62 C10 Step w/ 235 - Test Results

[bloody hammer]

I finally got around to picking up some tools I've been needing in my garage. I ran some tests today and here are the results...

Fuel Pressure = 4.5

Vacuum = 18 (steady at idle)

Compression (front to back) = 105, 130, 110, 130, 100, 130


As I understand it, the first two tests are good results but the compression... not so much. I guess the rings are going?

Is it at all odd that 2, 4, and 6 were all 130 but the others were around 100?

[markeb01]

It's been a long time since I've done a compression check, but if memory is correct the next thing is to squirt some oil in the cylinders and recheck. If the compression goes up it means rings, if it doesn't it means valves, or I may have that backwards. I'd do a quick Google search and go from there. The other numbers sound great, and 18 inches and steady at idle probably confirms your valves are sealing well.

[bloody hammer]

Thanks, Mark. I'm going to read up on it some more. I did discover one thing I forgot to do.... I did not open the throttle valve when "starting" the engine. I'm going to do the whole thing again except this time I'll jimmy the throttle open with a screwdriver or maybe just press down the accelerator each time. I'm curious to see how different the results are.

[bloody hammer]

Ran the compression test again but this time with the throttle valve open. Much better results...

Cylinder - First crank - Final

#1 - 60 - 125
#2 - 60 - 125
#3 - 90 - 130
#4 - 90 - 130
#5 - 70 - 125
#6 - 90 - 130

[bloody hammer]

Something I noticed after each time I tested.... for the first 5 minutes or so of running the engine the valves were tapping. Does anyone know why this would happen after running a compression test?

[markeb01]

Great news, glad to hear it turned out healthy. Perhaps it's noisy lifters you're hearing rather than valves - if you have hydraulic lifters. The engine may be turning over so slow during the compression testing there isn't enough oil pressure to keep the lifters filled? Once the engine is fires up the higher engine speed pressurizes the lifters eliminating the ticking.

[bloody hammer]

Originally Posted by markeb01

Great news, glad to hear it turned out healthy. Perhaps it's noisy lifters you're hearing rather than valves - if you have hydraulic lifters. The engine may be turning over so slow during the compression testing there isn't enough oil pressure to keep the lifters filled? Once the engine is fires up the higher engine speed pressurizes the lifters eliminating the ticking.

Yep, sorry... I meant to say lifters and what you said about not enough oil pressure makes sense. Thanks!