Assembling Long Stoke Pistons
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Thread: Assembling Long Stoke Pistons

  1. #1
    Fellow Frogger! citroenthusiast's Avatar
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    Default Assembling Long Stoke Pistons

    Shop manual for the long stroke engine says to insert the pistons into the cylinders from below (i.e. the crankshaft side) rather than the from the deck side. Why is this? It it absolutely necessary? I am not sure my ring compressor will fit and with a bit of caution, the big ends of the rods will pass through.

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    John T.

    54 11BL; 61DS19 LHM (son's); 71DS21 BVH; 73SM 3.0; 73SM 2.7EFI; 73SM 3.0 (other son's); 74 Maserati Merak

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    Member wilrex's Avatar
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    I think it may be that the sleeves must be settled and fixed firmly against the fragile shims on the base, to avoid water incursion.
    That means a fixture across the top face of the sleeves.
    I fitted mine from the top, but made up washers that held the flange but allowed access with the ring compressor.
    Be careful not to turn the motor while the sleeves are not fixed, and get the direction right for the offset of the big end bearings.
    Mine has done a couple of thousand Kms now, after fittings, but I still look at the dip stick for milky oil... None yet!
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    2CV6 Special Green, Riley RMB, RX7 Rotary, Jensen Healey, 1896 Ford A replica, and last but not least 1961 Citroen ID19-P... Previous include, 27 Chev Truck, 24 Bean Truck, 27 Chev Capitol, Rover S105, Humber Hawk x 2, MGB, Ford AA Truck, Ford A, elderly motorbikes x6, and more...

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    Fellow Frogger! citroenthusiast's Avatar
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    That makes sense. I have assembled a few DS-21 engines and so I knew about having to use a special fixture to keep the barrels in place. Glad to know yours worked out.
    Thanks.
    Cheers,
    John T.

    54 11BL; 61DS19 LHM (son's); 71DS21 BVH; 73SM 3.0; 73SM 2.7EFI; 73SM 3.0 (other son's); 74 Maserati Merak

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    DS19 manual has the bare liners in and the head on before the pistons, rods and crankshaft are fitted. There's a step after fitting the head to check for distortion of the liner bores. Seems an odd way to build and engine, but it would prevent the liners moving. Most people, faced with wet liners, would clamp the liners and fully assemble the bottom end with the head going on last.
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    When fitting the piston/rod assemblies from below, there is a generous lead in in the bottom of the sleeves, so a ring compressor is not needed. A few pokes with a wooden ruler or similar has them going in easily. Of course, a liberal drizzle of oil around the rings helps.

    I have also pre-assembled piston/rods into the sleeves, on the bench, then fitted these into the block. This makes it all very easy.
    Bob
    '57 Slough DS19, Buttercup
    '60 2CV 1220, Raid Runner
    Several DS19 and 2CV projects

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    Fellow Frogger! citroenthusiast's Avatar
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    Good tip. I think I will try assembling the pistons/rods on the bench.
    Cheers,
    John T.

    54 11BL; 61DS19 LHM (son's); 71DS21 BVH; 73SM 3.0; 73SM 2.7EFI; 73SM 3.0 (other son's); 74 Maserati Merak

  7. #7
    1000+ Posts gerrypro's Avatar
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    Quote Originally Posted by citroenthusiast View Post
    Good tip. I think I will try assembling the pistons/rods on the bench.
    I Totally Agree that it can be done this way HOWEVER!!!!!! It is imperative to get the rod and piston alignment correct for each barrel. The barrels have a small flat on the upper rim that fits against the next barrel of the pair. If using ID rods the offset of the bearing cap must slope towards the camshaft side. The piston assembly must not be rotated in the bore once fitted in order to avoid messing up the ring gap offsets, 180 degrees from each other and 90 degrees from the thrust side!
    59 Floride and Trading Estate like this.
    Cheers Gerry

  8. #8
    Fellow Frogger! Buttercup's Avatar
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    I have found that you can very easily rotate the piston in the bore.... the rings stay still, because they are gripping the bore much more tightly than the piston.

    So its important to approximately position the piston/rod, and position each ring to the bore more precisely, just before it enters the taper of the lead in.

    Mark the outside of the lower part of each barrel with a felt pen, its number, and a mark to indicate inlet side... so the top ring gap goes to that mark.

    The final rotational position of the piston is dictated by the crank. This is the same for any method.

    If you use a ring compressor from above the block, you will find that your ring gap positions are significantly disturbed by the tightening of the ring compressor...... because it reduces the circle diameter by taking length to 1 point around the circumference, and the dominant direction of grip of the ring varies with gap position within this.

    If you are really worried about gap position (which you shouldn't be) you will get a better result with my pre-assembly method.
    shanadoo likes this.
    Bob
    '57 Slough DS19, Buttercup
    '60 2CV 1220, Raid Runner
    Several DS19 and 2CV projects

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    Hello, unless the rings are staked (like a two stroke), when the engine is running, they will rotate around the piston at different speeds.

    One less thing to worry about

    Peter
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    Quote Originally Posted by badabec View Post
    Hello, unless the rings are staked (like a two stroke), when the engine is running, they will rotate around the piston at different speeds.

