Hey guys, I finally got my baby out of the paint shop after 4 years where they have been neglecting her. I knew she didn't feel right and today my worst fears came to light. Amidst all the other issues I've been dealing with today I ran a compression check. I have within a couple pounds, 200 pounds on #1-5 and anywhere ,6,7,8 have 147,152,and 168.

Without tearing it down any one have any suggestions? Could the fact all three low ones are together mean anything?

Thanks for your help guys

 

could be a bad head gasket causing it as usaully when you have two low cylinders next to each other, the main culprit is a bad gasket. 3 is a little less common. not sure what you are running for rocker arms, but if the factory style non-adjustable ones, could be the valves are not closing properly. you can usually tell as you can hear it leaking thru either the intake or exhaust.

a leak down test will be the best bet to tell what is causing the low compression.

rgds
Mike

 

A head gasket is kind of what I as wondering, although I am not getting any water in the oil nor any pressure in the coolant system. I built this motor prolly 20 years ago so I can't remember all the details but I know it does not have a stock valve train. Harland sharp 1.7?s. It is adjustBle.

How would I do a leak down test and what would it tell me? Would it show the difference between a head/ valve problem vs. a cylinder problem?

Thanks a bunch for your help.

 

make sure you have the rockers on those cylinders adjusted correctly. pretty easy to over adjust and cause the valves to not close all the way. also back off the rockers and check to see that all the valves are at the same height to make sure you don't have sticking valves.

a bad head gasket will not always lead to oil or water contamination. most of the time the area between the cylinders is where you get the leak, so no fluids get into the water passages or oil pan. just loose pressure to the cylinder next door.

a leak down test basically pressurizes the cylinder with air, then you can usually listen to wear the air is escaping, either thru the valves, pass the rings or even thru the head gasket.

rgds
Mike

 

ok heres my update, I must have had too weak of a battery because I pressure tested again and only one cylinder came up short. #6. it was about 20 pounds short. I tried pouring some oil in the cylinder and trying again but it made no difference.

I replaced all plugs, wires, rotor, cap etc but it still has a slight miss.

in yalls opinion is 20 pounds lower a lot or a little? is it enough to create the miss im hearing?

thanks guys!

 

Check your valve lash, adjust if necessary, and check it again.

 

If you're still at an average compression pressure of 200 psi, then 20psi on one cylinder isn't very bad. It would help if I could see all of the pressures.

And yes X2...double check your valve lash. Setting valves hot is more accurate than cold, just not as much fun.


I keep dreaming about stroking my 460, would you say that 514 is still a reliable easy street driver for a weekend cruiser style?

 

When I say average of 200 they are all within 2-3 pounds. Really close except no 6.

As far as the valve lash, I did set it hot and it's been some time ago, it's run good for a long time until now. I'm sure something could have come loose there but it's not likely. Now I'm leaning towards a burnt valve.

And yes I would def recommend a 514. Mine has been super reliable and easy( except on my drivetrain) �� The problems I'm having now are from neglect from the paint and body shop.