Cylinder Compression Specs for CBAA

GraniteRooster · Dec 22, 2010

Anyone know Cylinder Compression Specs for CBAA??

Hi all - need some help. Can someone with access to the right tech manual please post compression specs for the CBAA engine?

I know nominal 16.5:1. (Edit)

Please fill in:

New Engine - high limit
New Engine - low limit

Difference between cylinders (max)
Wear limit (low)

Thanks a lot.

740GLE · Dec 22, 2010

BTW, CJAA would be nice to know as well

GraniteRooster · Dec 22, 2010

Perhaps CJAA is what I'm looking for as well. CBAA is Euro I guess? Mine is 2010 TDI JSW sold in US - looks like CJAA is what I'm after.

Sorry for the confusion....

bsalbrig · Dec 25, 2010

It would be in the 500-550 psi range around 40000 just like the other diesels. On my first alh motor I remember the bad cylinders being around 50psi less than the good ones because I bent some rods. Why do you want to know are you going to check them?

DanG144 · Dec 25, 2010

CBEA and CJAA
New 25 to 31 bar (363-450 psig)
Wear limit 19 bar (276 psig)
max difference cylinder to cylinder 5 bar (73 psig)

Are the Bentley limits. These are pretty wide and generous limits, in my (not so valuable) opinion.

They are exactly the same as for a BRM, BEW, and ALH.

GraniteRooster · Dec 25, 2010

DanG144 said:
CBEA and CJAA
New 25 to 31 bar (363-450 psig)
Wear limit 19 bar (276 psig)
max difference cylinder to cylinder 5 bar (73 psig)

Are the Bentley limits. These are pretty wide and generous limits, in my (not so valuable) opinion.

They are exactly the same as for a BRM and that is the same as the BEW, if I recall correctly.

Thanks DanG - those are indeed generous limits. I am sure the engine runs fine at 276 psi, but that is a far cry from 400+ new.

I am planning to have my engine compression tested following my recent history of water-rich starts. Thanks for providing independent source of info

DanG144 · Dec 25, 2010

Good luck. I would do the same.

The Bentley still has you warming the engine, disabling the injectors, then pulling the glow plugs to check compression.

I guess the pressure sensors on the glow plugs are not accurate enough to be used at the relatively low pressures of the the compression check. They do normally sense combustion pressures, which are much higher. It is also best to spin the engine as fast as possible without starting it. It is much easier to spin with the glow plugs pulled so pressure cannot build up in the non-tested cylinders.

Either that or they did not think of it yet.

bruce846 · Dec 26, 2010

How can these numbers be so high, given the 16.5 : 1 compression ratio for the CJAA given by VWoA. I thought the earlier diesels were in the 19 to 20 range?

DanG144 · Dec 26, 2010

I rarely see one below 450 psig on the earlier engines, ALH, or PD. Though I have seen posts of lower than that here on the site. If it starts going much over 490 psig, then I wonder about deposits, WVO use, etc.

I edited my earlier post on the numbers - these are all the same ALH, BEW, BRM, CBEA,
CJAA.

Ski in NC · Dec 26, 2010

If CR is 16.5:1, then compression will be lower than an engine with a CR of 19:1. So if you do a compression test on the newer engine, don't expect to see 450-500 regardless of what the spec says. To look for damage from the hydrolock, you want to look for variations between readings. My gut feel is that if individual cylinders vary more than 5% on a new-ish engine, then something is up. That's around 20-25 psi.

DanG144 · Dec 26, 2010

I have seen no numbers from a CBEA or CJAA test.
The numbers are from the Bentley manual, and they can make a mistake.

DanG144 · Dec 26, 2010

If I did my math right, (never mind, my math was faulty.)

I also think that it would take less than 5 bar (73 psi) difference to be significant. But good luck trying to make that point with VW.

GraniteRooster · Dec 26, 2010

Ski in NC said:
My gut feel is that if individual cylinders vary more than 5% on a new-ish engine, then something is up. That's around 20-25 psi.

DanG144 said:
If I did my math right, 16.5 to 1 should give about 225 psig, and 19 to 1 about 260 psig.
I had noted the apparent discrepancy in the earlier engines numbers, and wondered about the very high readings we normally get on these engines.

I also think that it would take less than 5 bar (73 psi) difference to be significant. But good luck trying to make that point with VW.

I agree with both of you that individual cylinder variance should be low - much less than the 73psi acceptable spec. Unfortunately in this situation, a LOT of permanent deformation might be accomodated in the rods, etc. before the engine falls out of spec.

I am hoping for the best and expecting the worst - including the possible outcome that engine parts seem obviously damaged but are still within spec. That is not going to be a fun conversation to have...