    One less thing to worry about

    Peter
    Not in my experience...... they always come out in the same relationship that they went in.
    shanadoo likes this.
    Bob
    '57 Slough DS19, Buttercup
    '60 2CV 1220, Raid Runner
    Several DS19 and 2CV projects

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    1000+ Posts gerrypro's Avatar
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    Quote Originally Posted by Buttercup View Post
    Not in my experience...... they always come out in the same relationship that they went in.
    Absolutely!!!!!
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    Cheers Gerry

  12. #12
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    The only way I've ever fitted pistons in a wet liner engine is on the bench. The engine block/ liner seal area can then be checked for corrosion pitting at the same time. If the engine uses a gasket as a liner seal, clamp the liner down as soon as it's back in place but do not clamp it super tight, only nip it enough to stop it moving and let the head do the full clamp down. A soft material such as rubber under your clamping method will prevent the gaskets from being over compressed and hold the liner in place very well. Otherwise you're clamping a gasket twice and, in the first instance maybe unevenly, and so inviting a water leak. Why risk having to keep checking for milky oil after all that work and expense. Do it right the first time or don't bother is my motto.
    Cheers.

  13. #13
    Fellow Frogger! citroenthusiast's Avatar
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    What's wrong with this picture? (Manual says arrow points to the front, but in this case the arrow is perpendicular to the gudgeon pin bore and so must either point to the camshaft or away from it....) Any ideas which?

    Also how loose a fit can the gudgeon pin be in the bore? I can definitely move the pin in the bore enough to feel a rattle when it yaws (although not if I try it straight laterally).

    Assembling Long Stoke Pistons-new-piston.jpg
    Cheers,
    John T.

    54 11BL; 61DS19 LHM (son's); 71DS21 BVH; 73SM 3.0; 73SM 2.7EFI; 73SM 3.0 (other son's); 74 Maserati Merak

  14. #14
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    Quote Originally Posted by citroenthusiast View Post
    What's wrong with this picture? (Manual says arrow points to the front, but in this case the arrow is perpendicular to the gudgeon pin bore and so must either point to the camshaft or away from it....) Any ideas which?

    Also how loose a fit can the gudgeon pin be in the bore? I can definitely move the pin in the bore enough to feel a rattle when it yaws (although not if I try it straight laterally).

    Click image for larger version. 

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    Arrow to thrust side, renew gudgeon pin bush, there's excessive clearance there. [It'll be relying on the piston to bore clearance to keep the piston parallel].
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    Quote Originally Posted by shanadoo View Post
    Arrow to thrust side, renew gudgeon pin bush, there's excessive clearance there. [It'll be relying on the piston to bore clearance to keep the piston parallel].
    When you say thrust side.... do you mean the side that the rod pushes the piston to, during the power stroke... ie on a DS, the exhaust, opposite cam and right side ?
    Or do you mean the side that the crankpin is on during the power stroke.... ie on a DS, the inlet, cam and left side ?
    Bob
    '57 Slough DS19, Buttercup
    '60 2CV 1220, Raid Runner
    Several DS19 and 2CV projects

  16. #16
    Fellow Frogger! citroenthusiast's Avatar
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    Long stroke engine spins CW looking at the flywheel (i.e. looking at Plate #2) right? That means thrust side is toward the camshaft isn't it? So the arrow points in the same direction as the openings in the big ends?

    I used my telescoping gauges on the gudgeon pin and got .0008 to .0010 inch clearance, which is the same clearance between the new piston and pin. So in spite of my concern that I could feel a tiny bit of yaw, that doesn't seem excessive to me.
    Cheers,
    John T.

    54 11BL; 61DS19 LHM (son's); 71DS21 BVH; 73SM 3.0; 73SM 2.7EFI; 73SM 3.0 (other son's); 74 Maserati Merak

  17. #17
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    Quote Originally Posted by citroenthusiast View Post
    Long stroke engine spins CW looking at the flywheel (i.e. looking at Plate #2) right? That means thrust side is toward the camshaft isn't it? So the arrow points in the same direction as the openings in the big ends?
    I'm not sure... during the power stroke the crankpin is going down on the cam side... so the inclined position of the conrod reacts to the downward pressure of the piston, by creating a sideways reaction component... pushing the piston away from the cam...

    So which is the "thrust side" ?
    Bob
    '57 Slough DS19, Buttercup
    '60 2CV 1220, Raid Runner
    Several DS19 and 2CV projects

  18. #18
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    Good point.
    I did, however, finally receive word back from the supplier. "Arrows point in the direction of rotation, i.e. toward the cam"
    Cheers,
    John T.

    54 11BL; 61DS19 LHM (son's); 71DS21 BVH; 73SM 3.0; 73SM 2.7EFI; 73SM 3.0 (other son's); 74 Maserati Merak

  19. #19
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    Quote Originally Posted by citroenthusiast View Post
    Good point.
    I did, however, finally receive word back from the supplier. "Arrows point in the direction of rotation, i.e. toward the cam"



























    Quite correct. But still reckon the gudgeons need re machining, parallel bushes will have zero side rock. Direction marked pistons are usually cam ground and depending on the actual amount of gudgeon bush wear, the pistons may be subjected to increased skirt and crown loading, resulting in piston clatter on the overrun. But all in all consideration should be given to the fact that it's not a high rev high output unit, so your choice. Enjoy it. Cheers.

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