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Old 19th January 2013, 14:35   #1
AseanAero
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Compression Test Results

Delving into Taffy's M5 oil loss problem on GA25331 we took a compression test on his engine and got the following results

GA25331 is a UK spec high compression engine. Comp numbers with the engine warm (standing for 1.5hrs while we had our usual long lunch) and throttle closed (I forgot to open the throttle)

Cyls 1 to 6 - 180, 180, 180, 180, 180, 190

Then we took the compression on GA25324 (my M5) which has low compression tropical version 9.2:1

Cyls 1 to 6 - 175, 170, 165, 170, 170, 175

What's a normal compression reading for a normal and low compression version of the S38B36 ?

It looks like GA25331s oil leak is a combination of a poor sealing oil filler cap and dipstick and a stripped acorn nut on the cam cover
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1990 E34 M5 S38B36 GA25324 Schwarz II, 57,000kms, Tropical version, full Nappa leather interior, Superchip , staggered M-Par 235/40 ZR18 , 255/35 ZR18 Toyo T1-Sport. Mods : exhaust system - packing removed from centre + rear mufflers, Restoration items: Reinstall the SLS, interior tidy up, Bodywork : repair small dents and re-coat in the original color (done - February 2014)
GA25324

1991 E34 M5 S38B36 GA25388 Schwarz II. Non running 1/2 share parts car / track car project with BlueBiTurbo (Taffy)
GA25388

1995 E34 530i 5 speed Daytona Violet 170,000kms , TS staggered set up, M-Tech steering wheel mods planned: ENGINE: M60B40 (purchased), chip EXHAUST : 110mm big bore front Y pipe (done), centre muffler gutted (no packing), used M5 rear muffler (done) BRAKES: slotted + drilled discs TYRES: 235/45 ZR17 , 255/40 ZR17 Toyo T1R - my daily driver and a car that I can play with and modify. Long term dream - full E39 M5 drivetrain. Will be repainted Sebring Grey with black lower trim and full M5 bodykit.
530i 5 speed project, daily driver

1990 E34 M5 S38B36 GA25349 Engine only , the location of the rest of the M5 is a mystery

Other Projects : 1946 CJ2A Willys Jeep, 1980 Jeep J20 pick up (JeepZilla)

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Old 19th January 2013, 15:56   #2
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Finally found what we think is the cause of the oil leak ! YEAH !
Gotta order oil cap from the internet and wait 10 days


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Old 19th January 2013, 16:31   #3
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I changed the oil cap on mine when investigating oil consumption. Made no difference.

The system should be negative pressure there, it could be there is some splash (what I thought before buying a cap) but it was a red herring in my case,

Incidentally I got my cap from the BMW dealer... Stupidly cheap price, as it sometimes the case with BMW parts.
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Old 19th January 2013, 16:57   #4
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Mine was definitely leaking from there.
I wiped the surrounding area clean yesterday, it is oily again today after 6500 rpm run.
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Old 19th January 2013, 17:02   #5
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I hope it is that... Would be a great, easy, fix.

When I remove my cap (quite often for top ups) there is oil presence underneath the sealing faces.
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Old 19th January 2013, 17:08   #6
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My fingers are crossed
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Old 19th January 2013, 20:17   #7
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Compression Test Results

It wouldn't just be damp there at the amount of oil loss you're experiencing.

Pull the intake elbow off the plenum. Is it oily inside the plenum?

Last edited by Nikosx; 19th January 2013 at 20:18.
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Old 20th January 2013, 03:04   #8
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There aren't any real numbers that you should be striving for, since all compression tests are different. Density Altitude plays a huge effect in compression testing. Consistency across cylinders is more important. I usually say each cylinder within 5-10%. The testing gauge is also important, it's good to use an Aviation Grade tester vs the one you get at the tool store, as many sold at the tool stores aren't built to the same, if any, standards.

Leakdown tests are much better for determining engine health though.

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Old 20th January 2013, 17:50   #9
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Quote:
Originally Posted by Nikosx View Post
It wouldn't just be damp there at the amount of oil loss you're experiencing.

Pull the intake elbow off the plenum. Is it oily inside the plenum?
No significant quantities of oil in the plenum, just a very slight thin film of oil
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Old 21st January 2013, 00:50   #10
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Turns out that I DO HAVE a new spare oil filler cap !
Just installed it today. It is VERY tight seal.
I will drive it hard tomorrow and see the difference.
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