BTW - good light background reading on Compression Ratio and how CR relates to cylinder pressure tests can be found here for those interested:

http://en.wikipedia.org/wiki/Compression_ratio

There are a variety of mechanical and thermodynamic factors that influence now an engine will develop pressure and this starts to talk about some of them.

DanG144 · Dec 26, 2010

Thanks for the followup, I deleted my worthless numbers from my own calculations in a post above..

Ski in NC · Dec 26, 2010

Dan- I saw those numbers- To calculate compression psi readings for an engine test, you can't use the pv=nrt, as that assumes isothermic conditions. The process is more closely modeled as adiabatic or isentropic, which has the temperature rising with the pressure on compression. If you were to calculate adiabitic final pressure, it would be way higher than we see in a test. In real life, a good bit of the heat is sucked off by the relatively cooler surrounding metal.

Eric

bsalbrig · Dec 29, 2010

Could you post the numbers you get when you get the car tested. I am curious as I am sure other members are to see if there is any damage from the condensate .

GraniteRooster · Dec 30, 2010

Yep

I will post results after the test - it will be a week, maybe two before I have a chance to do this.

Happy Motoring

740GLE · Dec 30, 2010

you having the dealer do this? are you looking for warranty work out of it? or are you just looking to sleep better knowing no damage was done.

bsalbrig · Jan 19, 2011

GraniteRooster said:
I will post results after the test - it will be a week, maybe two before I have a chance to do this.

Happy Motoring

Did you have your car tested?

GraniteRooster · Jan 22, 2011

Will report back in a couple more weeks - I've been busy with other things....

GraniteRooster · Mar 4, 2011

Results

Car was compression tested yesterday, values as follows:

Cyl. 1 - 30.7 bar
Cyl. 2 - 30.7 bar
Cyl. 3 - 29.8 bar

Cyl. 4 - 30.8 bar

Factory Limits:
New Upper - 31 bar
New Lower - 25 bar
Wear Lower - 19 bar

I would have felt better if Cylinder 3 was exactly the same as the others. But they are all fairly close.

vwlogue · Mar 4, 2011

Could you share more details about those water-rich starts.. bad fuel? How did you find out?

bsalbrig · Mar 4, 2011

GraniteRooster said:
Car was compression tested yesterday, values as follows:

Cyl. 1 - 30.7 bar
Cyl. 2 - 30.7 bar
Cyl. 3 - 29.8 bar
Cyl. 4 - 30.8 bar

Factory Limits:
New Upper - 31 bar
New Lower - 25 bar
Wear Lower - 19 bar

I would have felt better if Cylinder 3 was exactly the same as the others. But they are all fairly close.

Out of curiosity have you done a vag-com check of compression to see if it gives meaningful data?

740GLE · Mar 4, 2011

vwlogue said:
Could you share more details about those water-rich starts.. bad fuel? How did you find out?

Intercooler icing and hard start/ingesting water on start.

GraniteRooster · Mar 4, 2011

bsalbrig said:
Out of curiosity have you done a vag-com check of compression to see if it gives meaningful data?

No - I do not have a VCDS and need to buy one or team up with someone near me. Would be interesting to see what the the glow plug pressure sensors read.

Ski in NC · Mar 4, 2011

variation 1bar, about 14psi, about 3%. Looks ok to me.

VCDS reading gp's will show not only compression, but firing pressure too. Unless injector is de-activated somehow while reading.

bmwM5power · Jun 6, 2013

Ski in NC said:
variation 1bar, about 14psi, about 3%. Looks ok to me.

VCDS reading gp's will show not only compression, but firing pressure too. Unless injector is de-activated somehow while reading.

is there any directions how to check this with VCDS?

c17chief · Jun 7, 2013

bmwM5power said:
is there any directions how to check this with VCDS?

Curious as well. Have had a few ingestion episodes myself. Also have VCDS, but haven't come across anything definitive as far as what to monitor and exactly what ranges to watch for between cylinders with VCDS. I know it's no sub for proper compression check, but comparing certain readings between cylinders could give some indication one way or the other. Everything operates fine so haven't felt like wasting time at the dealer to do compression check.

AlcoC420 · Jun 7, 2013

I seem to recall that the ECU recognizes variances in individual cylinder compression and varies the injection to suit. It's noted in the general training manual. Just amazing I thought. The manual further explains that it helps an aging engine maintain an even balance of power in all cylinders.

jasonTDI · Jun 8, 2013

That's water for sure. That difference is enough to make a slight vibration at specific rpm's that you would notice. It's likely enough to cause a CEL as well. Seeing this a lot. I recommend pulling the pass side intercooler pipe off (loose) in front of the oil pan and draining it every oil service.

Damn low pressure EGR....

Cylinder Compression Specs for CBAA

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