302 Diagnosis

Dennis. I have a 68 Shelby GT350. It is a 302. I have owned it since 1972. I don't profess to necessarily be the expert on anything, I rebuilt the engine two years ago completely into a 347.
I feel confident that I can offer you some accurate help on your situation.

A worn engine should still show a compression of no less then 125psi(cold). You should be expecting a reading of no less then 150#. A reading of around 180# is where it should be (warm).

Where is the compression going? The stock cylinder head has a non-adjustable rocker arm assembly with a positive stop stud. There are a couple of problems with it. First and formost, it only works correctly if you used the original valve train. That includes the original hydraulic lifters and pushrods. The camshaft really doesn't matter very much.

The problem is will an aftermarket lifter have the same plunger auto-adjusting range as stock?

Secondly, these are pressed in studs. There is no guaranty that with the stock springs they will stay at the correct height forever. They tend to pull out over time even with stock springs. When the valve seats are reground you change the relative height of the valve stem tip to the rest of the assembly, i.e., you have altered the geometry. The valve tip is now higher and the pushrod needs to be longer to compensate for how much the valves were cut.
The hydraulic lifter will adjust the plunger itself according to the oil pressure provided within a design limit of the plunger. In the old system this would be within 1/2 turn or the adjusting nut from zero clearance. Zero clearance would be when you can longer turn the pushrod with you fingers. That is also if the stud heights are still correct.

Your engine with that camshaft should give you stock type characteristics, namely around 18-20 in-mg at idle.

If the valves are not seating, particulary with an semi-open exhaust system like the 'goose, you will have popping through the exhaust. In all fairness it shouldn't even run and popping is an understatement. You will be at the firing range. Put on your earmuffs.

Make sure that you don't have a concealed vacuum leak under the carb like from the pcv connection under the carb, or the carb itself. You could also have a problem with an internal carb leak in the case of a holley between the metering body and the main carb body. Holleys are notorious for leaking on the pump transfer hole to the main body there.

Your problem is probably that you can't see around the engine properly because of the location of the engine in the car. This is an instance where it would be worth the extra money to pay a shop with a dyno to run the engine in on the stand. Then everything could be pre-adjusted, the engine run-in and just dropped in. Plug and play, so to speak.

Not that you need to know my preferences but I went to a solid lifter cam, screw in studs, triple spring .528 lift, 236 degrees duration @ .050 and 72 degrees of overlap. 10.4:1 cr with KB pistons. 3.4" stroke.

The lifters were pre-adjusted on the stand. Were right-on and will stay right on for as long as the hydraulics will.

With compression that low on all of the cylinders I don't think it is the valves, it sounds like something is wrong accross the board on the rings. Squirting oil into the cylinders and the compression rising up will confirm this. I hope not because that means it has to come out and come apart again.

Maybe someone else will see something that I am missing simple. Good luck, I hope it is very simple like you forgot the power brake hose.

PD,

Thanks for the reply. One of the first thoughts was an internal vacuum leak. The plugs were not showing oil fouling but the intake was pulled and resealed anyway but showed no improvement. Three different carbs were also run on the engine. The engine runs like a champ until it warms up, no popping or backfiring. I'm planning to try the oil in the cylinders and run the compression test again.

You have two different issues here. 1)low compression 2) low vacuum.

A mistimed cam could cause the vacuum.

Try another intake manifold, it may be damaged underneath. I don't rember if the iron 4v has iron plugs in the underbelly?

Low compression is low compression.

Sorry best I can do from NY in the snow. Guess I'm gonna have to catch a flight to HI and drop in?

Tried the compression test again after squirting some oil in the cylinders. No real difference, maybe about 5 psi at the most. I'm taking it that the rings should be OK and the problem probably lies in the valves?

Dennis,

is there a possibility the timing chain could have slipped, or the cam timing be out of sync?

cowboy from hell

The reason that I removed the engine to begin with is it started running a bit sour and eventually began dying out. The timing chain was severely stretched and was replace as was the cam. All was dialed in correctly at replacement and still should be as it has only run at cam break in RPM and idle. The motor runs great in any rpm or load condition until warm. Wouldn't an out of sync cam display symptoms at any temp? The funny thing is the low compression throughout all of the cylinders. I changed the valve seals during the engine work but did not have any other work done as all looked good at the time (regrets, regrets!) Could it be that after 35 years, the valves when disturbed by disassembly lost their seal? Or could the head gaskets be leaking without coolant or oil loss?

