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Abscate Samba Member
Joined: October 05, 2014 Posts: 22668 Location: NYC/Upstate/ROW
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Posted: Wed May 04, 2016 6:53 am Post subject: Checking compression with engine out - (No Bay Window Content) |
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I have an engine for sale which I would like to test and document compression with the engine out, rather than installing.
Whats the best way to do this?
I have motors, sockets, tools etc and could easily spin it with the flywheel nut and a motor, but am interested in what rpm a starter typically turns over at. Im guessing its low, like 50-100 rpm at best.
Anyone give guidance here?
Or, could I get a reasonable test of compression with using a lawnmower type strap on the generator pulley?? _________________ .ssS! |
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Wildthings Samba Member
Joined: March 13, 2005 Posts: 50351
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Posted: Wed May 04, 2016 7:32 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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You need to have a bellhousing you can bolt up to the engine if you want to generate compression numbers, plus you would have to connect up a starter, battery, and rig up the ignition. A leakdown test can be done without spinning the engine though and in many ways is preferable.
If you just rotate the engine a couple of turns by hand you can learn a lot but will get no numbers. |
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skills@eurocarsplus Samba Peckerhead
Joined: January 01, 2007 Posts: 16879 Location: sticksville, ct.
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Posted: Wed May 04, 2016 7:52 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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typical starters are between 250-350 rpm if my memory serves me _________________
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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Abscate Samba Member
Joined: October 05, 2014 Posts: 22668 Location: NYC/Upstate/ROW
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Posted: Wed May 04, 2016 8:00 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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skills@eurocarsplus wrote: |
typical starters are between 250-350 rpm if my memory serves me |
Is that starter rpm skills? That would make engine rpm something like 9/109 or 25-30 rom under crank... _________________ .ssS! |
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aeromech Samba Member
Joined: January 24, 2006 Posts: 16971 Location: San Diego, California
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Posted: Wed May 04, 2016 8:05 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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You're going to need a dc motor to turn that engine. I doubt something ac has enough start up power for the job. Plus I think just using a regular starter, 12V battery, and some kind of ring to mount the starter to the flywheel would simply work the best. As stated, a differential compression test could be done without needing to spin the engine. You could never pull the engine through with a rope like you do your lawnmower. Well, maybe Arnold could have done at one time. _________________ 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
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound |
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skills@eurocarsplus Samba Peckerhead
Joined: January 01, 2007 Posts: 16879 Location: sticksville, ct.
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Posted: Wed May 04, 2016 8:12 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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Abscate wrote: |
skills@eurocarsplus wrote: |
typical starters are between 250-350 rpm if my memory serves me |
Is that starter rpm skills? That would make engine rpm something like 9/109 or 25-30 rom under crank... |
that's just what I know from service info...not sure of the ratio per se _________________
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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Abscate Samba Member
Joined: October 05, 2014 Posts: 22668 Location: NYC/Upstate/ROW
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Posted: Wed May 04, 2016 8:34 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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aeromech wrote: |
You're going to need a dc motor to turn that engine. I doubt something ac has enough start up power for the job. Plus I think just using a regular starter, 12V battery, and some kind of ring to mount the starter to the flywheel would simply work the best. As stated, a differential compression test could be done without needing to spin the engine. You could never pull the engine through with a rope like you do your lawnmower. Well, maybe Arnold could have done at one time. |
I grew up watching my mother start her Beetle with a leather purse strap on the generator pulley whenever she left the lights on. Years later, you could buy that as an accessory from the JCW catalog.
With the plugs out for a comp test, I think a small motor would do it. I have big motors too, though, _________________ .ssS! |
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ROCKOROD71 Samba Member
Joined: January 18, 2012 Posts: 2770 Location: Boston, MA
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Posted: Wed May 04, 2016 8:36 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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aeromech wrote: |
You're going to need a dc motor to turn that engine. I doubt something ac has enough start up power for the job. Plus I think just using a regular starter, 12V battery, and some kind of ring to mount the starter to the flywheel would simply work the best. As stated, a differential compression test could be done without needing to spin the engine. You could never pull the engine through with a rope like you do your lawnmower. Well, maybe Arnold could have done at one time. |
i dunno....
Link
_________________ 1971 STD BEETLE- DD-1st car, 1st love. keepin' it stock! 1600DP, Solex 34-3 Mexi Bosch SVDA Dist NOW w/POINTS
1977 WESTY "KrustyKamper" 2L FI
79SuperVert wrote: |
30 years from now, the next guy may not want your girlfriend, but he may want your classic car, depending on how nice you were to it. |
asiab3 wrote: |
Careful guys, a petulant child can grow up to be president these days. |
**winter drivers: no survivors!**rust warrior**#keepbodyshopsbusy** |
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aeromech Samba Member
Joined: January 24, 2006 Posts: 16971 Location: San Diego, California
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Posted: Wed May 04, 2016 8:42 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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Okay, but why don't you try it for us and let us all know how it goes? It might just work. I've been wrong before. _________________ 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
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound |
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SGKent Samba Member
Joined: October 30, 2007 Posts: 41031 Location: Citrus Heights CA (Near Sacramento)
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Posted: Wed May 04, 2016 8:46 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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you need a consistent RPM to get even compression. You can use compressed air at TDC to check rings and valves for leakage. That is just as good. _________________ “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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ROCKOROD71 Samba Member
Joined: January 18, 2012 Posts: 2770 Location: Boston, MA
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Posted: Wed May 04, 2016 9:10 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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aeromech wrote: |
Okay, but why don't you try it for us and let us all know how it goes? It might just work. I've been wrong before. |
haha, not today good sir! I like my engines where they are, in the cars! But if you wanted to get real ghetto you could strap it to a pallet, hook up a battery and give it a pull. I dunno...was more of a tongue in cheek response. I mean, no one's gonna pay real money for a used engine they can't see run, so Steve's suggestion of compressed air test is just as good as any and doesn't require nearly as much effort as building a test stand or jury-rigging it somehow. _________________ 1971 STD BEETLE- DD-1st car, 1st love. keepin' it stock! 1600DP, Solex 34-3 Mexi Bosch SVDA Dist NOW w/POINTS
1977 WESTY "KrustyKamper" 2L FI
79SuperVert wrote: |
30 years from now, the next guy may not want your girlfriend, but he may want your classic car, depending on how nice you were to it. |
asiab3 wrote: |
Careful guys, a petulant child can grow up to be president these days. |
**winter drivers: no survivors!**rust warrior**#keepbodyshopsbusy** |
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Tcash Samba Member
Joined: July 20, 2011 Posts: 12844 Location: San Jose, California, USA
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Posted: Wed May 04, 2016 10:17 am Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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You need a minimum of 120 engine rpm for compression testing.
Good luck
Tcash |
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Abscate Samba Member
Joined: October 05, 2014 Posts: 22668 Location: NYC/Upstate/ROW
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Posted: Wed May 04, 2016 3:19 pm Post subject: Re: Checking compression with engine out - (No Bay Window Content) |
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Thanks TCash - on the spot again, as usual.
I can do that easily with available parts.. _________________ .ssS! |
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