Here is a link to a site that sells a Leakdown Tester. The instructions for using it are on this page. You can probably buy one at a good Auto Store in your area or try Ebay.
Maybe you can rent one.

If you have a bad cylinder, it should show up with a high leak down percentage.

You can build your own, if you have the fittings and gauges.

http://www.goodvibesracing.com/leakd...structions.htm

 

Thanks a bunch Dan, I wiill be doing so.

 

Make sure that a plug or the vacuum tree is in the intake runner to #4 cylinder. Sometimes the vacuum tree goes bad and leaks badly.

 

Update 04/19/05

This is a newly rebuilt 79 Ford 351 m converted to 400 engine for my 79 f150 4x4, that ran good when I removed it, but wanted it fresh with the rest of my restore project. My buddy did the work on it from the years 2000 to 2004. All external bolt on parts are now new on it. The engine cylinders have been bored .030 over, crank journals line bored, crank turned and balanced, block/heads milled square and flat, heads ported /polished, 3 angle valve job, new mild Crane rv cam/lifter set (dont have the card on it, he does tho) , HV Melling oil pump.

Last weekend I started out on a catastrophic vacuum leak venture. I removed the intake manifold to check for cracks/gasket leaks. Intake manifold has been magnafluxed and looks as good as new. All o.k. Reinstalled with new Felpro aluminum valley pan , per instructions. Removed vacuum tree from intake, applied air pressure to it while all ports were capped, no leaks. Reinstalled it with pipe sealant ...

Pulled new reman Motorcraft 2150-2v carb and egr valve. Replaced with another new reman 2150 2-v , installed all new egr spacer plate gaskets, egr valve and carb base gaskets. Egr spacer plate is in good condition, no cracks or burned spots on it...

Removed #1 cylinder spark plug and while using a wood dowel, found TDC while turning engine over with a 15/16 '' socket . Got # 1 cyl to TDC, checked timing pointer on Harmonic balancer, it was on the " 0" mark. Pulled dizzy cap, the rotor button was pointing just a tad past the #1 tower post, the #1 dizzy cap tower post is at the 1 o'clock position, looking down on it. The dizzy spark advance diaphram is facing straight toward the radiator. The new plug wires are plugged on to the dizzy cap starting at #1 tower post, counting CCW, cylinder wires are #1,#3,#7,#2,#6,#5,#4,#8 ...

Checked my pics of the engine he took of it while he was rebuilding it, that are in my restoration photo album. There is a close up pic of the front of the engine , just before he put the timing chain cover back on. I can see a dot on the cam gear and the dot on the crank gear. The cam gear dot is at the 6 o'clock postion, the crank gear dot is at the 12 o'clock position, and they are lined up vertically perfect. Timing chain looks to be good and tight. According to my 79 Ford factory engine manual , this is the right postion for a "0" timing setting of the crank and cam ? ...

I left the dizzy cap hold down bolt a little loose when I tried to start it. I plugged all vac ports everywhere to eliminate any vac leaks, even removed brake booster line and capped. Egr was closed tight. The engine was having a real hard time starting, so I moved the dizzy retard / advance a little at a time, no help really. The engine finally fired, after spitting some gas vapor out of the carb top, run a bit while shaking badly, the vac guage never came up or stabilized, then suddenly the engine died after a 10 second run. I did not attempt another start, for fear of messing up more parts, something is really screwed up here. I am no mechanic, but have been messing around with my own tuneups for thirty years, and know what a properly timed engine should sound like when it is firing, and this aint one of them. I think you guys have nailed it here already . The engine is acting like the valve timing/geometry is all screwed up....

I have been reading on the net about cam degreeing, and how one should always do that test on a rebuilt engine , to assure crank/cam alignment/valve opening will be right, whenever the geometry of the engine has been changed, like mine has been with the milling and a new cam kit. He has milled the block and heads squared and flat as I have pics of the milling machine doing so. So I know the heads are now down closer to the pistons. But, as I talked to him two months ago, he said he wants to do a cam degreeing test on it now ( still waiting on that one) . So, apparently he did not do the cam degree test when he put the engine back together with the new rv cam /lifter set. From my conversation with him, I think he even put the old rods back in it maybe...

