I'm getting ready to have my heads gone through because I think I have a burnt valve. I've just put a kit in the carberator and it's still backfireing. I have a lifter that knocks sometimes and sometimes not. My question is if I put stock valves in during the head rebuild does this limit me to a stock cam when when I can afford to replace it and the lifters. I'm short on funds right now so I can't do every thing I need to but I do plan to do the whole motor as soon as I can. Could someone give me some cam advice for valves and cam kit.

 

I don't think you'll be limited unless you're planning on installing some monster cam that will require massive valves to facilitate enough air flow. You may have to get new valve springs if you plan on getting a big cam, but this change can be done without removing the heads if you have a air compressor that you can hook up to hold the valves in place while you remove the springs.

also if you only plan on getting a slightly juiced up cam you could probably stick with the stock valves as well. you could easily go with an R.V. cam that will give you a bit more HP and torque at a minimal expense.

 

no the valves won't limit your cam selection at all but the springs will. If you go big on the cam you really should get new springs that will work. Some important factors are coil bind, seat pressure (lbs), open pressure(lbs), installed height. Some defintions, coil bind is when the spring stacks solid. Installed height is the height of the spring on the seat, you can alter this by using shims. Seat pressure is force in pounds the spring puts on the retainer at the installed height. Open pressure is the force on the retainers at a specifed height.
A generic example is a cam manufacturs wants 120lbs at 1.875 in installed height, has a .650 coil bind, and 300lbs at 1.410 inches. Now if the stock installed height was 1.9 inches you would use shims to add .025 and thus compress the spring by that much lowering the installed height to specs. If the stock spring have like 90lbs seat pressure, the springs will not be strong enough to close the valves fast enough at high rpm and thus valve float will happen earlier than the proper springs. As for the coil bind you want to minus .100 for clearance for the max lift allowed. A spring that binds at .600 would be good enough for only .500 lift.
I recommend comp cam 32-206-3 and i am not bias since i like crane better. THis is a rv cam that makes more power from idle to 4000rpm than any other comparable cam according to my software.

Good luck with your truck.

 

You've already gotten some good answers to your valve question, but I would like to offer a suggestion about your back firing.

First off, unless this "backfiring" as you call it is happening at engine speed, it is probably not a burnt valve. A burnt valve would kill one cylinder and pop through the carburetor rythmically if it were an intake valve.

Have you checked engine timing and advance? This would be more apt to cause what you describe. Also before going to the trouble and expense of pulling the heads, do a compression check or a cylinder leakdown test. A good poor boy way to check for a weak cylinder is to pull the coil wire so it won't start and spin the engine with the starter. If the sound is very even then you have relatively even compression on all cylinders. If the starter speeds up the engine when one cylinder is hit, then you do have a dead cylinder. If you were here I could make a sound for you that would tell you what I'm talking about.

An engine with even compression will have an even sound like wha wha wha wha wha..... While an engine with a dead cylinder while have one cylinder that will allow that wha wha wha sound to have a quicker "wha" in it, sort of like; wha wha wha w wha wha wha w wha wha wha w wha wha.

I'm sitting here laughing at myself at trying to tell you what it will sound like, but if all cylinders are strong the sound when turning with starter will be even, if not there will be a quick pulse in there periodically.

The best thing to do is to borrow a compression gauge from someone before doing all that work.

Good luck,
Doc
ASE Master

 

I guess i totally ignored the problem mentioned. The first thing would be to borrow a timing light. You would want around 6-12 degrees at idle with the vaccum hose unplugged. You will also want to check total timing which is more of a task but very important. You can mark your balancer at 36-40 degrees with chalk or something. Using a tach gauge or estimation you will want to rev the engine to 3000 rpm or so and look at the total timing. More than 40 degrees might lead to the backfiring you indicate.
Using a compression tester is also a very good idea. The min is 100psi but you also want the lowest cylinder to be within 75% of the highest cylinder. A burned valve will show very little or no psi reading.
The leakdown test is a fair test if you can get hold of one. It will work with a air compressor and read data in percentage of loss. Over 20% is bad, this must be done with both intake and exhaust valves closed of course. Its good to have a assistant for this test. If the exhaust valve is bad then air will escape out the tail pipe and yes you can feel it. A bad intake valve will have air come out thru the carb, and last the rings will have air coming out the breather caps holes in the valve covers.

Hope this will help add to Doc's reply.

 

Your timing chain may be worn and slipped a tooth.

 

What kind of carb? Was it backfiring before you built it? Did you cheak the sprak plugs? If it was dumping gas in the motor they are fuel fauled, even if you dumped to much gas in at one time they could be fauled. This will make one fire out the pipe and carb.

 

Thank you all for your suggestions. My truck has a 2bbl carb and it is backfireing running down the road. I don't think this engine has ever been rebuilt so the timing chain is probably worn and may have slipped. I'll check the timing and go from there. I want everyone to know that this engine hasn't run real well since I bought the truck but it hasn't let me down in almost a year. Starts every time an gets me back and forth to work everyday. I've never owned a FORD before but if their all as tough as this one I won't own enything else. Thanks to everyone!

 

You say it is backfiring going down the road. Do you mean that it is rythmically popping or is it random? If random, then you probably don't have a valve problem. You either have a lean condition or retarded timing for that situation.

Checking the timing at idle will not necessarily uncover a timing problem. With the timing light in place you need to rev up the engine and watch the mark to see that it advances. You also should apply vacuum to the vac advance to see that IT advances the timing mark.

Good luck,
Doc

 

Doc I see what you mean about the popping. It is popping at random and if the valve were burned it would pop consistantly. Think maybe the distributer could be bad and would changing the gear fix it? It was poping before I rebuilt the carb and it was my first time to rebuild. I didn't make any adjustments just replaced the parts. I was hoping this would stop the popping. If its running lean how do I make that adjustment. The carb is a Motorcraft 2150. I'll check the plugs also.

 

red,

Don't move forward blindly. You need to do some testing, otherwise you are just shooting in the dark.

Find someone who has a timing light and check the timing as well as mechanical and vacuum advance as I described above. If the timing is the problem correct it. If the timing is advancing like I described and the initial timing is set according to the sticker on the valve cover or a spec book, then you know that the problem is in the carburetor. If you put in a kit, then it is probably not the carb but it still could be.

There is really not a carb adjustment that will correct such a condition. When the carb is responsible for such behavior it is usually a bad power valve or whatever mechanism is in that brand carb that richens up the mixture as you open the throttle. It also could be a low float setting, or a float that is flooded with fuel making it too heavy. It also could be the accelerator pump. All these things take some carb savvy to troubleshoot. That's why I'm saying that checking the ignition first is your best approach, because most people who can use a timing light are able to otherwise check ignition advancing.

If the advance problem were mechanical, then check the weights and springs. It is probably not vacuum, but it could be, if so replace the cannister.

See if you can find a friend with a timing light.

Good luck,
Doc