Hey all.

1970 F100 2wd 390

I pulled my intake today in order to replace the cast iron 4 bbl with an Edelbrock standard aluminum intake. There are several reasons for this.

Anyway, When I pulled all the pushrods out, I discovered that no.4 exhaust pushrod was bent and has a gauge mark in the middle of it (which explains the valve noise I've been hearing lately.)
I have had this truck about 7 months and put a little over 2300 miles on it. The engine had a documented rebuild with 800 miles on it when I got it. It doesn't run bad per say but I always thought it had somewhat of an erratic idle to it. I figured it to be because they used the cork front and rear gaskets on the intake and it didn't get sealed very well around the ports (one reason I am doing this) and I could plainly see where the intake was sitting higher than the heads were where they come together and the intake gaskets were all soaked with oil around the lower half of the intake ports. Needless to say this all irritates the hell out of me. I think the PO (idiot) put the intake on at home after the long block was rebuilt by the machine shop.

Anyway. I can only imagine that the valve stuck for some reason. If not, Do any of you have any idea why this could have happened, and what if anything, I should check on that valve before I put it all back together? with a new pushrod obviously. Thanks

PS the length of the pushrods are 9.560

KOT390

 

Check the lifter and make sure it's not stuck. I had a couple pushrods get bent for no good reason myself.

 

OK, Yeah that's a good idea. I will pop it out and check it. I also have an air fitting to fill the cylinder with air and an overhead spring compressor. I wondered if I should take the spring off and check the movement of the valve in the guide. Not sure if that is necessary though.

A while back, I bought a Holley heat shield to go under the carb and put it on there. I have an overdrive tranny which calls for flooring the pedal to kickdown out of O/D. The first time I did that after putting the heat shield on, the throttle stuck wide open! I was so mad, because I checked throttle clearance but guess it was close. I had to grind relief in the plate for the fast idle screw which is what caught on the plate. Anyway, I wondered also if it over revved for a moment when that happened before I could shut it off and see WTF.
Thanks
KOT390

 

What may have happened, the PO did not seat the pushrod properly either in the lifter or under the rocker arm. You probably do not have any damage. I presume you will use silicon in place of the cork gaskets. I always add 2 more hose clamps in the middle of the by pass hose to keep it from expanding too much.

 

From the water pump to the intake.

I've had a few bent push rods in the past and just replace them. As it has been said, no good reason.

 

Maybe rewire the OD switch to cut off when you LIFT the throttle or wire it to the brake light switch?

 

Maybe the previous owner was like me, and started tugging on that intake before taking off the rocker arms. He then either didn't notice, forgot about it, or just said screw it and put it back anyway.

 

Well, thanks for the input fellas. I just spent the day putting the thing back together, Oreillys had a pushrod by noon. The worst part as you all know is the cleaning of the old crap and gasket surfaces and prep work. Yes, I did use black RTV and not the cork gaskets fore and aft. Hopefully it will be ok and just amounts to Chris's explanation of no real good reason. I can deal with that I guess. I barred the engine over a few times after I got the rockers back on and I didn't hear any funky noises so....
Anyway, I did take the lifter out of that spot and compressed it in a vice with a bolt in the rod spot. Gently. It compressed and squirted oil out so I suppose it will pump back up ok and was not stuck like was suggested could be a possibility. I don't think that would hurt it any. Thanks

KOT390

 

Well, now I have a new problem. So I am posting it in this thread so everyone knows the history.

I got the new intake on. I adjusted the initial timing and then drove it around the block and the timing had advanced itself. So I reset it back down. Then drove it around a minute and had to back the timing off again because it advanced itself again. finally after the fourth time, the timing is staying where I set it. The problem is that when I am in third gear or overdrive and hit the gas to accelerate, the engine studders like it is missing consistently. I thought it was just a vacuum advance adjustment but it doesn't seem to make a difference how far in or out it is adjusted. It still studders when I hit the gas at a moderate rate in third and O/D gears. Whether the vac advance is hooked or unhooked doesn't make much difference.

I put the timing light and dwell meter on it again and with the vac advance hooked up, the dwell drops from 29 to like 20 when I rev it. It stays at 29 if I unhook the vac advance. I'm guessing that is the problem but don't understand why. I'm hoping it's not due to the fact that when I put the intake on, I forgot to drop the distributor in before I torqued it down. Just wondering if anyone has any thoughts. Thanks

KOT390

 

How to Fix Old-School Ignition Points: DIY Auto

 

Another thing you might want to try. Rev it up with and without a rag over the carb. If it stumbles without the rag but not with it, then there is a problem with your carb adjustment.

 

The dwell dropping from 29 to 20 like that is caused by the points breaker plate is shot. You see. as vacuum is applied to the advance unit it pulls the upper 1/2 of the plate. The upper 1/2 is supposed to pivot on the lower 1/2. The points follow the upper 1/2 and this advances the timing. When the breaker plate assy is shot the upper 1/2 ***** up instead of pivoting smoothly. When it ***** up this moves the points closer which opens them up farther. When they are open farther that means they are "closed" a shorter dwell time. Like 29 to 20. A dwell meter measures how long the points are "closed" and the coil is saturating. Not how long they are open.

 

Thanks for the replies. Jeff I understand what you're saying and won't rule that out just yet. But, yesterday evening I took the cap off and used a vac pump and worked the plate in and out to watch the movement and it looked ok. Then I pulled the distributor back out to check things like shaft play and for a loose plate or points and didn't find anything. The distributor and everything in it is still pretty new and tight. So I don't know why the dwell is dropping like that. I will have to watch it I guess because when I put it back together I briefly checked it and it didn't seem to be dropping as much but I didn't spend a lot more time on it as the wife was home and it was dinner time

Anyway, what I did do was set the initial timing up to 10* BTDC where it has been at 6* this whole time. Even before switching the intake . Also gave it some more vac advance. Drove it around a minute and those things seemed to help. Basically, it's starting to seem like the new intake caused the motor to "want" more timing maybe. I don't understand that though, so I will have to watch it today and see how it goes. The only other thing I can think of is that there's not enough spring tension on the points and they are floating. I think that is adjustable. What are your thoughts on all this? Thanks

KOT390

 

If your distributor is new, then it is very likely your points are bouncing. Throw them away and get a Pertronix drop in unit. Very simple installation and will take away a lot of drivability and idle issues that you didn't even know you had.

 

Allow me to chime in here? My original distributor was doing the exact same dwell change at higher rpm (1000 and up). So I pulled it to check the bushing wear, slight movement, ordered a new distributor and it had almost exactly the same amount of bushing slop and the dwell changed at rpm just like the original one did. I agree it sounds appears the vac advance plate is the culprit???