Timing problem

[ScottH]

Recently picked up a 72 w/402 in it. I have a problem where it doesn't want to crank when hot. A few board members suggested checking the timing. What I found is it has to be really advanced to run without back firing through the carb. The timing mark is basically straight up instead of on the timing mark where it should be.

The PO said he installed a cam and lifters, but didn't leave me a card so I have no idea of lift/duration. I believe he mentioned it was a RV performance range.

Does anyone have any suggestions on properly timing the engine? Could the PO have installed the distributor off a bit?

Any info, suggestions, ideas are appreciated.

Thanks!

[Blue Beard]

Are you sure its timing...........could be starter related, wiring, or even the bat...

[JimKshortstep4x4]

I would check the front damper to make sure that the outside part has not slipped. If the damper is good, my guess is that the timing chain is not timed right. You should not have to advance the timing that far.


Jim

[cdowns]

if it's not cranking when hot it's your starter that's the problem

[redbowtie]

Could be the distributor is a tooth off.

Find TDC on cylinder #1, pull the distributor out and reinstall with the rotor pointing at the appropriate terminal on the cap....clockwise, 1-8-4-3-6-5-7-2 is the firing order.

Perhaps this will help....http://www.summitracing.com/tech/cha...iringorder.pdf

[shuttermutt]

Originally posted by cdowns
if it's not cranking when hot it's your starter that's the problem

More specifically, it's the solenoid. Sounds more like he's got a timing issue, though. If the PO swapped cams, I'll bet he stabbed the distributor off.

[Broken_down?]

Ok.. I thought I was going to get flamed for the last post about BB or SB. but this is going to TOP the bunch.

These old chevys have a problem with the celnoid getting to hot ( as I am told ) This is what we did.

Went to the parts house and got a ford celniod and jumped the started to the S and up to the fenderwell we placed the ford celnoid. and I have NEVER had a problem with the truck running all day in the 120 deg it gets here is oroville ca. Now when the other celniod gets hot you have the one on top that is not hot and it fires fine. I am chevyman as they come. But when you are a broke fool like me you do what you got to do.

Try it. it really works. just do NOT tell anyone you have a ford part on a chevy. You will never live it down. ( I know 1st hand as my family is ford people and me being the ONLY chevy you can imangine what goes on here )

---Broken_down?

edit: fixed me bad ass typing errors and bad grammer. gave up though..lol

[bpmcgee]

I have to suspect that it's timing related. I believe that can also cause issues with hot starting.

I don't think, though, that it would be the distributor. The important fact is that the rotor has to be under #1 wire at TDC. No matter where the distributor is facing, as long as you're timing off of #1 plug, it should fire at the right time.

A mis-wired firing order might cause this problem I guess. If your timing mark is straight up -- assuming your mark hasn't slipped, it would mean you're running maybe 20-30 degrees advanced initially. This would be really dangerous if your centrifugal advance is working -- you'd end up with around 50 degrees total advance!!

Does your timing change when you remove the vacuum advance line from the carb and cap the port?

Basically I'd be tempted to treat the starting as a symptom and address the timing.

Brian

[shuttermutt]

I probably shouldn't admit this in public, but the way I've always set the timing on my Chevy V8's is to advance it until it starts to ping under load or it's hard to start when hot. Sure, a timing light is accurate and all, but it's worked for me. Now, if I could just figure out why my truck is backfiring through the carb...

Oh, and Broken_down, the Ford solenoid trick is a great one. I've done it on several vehicles over the years. It works well on farm trucks, vehicles with headers that run close to the starter (don't they all?), and vehicles that get seriously wet and muddy. In a pinch, however, you can smack the bejeezus out of it with anything handy and make a temporary heat shield out of a beer can.

[Huck]

Let's separate the issues-----if there is a timing problem, when the engine is still cool, does it run ok? Does it give you a problem when it gets hot, if so what are the symptoms.

If there is a starting problem in that when hot, the engine doesn't want to crank??? If so, when it starts, does it run ok?
Does is crank over well when cold?? I would start with checking the battery terminal connections---clean and tight. next make sure your block is grounded to the firewall and that the battery negative connects to the block. If HEI, make sure the ignition wire from the switch/fuse box is heavy enough to handle the HEI. I would try a new starter to see how it works out.

After checking the above, what's happening???

[ScottH]

Thanks to everyone for their thoughts and suggestions, all are appreciated.

