3.5 with no compression ?

[pop058]

Had a look at an 87 County (3.5/5 spd) today with what appears to be no compression. The story I have is that the owner drove it home after work one day, went out next morning and it would not start. With a good battery the engine spins over very freely as if all the plugs are out. With the dissy cap off the rotor button is doing it's thing but there appears to no indication of compression at all.

Any thoughts gents ??

[DAMINK]

Wet and dry compression test.

[pop058]

Wet and dry compression test.

That was the plan. I was chasing a few options before things start coming apart.

[DAMINK]

That was the plan. I was chasing a few options before things start coming apart.

Just to rule out heads is all.
If the comp is gone and the previous owner can be believed then it must be rings that have seized somehow.
Or burnt! Even a stuffed head would start so it must be pretty serious to have no compression at all.
Ran dry is another possibility but none that i can think of are good!
Sounds to me like a replacement is the easiest option even before testing further.

Also nothing really comes apart to do the test apart from plugs.
And at this point plugs MUST be taken out to at least check there condition.

[pop058]

heads, rings, etc. are all possible culprits but all 8 pots at once ??

[DAMINK]

heads, rings, etc. are all possible culprits but all 8 pots at once ??

Oil pressure has been determined to be ok?

[pop058]

Oil pressure has been determined to be ok?

I believe so (yet to do checks myself) but still trying to think of something common to all 8 cyl than displays the symptoms I know of ATM.

[DAMINK]

I believe so (yet to do checks myself) but still trying to think of something common to all 8 cyl than displays the symptoms I know of ATM.


Trying to think of the best case scenario.
No oil and rings are dry. Comp pushing past them and feeling like no comp.
Although one would expect the pump to work after a few cranks?
A failed pump would give a warning light of some sort. No pressure.
Hope its something like that where priming the pump/replacing the pump would work.

Much better than a replacement which im still leaning towards.

[bee utey]

Many moons ago I bought a very cheap Holden Statesman V8 that had missed out on a lifetime of oil changes. It too had no compression. The camshaft had eaten out the bottoms of the lifters to the point that when oil pressure was lost the lifters bled out and no longer opened the valves enough to run. Another engine that I met with a similar amount of servicing was in a Stage One V8, There was as little a 1 litre of oil left for the engine to drive on, the rest of the reservoir was chock full of congealed sludge.

So as a test, pull off the driver's side rocker cover and observe the valve train operation on cranking. You'll also be able to see how much sludge has built up under the rocker covers.

[pop058]

Many moons ago I bought a very cheap Holden Statesman V8 that had missed out on a lifetime of oil changes. It too had no compression. The camshaft had eaten out the bottoms of the lifters to the point that when oil pressure was lost the lifters bled out and no longer opened the valves enough to run. Another engine that I met with a similar amount of servicing was in a Stage One V8, There was as little a 1 litre of oil left for the engine to drive on, the rest of the reservoir was chock full of congealed sludge.

So as a test, pull off the driver's side rocker cover and observe the valve train operation on cranking. You'll also be able to see how much sludge has built up under the rocker covers.

The young fellow that had this purchased it from the original owner very recently. He told me the original owner was fussy as hell and if you look at this County, I tend to believe it. It is amazingly clean. I was also told the heads have been done to suit un-leadeded. The speedo does only indicate 268 (ish) Kms.

Thanks for all the input people. It all helps diagnose the issue(s) prior to the actual work happening.

[djam1]

Dont take too much notice of people who tell you they did the valves on a Rover V8 for unleaded as this is a total nonsense.
All Rover V8s of that era had alloy heads with valve seat inserts that were more than capable of dealing with unleaded and LPG
Camshafts wear out pretty quickly on these things but I would doubt if all 8 were completely absent of compression lets face it they were not a high compression engine right from the start.

[pop058]

One of my first thoughts when I witnessed the motor turning over freely on the starter was that it is normal due the low compression (8.13:1 ?) of the motor from factory.

[DAMINK]

Many moons ago I bought a very cheap Holden Statesman V8 that had missed out on a lifetime of oil changes. It too had no compression. The camshaft had eaten out the bottoms of the lifters to the point that when oil pressure was lost the lifters bled out and no longer opened the valves enough to run.

If the lifters were gone that would stop valves opening.
That directly would have no effect on compression. Unless a valve was stuck open. Buggered lifters wont do that.

[bee utey]

If the lifters were gone that would stop valves opening.
That directly would have no effect on compression. Unless a valve was stuck open. Buggered lifters wont do that.

It would if the inlet valves weren't opening, in the same way as a closed throttle does.


One of my first thoughts when I witnessed the motor turning over freely on the starter was that it is normal due the low compression (8.13:1 ?) of the motor from factory.

