Comanche won't start

[AZJeff]

1 hour ago, Ωhm said:

From Wikipedia:

When I took engineering mechanics classes in college (a million years ago), we never discussed other variants of six cylinder engines beyond those used in ground transportation.    The focus was on vibration and balance, as land transport devices will convey that vibration to operators/passengers.

 

The straight six auto/truck engines have the added benefit of being balanced in both the primary shaking force, AND the secondary (harmonic) shaking force, thus making them very pleasant on passengers.   I wonder why they use an alternative order for marine applications?

[Ωhm]

1 hour ago, AZJeff said:

I wonder why they use an alternative order for marine applications?

 

IDK. This is something I learned today based off I6 firing order statement. Interesting. CAM???

[gogmorgo]

If you have no spark it would be good to check where the spark stops. If you’ve got nothing out of the coil, not making it out of the distributor, etc.
 

Firing order for an amc 2.5 is 1342 according to the internet. I’m too lazy to dig my ‘91 2.5 out from under the snow to read what’s on the intake.

If you had the distributor out it would be good to make sure the distributor wasn’t put in 180° out. You might get some coughs with the spark firing on the exhaust stroke but it definitely won’t run. Pull the spark plug out of the #1 hole while you turn the engine over by hand and hold your thumb over it until it makes pressure, then verify where the distributor rotor is pointed. You can also use a bit of wire or something to probe the cylinder and watch where the piston hits the top of its stroke at #1, and double check the rotor is actually pointed at the #1 button on the cap. If it’s out by a tooth you might sometimes get it to fire a bit but it won’t run very well.

Rotating the distributor to adjust timing is not a good option. The injector timing is determined by the cam sensor under the rotor, so rotating the housing will screw with injector timing.  This is what Cruiser’s distributor indexing tip is about. Injector timing is more tolerant to being out than spark timing but Jeep did eventually put ears on the hold down bolt to locate the distributor and stop people from screwing with it, because it will cause problems.

But if we’ve got no fire at all with starter fluid then that’s pretty indicative of a spark problem. 
 

I won’t pretend I know what “medium speed” means but the massive ship engines do like 100rpm flat out. I suspect vibrations aren’t such a big deal at 10hz. Running fuel delivery plumbing economically probably plays into it when the cylinders are the size of a hot tub and you can park a bus between them. It’s a very different world from what we deal with. And very irrelevant to this thread.