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furgo
Samba Member
Joined: September 06, 2016
Posts: 944
Location: Southern Germany
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 Posted: Sun Dec 03, 2017 5:19 pm Post subject: Compression test checklist |
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I've finally got time to take a closer look again at my now not running bus. As I'll be replacing the spark plugs, I'll do the one thing I didn't manage to do the last time I was diagnosing: a compression test. Plus, some alarms went off in my head when I recently read a thread in another forum with someone having similar symptoms to mine (motor starts, runs on idle as long as the foot is on the gas pedal, turns off as soon as foot is off the pedal *) and it turned out to be a cylinder with no compression.
It's the first time I've done this, so I thought I'd summon some of the Samba accumulated knowledge to make sure I do things right. Looking at the procedure described by ratwell, the steps would be:
0. Ensure battery is charged and starter is in working order
1. If you have hydraulic lifters, run the engine the night before for 30 minutes to make sure they are pumped up.
2. Adjust valves if it's near adjustment time
3. Break torque on the plugs with a cold engine so you aren't removing them when the threads in the head are softer from the heat. Just keep them snug.
4. Run the engine for 5 minutes to warm it up
5. Ensure the transmission is in neutral and the parking brake is set
6. Remove all four spark plugs
7. Key off to disable coil and injectors
8. Unplug double relay if you have FI (left plug is mandatory)
9. hook up your remote starter (very useful for this procedure; disconnect battery, connect between terminal 50 on starter and battery positive, reconnect).
10. thread in your compression gauge
11. open the throttle wide open for maximum breathing
12. run starter for 10 pulses of the needle (events)
13. repeat and average your readings
14. put a drop of oil on the threads of the plugs when you put them back in and torque them down when the engine is cold. Bentley says 22 ft. lbs which also jives with the value specified on the spark plug box (my NGK B6ES say 18 ft. lbs for aluminum head so I use that value).
So...
I'll be testing this without a helper or a remote starter, but that should be ok. I do happen to have hydraulic lifters, but as the motor doesn't really run for more than a couple of minutes, I'd be starting at step 5 with a cold motor and hydraulic lifters not pumped up.
• Any additional considerations I should be aware off given these constraints?
• Any advice on how to maintain the throttle wide open? Or shall I just floor the gas pedal while running the starter?
Thanks.
(*) Although in my case, it goes off after a couple of minutes, so I'm still hoping that it's either a vacuum leak or that the idle bypass needs to be readjusted after I actually fixed some vacuum leaks.
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'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)
Decode your M-Plate
Last edited by furgo on Mon Dec 04, 2017 11:30 am; edited 1 time in total |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50352
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| Posted: Sun Dec 03, 2017 6:35 pm Post subject: Re: Compression test checklist |
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I just fired my 1800 up after it sat all summer. Pulled the coil wire and disabled the fuel pump (carbureted engine). Cranked the engine to get the oil galleys filled and in doing so did a good enough leakdown/compression test as all the cylinders sound exactly the same when cranking.
If your compression is so bad the engine will not run, this is about all you really need to do. |
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Abscate
Samba Member
Joined: October 05, 2014
Posts: 22670
Location: NYC/Upstate/ROW
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| Posted: Sun Dec 03, 2017 11:57 pm Post subject: Re: Compression test checklist |
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One thing to add..la fully charged, good condition battery is required if you want absolute measurements to be relevant, and , of course, a fully serviceable cranking System.
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Willems
Samba Member
Joined: September 24, 2016
Posts: 56
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| Posted: Mon Dec 04, 2017 12:19 am Post subject: Re: Compression test checklist |
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| Abscate wrote: |
| One thing to add..la fully charged, good condition battery is required if you want absolute measurements to be relevant, and , of course, a fully serviceable cranking System. |
It also helps to connect a battery of a running car to your battery. |
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furgo
Samba Member
Joined: September 06, 2016
Posts: 944
Location: Southern Germany
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| Posted: Mon Dec 04, 2017 6:44 am Post subject: Re: Compression test checklist |
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| Wildthings wrote: |
I just fired my 1800 up after it sat all summer. Pulled the coil wire and disabled the fuel pump (carbureted engine). Cranked the engine to get the oil galleys filled and in doing so did a good enough leakdown/compression test as all the cylinders sound exactly the same when cranking.
If your compression is so bad the engine will not run, this is about all you really need to do. |
Thanks. I'm not sure I'm at a stage where I can tell whether the cylinders sound the same (or if they sound ok at all), but I'll give that a go and do the compression test.
| Abscate wrote: |
| One thing to add..la fully charged, good condition battery is required if you want absolute measurements to be relevant, [...]. |
Ah, really good point about the battery. I'll double-check and charge it if it's not.