That sounds reasonable. My crappy old ute's 3.5 spins over like crazy on a fully charged N70Z with a late D1 Bosch starter fitted, despite it being a 9.35:1 car motor. Perhaps it's just something simple like a failed ignition module or a burnt out rotor button.

[DAMINK]

It would if the inlet valves weren't opening, in the same way as a closed throttle does.

Interesting. I would have thought compression would remain if valves stuck or no cam etc.
Each stroke comp going up and down. Perhaps pushing the comp past the rings out of force and perhaps even drawing air in past the rings from the crankcase.

My understanding is compression is a fixed number. No relationship to throttle position.

[bee utey]

Interesting. I would have thought compression would remain if valves stuck or no cam etc.
Each stroke comp going up and down. Perhaps pushing the comp past the rings out of force and perhaps even drawing air in past the rings from the crankcase.

My understanding is compression is a fixed number. No relationship to throttle position.

Theoretical Compression Ratio is a fixed number (unless you bend the con rods). Actual cylinder cranking pressure as measured by a compression tester is a variable depending on lots of factors, cam timing, wear, cranking speed, throttle opening, temperature, altitude etc. The spark doesn't fire anything unless conditions are right.

[theelms66]

Pulls the plugs and perform compression test.start with the basics.

[DAMINK]

Theoretical Compression Ratio is a fixed number (unless you bend the con rods). Actual cylinder cranking pressure as measured by a compression tester is a variable depending on lots of factors, cam timing, wear, cranking speed, throttle opening, temperature, altitude etc. The spark doesn't fire anything unless conditions are right.

Agree totally man. Not trying to argue the point. Just trying to give the best advice to the problem at hand.
Generally speaking compression is a fixed number. So if he has lost all cylinders (which i suspect he has not!) then its something other than cam, valves etc one can surmise.

Again i am taking the OP on face value here and trying to discuss the compression specific issues. The OP stated the previous owner just parked the car and that was it. No mention of bending rods or dramatic stuff like that.
Thats why i started with the obvious. Do a comp test. Wet and Dry. Might bring up some interesting numbers. Perhaps a couple cylinders are dead or none. But its paramount to start there.
Even before checking oil. As no oil pressure could dry out the rings and perhaps lower the comp? Unlikely but gotta be checked at this point.
The wet dry comp test will possibly identify valve/cam issues also or atleast give a direction to look in if a couple of cylinders show bad numbers.

[Tins]

If you believe it to be a compression issue there is no substitute foe a proper compression test. However, pull one plug and stick your thumb over the plug hole and give it a crank.. Disable the ignition first, of course... I'm with bee utey. My 3.5 always sounded like it had zip in the comp department, but it ran just fine.

[pop058]

One of my first thoughts when I witnessed the motor turning over freely on the starter was that it is normal due the low compression (8.13:1 ?) of the motor from factory.



That sounds reasonable. My crappy old ute's 3.5 spins over like crazy on a fully charged N70Z with a late D1 Bosch starter fitted, despite it being a 9.35:1 car motor. Perhaps it's just something simple like a failed ignition module or a burnt out rotor button.


If you believe it to be a compression issue there is no substitute foe a proper compression test. However, pull one plug and stick your thumb over the plug hole and give it a crank.. Disable the ignition first, of course... I'm with bee utey. My 3.5 always sounded like it had zip in the comp department, but it ran just fine.

I am away for the weekend so I will do some basic checks next week. This may turn out simpler than expected. [thumbsupbig]

[DAMINK]

I was reading technical stuff regarding the topic compression to satisfy my own curiosity.
I did come across something that may be of some help here.

Again assuming there is no compression.


Consecutive Low Compression in All CylindersThis could happen because of fuel washed cylinders, when too much fuel is introduced into the engine and all oil has been washed off the walls of the cylinder. The oil creates a sealing effect between the ring assemblies of the piston and the cylinder walls of the engine block. When this thin layer of oil is washed off, the engine compression escapes into the crankcase. Engines with a flooding problem usually show this behavior.


Source What Is Engine Compression And How Is It Tested? - Apex Tool Company (https://www.apexinds.com/blog/engine-compression-tested/)

Just trying to offer possibilities.

[pop058]

It lives. Pulled the coil lead out of the dissy cap and got no spark. Swapped coils and got spark to the cap but nothing at the plugs. Fitted a new cap, some clean fuel, a breath of " startyabastard " and a new battery and it coughs into life and idles. [thumbsupbig]

[DAMINK]

It lives. Pulled the coil lead out of the dissy cap and got no spark. Swapped coils and got spark to the cap but nothing at the plugs. Fitted a new cap, some clean fuel, a breath of " startyabastard " and a new battery and it coughs into life and idles. [thumbsupbig]


I always check fuel at the rail first or carb, then SPARK and finally compression.