To answer a few questions, when the truck is cold it starts right up, never a problem. The battery terminals are clean, new heavy duty cables on both sides. The hot starting problem is that is barely turns over, if at all.

The reason I question the timing problem is because some time ago I posted another question relating to hard starting when hot, and was told that timing can cause this problem. So the first thing I looked at (or should I say easiest) was the timing. Since that appears to be way off, I started this post on how best to address this problem, hoping both would be solved.

Unfortunately I haven't had any time to look further into it but hopefully may find some free time soon. It's starting to get cold and with no garage I haven't even looked at getting to the starter.

The truck does have headers and HEI. I noticed the wire for the HEI is pretty thin, so I plan on replacing that as soon as I can. Not sure if that could affect the starting problem, but just for safety I will put in a heavier guage wire.

Again, thanks to everyone for their help.

[shuttermutt]

FYI, 12-gauge pink wire is "correct", but any color of 12-gauge wire should work a treat. I'm still betting that it's either A) the timing is too far advanced or B) the solenoid is locking up due to heat from the headers. Both are pretty common.

[lukecp]

I had a similiar problem back when i had a oil-burning worn out 355 in my truck.....cold it would start just fine. As soon as it would get hot, it wouldn't want to start at all. It would make a god-awful racket truning over......it turned out that my flexplate was pretty ground up....with a new motor came a new flexplate.

Now it is doing it again....and my flexplate is fine. I have headers on the truck....and they are cooking the starter. I would look into the remote solienoid option, or putting some kind of a heat shield on the starter

[oldtrucknut]

Yellow, Does your truck make a grinding noise when turning over? If so, your starter drive is bad and that is what ate the flex plate. In answer to the problem of the motor not turning over or turning slowly, I have had the same problem. Take your battery to have it tested. Yes, your timing can have something (even if correct) to do with it if the engine is modified. Some people use a seperate switch for the ignition wire rather than using the key. If timing is keeping the engine from turning, use the key to crank the motor (it should turn freely because ignition is off) then when the motor is cranking flip the switch for the ignition and vroom! If your starter does not turn over with ignition off, then try jumping the battery. Usually it makes the starter crank good, but if not the starter needs replaced.

[oldtrucknut]

One other thing, you should not expect to have your timing set to factory specs. Someone else mentioned to advance the timing until it ran bad, then back it off. That is really the only way to set the timing on a modified engine, then when you get it set by ear, you know where it should be.

[c10crazy]

You might be getting vapor lock! who knows?

[lukecp]

It dosent' grind or anything...just cranks over slowly. Usually happens after i run the truck pretty hard...and has stopped now that the weather is cold. I am almost dead sure that it is header related. I am going to throw a heat shield on it one of these days and it should help.

[oldtrucknut]

Yeah, those heat shields are supposed to make a big difference. If you have the $$$ to spend, check out a high torque starter.

[ScottH]

Oldtrucknut, you raise an interesting point. A PO (not the last one) installed at some point a separate pushbutton to crank the engine over (rather than the ignition switch).

If I understand you correctly, are you saying when the truck is hot and won't crank using the key, if I use the pushbutton and it does crank, then it is the timing causing the problem?

If this is so, am I correct in assuming the distributor was most likely installed off a tooth or two when the PO installed the cam?

Thanks again guys (BTW, haven't had the truck long enough to try the pushbutton when it gets hot - picking up plates this week).

[oldtrucknut]

Scott,
This is kind of hard to explain, there is really no problem with the timing if the truck runs well. You should probably check it with a timing light to make sure. Again, don't expect the timing to be set at factory specs. If I remember correctly, my small block 400 is advanced up to 12 degrees BTDC. That is quite a bit more than factory settings. When you crank the motor with the seperate pushbutton, all that does is make it easier for the starter to turn.

[ScottH]

Thanks again. But I'm a bit confused as to why a separate pushbutton switch would make it easier to turn over?

Any ideas are appreciated.

[oldtrucknut]

When you use the original key switch, first the ignition is turned on then you can crank the starter. With a seperate switch you can crank the starter then turn on the ignition. When the ignition is turned on, the motor is trying to fire, where as when the ignition is off, the motor is just cranking over without any combustion to put a load on it. So, when the motor is cranking over freely, switch on the ignition. Just try it, then you will see. I don't know how to explain it any better, but you will see what I mean when you do it.