345 Rebuild still not starting

GaryOR

GaryOR

Member
I've posted before with my basic problem of not being able to start a 345 rebuild that the po did right before selling his '78 Scout II to me and my son (ok, it's actually his, but he's not old enough to drive yet).

This is kind of basic engine question. I put a light bulb spark tester on each spark wire confirming that I am getting spark. The engine is turning over kinda slowly (compared to what I'm used to) and I'm trying to figure that one out. However, I'm not sure if I'm getting proper fire.

How fast should my tester be lighting? I know the faster I turn over, the faster it should. But, assuming a normal crank over speed, what should I expect-every 1 sec, 5 sec, 15....

I'm just trying to cover all of my bases and I'm questioning my coil right now.
 
Assuming you have the tester on one plug wire and not the coil.
You should be seeing about 2 hits/second. Cranking speed is around 200 normally on a healthy starting system but assuming you are having a slow crank problem expect so at like 120 rpm you would see 1 hit /second. The light should be consistent like a second hand. If it is erratic there is a problem.
 
Definitely a problem then. There are many seconds between each flash. I have put the tester inline with every plug, getting the same thing.

Distributor has been reseated many times, following the instructions in the tech manual and from a post here. Spark plug wires are all correct-checked and rechecked and rechecked.

Could a bad coil be the source of the problem? I don't want to go and spend the money on one if not necessary. Suggestions on the likely culprit?
 
This is just what I dug up on google:

msd blaster 2 (hi-performance)
Coil specs
turns ratio: 100:1
primary resistance: 0.7 ohms
Secondary resistance: 4.5k ohms
inductance: 8 mh
maximum voltage: 45,000 volts
peak current: 140 ma
spark duration: 350 us
Click to expand...

Do everything in your power to try and find a coil that is in the IH resistance range. To quote mr. Mayben in another thread I just found (and this is assuming the pertronix has not been set up to simply trigger the higher-capacity coil/ignition system):
the pertronix requires a coil with a primary resistance in the range of 1.4>2.0 ohms When used in a conventional system.
Click to expand...

It is entirely possible that the wrong primary resistance is causing one of your problems here, but then again I am just shooting in the dark. I can't use this to explain your slow cranking speed (mine might seem "slow.."). I just got used to what sounded like an internally heavy motor getting thrown around by a smallish 12v starter, and I know it sounds nothing like my friend's '68 Chevy, where the starter might even run him down the road if he installed a good cooling fan!

All bs aside, without seeing what's going on under your hood and being able to hear the slow cranking, or being able to measure the resistance your coil is factoring into the spark, there's absolutely no way to know how many different issues might be affecting this. And again, you might have the "air-gap adjustable" version of a pertronix conversion, and it might be too wide of a gap, providing the wrong kind of dwell.


I would suggest working with your wiring/ignition until you know it's up to snuff, and then things like fuel delivery and perhaps any other hidden issues can then be addressed. People much more knowledgeable than me are sure to provide help along the way, but if there's one thing this forum has taught me about IH vehicles... It's that they involve a process of verifying this, correcting that, and fiddling with these, until you have it "playing nice." so don't be disappointed if it doesn't act 100% better right off the bat.
 
Sometimes depending on ignition systems the tester lights can give erroneous readings. Take a known good sparkplug and widen the gap to about .075-.090" and plug it into your plug wire then ground the plug body and have a helper crakn the engine. You should see a good blue spark at the same 1 sec or so interval. If you see the randomness then also, you do need to dig deeper.

If you could post pictures of your engine bay with special attention to the ignition wiring, coil and dizzy etc. We could then make more sence of your situation.
 
When you start troubleshooting ignition problems you need to start at the source, the battery.

If the battery, the battery cables, and the battery cable ends are not in good condition nothing you do up the line is going to overcome the initial problem.

If you suspect a slow turing starter you need to put an amp meter on it to see how much current it is pulling. Much over 300 amps means you have a faulty starter. If the starter is not turning fast enough you will have starting issues.

Once the starter is turning fast enough then you are will be in a position of determining if the spark isn't firing correctly.

Good luck and keep us posted as to your progress.
 
Starter is a new rebuilt one.

Hooked timing light to 8 and still get 4-6 sec between each lighting.

Have 12v at battery, solenoid, input of 1.8 ohm ballast resistor, and at coil connection.

When turning over, I get a drop to 7v to the coil.

Coil is now brand new.

The engine still seems to be turning over slowly (at least slower than I think it should). However, I just found a couple of scouts being started on youtube and it might actually be within norm.

So, why the delay between firing?
 
Despite the printed instructions on the coil, I don't need an external ballast. Removed it per michael mayben's suggestion, and instant start on the first try.
 
Got the plugs yesterday but haven't put them in. Ran ok with 2 out, just a little smokey and noisy.
 
garyor said:
despite the printed instructions on the coil, I don't need an external ballast. Removed it per michael mayben's suggestion, and instant start on the first try.
Click to expand...

Good deal man! And ya lernt sumthin' too! I had to git lernt up guuder on this resistance shnizz from prof. Mayben in much the same way a couple yars back. It ain't what's stamped on the outside of the can that matters. It's what your given ignition components and engine configuration (v8 in this case) are that dictate the amount of resistance needed for proper induction.
 
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