I have a 79 trans am that I swapped a 301 to a 403. First engine swap and learning as I go and I have started running into problems. Whenever I go to turn the ignition half the time I will not turn over (just makes a quick thud sound and nothing happens) it may do this 2 or 3 times and then it will try to turn over or it could try to turn over on the first turn of the ignition. Whenever it does turn over it sounds very weak almost like the battery is almost dead or pulling pulled down a lot. Battery is fully charged.
Could it be something with the battery? cranking amps? / Could it be something with the starter? It is a new starter / Could it be something with compression?
Thanks for any ideas or input

 

Can the engine be rotated completely through a few turns with reasonable force/torque using a 1/2" drive ratchet on the bolt in the center of the harmonic balancer?

 

Don't discount a bad 'new' starter. Could be weak out of the box.

Get a meter and ck battery at rest and under load (during cranking) to see how far volts are dropping. If you have a battery load tester you could ck the battery itself.

Good luck.

 

with spark plugs in, no. With spark plugs out, yes

 

what is a reasonable voltage drop? how low should it not go?

 

Is your battery grounded to the engine block with at least 4ga. cable?

 

With the spark plugs in can it still be rotated one full turn just requiring more force? Has this engine run at all since the install? Auto or manual transmission?

 

yes it is grounded to block with 4ga

 

it can be rotated with a good bit more force, it has tried to fire a time or two (idle not even close at the moment) and it is an automatic transmission

 

Good that tells us that the problem probably is not related to the torque converter not being seated and more likely the starter/battery/cable issues that others have mentioned.

 

Interwebz mekaniks is hard sometimes. There are a lot of variables.
To me, it sounds like you have a weak battery or a bad starter, assuming everything else is good.

 

It does require a good bit of force to get it to turn, and it is turned little by little to go all the way around, not just a continuous motion once it starts. I just want to describe it best I can to forsure rule that out.

 

To rule it out did the transmission bell housing mate flush to the engine and not need to be pulled/clamped together with the 6 bolts AND did the torque converter need to be pulled forward about 3/8" to bolt it to the flex plate with the converter turning freely whilst the 3 flexplate bolts were aligned to be installed? If all of these ?'s are yes, you're good.

You should also be good if you can turn the engine freely and smoothly with the plugs out. With the plugs in compression will make it quite a bit harder to turn.