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'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)
Decode your M-Plate |
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sjbartnik
Samba Member
Joined: September 01, 2011
Posts: 5998
Location: Brooklyn
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| Posted: Mon Dec 04, 2017 9:17 am Post subject: Re: Compression test checklist |
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You don't necessarily have to count off 10 pulses of the starter, you can just crank until the needle on the gauge stops advancing (assuming you can see the gauge from the driver's seat or if you're using a remote starter trigger).
In your checklist, especially if using a remote starter, you should add to ensure the transmission is in neutral and the parking brake is set.
Since you said you will not be using a remote starter, you will have to have the ignition on to conduct the test. In this case you will want to disable the ignition coil so as not to have the spark plugs firing. Remove the black wire from the ignition switch from the + terminal of the coil and tape it up or set it somewhere where it can't touch bare metal. This will keep the spark plugs from firing.
Secondly, remove the white wire for the FI system from the negative terminal of the coil. This will keep the fuel injectors from firing. I would say you don't need to unplug the double relay if you simply remove that white wire from the coil.
That is unless you want to keep the fuel pump from running when the starter is operating. If the fuel injectors aren't firing it really doesn't matter if the pump is running except for the extra draw on the battery - it would only be running when starter is cranking.
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50352
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| Posted: Mon Dec 04, 2017 9:45 am Post subject: Re: Compression test checklist |
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| sjbartnik wrote: |
You don't necessarily have to count off 10 pulses of the starter, you can just crank until the needle on the gauge stops advancing (assuming you can see the gauge from the driver's seat or if you're using a remote starter trigger).
In your checklist, especially if using a remote starter, you should add to ensure the transmission is in neutral and the parking brake is set.
Since you said you will not be using a remote starter, you will have to have the ignition on to conduct the test. In this case you will want to disable the ignition coil so as not to have the spark plugs firing. Remove the black wire from the ignition switch from the + terminal of the coil and tape it up or set it somewhere where it can't touch bare metal. This will keep the spark plugs from firing.
Secondly, remove the white wire for the FI system from the negative terminal of the coil. This will keep the fuel injectors from firing. I would say you don't need to unplug the double relay if you simply remove that white wire from the coil.
That is unless you want to keep the fuel pump from running when the starter is operating. If the fuel injectors aren't firing it really doesn't matter if the pump is running except for the extra draw on the battery - it would only be running when starter is cranking. |
Removing the black wire from the coil kills the spark and the FI, including the fuel pump. The black wire from the ignition to the coil should always have a protective insulator over the female spade. This wire is hot whenever the ignition is on and is not fused. A short to ground is apt to be very expensive and inconvenient.
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sjbartnik
Samba Member
Joined: September 01, 2011
Posts: 5998
Location: Brooklyn
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| Posted: Mon Dec 04, 2017 10:30 am Post subject: Re: Compression test checklist |
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| Wildthings wrote: |
Removing the black wire from the coil kills the spark and the FI, including the fuel pump. |
Good call, I had forgotten that black wire from the coil was the trigger for the double relay to power up.
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1965 Volkswagen 1500 Variant S
2000 Kawasaki W650 |
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furgo
Samba Member
Joined: September 06, 2016
Posts: 944
Location: Southern Germany
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| Posted: Mon Dec 04, 2017 11:26 am Post subject: Re: Compression test checklist |
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| sjbartnik wrote: |
You don't necessarily have to count off 10 pulses of the starter, you can just crank until the needle on the gauge stops advancing (assuming you can see the gauge from the driver's seat or if you're using a remote starter trigger).
In your checklist, especially if using a remote starter, you should add to ensure the transmission is in neutral and the parking brake is set. |
Good points, I've added those to the checklist.
That said, I think I'll end up getting or fabricating a remote starter. It's a cheap and simple enough device that it's not worth much thinking whether to get or not for a one-off. It should make the measurement much easier, so I'll just use it.
| sjbartnik wrote: |
Since you said you will not be using a remote starter, you will have to have the ignition on to conduct the test. In this case you will want to disable the ignition coil so as not to have the spark plugs firing. Remove the black wire from the ignition switch from the + terminal of the coil and tape it up or set it somewhere where it can't touch bare metal. This will keep the spark plugs from firing.
Secondly, remove the white wire for the FI system from the negative terminal of the coil. This will keep the fuel injectors from firing. I would say you don't need to unplug the double relay if you simply remove that white wire from the coil.
