Trouble starting rebuilt 351 - Success!

[thegreatjustino]

Recently removed my 302 and dropped in a rebuilt 351. Engine turns over fine with the starter, but barely starts and when it does it runs really rough for just a couple of seconds before dying. I also get the occasional backfire when trying to re-start.

I've double checked my valve lash and triple checked my firing order. I can't keep it running long enough to even mess with the timing or carb idle mixture.

When hooking up the spark plug wires, I put my finger over the #1 spark plug hole and had a neighbor crank the engine to feel for the compression stroke, so I'm pretty sure I'm not 180 degrees off with the distributor, but at this point I'll try about anything.

 

[TexasBronco]

351C or 351W? Where are you starting the timing? What all was changed in the rebuild? Spark plugs gapped correctly? Electircal system working properly?

http://assets2.motorator.com/uploads/comment_images/0000/0023/Ford351.jpg?1297239450

 

[Boss351]

Firing orders right check dist. make sure its on number one on the cap.Witch should be mark. 351 has a different firing order than a 302 unless using a 302 cam is in it or its a 302 ho.If it seems as though its firing late try turning the dist. or idle up then try firing it again.

 

[DirtDonk]

Hey justino, can you try finding TDC again with just hand-cranking the engine by the front bolt? I'm just wondering if, when checking with the starter, it couldn't have spun past without you really catching it because it was going to fast?

And I know you said you triple-checked the order, but you are looking for 13726548, correct?
As Boss mentioned, not the same as your 302. But I think you knew that already.
Still, had to ask. You're describing the classic timing issue.
Is it backfiring through the carb or the exhaust? If the carb, it's almost guaranteed.

What else has changed on the engine? New ignition too by any chance? Different carb and manifold?

Paul

 

[thegreatjustino]

Funny you should mention that Paul. I just went out, removed the v-belts and slowly cranked the engine by hand. Put my finger over the hole and felt for the pressure to build. Once it did, I even put a long screwdriver in the hole to see at what point it stopped moving up and started moving back down. Sure enough, I am on the #1 cylinder on the distributor - have been all weekend.

I've triple checked the 351 firing order. I knew it was different than my old 302. I also pulled all the spark plugs and re-gapped them to .044.

The occasional backfire I get is through the exhaust. I double checked the gap on the pertronix setup too. Still can only get a rough idle for a second or two before it dies.

I don't know a heck of a lot about the engine. I bought a non running '73 Bronco that had the 351 in it. Took it out of the '73, put it in my '69, set the valve lash, installed the valve covers, all accessories, radiator, and have been trying to get it to run all weekend.

The engine was freshly rebuilt when I bought it a year and a half ago. There is an RV cam in it, which shouldn't affect the firing order should it? I primed the oil pump until the oil ran out of the push rods. Cranks fine, just won't start worth a darn, and when it does, it runs rough for a second or two before dying. Giving it throttle has no affect.

I'm pulling my hair out on this one. It really seems like the firing order is off, but I have checked the standard 351 firing order six or seven times now.

Carb is the same that was on my perfectly running 302. Distributor is the one that came with the engine, but I put my old pertronix in it.

The 351 uses a different distributor than the 302 doesn't it? I was thinking about swapping them since I know the 302 distributor works fine, but I don't think they are interchangeable.

 

[DirtDonk]

First, yes the cam can be a 302 firing order. The two engines use the same cams, and the cam dictates the firing order, so it depends entirely on what the PO put in.
So, one more time, check your TDC. Only this time, find out which piston comes up next. It'll be either 3 or 5, and it'll be within 1/4 turn of the crank, so put your finger over the number 3 hole, and if pressure doesn't build up right after your number 1 does, check number 5. If it's 5, then you've got a 302 firing order.
Chances are you're already correct, but it never hurts to do it one more time. Just to make sure.

Regarding the distributor, three things.
1. Make sure that the mating surfaces are clean so that the housing is well grounded to the engine block.

2. Make sure that you installed the ground strap that comes with the Pertronix units into this distributor. It makes sure that the backing plate is well connected to the distributor body.

3. And maybe the most important of all, make sure that the Ignitor is getting the full 12 volts, and not connected in any way to the resistor wire. In other words, if you've got a stock wiring harness and stock coil, you should not connect the Ignitor's Red wire to the positive side of the coil. Instead, you need to find another power source that's on with the key, but is full battery voltage.

Yes, there are several members here that have good running Ignitors hooked up to lower than specified voltage, but they're the exception, not the norm. Pertronix is very clear that you need 12 volts to the Ignitor's Red wire for reliable running.

