Hello guys,
1968 F250 camper special, 360 FE, c6, bone stock, 75,000 original miles.
I did a compression test today and #1 read 60, 2 thru 8 tested at 135 +/-. Squirted oil in cyl #1 and retested at 90.
I have a noticeable noise that sounds like an exhaust leak and gets louder according to how hard you are pushing the motor but there is no exhaust leak so it is probably valve noise. Its a tick tick tick type noise. There is quite a bit of crankcase smoke coming up thru the pcv valve and breather. Engine doesn't burn oil and doesn't smoke. Overall, the engine feels strong and tight, it really just feels like it's firing on 7 cylinders. I have spark at plugs, engine is tuned up, timing is 8 btdc. Took off valve cover and valve springs are good, pushrods are straight, rocker assembly is good. I have a 427 side-oiler in a cobra replica and a 390 in a 1963 galaxie. I know my FE motors but wanted to get your guys opinions on what you think my next step should be.
Thanks!!!
Jay

 

1. Vac test
2. leak down,
3. +30psi with oil seems to say rings, and blowby. Oil getting singed as blowby passes rings and creates compression in a vacuum zone. Ex leak sound..

 

Thanks for the reply. With a vacuum gauge on the intake manifold, I'm getting a steady needle at idle in the normal zone (15 inches of merc). I was surprised by that.

I can't help but think it is carbon build up around the exhaust valve keeping it from sealing. Also, at idle, listening at the the tail pipe there is a slight sucking sound, like "pop, pop, pop, slurp..."

 

x2 on the cyl leak down test . If you do not have a tester , easy to fab with a compression tester and an air regulator .

 

Those sounds do indicate a possible valve issue . Leak down / hold test will confirm .

 

Thank you for the response. I will rig up a leak down set up using a compressor and test it tomorrow. I'll probably just pull the manifold and the head also. The solution to my problem is going to require head removal anyway, even if its just a blown head gasket, so I might as well get a look at the cylinder walls and the valve seats. I fully intended to rebuild the engine, I just wasn't ready to do it yet. If I can get another year out of it that would be optimum, but I can't drive it like it is, it kills me when a motor isn't humming.

 

Ok, so, I'm assuming I set #1 to TDC, then pressurize the cylinder to 15lbs. I'm guessing at that point if stick my ear to the tail pipe/carb/dipstick I will hear a hissing sound coming from one of them, right??

 

Sucking: Take a piece of paper and hold it over the exhaust pipe exit. Should push away at all times. If it pulls, pull # 1 plug wire and retest. No pull, exh valve prob issue. leak down will confirm save teardown for last. KISS method...saves $$$

 

Be safe, lock rotation as air can cause crank rotation.

 

Thanks again for the reply. Good advice, I'll try it, but answer me one question. Why would spark plug firing have any effect on the suction at tailpipe?

 

Hahaha! Good point! I would have never thought of that!! I guess if I fill a cylinder with water and put the plug back in that will keep it from rotating, right???

 

You wont hear a pop from the exh pipe upon compression ign. Piston will cool and shrink drawing less.

Sure, fill it with water, whatever floats your troll raft.

 

Pulling the plug wire on #1 while engine running doesn't effect the idle speed. And, like I said, at the tail pipe, with plug connected, it isn't popping at #1, it's almost sucking.
I was kidding with you about water in the cylinder, obviously I would just shove my arm between the fan blades to keep the motor from turning.

 

I'm going through the same thing. just pulled a head and the valve seat is rusty. time for a valve job.

 

Hi guys, here's an update: tail pipe was sucking the dollar bill. Removed the spark plug wire at #1, per redmanbob advice. Still sucked the bill at tailpipe. (I'm still not sure how that would make any difference if the exhaust valve is leaking). So, at this point I know it's my exhaust valve causing the problems. That's enough data for me to know that the next step is to pull the head. I'll post some pics when I get the head off. Thanks again for all the help.