Timing chain stretch?

[Bill Musarra]

I continue having problems with the FAST XIM system. This system incorporates a crank trigger(set at 50º BTDC) and a cam sensor(set at 10-40º before the crank trigger signal) to determine the crank shaft position and the signal that TDC for the #1 cylinder is coming up in 50º. This is simple enough to understand. The problem has been there since about day 1, since the engine has been fired up. There continues to be backfiring up through the injectors, jerky sounding starter, flames up through the injectors and 4 sets of ring gears with missing teeth. The engine will fire up and runs great once running, as seen in the videos I have posted. We have tried almost everything to correct the issue. I had reached the point where I wanted to go with a standard distributor(MSD). The issue is a timing problem. The teeth were knocked off by the engine trying to turn backwards from the backfiring. I realized that the experts that have helped missed the boat with initial timing of the engine. The first expert could not get the crank trigger to be set at 50º, so he set the computer to 46º to compensate(didn't set the crank trigger properly). The second expert told me I had to get the trigger to 50º and set the computer inital timing to20º. The rpm settings in the software start at 400(cranking) then 900(idle). I altered the crank trigger to reach the 50º setting by adding an aluminum extension to the mounting bracket. More about that later. Trying to get it to start with the new info and pieces resulted in the fourth ring gear breaking teeth after only two attempts at starting. I studied all of the MSD videos and they described my problem to a T. It was a "rotor phasing" problem. How it was with this system I don't know as I have a magnetic sensor where the distributor is(cam sensor). One of the videos on timing discussed how for the small block Chevy the "normal" initial timing for cranking is set at 12º. They talked also about timing advancement as the rpms climb. At any rate a light went off in my head. I needed lower advancement(or retarding) of the timing for the cranking rpms(400). So I set the initial timing to 8-12º for the 400 rpm collum and 20º for idle working up to 32º at WOT. When the engine ran in the past it was set at 20º so nothing was changed. This time when I tried to start the motor, it spun faster as though it was flooded and was trying to start. There was some backfirng through the injectors but not as forceful or as loud. Previous backfires sounded like shotguns going off. This was now just a pop, but the motor just wouldn't start. The computer box has been sent back several times and declared in good working order. One of the earlier trips found a bad driver to one coil. It was repaired at no cost.
I had met a fellow at a car show who had a 351 like mine with 8 port injection but his ignition was an MSD and it started like a charm. He gave me a contact with the person who built his system. He was contacted and the car was taken to his shop. After 2 days of his checking things he noticed that the crankshaft would turn 6-10º before the distributor(cam sensor) would move. We believe it is timing chain stretch from all the backfiring, and the attempts to turn the engine backwards when this happened. He was going down to Daytona for the races (July 4th) as he is a member of one of the Nationwide pit crews and doubles as their tuner.
To save money and time, the car was brought home and the engine pulled. Inspection revealed the following. Notice the deflection and arrows.

I believe this introduced the rotor phasing I mentioned above and is retarding the timing even more so there is no real power stroke as firing is occurring on or about TDC. It still doesn't explain the backfiring up through the injectors though. Does this sound reasonable???
I have made the decision the go the MSD route and will install a new timing chain and either the digital 6AL-2, or the programmable unit as it will give me a rotor that will keep the fire on one cylinder at a time.
It was also discovered the crank trigger is an old one that has been altered(rounded out holes) so it can't be set to use the normal mounting holes as described in their video. It also has gouges out of the back of it. It isn't a new unit, and will be replaced.
Should the cam be "degreed in" or installed straight up? If degreed, should it be advanced or retarded? The car will be a street car with occasional track days.
Any suggestions would be appreciated.

