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JerrietheBus Samba Member
Joined: August 16, 2020 Posts: 73 Location: Eugene, OR
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Posted: Sun Jul 25, 2021 3:21 pm Post subject: Diagnosing compression issues in '79 Bay |
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Hello all!
I recently did a compression test on my 79 Bay Window after noticing some performance issues and almost breaking down. 1st and 3rd cylinders were only around 50-60 psi and the 2nd and 4th were fine (150ish). So I've since been working away at diagnosing. I've got the engine dropped and stripped, and took the heads off this morning.
I didn't see anything obviously wrong with the heads or valves, but I don't want to go too much further without a second opinion, since everything under the heads is new territory for me. Am I missing an obvious issue? What should my next steps be?
Left Side:
Valves. They all look good to me.
Cylinder 1 (This one was at 53 psi)
Right Side:
Cylinder 3 (65 psi)
Thank you so much for whatever help you can offer! |
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timvw7476 Samba Member
Joined: June 03, 2013 Posts: 2180 Location: seattle
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Posted: Sun Jul 25, 2021 4:07 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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you are, or were running very rich (too much gasoline)
my guess is the 1 & 3 paid the price. The engine is naturally canted towards the transaxle, so excess fluid in the intake tract goes straight to those two cylinders.
I think gas washed the 1 & 3 cylinder walls dry. fwiw. |
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SGKent Samba Member
Joined: October 30, 2007 Posts: 41031 Location: Citrus Heights CA (Near Sacramento)
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Posted: Sun Jul 25, 2021 4:11 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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doesn't look right.
That said, since you are so far in now I'd redo the rings, bearings, and heads. You might ask Len Hoffman if he would consider rebuilding those. _________________ “Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin |
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skills@eurocarsplus Samba Peckerhead
Joined: January 01, 2007 Posts: 16802 Location: sticksville, ct.
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Posted: Sun Jul 25, 2021 4:19 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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your bores look like mirrors.
that's not good. _________________
gprudenciop wrote: |
my reason for switching to subaru is my german car was turning chinese so i said fuck it and went japanese....... |
Jake Raby wrote: |
Thanks for the correction. I used to be a nice guy, then I ruined it by exposing myself to the public. |
Brian wrote: |
Also the fact that people are agreeing with Skills, it's a turn of events for samba history |
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aeromech Samba Member
Joined: January 24, 2006 Posts: 16922 Location: San Diego, California
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Posted: Sun Jul 25, 2021 7:13 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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Take the heads. Turn them so the valve heads are vertical. Squirt some fluid onto the valves and fill it up. Use anything like acetone, etc. if the valves are leaking the fluid will show on the bottom side _________________ Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
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DC9/MD80
BAe146
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VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
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Capable of leaping tall buildings in a single bound |
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skills@eurocarsplus Samba Peckerhead
Joined: January 01, 2007 Posts: 16802 Location: sticksville, ct.
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Posted: Sun Jul 25, 2021 7:33 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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aeromech wrote: |
Take the heads. Turn them so the valve heads are vertical. Squirt some fluid onto the valves and fill it up. Use anything like acetone, etc. if the valves are leaking the fluid will show on the bottom side |
to add to that, you want something THIN like a solvent/carb clean etc.
i take a air hose to the ports and look for bubbles too _________________
gprudenciop wrote: |
my reason for switching to subaru is my german car was turning chinese so i said fuck it and went japanese....... |
Jake Raby wrote: |
Thanks for the correction. I used to be a nice guy, then I ruined it by exposing myself to the public. |
Brian wrote: |
Also the fact that people are agreeing with Skills, it's a turn of events for samba history |
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JerrietheBus Samba Member
Joined: August 16, 2020 Posts: 73 Location: Eugene, OR
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Posted: Sun Jul 25, 2021 9:08 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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timvw7476 wrote: |
you are, or were running very rich (too much gasoline)
my guess is the 1 & 3 paid the price. The engine is naturally canted towards the transaxle, so excess fluid in the intake tract goes straight to those two cylinders.
I think gas washed the 1 & 3 cylinder walls dry. fwiw. |
That makes sense. Would this have been a long term thing or something recent? I had fuel consumption issues about a year ago, would that be related? |
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timvw7476 Samba Member
Joined: June 03, 2013 Posts: 2180 Location: seattle
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Posted: Sun Jul 25, 2021 9:25 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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JerrietheBus wrote: |
timvw7476 wrote: |
you are, or were running very rich (too much gasoline)
my guess is the 1 & 3 paid the price. The engine is naturally canted towards the transaxle, so excess fluid in the intake tract goes straight to those two cylinders.
