N54 Compression Test: Harbor Freight vs OTC

[The Convert]

I bought the OTC gauges a few months ago at the recommendations on this forum...mine are all sitting at zero though...

 

[NoQuarter]

I just added the FIT kit to my Amazon list

 

[fmorelli]

Let me know what you guys think of these results.

First off, great post!
In an ideal world we'd have an easy way to do a calibration test ... but I know of no DIY compression test calibration. There are places one can send compression gauges for NIST-based testing. Kind of overkill for this conversation. I'm not sure what compression testers get sold with a calibration certificate - Mac/Snap-On I surmise. For example, this one is certified +/-2%. One could do back-to-back with a calibrated compression tester, if a buddy has one.

One interesting thing to keep in mind - if the compression gauge male end does not displace the same space that the spark plug displaces, you are going to read a lower compression value given the volume of the cavity has actually increased. Kind of one of those, "never thought about that" kind of things. Barometric pressure and engine temp likely also play factors.

At the end of the day you're probably looking for repeatability and measurement differential across cylinders more than anything.

Filippo

 

[SLOWESTN54]

Sorry to bring back a old thread, But this thread literally saved me tons of time, money, headaches, and sadness .

This Sunday i had decided to compression test my 535i as i thought it was running a little funny in my head. Cylinder1 read at 150 and cylinder 2 read in the low 130's. By this point i had given up and decided it was time to sell or find a new engine as my original tester was climbing very slowly, and at least to me the idle sounded very odd. Read this thread and ordered a OTC with next day shipping and retried it.

Cylinder 1- 184
Cylinder 2- 172
Cylinder 3- 181
Cylinder 4- 180
Cylinder 5- 176
Cylinder 6- 174

For Good measure I retried my old tester in cylinder 1

It showed cylinder 1 at 155, also climbed way slower. My main concern originally also came from how slow the tester was climbing.

I hope this saves someone in the future, and thank you @doublespaces for originally posting about this.

 

[wheela]

Giddyup, glad your motor isn't toast