compression low
Thread Starter
|
New User
Joined: Aug 2004
Posts: 4
Likes: 0
compression low
70 ford pu/360ci/110,000 miles
rear cylinders on both sides are reading low all the rest are good
Rear left and Right side are approx 35psi.
All the rest of the cylinders read approx 110-150 psi.
Added oil to Rear Cylinder's - no help. same readings, still low
NEXT:
Removed heads, inspected Rear cylinders for obvious and all looks good in the bore. Rotated eng to inspect cylinders. all looks good. The exhaust valve seats were recessed (hammered)
Rebuilt the heads and installed new seats/valves/guides/seals, and pressure checked heads. then installed the heads.
NEXT:
Set timming, all new plugs wires cap rotor, ran engine. It seem to run fairly good, except a little ruff. I pulled the rear spark plug wire while running at idle and there was no change in eng performance like that cylinder was dead. and same with the other side rear spark plug wire.
Rechecked compression and still 35 psi on rear cylinders.
Seems like the only thing left is the Rings are bad.
What else could it be and how long can you run the eng in this condition.
MY intentions was to sell the truck and not put a lot of money in it.
rear cylinders on both sides are reading low all the rest are good
Rear left and Right side are approx 35psi.
All the rest of the cylinders read approx 110-150 psi.
Added oil to Rear Cylinder's - no help. same readings, still low
NEXT:
Removed heads, inspected Rear cylinders for obvious and all looks good in the bore. Rotated eng to inspect cylinders. all looks good. The exhaust valve seats were recessed (hammered)
Rebuilt the heads and installed new seats/valves/guides/seals, and pressure checked heads. then installed the heads.
NEXT:
Set timming, all new plugs wires cap rotor, ran engine. It seem to run fairly good, except a little ruff. I pulled the rear spark plug wire while running at idle and there was no change in eng performance like that cylinder was dead. and same with the other side rear spark plug wire.
Rechecked compression and still 35 psi on rear cylinders.
Seems like the only thing left is the Rings are bad.
What else could it be and how long can you run the eng in this condition.
MY intentions was to sell the truck and not put a lot of money in it.
Thread Starter
|
New User
Joined: Aug 2004
Posts: 4
Likes: 0
I see your point. First the heads were done buy the machine shop and check for cracks and pressure checked, and still the compression is low. I can rule the heads out.
the cylinder, I checked, did not see anything that would cause this low compression.(35 psi)
So if the problem is in the cam/lifters or the rockers, are you saying that the valve is staying open and this is where the compression is escaping.
If there is wear in these area's lifter/push rod/rocker,then I would think the valve would not stay open as long.
the cylinder, I checked, did not see anything that would cause this low compression.(35 psi)
So if the problem is in the cam/lifters or the rockers, are you saying that the valve is staying open and this is where the compression is escaping.
If there is wear in these area's lifter/push rod/rocker,then I would think the valve would not stay open as long.
Post Fiend
Joined: Feb 2001
Posts: 6,624
Likes: 8
From: Missouri
If your cam is worn down flat the intake valve can be held open for only a very short period of time creating a negative pressure in the cylinder. When the piston comes back up there would be little to compress. I think you have a flat lobe. This is easy to check though. You will be able to see an obvious difference by pulling a lifter on a good cylinder and pulling one on a bad cylinder and just looking at the lifter bottom. If your intake is stock you may not even need to remove it. You can usually get them out with a magnet.
If that isn't it then you have bad rings.
If that isn't it then you have bad rings.
Thread
Thread Starter
Forum
Replies
Last Post
Sea2jet
Fuel Injection, Carburetion & Fuel System
2
Aug 4, 2011 09:52 PM
geoaigel
Small Block V8 (221, 260, 289, 5.0/302, 5.8/351W)
6
Jun 11, 2010 11:23 AM
WhitVT
Small Block V8 (221, 260, 289, 5.0/302, 5.8/351W)
3
Jan 3, 2008 07:36 PM
PHOTOG101
Big Block V8 - 385 Series (6.1/370, 7.0/429, 7.5/460)
1
Sep 9, 2005 12:20 AM