I think gas washed the 1 & 3 cylinder walls dry. fwiw. |
That makes sense. Would this have been a long term thing or something recent? I had fuel consumption issues about a year ago, would that be related? |
I'm a dual carb driving bus operator, there's a fuel pressure regulator on the front tin, threaded to the sheetmetal, and a pressure tap on the cylinder 3/4 metal line between those two cylinders to check for the 36 pounds -ish required pressure to run AFC Bosch FI system. I've run & repaired those buses, but never lived with them year in/ year out. That's the rub, a set of rings & honing the glazed cylinders are cheap enough, but why the fuel is flowing out of those injectors at that quantity is the real question that must be solved. You actually have two issues, the poor sealing of those rings & the excess fueling that caused it. There may be others, as others mentioned the valves. My view isn't as sharp, but I'd do a fluid check mentioned above to see if they truly seal. Good Luck & enjoy yourself, this is supposed to be somewhat fun when all is said & done.
>>edit: as far as 'long term', well over-fueling can cause oil washing off cylinders, which directly effects the quality of seal between piston rings & the walls, also over time oil dilution occurs, you'd smell gasoline mingled with the crankcase oil at oil change intervals. Maybe an increase in oil level in the case is possible as gas blends with the lubricant.<< |
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airschooled Air-Schooled
Joined: April 04, 2012 Posts: 12687 Location: on a bike ride somewhere
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Posted: Sun Jul 25, 2021 9:31 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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Bring the parts in question to the Lucky Lab Brewpub on Hawthorne tomorrow evening and a dozen folks can weigh in on it.
See you there
Robbie _________________ Learn how your vintage VW works. And why it doesn't!
One-on-one tech help for your Volkswagen:
www.airschooled.com |
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JerrietheBus Samba Member
Joined: August 16, 2020 Posts: 73 Location: Eugene, OR
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Posted: Mon Jul 26, 2021 7:38 am Post subject: Re: Diagnosing compression issues in '79 Bay |
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airschooled wrote: |
Bring the parts in question to the Lucky Lab Brewpub on Hawthorne tomorrow evening and a dozen folks can weigh in on it.
See you there
Robbie |
Lucky Lab in Portland?! We could do that. What time? |
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Mon Jul 26, 2021 8:27 am Post subject: Re: Diagnosing compression issues in '79 Bay |
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Everything thats already been said....and.....
You have oil leak/fuel staining on the heads under each cylinder. And....you have a few blackish rings on the cylinder seating areas versus one color all the way around.
1st.....were you using cylinder sealing rings between heads and cylinders?
2nd.....get some sections of steel conduit, your head nuts and washers. Clamp all four cylinders down without heads....each side at a time. Put a quality steel rule across the tops of two cylinders at a time. Look for gaps between steel rule and cylinder sealing areas right at the closest point between each pair of cylinders.
Betting you were leaking compression at the head to cylinder joint as well as rings wiped out. Ray |
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skills@eurocarsplus Samba Peckerhead
Joined: January 01, 2007 Posts: 16802 Location: sticksville, ct.
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Posted: Mon Jul 26, 2021 9:47 am Post subject: Re: Diagnosing compression issues in '79 Bay |
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at this point you need a top end overhaul.
what you posted as "right side" and "cylinder 3" has signs of being washed out represented by the clean spots on the piston.
if you're lucky you may get away with a hone and re-ring and since you're there get the heads gone thru.
no matter what i am betting you need exhaust valve guides, they always do. but i'd just do a top end overhaul. it's the only way you're going to restore compression.
if you did a leak down test before tear down it could have helped take some of they mystery out of this but either way it's top end time assuming all else is well with it _________________
gprudenciop wrote: |
my reason for switching to subaru is my german car was turning chinese so i said fuck it and went japanese....... |
Jake Raby wrote: |
Thanks for the correction. I used to be a nice guy, then I ruined it by exposing myself to the public. |
Brian wrote: |
Also the fact that people are agreeing with Skills, it's a turn of events for samba history |
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SGKent Samba Member
Joined: October 30, 2007 Posts: 41031 Location: Citrus Heights CA (Near Sacramento)
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Posted: Mon Jul 26, 2021 11:09 am Post subject: Re: Diagnosing compression issues in '79 Bay |
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again, this does not look right. oil and fuel is washing away the carbon & it looks like there is damage to the seat, or seat area. That seat may be loose.
