351C problems - Help please!

[Cracker]

A friend of mine is doing some work on a 351C that is in a Pantera. The heads were professionally rebuilt completely and original intake reused but port matched. The carb was completely overhauled by Pony Restorers in NY to like new (better) condition. Bottom end/pistons/cyliders all looked good and left alone.

Here is the problem. Engine fired right up but had a consistant backfire through the carb. Timing and firing order are right on and it is using the original dual point distributor BTW. A compression check revealed about 130 psi on cylinders 5-8 but goofy things a happening on 1-4. Guage spikes to around 100 and immediatey settles around 50 on 2&4 and 75 psi on 1 &3. The guage works fine on the other side so we think it could only be either:
1) head gasket problem
2) Cam timing/installation off
3) bad cam (it is original though and has never been removed)
4) bad valve components (unlikely due to complete overhaul by excellent group)
5) ??? What would you say???

One more thing - it could almost seem like pressure is leaking from one cylinder to the next on compression test on 1-4. He is doing a leak down test next on that side to eliminate valve train/headgasket/cylinder/ rings options. Thanks!

[Woodz428]

Was the lifter preload checked on reassembly? Since the rockers are non adjustable, you need either factory +/- pushrods or shims available from various cam companies to adjust. If preload wasn't checked,it's possible that some valves aren't fully seating.

[Cracker]

woodz428,

I did forget to mention that we thought maybe a lifter hadn't pumped up and was possibly causing the problem but we discounted this since that problem would allow the valve to seat completely rather than holding it open. It is also unlikely that all the lifters on one side of the motor were experiencing the same problem while the other side was fine.

Regarding the pushrods/adjustments all is the same as when the engine was originally built. The car has 23K miles on it since new and experienced no major problems when disassembled.

[bittentoo]

Cracker,

A few flags went up when I read your cleveland problems.
The first one that jumps out at me is, "bottom end/pistons/cylinders all looked good and left alone."

"bad cam (it is original though and has never been removed)"

Then you stated that "bad valve components (unlikely due to complete overhaul by excellent group)."

Please clear up a few things:

Was the short block left alone, or did it recieve new rings and bearings?

Or did you just pull the intake and heads off and the "complete overhaul is refering to the heads?

If you just pulled the heads off, then the most likely problem (and going by the compression test) is a blown head gasket. you have all of the symptoms, close to equal pressure on adjacent cylinders, popping back thru the carb.

It is very easy to get one of the head gaskets on backwards on a cleveland, I know, been there-done that!

If the mech. was not a "Ford" guy, head gasket is my guess.

Now, if the engine was overhauled, and you stated that the cam was not removed, then we have a whole new can of worms!

I'll wait and hear back from you before we open that can

[Cracker]

Bottom end was left untouched(no new rings or bearings & cam left in place). Complete overhaul is referring to the heads only. Lifters were removed and inspected and put back into orginial bores. Heads were removed and the head gasket being on backwards is I think my #1 option above by possibilities.

[bittentoo]

I agree.

Good luck

[gsharapa]

I would agree it is mostly the head gasket but were the heads ported or C & C at all?

I had a 351 built with Brodix heads that were C & C from Brodix and when we fired up the motor to dyno it everything seemed fine for a couple of pulls. Then the HP dropped and we lost cyl pressure like you are explaining in your post.

Turned out the C & C job was incorrect on the Brodix heads and the intake and exhaust ports burned through on several of the cyl. If you take the intake off you can look in the ports and see if that happened or not. Hopefully just a head gasket.

[Cracker]

Gary & Bittintoo:

Thanks for your imput. To my knowledge no porting was done other port match intake to head. After the leak down test I'll tell him what feedback you guys have offered and check that head gasket. I'll let you know what we find. Thanks again!

[Cracker]

Here we go again guys!

I'm going to need some info from you Cleveland folks to make sure we are doing something stupid.

1: head gasket was on properly - not the problem.
2: Head was removed and vacuum checked - perfect % leaks
There is also no signs of valve contact on pistons.
3: The rocker system was missing the shims that fit under the
fulcrum to avoid contact with VS retainer but that is now fixed
and didn't solve the compression issue.
4: We are now replacing the timing chain, cam, and lifters.
5: We also think it has to be timing - any more thoughts since the
obvious is already passed inspection.
6: What is the firing order for a 1972 351 Clev.?
7: What intial & total timing is a benchmark for a stock engine?
8: What should the cyl. compression be on a cold & stock motor?
Our good side ranges between 128-130.

Thanks again for your help in I'm sure we can't be far away - there isn't much left!

[Jim Colman]

Maybe I can help a bit. I also had a 351C that was experiencing some backfiring problems. Turned out that it was simply a timing issue.

First, make sure your distributor isn't installed 180 degrees out of whack. The rotor should be pointing to the number one plug terminal when the number one piston is at TDC. You can pretty much gauge TDC by taking your plugs out, and hand cranking the engine. You will feel a whoosh of air come out the spark plug hole and your rocker arms will be in the closed position.

The timing needs to be set with the vacuum advance plugged. Also, make sure your vacuum advance isn't plugged into a timed vacuum port on the carb.

Total timing should be in the 34-36 degree range with initial timing set to about 12 degrees.