Bill

 

[Woody]

Hi Bill
Sorry to hear you are still having engine trouble. Fault finding can get really complex and frustrating. A couple of "rule of thumbs" If she is backfiring through the intake it has to much ignition timing or is to far advanced. If it backfires through the exhaust it is retarded.
With the camshaft timing if its advanced it will give you low end power and if its retarded it will give you top end. For a stock or near stock street engine adding a couple of degree's tends to help. I can't quite read the numbers in your photo but it appears to be 2 degree's retarded.However that wont give you the problems your having. Its allways best to degree the cam, Its suprising how many gearsets and cams that are out of spec. Dial it in to the manufacturer's or camgrinder's spec card that comes with the cam.
I hope thats of some help
Woody

 

[Bill Musarra]

Woody,
Thanks for your response. Every wire in the harness has been checked and rechecked. Not one fault was found from the wiring standpoint. Only one driver to the #3 coil was bad and this was found by me, not FAST. Even the sensors have been checked with an ohm meter and check out at 70 ohms. They say to use an oscilloscope for checking but an ohm meter will tell you the same thing. Good is between 50-80 ohms. I am just tired of fighting this system and will go with something that has a better reputation. With EFI out there as long as it has, it should be an easier working system. Just not for me. We even swapped out the XIM harness without luck. So its time to move on and start enjoying this car and stop spending on things that are not working.

Bill

 

[Cliff Beer]

Bill, this may be a silly suggestion but perhaps just bolt on a Holley and a real basic (electronic) ignition system and get her running out on the road for a bit?

Once she's running reliably then it's easier to change/upgrade one thing at a time.....ignition or injection, etc.

 

[Rich Roy]

I have found that most brands of timing chains for a SBF have 6-10 degrees of play right out of the box, before even firing the engine. To verify, just bring the timing mark to TDC and roll the engine over by hand at the crank until the distributor rotor just starts to move. Then note the mark on the crank it is at and roll the engine over in reverse direction to verify the amount of play present. Since you have an electric fuel pump just pick out a set of drive gears and toss the chain..............

 

[Jim Cowden]

Bill
Have you actually put a timing light on it to see what the timing is on cranking.
You say the ignition timing is X but what is it in real life.

Are you running ign modules.

Jim

 

[Bill Musarra]

Cliff,
The ignition setup that I have on the car is the original setup. We had it running, but with a lot of spitting back through the injectors even then. It progressed to actual backfiring and now just popping. The engine has run and the EFI setup is great and the engine runs good, WHEN it runs. So all I need is a good ignition setup. I am going with the MSD 6AL-2 programmable setup that will allow me to set the ignition curves and rev limiters etc. I don't need a lot of the features that it can do like nitrous etc. but it will do what I want. With the backfiring through the injectors, it is getting fire when the intake valve is open or opening. Either is a bad thing. The computer has been checked several times and I have done continuity and voltage checks on every wire and even the wires that shouldn't have it(continuity) and can't find anything amiss. The backfiring is causing the engine to run backwards, or at least try to and its breaking parts. The running backwards is a symptom of what some call rotor phasing. That is it is is advancing or retarding the timing. Since I have a magnetic pickup in the distributor slot, it changes things a little. So for me its time to move along with something else.

Rich,
The Comp cam setup is a beefy double chain setup. I have purchased a new one through Barnett Performance, a retro fit that allows the degreeing of the cam but at 4 degrees advance or retard where the Comp unit is at 2 degree intervals. If this unit gives me any trouble I will go with a Jessel(?) belt or go to the gears. I hope it doesn't come to that.

Jim,
We have used the timing light extensively as we have gone through this jungle. We haven't seen any weird numbers while it is running, but we just discovered this with the no start scenario. When I tried starting the engine after the third break of the ring gear, it took only two tries to break the ring gear the 4th time(with loud backfiring). After the repair, I changed the initial timing(400rpm) to 12 degrees(down from 20, the EXPERTS setting). Now after 3-4 tries it didn't damage the ring gear, it turned over much faster than before acting as though it was flooded, with just popping back, no big backfires, and no start. So I have lost all confidence in the XIM box, and will give the MSD unit a try. I like the idea of the distributor, because it forces the fire to one cylinder(excluding rotor phasing) and there are only 5-6 wires to fool with(as opposed to the 48 in the XIM) and they are laid out for you. They have many videos on their site to show you how these things work and how to set them up. I was impress with the simplicity of them. It is tough to mess this up. But then they haven't met me yet.

