Compression readings...what am I in for?

[PhilC64]

I recently took compression readings on my 74' F motor and found some big disparities in the numbers. Mind you, I'm pulling the head tomorrow to have it checked at a local machine shop. What am I looking at with these numbers?

cyl 1 90 psi
cyl 2 75 psi
cyl 3 70 psi
cyl 4 85 psi
cyl 5 90 psi
cyl 6 85 psi

I know these numbers are low. Would these low readings be caused by just a head gasket failure or am I also looking at replacing the piston rings?

 

[Pighead]

Low across the board would indicate rings. Maybe just a valve job would do...
How many miles on the engine?

 

[RockDoc]

Throttle wide open and all spark plugs out?

 

[Rocky_LC]

At least they are consistent.

I would be sure they are really low (i.e. measured correctly) before I tore into the engine. Those numbers certainly do not indicate a bad head gasket.

You can fix bad valve seats / seals on the head... but rings means serious work. Are you sure you want to pull it apart?

How does it run?

Rocky

 

[PhilC64]

Low across the board would indicate rings. Maybe just a valve job would do...
How many miles on the engine?

Probably over 100k. Odometer wasn't hooked up when I bought it. I was thinking of just a mild 3 angle valve job to get them cleaned up and have them check for warping.

Throttle wide open and all spark plugs out?

I took all numbers with plugs out and carb off the manifold.

At least they are consistent.

I would be sure they are really low (i.e. measured correctly) before I tore into the engine. Those numbers certainly do not indicate a bad head gasket.

You can fix bad valve seats / seals on the head... but rings means serious work. Are you sure you want to pull it apart?

How does it run?

Rocky

It ran ok until the rear rocker shaft snapped in two causing an uncurable backfire. IH8MUD Forums - View Single Post - Backfire with Weber 32/36...any ideas?

The head gasket needs to get swapped since I have a small coolant leak from between the head and block. A complete gasket kit and a full set of rings came with the cruiser when I bought it. I figured since I'll have the head off, and oil pan dropped, it won't be much more work to put the rings on if needed. If I can get away with just a head gasket swap, I'd live with that.

 

[Trollhole]

If your dropping the pan take go ahead and take the pistons out and rering. At least post pics of the bores. A set of piston rings and new bearings would be wise. You not talking about a lot of money for something you might not need to do for a long long long time. Even so I'm pretty sure you could change the mains with the engine still in the block.

 

[dargreg]

X2 A real simple job reringing and bearings make sure you number the rod caps.If you are takeing the head of anyway that to me is the hard part , pulling the pistons isnt,borrow a ridge reamer if need be and hone.Remember its only people that do it anyway and your a people.

 

[bsmith123]

wet

put a squirt of oil in the cylinders and retest ---if the numbers go up its the rings