[Vwdiesel] 1.6TD compression numbers

Shawn Wright swright at zuiko.sls.bc.ca
Mon Dec 12 00:21:44 EST 2005

On 11 Dec 2005 at 22:13, James Hansen <jhsg at sasktel.net> wrote:
> Today marked our last trip in the Westy this year, so I pulled the injectors as
> soon as I got home and did a hot compression test. The numbers were as I
> expected, quite low at 390 - 375 - 330 - 330. It's possible the weak battery
> resulted in decreasing values as I went along, as the cranking speed was getting
> slower. Pulses on the gauge went something like 75- 150-200-250-300, which
> explains why it takes several seconds to start when the GPs don't come on - it
> takes several full revolutions just to get 300psi. _____
> Don't worry about getting to 300psi over many revolutions... that's because the
> volume of the precup is larger than it usually is because you have a hose and
> and gauge connected to it.  They don't build up pressure to start, they see the
> same pressure every time, and you are measuring that when you crank the starter
> putting a little wind into the hose of the compression tester each revolution,
> until it matches the compression that the precup usually sees.

ok, that makes sense. My tester seems to have a leak, I think at the quick release. I 
wonder how much this would affect the readings? I can hear it hissing when the 
cranking stops.
> I would however be some concerned at the difference between the cylinders.
> They should all break in relatively the same at the same rate. Yours haven't and
> that sucks. If it was me, I would do another compression test so you can monkey
> with the engine this winter, or plan on doing another test in spring. I know
> it's in a vanagon, and gets driven hard just sauntering around, but did you
> drive the bag off it at the start? Worst case,you may have to re-ring and
> re-hone. How is oil usage and crankcase blowby?

Blowby is much more than it was just after rebuild, close to what my 300k km NA 
Jetta has at idle. Oil usage hard to tell for sure, but I do see blue smoke for the first 
5-10 minutes at cold start. None once warmed up.
The first trip was over Hwy2 from Seattle to Leavenworth, hard climb in 3rd & 4th for 
20 minutes, peak oil temps 265F. This after only about 400 kms of gentle breakin. 
Mostly hwy miles for another 1000 kms after that, with a few mtn passes, then 
another 1000 kms of gentle backroads. I've heard that overheating new rings can 
cause them to loose their 'spring'. I'm wondering if that's what I did... I recall the 
cranking on warm starts beginning while we were on that trip.

I think I will try another compression test at some point. So you don't think slower 
cranking speed will affect numbers that much? I might try running two batteries next 
time just to see. But even after running the battery down, and cranking another 20 
secs or so to purge the air from the lines, it started and idled smooth with no smoke 
right after the test. 

If the hard breakin was to blame, then I will need to re-ring and do a breakin around 
town somehow, as any driving on trips is mostly fully loaded and dealing with hilly 


Shawn Wright
'85 Jetta D 
'88 Westy 1.6TD 5 speed
 (see progress at http://members.shaw.ca/vwdiesels)
'82 Diesel Westy

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