_________________ “Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin |
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JerrietheBus Samba Member
Joined: August 16, 2020 Posts: 73 Location: Eugene, OR
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Posted: Mon Jul 26, 2021 5:05 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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Thank you everyone! A top end rebuild was about what I was expecting, I was just trying to see what was specifically wrong! I really appreciate all the help. Someone said to go to the lucky lab in Portland so I’m loading it in a truck and bringing it there for some more work, I really appreciate all the help |
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airschooled Air-Schooled
Joined: April 04, 2012 Posts: 12687 Location: on a bike ride somewhere
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Posted: Mon Jul 26, 2021 6:03 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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Xevin wrote: |
Robbie (airschooled/asia3b) from San Diego and Brian (Bay forum moderator)
in town. Swing by the Hawthorne Lucky Lab tonight if you can. 7ish |
_________________ Learn how your vintage VW works. And why it doesn't!
One-on-one tech help for your Volkswagen:
www.airschooled.com |
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Wildthings Samba Member
Joined: March 13, 2005 Posts: 50255
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Posted: Tue Jul 27, 2021 11:04 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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Get a valve spring compressor and remove the valves from the heads and I suspect your problem will be obvious enough. Your heads are aftermarket and I would bet the springs, valves, and other components are less than high quality which has led to low seat pressure and thus burnt valves and seats. |
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airschooled Air-Schooled
Joined: April 04, 2012 Posts: 12687 Location: on a bike ride somewhere
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Posted: Wed Jul 28, 2021 12:51 pm Post subject: Re: Diagnosing compression issues in '79 Bay |
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A few takeaways from my quick look Monday:
- All four lifters were deflated on the offending cylinders.
- Several exhaust valves are receding. Not sure if info the seat, or seat into head.
- The cam lobes do not look bad enough to warrant replacement
- Lifters are perfectly flat and mirror-finished.
Recommendations:
- Check cylinders for leaks by filling chamber with soapy water or solvent. Look for leaks in the intake and exhaust ports. Surface tension prevents pure water from working for this test. This may give you answers, but the heads need work anyway…
- Install one head/rockers and read valve lift with a dial micrometer on all four valves. Bentley lists a max deviation; this will confirm the camshaft is not at fault. (This is also my default test any time an otherwise healthy engine has low compression on two opposing cylinders- a worn cam lobe usually shows symmetrical issues.)
What else did we talk about? Xevin brought out a pitcher at this point…
Robbie _________________ Learn how your vintage VW works. And why it doesn't!
One-on-one tech help for your Volkswagen:
www.airschooled.com |
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JerrietheBus Samba Member
Joined: August 16, 2020 Posts: 73 Location: Eugene, OR
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Posted: Tue Aug 03, 2021 7:16 am Post subject: Re: Diagnosing compression issues in '79 Bay |
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airschooled wrote: |
A few takeaways from my quick look Monday:
- All four lifters were deflated on the offending cylinders.
- Several exhaust valves are receding. Not sure if info the seat, or seat into head.
- The cam lobes do not look bad enough to warrant replacement
- Lifters are perfectly flat and mirror-finished.
Recommendations:
- Check cylinders for leaks by filling chamber with soapy water or solvent. Look for leaks in the intake and exhaust ports. Surface tension prevents pure water from working for this test. This may give you answers, but the heads need work anyway…
- Install one head/rockers and read valve lift with a dial micrometer on all four valves. Bentley lists a max deviation; this will confirm the camshaft is not at fault. (This is also my default test any time an otherwise healthy engine has low compression on two opposing cylinders- a worn cam lobe usually shows symmetrical issues.)
What else did we talk about? Xevin brought out a pitcher at this point…
Robbie |
Thank you so much for your help the other night! We did the leakage test and found leak in the third cylinder. Do you have a machine shop recommendation in Portland, because I think that’s our next step |
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SGKent Samba Member
Joined: October 30, 2007 Posts: 41031 Location: Citrus Heights CA (Near Sacramento)
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Posted: Tue Aug 03, 2021 7:33 am Post subject: Re: Diagnosing compression issues in '79 Bay |
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that one valve seat shows signs of failure if the photos are correct. To me it looks like the staked areas have cracked and eroded away. Leakage is the secondary issue. All seats should be replaced and not many shops are equipped to do that on air cooled heads, Adrian in San Diego, and Len in GA are the only ones I know who will do that on T4 heads - and Len won't touch used VW bus heads because once cleaned up one usually find cracks. RIMCO in Santa Ana used to do that but they have been sold so many times I don't know if they have the tooling and skills anymore - or even interest in it. _________________ “Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin |
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