Paul

 

[Viperwolf1]

Firing order could be 13726548 or 15426378 depending on cam. You already know TDC is correct. Take the extra step to verify firing order by pulling #3 and #5 plugs. One of those two are ready to fire exactly 90 crankshaft degrees after #1. Remember rotor spins ccw too.

Take the pertronix out and drop in a set of points. Once you get it running you can put the pertronix back in.

 

[thegreatjustino]

Well, I pulled both the #3 and #5 spark plugs and rotated the engine by hand. Both pistons come up after the #1 cylinder, but only the #3 is building any pressure. So, it seems that I am correct with the 351 firing order.

I looked through the receipts the previous owner gave me, and I have the receipt for the engine rebuild kit he used. It was ordered from enginekits.com with an RV cam, so it looks like I will be calling them tomorrow to see what they can tell me.

My biggest concern is doing damage to the new cam from all of the cranking I have been doing on the engine.

 

[Viperwolf1]

#5 doesn't build pressure because it's on the exhaust stroke. Put some points in and fire it up.

 

[thegreatjustino]

OK, well I think I may have figured out what the problem is. I tried starting it with the points, but it does the same thing. Swapped the distributor cap, same thing.

So, I decided to remove the valve covers and set the valve lash once again. I also took all the spark plugs out so I could put my finger over each hole as I was on the compression stroke as I rotated the engine by hand.

On seven of the eight cylinders, I could easily feel compression building against my finger in the hole as I turned the engine. However, on the #4 cylinder, the piston comes up on the compression stroke, but no pressure is being built up. I tried it three times and the same thing each time, no pressure.

So, something is definitely wrong there - the question is, would this give me the starting issues and how do I fix it? I'm assuming I'll have to take most of the engine apart to get to the compression rings on the piston?

 

[Viperwolf1]

How are you adjusting the lash and what type of rockers does it have?

Valve problem would require removing the head, maybe even camshaft. Rings might be replaced by removing head and oil pan. Need to find out what valves are doing first. Could just be adjustment.

 

[thegreatjustino]

I'm adjusting valve lash by getting the #1 piston at TDC on the compression stroke. Then slowly tightening the rocker nuts as I spin the push rods. Once I get to the point that I can't spin the push rods anymore, I torque the rocker nut down another 1/4 turn. I do this to both valves on the #1 cylinder. I then rotate the engine 90 degrees and do the same thing to the #3 cylinder. Then #7, #2, etc. etc. until I have done this through the entire firing order.

What do you mean by what type of rockers? They are not roller rockers if that is what you are asking. Just standard Ford Windsor hydraulic lifters, push rods, and rockers. Look just like the 302 I took out of my Bronco to do this swap and the 260 that's in my '64-1/2 Mustang.

 

[broncnaz]

might have a little to much lash. Basically you want the slack taken out of the pushrod to the point where you just start to feel the tension of the lifter then do the final 1/4 turn.
tightening down until you cant spin the pushrod may mean that the spring is bottomed out in the lifter and your over adjusted.
basically he's asking what type of rockers because most ford engines have non adjustable rockers

 

[Viperwolf1]

The old "spin the pushrod" technique would be more accurately described as "tighten the nut only to the point where there is no more up and down movement possible, the go another 1/4 turn".

 

[mudslut]

doyou have A nother carb laying around or that you could borrow, i would try a quick swap just so you can nock it out for sure incase your chasing the wrong part. would also try adjusting dist both directions a little ata atime to see what happens

 

[thegreatjustino]

Carb was working well on the old 302. Even if it was the carb, the engine should run for a bit with the fuel that I dumped into it to prime it I would think.

I've tried starting it with the distributora fully advanced, fully retarded, and everywhere in between. If it isn't the lack of compression on the #4 cylinder that's causing the problem, the actual distributor may be the next thing I try. Although I hate simply throwing parts/money at a problem without properly diagnosing it.

 

[mudslut]

have you ran a compression check on the cylinder to see what it is and it should still run with just one dead cylinder it would have the miss but still run

 

[thegreatjustino]

Ran the compression test with a friend today. Turns out the valve lash was a little tight, but after adjusting, all cylinders are at 130 compression dry. At this point the only thing I have not swapped externally on the engine is the distributor. Is there a way to test a distributor, or is my only option buying a new one and trying it?

 

[Viperwolf1]

Have you tried to start it after fixing the valve adjustment?

 

[DirtDonk]

Testing distributors is pretty easy. Basically, for physical issues, just grab the shaft and twist and turn it to feel for smoothness and evenness. Then rock it back and forth at both ends to see if the bushings are worn.
If any of that doesn't feel right, just buy a new/rebuilt one.

For the magnetic pickup, Viper's got the specs. Easy enough to test the resistance via the two wires.

Paul