Bill

 

[Terry Oxandale]

Reminds me of the time that I inserted a new distributor that did NOT have the pin installed for the cam-gear. It was all nice and tight (so I thought), but it did exactly what you've noted, and I couldn't understand why the timing was changing...until a close inspection of the distributor. I'm sure that's not your problem, but couldn't help myself to share that.

 

[Ian Anderson]

Bill

Do you have a cam for a 351 as opposed to a 302?

They have a different firing order and would cause backfiring if you have the opposite one to the one your think you have.

It might be a god idea too check each set of valves opening and closing to make sure you have the right lead to the right cylinder

Ian

 

[Randy V]

We've used 8 degrees as the max stretch for replacement on timing chains.. It's also why many cam mfgrs set the alignment dowel / key to advance by 2 to 4 degrees. If not, I typically install the cam 4 degrees to help compensate.

For something that needs absolute precision in timing, there are a number of very nice alternatives out there. Such as the Jesel belt drive system, or some of the gear drives which hold tolerances to +/- 2 degrees..

 

[Bill Musarra]

Ian,
Checked yesterday to confirm to myself, that I had the right cam/crankshaft. The firing order was correct for the 351 with the old thumb on the spark hole. All held their pressure at 90º after the prior cylinder. See if you notice the coincidence of the firing orders
Firing order 351: 13726548
Firing order 302: 15426378

Its 3 7 and 5 4
When #3 is firing on the 351, the 302 is at overlap, the end of exhaust and the beginning of intake. The four cylinders involved are off exactly 360º. Every time their order came up while cranking(12º BTDC) or idling(20º BTDC) they would/should/could backfire through the intake, and the engine would be running on four cylinders. My backfiring up the intakes is not on every revolution, just every now and then. The engine runs great when it runs.

Randy,
The original crank shaft gear for the chain is installed straight up. It can advance or retard 2º up to 8º. I will try to get hold of the guys at Comp and see what is the best setting for the cam. Don't have the card. The new chain I have only sets at 0º, and 4º advance or retarded. It also isn't as beefy as the Comp unit. May have to get theirs.

My thoughts are that for this to be doing what it is doing, it has to be a wiring/electronic issue,,,, somehow. I will go back over it one more time to see if there is a "communication" between two or more wires.

Thanks for the thoughts guys,

Bill

 

[Chris Coote]

Hi Bill,
If you have not purchased the MSD unit have a look at the Electromotive units.
I have run for years and swear by them.Very simple to set up.Just my 2 cents.
Cheers

 

[Dave Wharran]

Bill,
I had ignition problems when first firing my engine with a Haltech ECU unit. As you say, spitting, sputtering, backfiring. I did the o-scope thing and could see that randomly, the wrong coil was getting the signal to fire.
The Haltech uses 4 magnets embedded in the flywheel with one being opposite polarity of the other 3. They pass in front of a hall type switch which is mounted to the block about 70 degrees BTDC of #1. The odd polarity switch is both a trigger and a sync that tells the engine #1 is coming up to fire. It is a wasted spark system with 4 coils. Like you, I too suspected the ECU and sent it back to the manufacturer. It tested fine.

I was about ready to throw in the towel when I discovered what was going on. I had purchased the hall switch about a year before I purchased the ECU (so the bracket that holds the switch could be fabricated while the engine was being built). Turns out that Haltech changed the ECU's for a newer ignition configuration that used pull up (or pull down, can't remember which!) resistors inside the ECU that the hall switch connected to. I had to purchase the newer hall switch (they distinguish them as a gray gland or black gland) to match the newer electronics. Presto. No more misfire.

I feel your pain trying to figure this out. As you say, everything looks right....except that it isn't. Very frustrating.

