DS20 Compression PSI
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Thread: DS20 Compression PSI

  1. #1
    Fellow Frogger! Errol_S's Avatar
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    Default DS20 Compression PSI

    Could someone please advise what compression psi should be expected from a DS20. I tested mine cold, all plugs out, and accelerator to the floor. It was 110, 103, 113, and 90. On another post I saw results of 160, 150, 165, and 150 which tells me I have a problem. The only difference was those readings were when the engine was hot - would this make such a difference?

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    I have just refurbished the head so well seated valves and a new head gasket are fitted.

    Do I have a rebuild on my hands?

    Regards
    Errol

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    Fellow Frogger! JAJEA's Avatar
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    G'day Errol, I'll be the first to respond to let you know that Australia is still on the map.

    I do not "know" what the pressures should be for the DS 20 (are they not in the workshop manual) but in any case and reason for my response; I would not be at all happy with those figures irrespective of hot or cold. Until you get the figures (irrespective from where) may I suggest that you pour a small quantity of engine oil in each cylinder and repeat the pressure testing as before. The oil will seal the piston rings and give high pressures than before if the low pressures are due to worn rings/pistons.

    When the head was off did you rotate motor and checked the bores for glazing and or broken rings.

    Lets hope that it's pressure gauge operator problem and all is well below the head.

    Regards,

    John

    Quote Originally Posted by Errol_S View Post
    Could someone please advise what compression psi should be expected from a DS20. I tested mine cold, all plugs out, and accelerator to the floor. It was 110, 103, 113, and 90. On another post I saw results of 160, 150, 165, and 150 which tells me I have a problem. The only difference was those readings were when the engine was hot - would this make such a difference?

    I have just refurbished the head so well seated valves and a new head gasket are fitted.

    Do I have a rebuild on my hands?

    Regards
    Errol

  3. #3
    Fellow Frogger! Errol_S's Avatar
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    Hello John

    Thanks for responding. I was beginning to think that I had "the boys" flummoxed - and that would be a first.

    I removed the head because of water seepage into the oil. I would assume this was the first time the head had been off as it was absolute hell to loosen and retract the bolts through the head, due to corrosion and distortion. Some bolts had to be ground off and removed from the bottom. The gasket had blown, however the head only needed a slight skim. New valves, guides etc. were fitted and the head was pressure tested.

    However to answer your question, I did not rotate the motor, I simply felt the sleeves for ridging and visually inspected what was showing. These did not look particularly bad. After reassembly it was the plugs that prompted me to do a pressure test as they looked somewhat oily. Unfortunately I do not know the mileage as the speedo only shows a few thousand - maybe it has been around the clock, or more likely replaced.

    I also believe these pressures are too low, but one grasps at straws to avoid lifting the engine. I will squirt some oil and retest - just in case!!

    Regards
    Errol

  4. #4
    Fellow Frogger! JAJEA's Avatar
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    Also consider what sort of mileage you propose before you rebuild lower end if not a daily drive. There are a few products on the market for "smoky" vehicles.

    John

    Quote Originally Posted by Errol_S View Post
    Hello John

    Thanks for responding. I was beginning to think that I had "the boys" flummoxed - and that would be a first.

    I removed the head because of water seepage into the oil. I would assume this was the first time the head had been off as it was absolute hell to loosen and retract the bolts through the head, due to corrosion and distortion. Some bolts had to be ground off and removed from the bottom. The gasket had blown, however the head only needed a slight skim. New valves, guides etc. were fitted and the head was pressure tested.

    However to answer your question, I did not rotate the motor, I simply felt the sleeves for ridging and visually inspected what was showing. These did not look particularly bad. After reassembly it was the plugs that prompted me to do a pressure test as they looked somewhat oily. Unfortunately I do not know the mileage as the speedo only shows a few thousand - maybe it has been around the clock, or more likely replaced.

    I also believe these pressures are too low, but one grasps at straws to avoid lifting the engine. I will squirt some oil and retest - just in case!!

    Regards
    Errol

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    Fellow Frogger! badabec's Avatar
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    Hello, is it running well enough? Is it a daily or weekend drive? I ask because my DSuper5 had compressions in the 150s. It ran perfectly, good acceleration, mpg etc. I pulled the engine out to replace the timing chain and found every single part was worn out.

    My parts bill will be around the £3000 mark. I'll be on the spanners.

    Happy days

  6. #6
    Now go make me a sandwich Hotrodelectric's Avatar
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    Quote Originally Posted by JAJEA View Post
    G'day Errol, I'll be the first to respond to let you know that Australia is still on the map.
    Damn!! Why wasn't I informed??


    Quote Originally Posted by JAJEA View Post
    I do not "know" what the pressures should be for the DS 20 (are they not in the workshop manual) but in any case and reason for my response; I would not be at all happy with those figures irrespective of hot or cold. Until you get the figures (irrespective from where) may I suggest that you pour a small quantity of engine oil in each cylinder and repeat the pressure testing as before. The oil will seal the piston rings and give high pressures than before if the low pressures are due to worn rings/pistons.

    When the head was off did you rotate motor and checked the bores for glazing and or broken rings.

    Lets hope that it's pressure gauge operator problem and all is well below the head.

    Regards,

    John
    Exactly my thoughts on the whole thing. A test with the engine hot will give false readings. Always cold, or at least cool. Also, pull all four plugs before you test. This makes the engine turn easier, and you're not measuring the one cylinder compressing against another.
    The measure of your character isn't what you do when people are watching- it's what you do when they aren't watching.

