is supposed to represent 20,000 volts give or take. Mine sparks only at about 12. If I can trust it then my spark is indeed weak.

I am off to work. I'll report back.

Thanks again.
Scott

[aigel]

+5 on it's not your cam timing.

George

[Gunter]

Scott:
Forget the cheap spark tester.
I would go back to a Bosch CDI, coil included, and take a good look at the green wire in the distributor. There is a possibility that the signal is impaired. PP sells the short replacement.
That's what I would do: Service the distributor, possibly replace the green wire, throw out the Permatune and go back to Bosch CDI with a black coil.

[scottgoing]

Of course my green wire is mostly brown now as I assume most 25 year old ones are. Coated in a lot of oil discharging from the hose directly behind it.

I put a Fluke 179 digital meter between pins 7 and 31d on the harness that plugs into the CD box. This read 583 Ohms (no cranking). As I cranked, it jumped too crazily to read. I set the meter on MAX-MIN-AVG and got something like 3,000MAX, a negative number for MIN, and an average of 610 Ohms.

I put my cheaper analog (Radio Shack) on it an got a 530 Ohm meter that didn't change much when I cranked it.

I am not sure what to make of my findings above.

I moved on to the distributor. Using extra vacuum hose, I sucked mightily on the advance pot (red hose from throttle body), but failed to budge the outer ring (armature?). I also blew gently and heard air escaping briefly that would then stop. I coult repeat this over and over. This seemed to indicate to me that at least the advance side of the pot was not working.

My distributor (1981 SC) has a retard (blue hose) as well, so I moved my test hose to that side. For the retard, I moved the outer ring not quite 1/4" and it was able to hold it if I plugged the end with my tongue.

Could my vacuum advance give way without notice and cause my car to die while cruising on the highway? Combined with a poor coil and partially clogged injectors, could it have been the last straw so to speak?

Scott

[scottgoing]

I verified that the pop-off valve was firmly in place.

I need to get some circlips and some time (this weekend) to do the distributor service, but have read the posts on doing this. I am thinking it is the ideal time to do that when and if I replace the green wire and the vacuum advance. Thoughts?

Scott

[Gunter]

Scott:
You can re-use the old circlips if you use circlip-pliers.
Follow the instructions on my post carefully; use the pliers!
Test the vac. pod again when it is off because it could be that the pulse generator ring is frozen. Use penetrating oil liberally to free the ring.
Let us know what you find re: distributor.

Not sure if you are testing the Permatune or if you are back to Bosch CDI.
Bosch module has to have power on pin #15.
As for the rest, specific readings are in the Bentley.

[scottgoing]

definitely will get circlip pliers and do service this weekend...I'll upload pictures (I know everyone is so excited to see them).

as far as my green wire resistance. I had the Bosch installed, but had the harness disconnected to test the resistance. I suppose I didn't catch that I needed to rig my test leads with the harness connected - OR - is it that I need to jumper pin 15 with some power? Just so I understand what is going on, how does this affect the green wire that is sending a pulse?

Once again I appreciate the assistance here.

Scott

[Gunter]

To fully understand Bosch CDI, you'll need to do a search here.
Several people have posted the various values like signal etc.
The Bentley SC Manual shows a schematic for the CDI under ignition system 280-9.
I suggest not to do anything until you know what you are doing.
Pin #15 gets 12V to power the module provided the harness is connected OEM.
Ignition ON: Do you have 12V in the 6-pin plug for #15?
If not, check fuse 22 and/or wiring.
Next: Ignition ON, with engine cranking, test for Voltage (VAC) between terminals 7 and 31d in the plug.
That's an AC pulse!
Do a search and look at the Bentley.

[scottgoing]

I got in the middle of my distributor tear-down and service this weekend.

Before I got started, I check a couple of other things with the distributor on the car.

I measured 583 Ohms for the between pins 7 & 31 on the CDI harness. I tugged a little on the wire in different places, but it did not change. When cranking I got a VAC pulse of 1.2. The 1.2 VAC pulse was steady, but I am not sure if this is a strong pulse or not.

I also checked many of the ground connections on the car. Everything looked pretty good, save for maybe 1.5 Ohms between the battery and chassis ground. I was looking for 0.5 Ohms or less. I am going to replace the ground cable and I also took the battery out and will take that to the local Interstate battery shop for a check as well - just in case.