Dave

 

[Jim Cowden]

Hope this helps, you can get to a point of yea yea checked all that, bla bla

Bill sounds alot like a the cam senser is not seeing #1 cylinder.
A bit like the rotor phasing you googled.
The relationship between the cam and crank sensers are out.
some systems will read the rising signal some the falling I would check what you system likes to see, this would throw the phasing out if you are giving it a rising instead off a falling or vise versa.

This would explain the way it is behaving, you pull timing out but the phasing gets further apart and back fires.
you advance the timing it runs because the phasing is getting closer but the ring rear getrs hammered.
The can senser is to tell it where # 1 cylinder is to start the firing sequence.
It may not know where # 1 is and that makes sense.

I would check you have the firing order correct out off the ecu to the coil packs.

I pressume you are using coils without modules built into them ,like OEM.
My modular runds waist spark but I had to ditch the ford coils as they had a built in module and it would not run.

Somes systems will only read a square wave signal (hall effect),you can use a reluctor pick up(sine wave) but it needs to be converted to a square wave through a module, your system can read whatever you have in the senser dept?

Most systems sheild the cam/crank senser againt interferance,are yours sheilded

Reading you posts I recon you have checked all this stuff but it has that feel to it.

Jim

 

[Bill Musarra]

I want to thank all of you for your input on these issues I have been having. I have found a way, or better been shown, how to use the MSD distributor to cam sync for the EFI & fire the plugs at the same time. My engine builder has known this for a long time and has built many cars with this technique, two of them with 8 stack injection. I was just too stubborn to listen to him because I wanted the distributor less system to work. Silly me!!
The MSD distributor that works for the 351(8578) comes with the short cap that will fit under the TWM injectors(the fuel connectors hang out over the distributor). This distributor has a magnetic sensor and a rotor button. The magnetic sensor will be used for the EFI to tell it when to do its thing as it has so far. The rotor button will be controlled by a coil, which will be controlled by the leftover white wire of the EFI harness that is made for a points type ignition. The crank trigger will stil be imployed to tell the EFI where the crankshaft is at, and the cam sync will tell it when the TDC will occur. It decides from there from other info when to do its job. The rotor button will decide which cylinder is to get the spark, one at a time. No more jumping around. You still need an amplifier box, but you don't need the new types that slice and dice. Just the basic 6A box will do. The advance mechanism of the distributor has a lock out option that sets the timing to a fixed point, that is your initial timing(cranking timing) when you install the unit into the motor. It winds up that the timing curves of the distributor are controlled by the EFI box along with rev limiters, fuel pump controllers, water pumps and fans. The initial setting for the rotor button is of course to the #1 cylinder. It has to be set correctly to avoid the dreaded rotor phasing that can come with a fixed or mechanical advance setup. If you go to the MSD web site their videos will explain how to setup the timing of your engine for the first time for engines you are just changing out the distributor or for a new build. When I get this thing running, I will convert some of these features I need to run this car over to this box, but will retain the switches on the dash as a secondary system or over ride. This box does a lot more than I thought it would.
But without input from you guys, I would never have come to the pint of learning this process on my own. You guys turned on the lights and got me to thinking and heading in the right direction.
I will keep you updated on the progress as it unfolds. I will say one more time,,,,, It should be running in a week or two. Any takers???
Thanks again,

Bill

 

[Dave]

Sounds like you got it sorted but I will tell about an experience I had setting up my EFI (Wolf V4) with 8 Stack on 302 Windsor

My engine would start and seemed to run ok, a few back fires through the 8 stack and so on but would not start properly. It would try to back fire and sound like a flat battery when turning over . After trying different timing settings and changing from crank sensing to Cam type dissy set up, it came down to the fact I had the wrong timing cover for the balancer I was using.

After we worked this out ,we set top dead with a mechanical gauge. we remarked the balancer, adjusted the timing to suit. The motor started fine, no more coughs and flat spots. It turned out the motor was about 35deg retarded. But because the timing marks where wrong it looked like we had 12 deg btdc.

Pays when you are building your motor to mark TDC on your balancer using a mechanical lock and degree wheel.