  7. #7
    Contented Peugeot Driver addo's Avatar
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    Did you set valve clearances from first principles?

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    Fellow Frogger! Errol_S's Avatar
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    Did a retest which returned +- the same readings.

    To answer some of the questions asked;
    * Valve clearances were set correctly prior to the test
    * All plugs removed, engine cold, accelerator depressed
    * The engine was running, but I have not had the opportunity to test it on the road as I was stripping and preparing the body for paintwork at the same time as working on the motor. Prior to this it stood for a few years.
    * Once on the road this will be a weekend vehicle, but it will need to be capable of a 2k trip on open roads for club outings.

    To take advantage of family travelling home from the UK I had my daughter collect a set of DS21 piston/sleeves from Darrin, at least this will save some freight and customs duty expense, and if needed I will have them on hand. However Badabec at UKP275 that is a far cry from UKP3000. You make me scared to go down below!!

    I am delaying my decision.....

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    Fellow Frogger! badabec's Avatar
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    Hello, the cost of mine escalated once I had decided to remove the engine. With the engine out, everything else becomes so much easier to do, that you may as well just do it. With the head off, I checked the state of the cam followers (oh dear) and with the sump off, the mains and big ends (oh dear). Starter motor? Clutch? Timing chain? Oil pump? Rocker gear? May as well check whilst I'm here, oh dear.
    And so it went on.

    Might as well sand blast all the brackets coming off, and powder coat, and that is another £500 gone. I had the front under tray sand blasted and zinc coated. Unfortunately once all the filler had been removed, there was hardly anything left (£300 for a glass fibre one and then plus paint)

    Jamie, at the DS Workshop where I get all my bits, advised me to put up with the timing chain rattle. But I just had to do it! And am I really going to put it back together with manky rubber grommets, old belts and crappy wiring?

    I used nearly two (UK) gallons of degreaser.
    Greg C likes this.

  10. #10
    Fellow Frogger! Errol_S's Avatar
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    Phew! And that is just the engine. However I am sure the end product will justify all the effort, and cost.

  11. #11
    Fellow Frogger! JAJEA's Avatar
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    So, no test with oil in the cylinders. Oil in the cylinders will greatly improve the compression if the "leak" is via the rings. If oil in the cylinders does not improve compression, leak is in the gasket or valve areas.

    Regards,

    John

    Quote Originally Posted by Errol_S View Post
    Did a retest which returned +- the same readings.

    To answer some of the questions asked;
    * Valve clearances were set correctly prior to the test
    * All plugs removed, engine cold, accelerator depressed
    * The engine was running, but I have not had the opportunity to test it on the road as I was stripping and preparing the body for paintwork at the same time as working on the motor. Prior to this it stood for a few years.
    * Once on the road this will be a weekend vehicle, but it will need to be capable of a 2k trip on open roads for club outings.

    To take advantage of family travelling home from the UK I had my daughter collect a set of DS21 piston/sleeves from Darrin, at least this will save some freight and customs duty expense, and if needed I will have them on hand. However Badabec at UKP275 that is a far cry from UKP3000. You make me scared to go down below!!

    I am delaying my decision.....

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    Well, that had me worried, in case I've been carrying out compression tests incorrectly for over 50 years.
    Luckily, a search for instructions on how to use compression testers manufactured by some respected companies soon put my mind at ease...

    From Snap-on's manual.
    "The engine must be at operating temperature.
    A cold engine does not ensure proper tolerances, lubrication at the rings or proper ring seating."

    http://buy1.snapon.com/products/diag...al/zmt308l.pdf

    http://www.gunsontools.co.uk/items/p...structions.JPG

    https://actron.com/sites/default/fil...lish_16172.pdf

    https://www.clarkeservice.co.uk/manu...ols/cht693.pdf


    Quote Originally Posted by Hotrodelectric View Post
    A test with the engine hot will give false readings. Always cold, or at least cool.
    Last edited by Ken H; 27th May 2016 at 12:58 AM.

  13. #13
    Now go make me a sandwich Hotrodelectric's Avatar
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    Quote Originally Posted by Ken H View Post
    Well, that had me worried, in case I've been carrying out compression tests incorrectly for over 50 years.
    Luckily, a search for instructions on how to use compression testers manufactured by some respected companies soon put my mind at ease...

    From Snap-on's manual.
    "The engine must be at operating temperature.
    A cold engine does not ensure proper tolerances, lubrication at the rings or proper ring seating."

    http://buy1.snapon.com/products/diag...al/zmt308l.pdf

    http://www.gunsontools.co.uk/items/p...structions.JPG

    https://actron.com/sites/default/fil...lish_16172.pdf

    https://www.clarkeservice.co.uk/manu...ols/cht693.pdf
    I had always understood it to be cold. It appears I'M the one that's wrong. I will change.
    The measure of your character isn't what you do when people are watching- it's what you do when they aren't watching.

  14. #14
    Fellow Frogger! badabec's Avatar
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    Quote Originally Posted by Errol_S View Post
    Phew! And that is just the engine. However I am sure the end product will justify all the effort, and cost.
    Hello, why not just run the engine and use it. See how it goes. If you have time, a bit of diesel down each plug hole will loosen things up.
    When I had my Mini, it just had a speedo and a fuel gauge, so nothing else to worry about. Put the compression tester back in its box, back on the shelf, and check the bonnet is closed properly. No need to even look at the fuel gauge, it's useless.

    Have fun

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