Hi Having random engine misses at 1000-1500 rpm and idle. Well at idle it runs kind of rough because of the cam.


I have a 72 F100 with a re-ringed engine and a Comps cam 31-218-2
Pertonics 1208 ford ignition and Flamethower 40KV coil.

88 AOD tranny.
Edlebrock 1406 4 barrel clean and rebuilt.
All new Accell wires and cap.
Original OEM distro.


Vacuum seems to be OK at 15-20 and idle is set to about 600. Carb Idle is set to lean best Idle.

When I put it in gear the AOD torque converter slows the engine to about 500 RPMs.( I guess I should have real numbers I don' have a tach installed.) But, the engine starts to shake (miss) as though 1 cylinder isn't firing.

If I have the tranny in park and bring the rpms up to 1500 the engine intermittently sounds as though 1 cylinder is missing randomly.

Could it be the distributor counterweights sticking? carb body vacuum leak, a sticky valve? I can't figure it out.

I din't use a timing light to set the timing Just set it by ear with the Carb Vac plugged.

Any Ideas?

 

With 110 LSA and 218 deg duration at 0.050" lift it's not going to idle smooth, but are you sure you have the correct firing order on the plugs? Also make sure all plug wires are seated properly and all plugs are torqued to spec.

 

Yes I have the firing order correct, But, whats strange is, I just checked the timing with a timing light and the 0 BTC mark on the crank is about 2.5 inches Advanced down from the pointer. Thats where it likes to run.

I thought we were 1 tooth off on the distributor gear and I did move the dizzy clockwise 1 tooth.... Maybe I need to move it 1 more tooth. Please don't tell me the cam chain is off by 1 link I'll kill my mechanic.

You know how people say an engine is "loading up" When I goose it, it seems to hit on all cylinders then when the RPMs settle back down it starts to randomly miss again.

I'll pull the Autolite plugs and check the gap to .035 and torque them to I guess 10 Lb


I'll keep you posted.

 

Need to know the exact initial timing setting here. The 268H isn't a "big" cam, it will have a slight lope at idle, but nothing radical. The initial timing should be set at about 12*BTC and then the idle speed set to where it doesn't stall when you slip the transmission into gear.

 

Thanks for the timing information at 12 deg initial timing. With Vacuum connected to the dizzy and running it looks to be at 40-48 deg advanced.


I checked the exhaust header temp with a infrared thermometer cyl #1 was 40 degrees cooler.

This morning I pulled the plugs and did a compression check cyl #1 has no compression, zero. both of the valves were closed and push rods were slack but touching the rocker arms.

The #1 plug is wet with fuel and oil. Very light tan color where the rest of the plugs had coco powder color brown dust on them.

Time to Tear it down again. Check for burnt valve of blown headgasket to the oil passage. The engine does have a lot of blowby for a newly re-ringed engine.

 

Sounds like a wiped cam lobe to me. Pull those two lifters first nad look to see if they have new oiling holes in their bottoms.

 

Will check out the lifters. Thats what I was thinking too Wiped cam. I just didn't want to face a two week tear down, and re buy all those parts.

My engine was built by a neighbor guy, who said the Comps cam red gooey cam lube was all that was needed. He said just break it in with Valvoline 10-40. I wanted to use the Royal Purple break in oil.

Any way I've learned a LOT of things not to do from the neighbor.

He cost me a lot of time and money but I' richer in experience.

 

The regular break in goo should have been fine. How many miles? Zinc in the oil?

 

The presence (or lack of) zinc, nor the use of the red "goo" to break in the cam is not the problem with wiped cam lobes. The problem is poorly machined lifters. The lifter face has to be machined with a convex shape in order for it to ride the cam lobe the way it's supposed to. The lifter rides the side of the lobe and the lobe sets the lifter into a rotation while the engine is running. No rotation = wiped cam lobes in the 20-30 minute's breakin period. If the lifter face is not machined as it's supposed to be, the cam lobe will not set it into rotation. The lifter faces should all be inspected before they're dropped into their holes. And too much "goo" on the faces is just as bad as not enough. You will notice that the cam lobes are rough, this is to give them traction on the lifter bottom to set them into rotation at the initial startup. Too much lube can cause them to loose traction on the lifter. I have had two cam failures, in both instances, there was only a single cam lobe/lifter failed. If it were caused by the lubrication or lack of zinc, there would have been more than one lobe/lifter failed. I didn't inspect either (this was about ten years ago when it happened) set of lifters. On the first, I slathered the cam lobes and lifter faces with moly lube, that could have caused either the lobe to loose traction combined with the lube on the sides of the lifter causing it to be harder to spin in the bore, or it could have been a poorly machined lifter, or a combination of all three. On the second failure, I started the engine up when the temps outside were in the low 30's, that made the straight 30 weight oil to be too thick preventing the lifter from spinning, or again, could have been a poorly machined lifter. Don't be so quick to jump on the goo/lack of zinc bandwagon, if it were that, you would have more than a single (or possibly a couple) of lifters/lobes failed and it would do so in a longer period of time, not during the break-in

 

If you want to completely eliminate the possibility of a cam failure, do as I did and switch to roller cams.

 

We had problems with my dad's 350 years ago, replaced the cam because of a bad lobe, dropped the same lobe on two new camshafts. The engine is sitting in the shop untouched after it wiped out the second cam. Pretty sure it was an oiling problem or a burr in the lifter bore.

