86 CJ7 Timing

[Marco]

  Hi everyone, i have a question regarding timing. I have completely rebuilt dads 258 in his jeep cj7 which is now bored 60 over. All parts i received are factory spec other then piston size. All parts are new in engine also. I managed to get it running but when i revved it even a bit it started pinging?  (kind of rattle sound). Now without a timing gun we retarded it back like closer to 0 on the marks and with a poor idle the sounds went away but i could rev it up. Thinking this was ok i ran it revved up for about 30 minutes to break it in. Tempurature was 190 the whole time, oil pressure was around 40 the whole time and sounded great. Changed oil and filter.
  
     After more research it seems that timing should be way more then where i have it.( about 2 with the gun now) if i advance it any it will start rattling again?. I have overcome a lot of hurdles on the project and has been a low buck build with good success. I know of several reputable shops but need someone with this older technology to bring it to (i like my computer tj haha). Any ideas, or which shop i could pay to set it right would be would be greatly appreciated.

     Side note, seems starting it when its "timed right" the crank wants to go one way and combustion process wants to go the other way making it barely turn over. Im stuck.

[Vinman]

I always used the rule of thumb that you should advance it as much as possible without causing pinging. If you want a bit more power, run premium fuel which should allow a bit more advancement before pinging (and yes, I know the correct term is pre-detonation).
Good luck

[Marco]

so does it HAVE to match the degrees in the book, or can one tune it by "feel"  that it seems to like running at?   i have now learned the vacumn advance has a lot to do with it. Sheesh

[morerpmfred]

2x on premium fuel. If regular gas which cantains ethanol is in the gas tank then the gas lasts about three months then it steadily loses octane. How long has the gas been sitting?

[Marco]

added a jerry can of new premium to an almost empty tank. fired right up. Is there a way i can test the vacumn advance? i would imagine it has to be operational and not just a set degrees. thanks again

[Vinman]

added a jerry can of new premium to an almost empty tank. fired right up. Is there a way i can test the vacumn advance? i would imagine it has to be operational and not just a set degrees. thanks again

Hook a timing light and watch the timing as you rev the engine. Do this the vacuum hose connected then disconect and plug the hose.
If it!s working correctly, the timing will change with the  hose connected. I'm not sure if theres a mechanical advance as well that may add some confusion to my method. Sorry its been about 20 years since I messed with a distributor.

[Marco]

ok, update. new premium fuel in the jeep and i can fire  it right up. I have most all the vacuum lines plugged except the one too distributer.
Detonation occurs when i have it timed to anything over 0*.
Mechanical advance on distributor is evident when throttle applied and viewing timing light. (vacuum disconected)
Vacuum advance VERY evident when i look at timing light and throttle up, cant get past 2k before it starts pinging.

The only way i was able to idle or give it a drive down the street with out pre-detonation symptoms was with vacuum advance disconnected and timing at like 0 or -2
any ideas are greatly appreciated. In the meantime i will continue my research. cheers

[Spinalguy]

As far as premium gas goes, ONLY Shell has no ethanol.

[cLAY]

0 to -2 is way too low/retarded. Many vehicles start to backfire thru the intake at that setting.  Typically you are around 4-8*. What is the book spec? Are you sure the pointer on the crank is installed correctly, not bent? Is the dampener with the mark on it installed correctly onto the crank? Are you using a timing gun that is adjustable? If so is it zeroed?

I'm guessing something is off. Recheck that you have the correct firing order and plug routing. I have seen where someone has plugged the wires into the dist one hole off and caused some really weird timing issues but it did run.

Check that the dist is installed correctly, it runs on a gear hooked to the cam, its sometimes hard to get it lined up properly, especially if there is a slot drive on the bottom for the oil pump.

Lastly, you may need to pull the timing cover and check the timing chain alignment.

When you did your rebuild did you have the block decked or the head shaved? Did you use regular pistons or domed pistons? If you had a lot taken off of the block AND head or used domed pistons you could have ended up with a motor with really high compression ratio.

You should be able to get it to run fine on good quality regular gas.

[morerpmfred]

The vacuum advance. Is it hooked up to ported vacuum or is it hooked up to vacuum of the carb?
If it hooked up to ported then the timing will be advanced all the time. If hooked up to the carb then the timing will be retarded when you hit the gas. Ie low vacuum then as soon as rpms are  mantained then you get a high vacuum signal and the timing changes again.
Pretty sure there is a vacuum switch as well.

[Marco]

Great responses guys appreciate it. I just finished rebuilding the motor. everything is new and oem except pistons 60 over. head was rebuilt and slightly machined to check flatness. Timing chain and gears installed i made are extremely close to book if not exact. I have the ignition going strait to distributor (nutter bypass?) and the vacuum line on the small outlet facing rad on my carter carb.

Interesting point that the balancer mark or the cast lines are perfect? not sure. i didnt change them so i would think they are fine. Im going to pull the distributor right now and clean it up. maybe the advance isn't working correct. thanks again! Timing light isnt adjustable and borrowed from a professional.

[cLAY]

Maybe someone can chime in here if I'm wrong, I've done lots of dodge motors but not sure I've ever done a dust swap on a 258.

On the Dodges its a real pain to get the dist. installed correctly. The dist runs on a helical cut gear on the cam shaft, as you drop it in it will spin the rotor as it goes down so you have to start with the rotor trend back a bit so that once its finally seated its pointed at the number on cylinder. To compound that the oil pump drives off the bottom of the dist via a slot engagement. That has to be indexed so it lines up as well. It often takes a few tries before its in correctly. Not sure if the 258 is like this or not.

When setting the base timing do you have the engine at idle with the vacuum line disconected from the dist and the line coming off the carb plugged?

Is the dist new or original?

With the vacuum advance disconnected and timing set to TDC you shouldn't have pinging. What's the total timing at when reved to 2000rpm and the vacuum advance disconnected?

[Marco]

Ya i remember my Dakota distributer pita to install as you explain. This seems to have a ton of movement before tightening down the screw and clamp.  I don't think it is new by any means, but I have it out and it's super clean.  Applying vacuum to it does move the piece back and forth,  so I'm thinking it is operational. Grabbing a new cap and rotor as it looks a bit burnt. Which line off of the carb or manifold should the advance hook to? Thanks

[morerpmfred]

Ported vacuum is of the manifold. Vacuum advance is off the carb.

[Marco]

i attempted to start from scratch with the timing and some how managed to break the plastic rotor inside the cap. No parts until monday in stock. will post results after i get another one.