Your distributor could also be part of your problem. According to one person who helped me with my problem, most non performance Ford distributers have too much mechanical advance for performance use. The distributers don't achieve full advance until over 4000 rpms and may have as much as 30 degrees of more mechanical advance built into the distributer. This doesn't allow enought initial advance for good response. A distributer with 20 degrees mechanical advance will allow you run around 16 degrees or so of initial advance. For best results, a distributer needs to deliver only around 20 degrees of advance and have all advance in around 3000 rpms.

You can buy ans MSD billet distributer that comes with a variety of springs and bushings to control advcance rate and total advance.

I kept the duraspark distributor on my car and simply reset the timing. It made plenty of power for my street use.

Hope this helps.

Jim

[Cracker]

Jim,

Thanks for your thoughts. Just to note, we are using the original dual point distributor which has been completely overhauled. I'll check and see how he went about setting initial timing in regards to the vacuum advance. The dist. is not 180 out - it was one of the first things we checked intially.

The only problem with this whole timing concept is I have found it hard to believe that timing can allow one side of the engine to be so steady and yet the other so poor.? Another friend claims it can happen so we'll see when everything is reassembled.

Thanks for the timing answers but I still need the firing order if anyone knows it. Thanks again!

[Jim Colman]

Sorry, forgot to add the firing order:
1-3-7-2-6-5-4-8
(Number 1 cylinder is front, on right from drivers pov)

Here is a helpful site as well:
http://www.boss351registry.com/351_Cleveland.htm

Also, just type in "351 cleveland" on google and you'll come up with a lot of good hits for helpful sites.

Jim

[Woodz428]

I've read in other forums where someone gets an engine fired up and then it starts running funny and someone suggests that the dist. is in 180 degrees. If that was the case the engine would never start, so it can't be 180 out. The firing order possibly but not a 180 out dist. Actually I'd pay to see an engine run,at all, with a dist. installed 180 out. In my earlier post when I was talking about preload, I was referring to the amount a lifter will pump up and the clearance that is needed between the rocker and valve when the lifter is collapsed. If the heads have had the valves done and the valve stems weren't butted enough when the lifter pumps up it can hold the valves off the seat and cause some of the problems you refer to. I spent many an hour diagnosing a 351C that would drop cylinders and pop through the intake after it was wound to 4500 and dropped back to idle. The lifters would pump up and then the tight cylinders would hang open valves and it would miss. I replaced 4-5 pushrods with Ford service ones that were .060 shorter.If the preload wasn't checked it is pretty easy to do and could be the problem.

[Jim Colman]

I guess it doesn't make sense that if a distributor was 180 degrees out that the engine would even fire. I was thinking that the plug would fire when the piston was at or near BDC, thereby causing a backfire. Good point Woodz428.

Jim

[Cracker]

Jim/Woodz428:

Jim, you wrote: "Sorry, forgot to add the firing order:
1-3-7-2-6-5-4-8
(Number 1 cylinder is front, on right from drivers pov)"

The #1 piston on a Cleveland is on the right/drivers side?

This would be totally contrary to my 427 in which #1-4 is on the left/Passenger side.

Woodz428,

He has taken into account pre-load with the lifters. The problem goes back to compression on those cylinders and until just now I hadn't thought of just havinghim remove the rocker arms on 1-4 and then check compression - and here I thought I had thought of everything - stupid me!

Thanks guys!

[Woodz428]

Cracker,
You can take the exhaust rockers off and get a compression test, and probably a little bit if you pull just the intake rockers off. But if you take them both off you won't get any noticeable compression because it isn't taking anything in to compress. You could back them off some, but removing them would be fruitless. I also prefer a leakdown test over a compression test, it's more accurate and can help pinpoint problems right away.

[bittentoo]

Woodz428 might be on to something with the lifter preload.

Did you put new valves in the heads? If so, then the vavle stems could be longer than the stock valves, or.......
is it possibe that when the valves and seats were ground down, to much material was removed and allowing the valves to seat deeper in the head, thus, in effect, making the valve stems "longer" on the top of the head. This in turn would load the non-adjustable lifters sooner.

Just some thoughts

[Jim Colman]

Originally posted by Cracker


[b]Jim/Woodz428:

Jim, you wrote: "Sorry, forgot to add the firing order:
1-3-7-2-6-5-4-8
(Number 1 cylinder is front, on right from drivers pov)"

The #1 piston on a Cleveland is on the right/drivers side?

This would be totally contrary to my 427 in which #1-4 is on the left/Passenger side.

Woodz428,

From the drivers POV (point of view) the passengers side is the right side. I should have simply said "passenger side" in the U.S.

Jim

[Cracker]

Woodz

I was just talking to the fella doing the work and we thought any vacuum condition that existed in that cylider would be concelled by just opening a valve. Other than that, when the piston compresses you would get a somewhat accurate compression figure. Just food for thought - no real need to reply since the heads were taken off anyway for vacuum tests.

This is going to sound like a silly question but I'm a little unclear regarding where the #1 cly. is. We assumed it was like my BB in which 1-4 is on the left side/Passenger side if you will, of the motor. Is this correct? Sorry for the stupid questions - I don't have the car here and neither am I the one doing the actual work.

[Cracker]

Sorry Jim - that's what we understood it to be - thanks agian for your advice.