Compression Test on A110 motor
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  1. #1
    Fellow Frogger!
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    Default Compression Test on A110 motor

    Hi all

    Just completed a compression test (hot) today on the engine in my A110. As far as I know the engine is a type 688 used in R8s and R10s (there was no aluminium tag above the oil filter to identify type). The compression readings were 150 on cylinder number 4, 140 on 3, 140 on 2 and 145 on 1. These seem reasonable to me (comparable to what I get in my Fuegos) but have not seen any manufacturer's specifications to say what the standard is. Given that the readings seem good, did not proceed to the next step of a "wet" test. What do others think of the readings I got?

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    bazzamac

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    Quote Originally Posted by bazzamac View Post
    Hi all

    Just completed a compression test (hot) today on the engine in my A110. As far as I know the engine is a type 688 used in R8s and R10s (there was no aluminium tag above the oil filter to identify type). The compression readings were 150 on cylinder number 4, 140 on 3, 140 on 2 and 145 on 1. These seem reasonable to me (comparable to what I get in my Fuegos) but have not seen any manufacturer's specifications to say what the standard is. Given that the readings seem good, did not proceed to the next step of a "wet" test. What do others think of the readings I got?

    bazzamac
    I seem to remember my 2.0 Fuego being about 140psi across the board (8.6:1 compression)

    As a comparison, the 3 good cylinders on my Fuego were all 190psi +/- 5.

    That was a 9.9:1 compression ratio motor.

  3. #3
    1000+ Posts renault8&10's Avatar
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    There was some discussion on a thread I had recently where Simon and Floride59 helped determine which block based on some photos etc the biggest is the lump on the side of the bigger blocks compared to the 688 style. I think it was the Gordini done and dusted thread in relation to my clutch change in the green car recently.
    KB


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    I saw that thread Kevin and that's when I worked out my motor was a 688 type. Those photos by Floride 59 were very useful.

    Cheers

    bazzamac

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    1000+ Posts renault8&10's Avatar
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    Must be time to stick a warm 1.4 or 1.3 in it then!
    KB


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    Is installation of a 1.4 litre piston liner kit possible in the 688 type motor? In any case, looking at a R5 Alpine motor down the track.

  7. #7
    1000+ Posts renault8&10's Avatar
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    It certainly is and has been done before, BUT, it requires machining of the block to suit the bigger liner and o ring seal. Hardly worth the trouble if you have another block to go in, or; you are a stickler for originality. They don't just drop in without modification.

    This was a popular Collier mod in Sydney in the 70's/80's, and in fact the red R8 I bought off Jim C has such a motor in it apparently. I haven't driven it yet so can't comment on whether the engine has the same power/torque as a normal 1.4. Jim was certainly happy when he had the red car.

    I'm guessing if you are planning an R5 Alpine motor, then originality isn't a worry.
    KB


  8. #8
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    Hi Kevin

    I won't go there. The compression readings on the existing motor seem good enough to me so will keep it as is. Instead I will instal an R5 Alpine motor. This allows the car to be returned to original if needed later as it will not involve downstream mods like relocating the radiator altho I understand this would improve cooling and weight distribution. The label on the inside of the boot lid says it is an 1100 -VA but it is badged as a 1300S. In France, a 1300S A110 would have had an R8G motor but the Mexicans did other things like using mainsteam R8 Major motors instead which do not have a cross flow head or nice side draught Webers. Of course, this can be fixed by installing different engines like the R5 Alpine or you could go further by installing the R12, R16TS or TX engines or even the R8G or R17TS fuel injected version (I would not mind doing the later if one was available somewhere). The options seem endless but then there is the question of availability and whether one wants to do all the downstream modifications. So at this stage, I'll be going with the R5 Alpine engine with twin side draught Webers. In the meantime, my hand has been forced by the fact that I have lost reverse gear in the Type 330 gearbox. The linkages are fine and I checked it out by disconnecting the linkages and moving the gear selector by hand. Still no reverse so I am concluding that the reverse gear selector has jumped out of its slot or the pivot bolt holding the reverse gear selector has either come loose or broke. Next step, which I didn't plan till later, is to remove the engine and gearbox, instal the 5 speed box and either use the existing 688 Type engine or, depending on how soon it will arrive, the R5 Alpine motor. In between time, I will clean up the rear beam that holds the gearbox (it has surface rust) and the engine bay which are the only bits left to do. The rest of the chassis, suspension etc has been done using POR15 which is a pain to do but good stuff. Then the car will be totally done to my satisfaction.

    Cheers

    bazzamac

  9. #9
    1000+ Posts Frans's Avatar
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    That compression is good. One cannot tel what compression should be on a used or modified engine. If you have a hotter cam in there (and you don't know) the compression will be lower because of the longer duration that causes a bigger overlap. Rocker clearance should be checked before a compression test is done. If you increase your rocker clearance now and do another test, it will be substantially higher. I have done a test like that with the results at home, I might post it tonight.

    Importance is that they are all close to one another.

    Frans.
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    Young enough to do it anyway.

  10. #10
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    Thanks Frans. It is comforting to know the compression readings I got are good. As far as I know the engine has not been modified and I did not check the rocker clearances beforehand but there was no sound of loose tappets. It runs sweet as..As you mention, it is important that the readings are close together (usual minimum variation is 10 or 15 %). Will be interesting to see your results and on what engine type.

    Cheers

    bazzamac

  11. #11
    1000+ Posts Frans's Avatar
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    Bazzamac,

    In 1994 I developed and patented a variable cam. The idea behind it was as follows. Tow your caravan with plenty of torque to the racetrack and then race that same car with plenty of hp and rpm's and probably win races. It was an infinitely/analoguesly variable cam, different from a Vtec that is a digitally activated 2 stage cam, that changed 1) the lobe centers or cam timing 2) the lift 3) the duration continuously as you were driving to have the optimum profile at any given time and conditions.
    I was limited on the duration on the low profile (high torque) because of this compression change hence the test that I did.

    It was on a 1800 BMW SOHC that the prototype was built and this was the figures. You can also see how the duration of the standard cam changes with rocker clearance.

    0.2mm 1150kpa duration 244 deg
    0.3mm 1270 kpa duration 211 deg
    0.4mm 1350 kpa duration 201 deg
    0.5mm 1420 kpa duration 194 deg

    Cam duration is given here as advertised duration.

    Of interest here is the changes in compression compared to the clearances.

    Frans.
    Last edited by Frans; 30th January 2013 at 09:30 PM. Reason: typo
    Old enough to know better
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