That is unless you want to keep the fuel pump from running when the starter is operating. If the fuel injectors aren't firing it really doesn't matter if the pump is running except for the extra draw on the battery - it would only be running when starter is cranking. |
| Wildthings wrote: |
| Removing the black wire from the coil kills the spark and the FI, including the fuel pump. The black wire from the ignition to the coil should always have a protective insulator over the female spade. This wire is hot whenever the ignition is on and is not fused. A short to ground is apt to be very expensive and inconvenient. |
Good points again. Here's the wiring diagram for a more visual reference of this. ratwell's method of disconnecting only the left double relay plug would work (no power to ECU or fuel pump). However, disconnecting the black wire directly at the coil (+) is better as in addition it kills the spark, as Wildthings noted.
These should apply for doing the compression test with either a remote switch or via the ignition switch:
• Do: disconnect the correct black wire from the ignition coil (+). Removing the switched power line from the ignition coil's (+ or #15) terminal removes the power from the ECU (i.e. injectors will be off) and the fuel pump's relay (i.e. no fuel being pumped).
• Don't: disconnect the white wire from the ignition coil (-). The engine speed signal to the ECU (white wire from the ignition coil's #1 terminal, or "-") does not need to be removed, as the ECU will be powered off, and the actual input line won't be generating a signal anyway.
• Don't: disconnect the double relay connector. The switched +12 V line to the fuel pump will have been disconnected by removing the other black wire already.
I'm ok with the electrical bits, it's always the mechanical part where I often head into unknown territory, hence this post.
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'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)
Decode your M-Plate |
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Randy in Maine
Samba Member
Joined: August 03, 2003
Posts: 34890
Location: The Beach
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| Posted: Mon Dec 04, 2017 12:16 pm Post subject: Re: Compression test checklist |
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I just put a brick on the accelerator pedal to keep the throttle wide open.
I also do "the squirt of oil in the spark plug hole" as the last thing to do and note any changes in the numbers.
A warm engine helps with more accurate numbers unless you can't easily get it running. |
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lil-jinx
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Joined: August 14, 2013
Posts: 1109
Location: New Brunswick,Canada
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furgo
Samba Member
Joined: September 06, 2016
Posts: 944
Location: Southern Germany
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| Posted: Mon Dec 04, 2017 12:26 pm Post subject: Re: Compression test checklist |
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| Randy in Maine wrote: |
| I just put a brick on the accelerator pedal to keep the throttle wide open. |
I had also thought of this, but didn't bring myself to admit it 
I just thought there might be an established way of clamping the throttle open directly.
| Randy in Maine wrote: |
I also do "the squirt of oil in the spark plug hole" as the last thing to do and note any changes in the numbers.
A warm engine helps with more accurate numbers unless you can't easily get it running. |
Yeah, that's unfortunately my issue, otherwise I'd do it with a warm engine. In this case, I should probably run the compression test twice:
- Once dry
- Once with the squirt of oil in each plug hole
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'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)
Decode your M-Plate |
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Randy in Maine
Samba Member
Joined: August 03, 2003
Posts: 34890
Location: The Beach
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sodbuster
Samba Member
Joined: August 08, 2004
Posts: 1086
Location: wherever my baywindow takes me.
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| Posted: Mon Dec 04, 2017 2:54 pm Post subject: Re: Compression test checklist |
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| Randy in Maine wrote: |
I just put a brick on the accelerator pedal to keep the throttle wide open.
I also do "the squirt of oil in the spark plug hole" as the last thing to do and note any changes in the numbers.
A warm engine helps with more accurate numbers unless you can't easily get it running. |
I've only used squirting oil in the cylinder when a low compression reading is found. It helps to narrow down the source of the low compression.
Squirt some oil in the low cylinder and test for compression again. If the figure comes up or increases then it is most likely worn piston rings. No increase in compression indicates a problem with the valves.
If I really want to know for sure I do a cylinder leak down test as well as a compression test. Those two tests in conjunction with each other will usually reveal all. |
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furgo
Samba Member
Joined: September 06, 2016
Posts: 944
Location: Southern Germany
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| Posted: Fri Dec 15, 2017 1:51 pm Post subject: Re: Compression test checklist |
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I finished the compression testing earlier on today. Here's what came out of it.
Test conditions
• Motor was cold [1]
• Battery 12.48 V [2]
• Remote starter switch
• 0-300 PSI gauge
• All spark plugs off
• Throttle wide open
• AFM removed [3]
• Double relay connector (vehicle harness) disconnected [4]
• +12 V switched power removed from terminal #15 (+) of the ignition coil (i.e. the black wire)
[1] As mentioned before, the motor dies after a couple of minutes, hence I can't really warm it up. Also one of the reasons why I'm doing the compression test at all.
[2] Battery was not fully charged. I might repeat the test tomorrow, but I'm not sure if the extra voltage will affect the readings at all
[3] Not strictly necessary I guess. I just happened to remove it to in turn ease the removal of spark plugs #1 and #2.
