PLEASE HELP! Bad engine kickback

So I installed a new single carb tunnel ram several months ago. Put on the same carb I was running before, but also replaced the distributor. Fired right up and ran like a champ. Never any issues. About 2 months after I went to start it and got reallllly bad starter grinding. Checked pinion clearance and was dead on accurate and within limits. Did everything possible to correct the problem. No go. I started to work on some other things, one of which was a ignition kill switch. I got to crank the engine again with out ign. Cranked smooth, as I flipped the ignition switch boom...BAD grinding, but it started. Now I crank it, hit the ignition and will just grind, no starting whats so ever. Keep in mind, since it started with the new tunnel ram timing has NOT changed either. Seems obvious that I am getting kickback. I do not care about it being a major problem so long as I can fix it. I am starting to think it is a timing chain issue. Its a 406 SBC

Any input?

 

You have a belt drive instead of a chain? How many miles on the belt. If it uses a tensioner is the tensioner still working properly?

Sounds like it may have jumped time. Easy check is to roll it up on TDC then pull the dist. cap and sss if it is pointing in the right direction.

Is it an electronic dist.? Nothing against them I run them myself. Sometimes the control mods take a dump, if this is the case it may get fire but get fire at the wrong time. Or get fire sopradically.

Just a couple of things to think about.

 

Have you checked the timing? Or are you saying that you didn't move the timing? Cuz it sure sounds like a timing issue to me.

 

I have not touched the timing. I'm sure it is a timing issue. I'm just wondering how it just suddenly jumps timing. It is a timing chain not a belt. I did put belt originally but changed to the correct equipment which is a chain. Not digital timing. Just old school dist. With Coil.

 

The distributor may have moved. Slowly worked loose.

 

This happens but a timming chain jumping a tooth is not out of the question either. When they decide to let go they just do it, it normally doesn't happen while you are driving either it happens when you shut it off. Or maybe it happens while you are driving and it just isn't as noticable until you shut it off.

 

Sounds like too much advance. Pull the cap and make sure the advance unit is not stuck at full advance.

 

Does this have a MAG?

 

Bingo

 

Timing lights are your friend.

 

Well I took the vacuum line off the carb and vacuumed air out. There was no movement inside the distributor whatsoever.That means there is probably a hole in the diaphragm and just drawing air. But, can it be fully advanced if there is a hole in the diaphragm? Also this issue has been getting steadily worse over time. How about we assume this. Could the advance move more and more overtime getting stuck in position until its just fully advanced? Yes light gun would be awesome to use if I could start the engine, but I would have to replace the flywheel and probably starter as well.

 

Retard the timing and start it. Then put a light on it.

 

The dist. is still in the car. I tried moving it today, but got the same results.I cant move it enough to retard it all the way back with the wires and space issues. My guess is take the dist. out and take it apart to figure this out.

 

Did it really go boom when you put the spark to it, or was that just a figure of speech ? If it did you may have stripped the distributor or cam gear, or sheared the roll pin that holds the gear on the bottom of the distributor shaft. As you have probably figured out it is not a good idea to load an engine up with raw fuel and then put spark to it.

 

I pulled the dist.this morning. No chunks taken out of the gears and the advance is not stuck because I finally was able to create a enough vacuum where the advance moved and sprung right back into position. Wow I am stumped! i guess the next thing to do is pull the timing cover and check the chain.

 

Your timing chain has jumped a tooth on the timing gears. Not an unusuual thing to have happen.

 

2 months it sat? Pull the back two plugs and see if gas runs out. You may have a "hydraulic" situation. This depends on the type gas you use. If ethanol then I bet this is your prob. G luck! peace

 

What about the mechanical advance?

 

Yes the MECHANICAL advance. Normal automotive dists have 2 advance systems ,vac and mech. Twist the rotor in the direction of rotation while preventing the gear from moving now that the dist is out of the car. The rotor should turn against some spring resistance then move back when you release the rotor.