Thanks for all the help. I found the bolt, but none of the 4 parts store close to me (NAPA, Pep Boys, Autozone, Oreilly, all within half mile of each other) has the right wrench. They all have the same distributor wrench (with different brand names on each),but it won't fit because the short leg is too long. I think I need the VIM-V108 because it has much shorter short leg.

I started to remove the AC compressor to free up some space, but I think I can get the bolt loosened with the right wrench. It has been ordered from Amazon.

 

OK. I ended up timing the engine 10 BTDC. Seemed stable to me. Still backfires. I replaced ignition coil (cheap enough). Still backfires. I have no more spare time to put on this, at least I didn't think so, and took it to a shop I have been using for some years.

They tell me the distributor was loose (but when quizzed, mechanic said it was tight). Anyway they pulled distributor and are telling me it is worn camshaft. That is what they are called the worm gear that engages the distributor. They say gear is worn, allowing timing to slop causing backfire.

First they quote $1800 to replace it. That seem was high. If that is fair price, I won't be having that work done. Second, is that likely to cause that problem?

They admit is could be slop in timing chain also.

 

Get other opinions, they don't want to phuque with it and are pricing themselves out of it.

 

Fuzz Face
You were talking about how to check for timing chain stretch.
Do you know what maximum degree is acceptable?
I really like the stud for the distributor hold down!
I am going to have to do that to mine!

 

The cam lobes may be worn (I've seen that plenty of times) but the cam/distributor gear wearing out is unusual. Not so unusual in a performance engine with a high volume oil pump or if the cam was replaced with billet cam and distributor gear wasn't changed to matched (but obviously this didn't happen in your engine), but I have not seen/heard of that in a stock engine before (anything is possible I suppose).


A timing chain will stretch. When it does it alters the valve timing. You can check for stretch by watching the distributor rotor while slowly turning the crankshaft by hand. First you rotate the engine id reverse to remove the chain slack, then mark the crankshaft damper (note timing mark) position. Then with the distributor cap removed (and it helps to have spark plugs out) you rotate the engine in normal direction watching distributor rotor. When the rotor just starts to move stop turning. See how far the crank has turned from the mark you noted on the damper. A few degrees movement is okay. More than 5 degrees is a sign of a problem.


At that point you need to pull the timing cover and further inspect.

 

Timehunter, What Bumkin said is right on the chain stretch & checking.
Dave ----

 

When does it backfire? Just sitting there idling? If so, I would hook the timing light back up and point it from up above and stare at the timing marks and the timing pointer. If the idle is stable, the marks should be stable on the pointer. When it backfires, do the timing marks suddenly change?

I know you said you had problems looking from above, but if you are in a dark garage or it's a little bit dark outside, you can shine the light way up beside your head and it will still cast light all over the engine and down onto the pointer. I think that is what you were doing before, shining the light from below and it was reflecting light all around and on top of the engine where the pointer is?

 

Dave's post reminded me that another symptom of a stretched timing chain can be a "wandering timing mark" (when viewed with a timing light, of course). A wandering timing mark can also mean slop in the distributor bushings, incorrect distributor shaft/gear end play, and ignition wire cross-firing. All of which can lead to your problem.
I mention this because it's an easy check/test to perform.

 

Turns out the right mechanic at another shop found the wires going to distributor were intermittently shorting out. That would cause unburnt fuel to head down exhaust I believe. Anyway, $165 later (and $120 for muffler and new tailpipe), I don't think this truck has every run this good in the 10 years I've owned it.

 

Hate it when that happens.