So, I know I need the valve /cam timing , rod length issues checked before spending anymore time or money on it. I know I can purchase a Crane cam degree kit which incudes the degree wheel, dial indicator, stops, etc., for 195 bucks. But I am not confident enough in my mechanic skills to know what I would be doing with it, or how to correct the problem if I find one, so I would be basically blowing another 200 bucks. If I put it on a rollback and haul in to a garage, I would be giving the shop owner a blank check to get it running, that option is not too cool for my checkbook. I have left the newly painted hood off, while doing this work, for fear I may have to pull the engine again, so it cannot sit outside in the rain. Only want to put it on once, its a BIG hood...


So, after reading about my mess I am in, is there anyone on here that can fix this engine, that lives in Ky or a bordering state, that wants to make some GOOD pocket money for a couple of weekends ???

 

You say that the block was decked and the heads milled. Did you shim the rockers to compensate for the shorter dimension from lifter to rocker? Your valves may not be closing due to the milling/decking.

I live in Delaware, so I can't help you in person. Maybe there is someone who can.

 

With all that milling, you may need shorter push rods.

 

Update :

I have the valve covers off now and put one new Crane .030 shim under each rocker pedestals. While doing that , I found out that the #4 cylinder (it has never fired) intake rocker arm is very loose, even when the fulcrum bolt is torqued to 22 fl.lbs. ..

While bumping the engine over, the pushrod will come up and make contact, but the rocker arm stays really loose, the others have only slight movement in them. These rocker arms are new , so I am assuming I have a new lifter that is collasped ? Also, should the pushrods just be sitting on top of the lifter ? ( I can see down in the engine and look at the top of each lifter) . I would think that they need to "snap" down in to the lifter ? All 16 of them are just floating on top of the lifter nose. It looks like at high rpm ( if this engine ever runs ) the rods would just fly off the lifter. thanks

 

check all of the pushrods for straightness. they just sit on top of the lifters, ther preload from the rocker arms holds them in plenty good if all is well. to check for straightness just loosen the rockers and pull the pushrods out, wipe them off, and let them roll on a smooth flat suface.

 

It sounds like your vacuum problem was a manifold gasket, I have had the same problem. The problem you have now is probably that you are 180 degrees out of time. The piston will come to top dead center twice, once for exaust, and once for compression. Put your finger over the spark plug hole, and you will feel the compression stroke. That is where you put the timing to fire. These are both easy problems to fix. The lifters may not be pumped up to lift the pushrods, did you prime them prior to installation? You just submerge them in oil and push down the center of the lifter with a pushrod, and you will feel them pump up. Or you may have the wrong rockers. Good luck.

 

are you sure you have the right lifters?

 

I pulled the intake manifold and reinstalled it last week. Only this time rather than using just the Felpro aluminum valley pan gasket by itself, I put Mr. Gasket #222 gaskets on the heads with Permatex Hi-Tac to stick'em. and trimmed the valley pan back to allow the pan to clear the #222 gaskets. After reinstalling the intake, I reinstalled the dizzy, got #1 cylinder to TDC, had the rotor button pointing under # 1 post on the dizzy. It start and ran, wanted to pull 18 in of vac, but kept stumbling like the timing is way off. No help advancing /retarding the dizzy either. The new Crane blueracer cam was installed with matching new lifters. So,...

I called my buddy that rebuilt it for me, he is back on second shift now. I am not qualified to work on whatever is ailing this engine, so I am putting the truck on a rollback this coming Sat. and taking it back to his house , that is a 100 miles away. The way I got it figured, after this big old truck sits disabled in his garage for a week or so, he will get it running just to get it out of his way. thanks for the replies