I began the distributor tear-down following Gunter's well-written instructions and things went well. In my mind I didn't find a lot of dirt and grime, but some down by the weights and springs (my 81 SC has a dust cover). I did find one thing that might be important. It appears to me like a non-metallic spacer/washer that I found in three pieces underneath the springs and weights. Does anyone know what this is? I have about as much end-play on the main shaft as the thickness of this washer. I suppose this could effect the pulse generation as well.



[img]
http://forums.pelicanparts.com/uploads10/IMG_20361177301800.jpg[/img]

I thought the poles and connector pins looked pretty good.




Thanks,
Scott

[Gunter]

The inside looks a lot cleaner than some.
Fish out the broken washer and submerge the whole thing into solvent for thorough cleaning.
Don't worry too much about the axial play; they all have it.
I see some rust. Scrape and clean. I use fine sand paper.
Use a few drops of penetrating oil into the center of the shaft where the felt would sit and make sure that the top portion moves freely.
Thats your advance mechanism movement in the shaft.
Oil/grease the weights/springs.
When reassembling, leave the 3 Allens just snug so you can center the Magnetic Pulse Generator after the Timer Core is installed.
When you have equal distance between the teeth, tighten the 3 Allen screws.
On the other end you should have 2 washers between the gear and body.
You can tell where the gear meshes by the wear marks in the middle of the gear.
There are 2 pins 31. One is ground: 31/1.
The one you want is 31d.
Sounds like you have an AC pulse between 7 and 31d?

[scottgoing]

By the way Gunter, thanks for hanging in there with me on this.

Yes, it was pins #7 and #31d that I checked. The two right across from each other on the plug. Doing some other searching here it seemed that my 1.2 VAC reading would be high. Anyone know if that would be a problem?

This washer and the resultant end play still bothers me.




I was reading about voltage regulator failures causing a no start condition (chadwallen). My battery is out being checked right now. If I have to put a new battery in and it starts, I'll check right away if 16+ volts is present at the battery terminals. Does this sound right?


Scott

[Gunter]

Ignore the washer, most distributors have an axial play (Up and down) of 2mm+
Look at the wear marks on the gear. That's where it wants to be when running.
16V? No, No........

Test battery at rest 12.5v
test battery at idle 13.0-13.5
test at 2500 rpms 13.5-14.5 MAX

If your alternator puts out 16V, you need to have it checked/rebuild.
A faulty VR will show up then.
Is your distributor service finished?
Install it at TDC (Compression stroke) for #1 cylinder with rotor pointing at the notch in the D-housing.
Ignition ON, do you have 12V at #15 in the 6-pin plug?
Then try starting.

[scottgoing]

OK, I'll ignore the washer (heck I wasn't having any luck finding one anyway). The wear marks on the gear aren't exactly in the middle, but seem happy enough.

By checking for 16+ volts I was hoping to actually find a problem. My logic has become backwards on me since my car hasn't started in a year - I am sure everyone understands. I know that 16+ volts would destroy the battery. BTW - alternator was replaced in 2002 with a brand new AL400N with internal regulator. Curiously, the old external regulator was still on the car hooked up (and has been for 4 years). I disconnected the old regulator and removed it about 4 weeks ago.

My distributor service is finished, but I am going to order a new vacuum advance and install it before I re-mount on the car (this weekend?)

I checked on several occassions that 12V on pin #15. When I get things remounted I plan to check it again, especially while cranking to see if it falls considerably; possibly suggesting an ignition switch issue.

I'll provide an update after this weekend. Thanks for staying tuned. To keep everyone focues...LOL...here is a picture of my car and I about 6 years ago....

[scottgoing]

July 8, 2007 – Voila! A shot in the dark worked. Bought the SC010 coil from PermaTune to replace the silver Brazilian Bosch coil and I am back in business. There was no doubt, she started right up.

Thanks to everyone for their assistance and keeping me focused on the ignition. I eventually got it solved, but was headed off in other directions.

I feel good about some of the work I did, though, especially pulling the injector and sending them out for a thorough cleaning. The difference in spray pattern is obvious. I think anyone with an older car should consider it. Combustion has to be better, although I can't say I feel more power.

I know a lot of people have different things to say about Permatune, but I found their technical literature helpful in diagnosing my problem. So far the ignition and coil are running fine. Whether I intended to or not, I am now performing a trial of the "new" Permatune box for which I may never have purchased after some of the things I read. Of course, I still have my old box which I think I'll have repaired and put on the shelf.