[4] I double checked the wiring diagrams, and as ratwell mentioned, it indeed needs to be disconnected so that the fuel pump is not activated while cranking.
Results
| Code: |
Cylinder Compression (PSI) Compression (bar) Relative to max. reading Relative to max. spec
======== ================= ================= ======================== =====================
1 110 7,5 84,6 % 81,5 %
2 130 8,9 100,0 % 96,3 %
3 112 7,7 86,2 % 83,0 %
4 125 8,6 96,2 % 92,6 %
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Relative to max. reading: percentage of compression relative to the max reading (130 PSI on cylinder #2)
Relative to max. spec: percentage of compression relative to the max spec value (135 PSI for a 2.0 l engine)
Conclusions
From ratwell's "When to rebuild" page, I gather:
• Compression spec max: 135 PSI
• Compression spec min: 85 PSI (no lower than 71 PSI)
• Max. difference (highest - lowest reading): 28 PSI
That's for a 1.8/2.0l engine.
In my case:
• Compression reading max: 130 PSI
• Compression spec min: 110 PSI
• Max. difference (highest - lowest reading): 20 PSI
From this I conclude:
• I've got compression on all four cylinders (yay)
• All compression values are within spec (excellent)
• Cylinders 1, 3 seem to have less compression as a pair than 2, 4
Other things I learned
If you're going to do something, do it properly (well, at least to the best of your abilities). I found using a remote starter switch allowed for a more controlled measurement: you don't have to run from front to back, and you can see the readings as you are cranking.
These are cheap and simple devices: a switch, cable and alligator clips. I could have bought one, but since I already had nearly all pieces to build one, that's what I did. A bike grip makes for a nice holder (I read this tip from someone else at The Samba), so here's what my homemade remote starter ended up looking like:
As the clips are pluggable, I ended up replacing one of them with a flat 6.3 mm female connector, as it then makes a better contact with the starter's #50 terminal.
Looking at the circuit diagrams, and if you've got a FI bus, you can spare yourself crawling under the bus to connect the remote ignition switch to the starter solenoid. Instead, you can simply unplug the left connector from the double relay (the one from the vehicle harness) and connect your remote starter to terminal 86a. That is, one end of the remote starter to the battery, and the other end to terminal 86a of the unplugged double relay (left) connector. I only realized this later and did not try it though, so do double-check the wiring yourself before attempting this.
A 1 ft piece of hose works wonders to initially hand tighten spark plugs #2 and #4.
My spark plugs were pretty much covered in carbon and wet. I'm not sure there's much to read into that, as they could have become like that from the short runs when I was trying to let the engine not die. On the other hand, it's a pretty thick and hard carbon layer, so I doubt it comes just from that time. It might then mean that the engine was running rich and the spark plugs have got the wrong heat range (they have).
Even when not present, POs are always in for a laugh (or a shock). Here's what I found underneath the engine tin (on top of the cylinder head, that is) when I removed spark plug #2:
It must have been there since the last time someone (else) had replaced the spark plugs or done a compression test. When that was is anyone's guess...
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'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)
Decode your M-Plate
Last edited by furgo on Fri Dec 15, 2017 5:53 pm; edited 1 time in total |
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 12728
Location: on a bike ride somewhere
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| Posted: Fri Dec 15, 2017 1:54 pm Post subject: Re: Compression test checklist |
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That looks like my vintage Proto socket
Are your plugs wet with oil or fuel?
I have some “stupid questions” to ask once you figure out your issues, so good luck!
Robbie
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furgo
Samba Member
Joined: September 06, 2016
Posts: 944
Location: Southern Germany
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| Posted: Fri Dec 15, 2017 2:16 pm Post subject: Re: Compression test checklist |
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| asiab3 wrote: |
| That looks like my vintage Proto socket |
That's clearly an engraved "A", not an "R". Not yours  .
| asiab3 wrote: |
| Are your plugs wet with oil or fuel? |
I'm not 100% sure. But given the fact that if it were fuel the whole interior of the bus would be stinking by now, and that the fluid did not evaporate after a while, I'd say it's oil.
Also to add to that, I managed to break the torque on spark plug #2 by hand (wtf). The other spark plugs weren't loose to that extreme, but still not very tight.
I'm struggling a bit with the forensics here: on the one hand the last person to tighten the spark plugs might have been ultra careful with torque (or my grandma) and also used oil as an anti-seize of sorts; on the other hand, it looks like the fluid is only on the lower third of the thread (the electrode end), so it might be coming from the cylinder.
| asiab3 wrote: |
| I have some “stupid questions” to ask once you figure out your issues, so good luck! |
Thanks.
If these are something I can answer, ask away. I'm usually the one asking the stupid questions, so it might be a welcome change
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'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)
Decode your M-Plate |
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