Often I've read on Google to consult my manual for the compression figures for my engine but just can't them listed.

I have a 1979 Leyland Sherpa 230 with a Morris "O - Series" engine 1.7l.

I believe I should have a compression ratio of 8-1 but can't be sure. The compression tester came out at 150 psi ( + or- 2psi ) which I thought sounded really high. I've read that carbon build up can cause higher compression as a result of a sealing effect but the cylinder was removed and cleaned up a short while ago.

What would your guess be for a 40 year old 70,000 mile Leyland van - be? And do you know of any other reasons (if indeed the figures are too high) which could create a higher reading. (Tester was checked against another)

Chapter 2 in my book is for the cooling system. I'm in the Engines section, under specifications and then "general" and still there is no mention of compression pressure.

Has anyone else out there not managed to find the expected compression in their manual?

  • what actual problem do you have? – agentp Feb 20 '18 at 11:23
  • Remember to test with the throttle fully depressed. Otherwise there is a restriction which can result in a lower reading. (Mostly it doesn't matter that much, but sometimes it does) – Bart Feb 20 '18 at 18:16
  • Thanks @Bart - easy 1 to forget. I'm pretty sure I remembered to do that and anyhow I was trying to establish if psi was too high not too low. Although I have a reasonable understanding of how an engine works - it's mainly from reading. I don't have experience from other or previous vehicles to compare to. – Michael Sherpa Feb 20 '18 at 19:03
  • Hi @agentp When I do a power balance test by removing cylinder 1 plug lead the revs drop very little compared to when I pull the others. I have a separate post discussing this for the last few days. Thank you for your interest. – Michael Sherpa Feb 20 '18 at 19:07

It should be at the beginning of the Chapter 2 portion which covers General engine overhaul procedures. Whether it's in 2B or 2C or subsequent sub-chapters will depend on how many engine options there are for any specific vehicle. When you find the section on the overhaul procedures, it should be locate under the "Specifications", with a sub-heading of "General". This usually comes first under Specifications, so is pretty easy to find. It was the same in four different manuals I checked.

As for your compression figures of 150 psi +/- 2psi, those seem like very good numbers ... especially since the variance is so small.


This is from page 2E-1 of my Chevrolet Camaro/Pontiac Firebird Haynes Manual. This is the section for the 3.4L V6, but there are four more engines which can be found later on in the sub-chapter.

enter image description here

  • Thanks @paulsteer2 The section I believe you are referring to under "General" gives specs for Bore, Type, Stroke, Capacity, Firing Order and compression Ratio (8:1.) No mention of compression. So although good PSI's you don't think necessarily too high? Just to add - I'm not asking out of curiosity but an trying to diagnose a long standing problem and everything to do with my engine is up for scrutiny. – Michael Sherpa Feb 20 '18 at 0:33
  • @MichaelSherpa - Like I said in my answer, each of the manuals I looked at had the compression value given exactly where I stated it would be. I've attached an image into my answer which shows exactly what I'm talking about. – Pᴀᴜʟsᴛᴇʀ2 Feb 20 '18 at 1:29
  • @MichaelSherpa - As for the pressure you state, I absolutely would not call it into question. As long as you've measured the cylinders correctly, 150psi on most engines with only the very small amount of variance (look above where it says 30% from highest reading is still good), especially for an engine as old as you're talking about. There's no problem there. – Pᴀᴜʟsᴛᴇʀ2 Feb 20 '18 at 1:33
  • Thanks very much @paulsteer2 for your work on photos ect but it seems my manual is different. Chapter 2 in my book is for the cooling system. I'm in the Engines section, under specifications and then "general" and still there is no mention of compression pressure. I've updated my question to give this info. Thanks – Michael Sherpa Feb 20 '18 at 17:12

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