We put in a 1979 351 modified into my son's 1975 F100 that originally had a 390 last night we filled it up with fluids got everything cinched up and try to crank it over just a little bit did not start but we did hear upon cranking a loud pounding to one side that was never present before this.sounds like it's on as the passenger side. We have not opened up the motor other than changing the h2o pump and replacing pan gasket. Valve cover gaskets and installing new gas pump. Sons so discouraged after all that work.

 

My first thought is to check the starter....loose bolt(s), correct starter for the type of trans you're running, mebbe starter engagement/flywheel or flexplate teeth problems...

Ford starters don't require shims, either....

Another thought is engine mount(s) mebbe somewhat loose....?

 

Ck on what has changed from when the 351M was in the the other truck. Different transmission? FE to 335 series? X2 on check for the correct starter for the transmission. You do know you use different one for an auto trans versus a standard trans. Flex plate? Fly wheel correct? Torque converter bolts correct?

Tell the son to hang in there and welcome to the club, you all are not alone.

 

The motor and the transmission were originally a 390 and np435 4 speed with Granny low the donor vehicle was a 351 modified with C6 mated transmission automatic we transferred basically everything from the 79 to the 75 so torque converter starter flywheel everything else swapped over directly from one truck to the other so there was no mismatching the other one was a fully running vehicle that was fine except it was a 79. Sound is a heavy knock.

 

Another thought:
If the trans or engine were separated....or installed separately, the torque converter could have slipped and not have seated right upon install. Pull the inspection plate (2 screws) off the bottom of the metal gasket and check the converter....wiggle it a bit to see if it's loose. To seat properly if it came unhitched, you need to hear/feel a coupla 'clicks'.....then snug up the four bolts.

Agree with Rich....you (and son) are not alone in discouragement...we've all been there a time or two.

 

Are you sure the noise is from the engine?

That project required some pretty significant changes with the clutch, column shift, motor mounts, transmission mount, crossmember and driveshaft. Lots of places to check for bounces, klunks and maybe even a carrier bearing

 

Are well aware of all the things that have to be changed that is not to sound sarcastic that's from trial and error. The motor mounts actually had to be taken relocated, we had to take the motor out of second time and relocate the motor mounts we did have the correct ones off the donor vehicle but they were too far forward so we had to take them out and reinstall them . Everything mated it up we have yet to hook up the drive shaft even though we have mock them up because we are changing the universal joints on them so we know that those fit as well. the torque converter was spun till it clunked in and would not pull out, installed new TC nuts(it's snug!). The headers are installed but barely clear it is tight, the frame on the 79 is just little bit different than the 75 I don't care what people say, cuz we have another build going for my brother-in-law and it is been hell, everybody says that it's real simple to swap over an earlier 69 through 72 short bed onto a 79 short bed 4 wheel drive frame. Yeah the front portion is easy, the back is a bear and a half, if you want it to look stock. It's not just moving the axle forward 2 inches, there is a lot of modifications that we are having to do, to the frame to make it look like it came stock,on this nut and bolt restroration for my brother-in-law. It's got to be bone stock looking, that's what he's going for, on his high school truck that he bought back from someone after having sold it three decades ago. So sorry back to our project. We swapped out the column from the 79 the pedal assembly from the 79 also as well linkage we made a custom setup using Lokar parts to bypass all the swing type bracketry that are on the C6 and it works so it accutates the way it's supposed to. We have not driven this, we are just trying to start it at this point to make sure that we have everything where it should be I am starting to lean towards the possibility that we swapped out the wrong starter from the manual versus the automatic because it does make that clunking sound upon trying to crank it and it's not a high revving type pound it's more along the lines of when it's trying to start so I'm thinking that the Bendix might be engaging when it shouldn't be or vice versa.

 

In that case, it does sound like the starter

 

As per side of caution we removed the trans again, TC felt like iot was located right, pulled it off replaced the trans on w/o TC and tried to crank, Noise is still present, we have a Brand new starter, we are thinking that the problem is with the hybrid harness 75/79 the starter is engaging and disengaging cyclically. No fire at all, so can't say the clunking goes away at startup. That being said we are hooking the trans back up and approaching this as wiring problem. I had bought the 79 Ford wiring schematic, the big one with the tan cover, but can't find the same for the 75( not sure if it was even available). Whats the best I can do as far as a wire by wire breakdown manual /diagram cd? Short of a complete wire what to do? Can't afford to do that right now as we have a incurred a huge expenditure, getting my son ready to ship him off to Alabama for school. We thought we would have this done so we could take it out to him, so he could enjoy it while there, but it's turned into a nightmare. By the way I would like to thank the Forum in advance, great group of people who have helped me on my other builds in the past.

 

Perhaps breaking down the problem into small pieces will help.

Did you try a different starter? Is the starter correct for the automatic transmission?

Instead of tracing all the wiring out, can you disconnect everything and try just:
1) the hot from the starter to the solenoid
2) the lead from the solenoid to the starter
3) the ground from the block to the battery
4) jumper the solenoid to energize the starter

I know you're bummed out by the outcome, and my suggestion may be stupid or generic...but sometimes the village needs an idiot!

 

Your suggestions are not stupid or simple. We did go thru the entire starter scenario. Another new starter just in case, yes for the correct motor/trans combo. Since we did a hybrid hanesswe think the the problem s gonna lie there,but the start is at issue as well due to it.

 

I think you found the problem.

Some electrons are telling the starter - through the solenoid connections - to START (solenoid contacts closed - 'S' terminal) and then to RUN ( solenoid contacts open - 'I' terminal) without knowing if the engine is running, then START again, ad infinitum....the START bypass circuit which is tied together at the ignition switch with ballast resistor circuit are not communicating....

Mebbe the ignition switch is yakking in Greek and the solenoid, bypass/ballast resistor circuit is talking Nordic at the same time...?

 

Well we got it fired up. we stole the ignition. Harnessoff my other build 75 SC SB F250.It matched up. Checked an set DTC played with the dist. Timing. There's still wire cleanup to do, bit no more clunking woo hoo!!!

 

Congratulations on finding the problem and getting it going. A very satisfying feeling to get something like that fixed. Hope your boy is motivated again