1600 ‘71 compression test

[OliTom]

I must be doing something wrong...

I’ve just done a compression test and got the following readings;

1 & 2 35psi
3 & 4 45psi

I was expecting readings of 100 plus so I can only presume I’ve either done it wrong or my engine is past its best.

How I did it.

Removed coil connector from dizzy, removed one spark plug at a time and tested each one by ....Turning the engine over for around 7 seconds with my foot on the accelerator floor.

Newby, so any help much appreciated

 

[OliTom]

Can I add, I warmed the engine first.

Plus it drives and starts really well, cruises at 55 quite happily fully loaded.

 

[Moseley]

Have you set your valve clearances recently? A tight valve would potentially be held open slightly, but it would have to be on all 4, some maybe not the logical answer - unless they haven’t been adjusted for a long time!


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[OliTom]

No, I’ve had the bus 2 years and not had anything like that done.

 

[Tofufi]

You'll get higher readings the faster the engine can turn. If your starter motor is a bit tired, it might only turn over slowly with plugs in. It's generally recommended to remove all 4 to do a compression test, though I have historically done mine with only one plug removed and got reasonable results.

It's possible your gauge is knackered/reading low. At least the readings are consistent between cylinders

 

[Moseley]

No, I’ve had the bus 2 years and not had anything like that done.

I would certainly do these as a starting point. They need to be done every 3k miles on these engines, so you might find that if you’ve done a lot since they were last adjusted, that they might be well out. There’s plenty of guides online or in Bentley to take you through how it’s done. But as with oil changes, it is absolutely necessary to do to prolong the life of your engine every 3k.


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[OliTom]

No, I’ve had the bus 2 years and not had anything like that done.

I would certainly do these as a starting point. They need to be done every 3k miles on these engines, so you might find that if you’ve done a lot since they were last adjusted, that they might be well out. There’s plenty of guides online or in Bentley to take you through how it’s done. But as with oil changes, it is absolutely necessary to do to prolong the life of your engine every 3k.


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Thanks

 

[smokehouse]

I think the book says something about squirting a little oil down in the cyl you are checking if the psi goes up then it's the rings if i remember correctly. That is extremely low but at least they are not to far from one another that's probably why it runs pretty good. i had a friend and his motor in his bug was all 85 psi and it ran like a top because they were all the same.