I was more of the stance that the neighbor may not have been completely wrong (not enough info really to make that call either way). I've got several buddies around here that have wiped out cams recently. Could be that the manufacturers are getting cheaper with quality control on the lifters, could be related to the lowering of zinc in the oils. Some made it several thousand miles before wearing out. That is why I was questioning zinc and why I was asking how many miles he had on it.

 

Update:

got a "better" compression tester from Horrible Freight. Tested all the cylinders with all the spark plugs removed. all the cylinders had 150 to 170 Lbs except for #1 it had 30, I loosened up the rocker arms until they were sloppy and retested #1 it climbed to 60 Lbs but no higher.

I retightened #1 rockers as per spec snug plus 1 turn I got Zero compression. Loosened a half turn got 30. Now I'm thinking its a bad valve seat

The story on the heads. The heads were a trade for labor from my engine builder neighbor. He went to this Mom and Pop machine shop wanting to get my original 302 heads reseated and valve job. The grumpy old 70 something grizzly owner said I aint got no time to do heads. My shop is backed up. Can you put in a diesel injector pump in that there International ? Neighbor said sure. So he did and the old man swapped him a set of 1967 289 heads

The 289 heads have a stamp on the middle intake that says, polished and ported at Rogers Heads No Hollywood California. They were also shaved .010. Rogers is the same place Carroll Shelby had his heads done. Ports are smooth and exhaust is gasket matched. They had been setting on the shelf for at the machine shop for 15 -20 maybe 30 years.

The block is a 1971 truck 302 block according to the numbers. The odometer said 147k miles but the odometer was broken. The truck was used on a cattle ranch/ orchard/vineyard in Galt Ca and sat out in the foggy winter and hot summer weather for 12 years not started, just abandoned.

We just honed the cylinders and re ringed it since the bottom end looked fairly good. We installed the Comps Cam since the original OEM cam cog was nylon and the teef were shot. Bought new hydraulic stock lifters and cleaned out the oil journals with a long spiral brush we borrowed from a mechanic friend.

On the zink question, No zinc additives were used unless there was some in the red goop. I wasnt aware of how important zinc was as a cushioning agent at the time.

The original break in was about 5 hrs drive time then I changed the Valvoline 10-40 for new and added 1 Qt of royal purple break in oil with zinc.

I had a magnetic oil plug and there was fine fuzz on it. Looked like cast iron ring wear fuzz.

Cam wipe: I pulled the lifters out and they were barely scuffed on the face they looked new.
The lift or compression of the springs was almost a 1/2 inch or better. I didnt measure the distance between coils on the compressed spring but it was almost touching maybe .020 clearance.

Summary:
Since I know so little about the heads I feel I should eliminate any problems by taking them in for a full rebuild. Performance Machine in Carmichael said they can Hot Tank Magnaflux, reseat, re valve, re guide, re seal and re spring the heads for $350-400 the pair.

I also am going to bring in the push rods and have them measured and checked for bends. The lift really looked high and the heads have been shaved so the push rods may be a little too long.

Comp Cams recommends new springs which I haven't done. Guess I'll have to call and get a recommendation for springs and pushrods.

I hate re-dos So If I start from a known good baseline, being the heads are known good, My blood pressure goes down and I can skip a few AA meetings

Anybody near Sacramento know if Performance Machine is good? Or have a better recommendation? NAPA Machine shop in Auburn I've heard is hit and miss. Prolly 75 % good work.

BTW: Thanks for all the advice I hope this thread helps somebody in the future. I'll keep updating as I find out more.

 

A quick failure would point to bad lifters. A failure over a long period of time, would indicate a lack of zinc. Worn lifters bores are another problem as you've indicated. I'd forgotten that aspect

 

Update

Well I took me heads into the NAPA machine shop to get them looked over since I was getting a max of 60 Lbs compression in cyl #1.
I wanted to start from Something anything as a baseline "known Good".

The guys checked them all out and found a bent intake valve and the heads were 5-6 thou warped. They shaved the heads 6 thou replaced the bent valve ground the valves and seats new guides. The springs and all the other stuff was good Magnaflux showed no cracks. Yippee.

They needed a gasket set for the valve stem seals so that was $85 so I was out the door $421 lighter in the wallet.

I torqued down the heads and did a compression check Cyl 1 was at 150 along with the others. Thats a good sign.

Yesterday I fired her up and found a NAPA 5 month old fuel pump had failed. Rats! Lucky I have the reciept.

Lucky I had an electric fuel pump on hand. Installed it with some yellow Tygon hose up to the carb and filter, and Vroom She fired and idled pretty smooth.

Got her all back together today. Hood on Grill on, ready to go to the Chevron station for a little Premium motion lotion.

I still have a few issues.
I can see air bubbles in the fuel line to the Carb. That bugs me but no leaks. One day I'll take the behind seat tank out and clean it real good and get a new gauge sender.

I Still have the timing mark at about 30-40 degrees advanced at Idle because thats where she runs best. I dont know if the harmonic balancer is original since the truck is a 72 and the block is a 70 and may have been a remanufactured short block.

I heard aftermarket Harmonic balancers are notorious for having the timing marks off. So I still wonder if I'm one tooth off on the new timing chain. When I get some time Ill pull the grill, radiator, Water Pump and TC cover and check it out.

PS: I did add a quart of Royal Purple break in oil with ZINC for good measure.