Dennis,

I'm no expert here, but I sat and tried to figure this one through in my head and end up in the same place as George, cam timing out of sync. for some reason (cam to sprocket pin sheared?)

You have low compression on all cylinders, poor vacuum and the problem worsens when the engine warms up. Can you pull a rocker cover and loosen off a pair of rockers, see if the compression test jumps up on that cylinder. I suppose you are going to have to pull the engine to get to the timing cover anyway?

Good luck

I have to agree with Doug on this one. I had a similar issue when one of my pushrods jumped out of the rocker socket and sat on the edge of the adjuster. It cranked up but would not run well and because of the compression leaking back into the intake showed a 6-10 in/hg on my gauge. The only thing is I figure it would get better as the engine heated up as the block and heads would expand increasing the push rod/rocker clearance. I cant imagine it would be your head gaskets as the likelihood of every cylinder having a leak would be slim.

Blaine

All makes sense except the engine runs perfect until warmed up. If the sync was off wouldn't it run crappy all the time? Even when it starts acting up, if you throttle up a bit and hold it at say 1100 rpm, the engine runs well even when reved up. Inquiring minds want to know! Thanks

To check for vacuum leaks spray "starting fluid" around where the intake manifold bolts to the heads & where the carb bolts to the manifold & see if you find a spot where the motor speeds up, indicating a vacuum leak.

Is it possible the lifters are too compressed & as things heat up the plungers are bottoming out & holding the valves open (long shot).
this can happen when the heads have new valve seat inserts, or with new heads.

cowboy from hell

Pull off the valve covers. Put an index mark with a black flair pen on each of the nuts. Back off 3/4 of a turn. Run it and see what happens.

You probably have the wrong pushrods.

I MIGHT have a partial set of original Ford pushrods for it here. Maybe? The signifigance of that would be I can give you a length on them.

I am thinking that it is the most likely culpret. There 68 pushrods are unique to the 68 J engine. You may have 69 pushrods. I have found many mistakes in the aftermarket listings including TRW. A 20 year old counter person won't even be in the correct century, so put away your service revolver before you get carried away.

I'll look in "the secret parts drawer" for the pushrods before I go out to work. I have all my fingers and toes crossed. (hard to type). Book 'em Dan'O.

OK. Good news and bad news. I found the package of 4 in the Ford wrapper.

Bad news. 1)The package isn't in good shape> I can read C2....65B.

2)I don't have a caliper big enough to measure the length accurately. Not only that three of my know measuring devises are not in my desk, in the shop, or in the garage.

It would seem that the hole in the wall gang has obsonded with them all. We need an aexact accurat measurement here in thousands of an inch and I can't provide that to you.

Hopefully the partial part number will help you out and you will need to cross reference to a TRW number.

Maybe there will be a reversal of this reversal of fourtune later. I can only hope. Later, good luck.

I'm no expert, but I have '65 Mustang with a '69 302 and had a '66 K-code with a solid lifter 289.

Did you change out the lifters when you replaced the cam? It sounds like the lifters may be colapsing when the engine warms up. How's your oil pressure when warm? What viscosity oil are you using?

Lifters and cam are new. Oil pressure is good throughout and oil is Chevron Delo 10-40.

[QUOTE]Originally posted by Cowboy from Hell:
To check for vacuum leaks spray "starting fluid" around where the intake manifold bolts to the heads & where the carb bolts to the manifold & see if you find a spot where the motor speeds up, indicating a vacuum leak.

I've already done this test and no leaks were found. I've also plugged all vacuum ports at the source. Thinking it may have been an internal vacuum leak I have already re installed the intake with no improvement.

[QUOTE]Originally posted by Cowboy from Hell:
Is it possible the lifters are too compressed & as things heat up the plungers are bottoming out & holding the valves open (long shot).
this can happen when the heads have new valve seat inserts, or with new heads.

How can you tell if lifters are stuck compressed? Do you have to remove them and visually check if they are stuck down?

I think the problem is finally sorted out. The winner is "Mangusta Steve" Liebenow who figured valve adjustment. Backing off the adjustment just a bit boosted the vacuum to 18hg. The motor ran strong and didn't die when it heated up. I haven't had time for a real road test yet but it looks promising. It was interesting adjusting the valves and watching the vacuum gauge. Just a bit of over tightening would send the needle down. I guess that spread over 16 valves added up to the vacuum loss! My adjustments were all no more that a quarter turn off but it made all the difference. Thanks to all that offered help!