Piston Direction When Fitting

[wardy18 33 1 Cars]

Sorry another quick question, i have now worked on 2 1900 8v blocks in the past week and have noticed something quite concerning. each piston has DIST and an arrow on the top, now in one block the arrows on each were facing the Flywheel and in the other block they were all facing the cambelt........

 

I assume obviously the DIST means Distributor so face the arrow towards the flywheel side of the engine, so why would one block i have pulled apart have all pistons with this arrow facing the cambelt.....strange!!!!!!

 

should i correct this when re-fitting the pistons or refit it as it came out?!?

[welshpug 1,657]

DIST should point at the timing belt end.

Edited April 21, 2009 by welshpug

[Ryan 99]

DIST is short for something French that means "timing belt", so it should point to that end.

[wardy18 33 1 Cars]

ok excellent so obviously whoever built one of these blocks I have made the same error as I thought about in pointing DIST to the distributor lol

 

Thanx for clearin that up

 

So if a block was fitted with the wrong way but never fired up would it be safe turn them around to face the right way on rebuild???? Assuming the rods can be fitted either way????

[mattbenselin 0]

I had my head off recently and the pistons were in the wrong way; dist pointed to dizzy end. No problems in running though so...?

[wardy18 33 1 Cars]

It shouldn't actually matter with reference to the dish in the pistons as the valves come down square with the block, just didn't know if there was anything technical

[James_R 3]

They are shaped to match the chamber, so the flat bits on the chamber and pistons match (squish area) not a massive issue if they don't just won't "burn" as well due to the odd shaped chamber (piston and head together)

[wardy18 33 1 Cars]

so the big question is, if they were fitted the wrong way can I simply turn everything round on rebuild?

[Miles 331 1 Cars]

The rods and Pistons must be fitted correctly, the Tag on the bearings face's the rear of the block, As said Dist is the cam belt end and it does effect the running of the engine performace unless there flat top pistons

[dch1950 37 1 Cars]

Hi all,

just to add my 3 pennyworth. I was always taught that the piston (during it's travel up and down the bore) took the thrust from the con rod (via it's connection through the small end with it's gudgeon pin) on one side. The side depends on the direction of rotation of the crank; the piston being cast and preferentially machined to be thicker on that side. Hence the arrow to mark the fitting direction.

regards

Dave

[James_R 3]

In answer to your question yes provided the rods aren't installed backwards you just undo the big end, rotate 180degrees and put the bearing cap back on (to match the new way round the rod is)

[wardy18 33 1 Cars]

how do you mean the rods arnt installed backwards????? Does it matter which way the rods are fitted as they look pretty symmetrical????

[James_R 3]

the Tag on the bearings face's the rear of the block

[wardy18 33 1 Cars]

ah ok I see, ill check, many thanx all

[wardy18 33 1 Cars]

well it looks like at last I have a little luck, the locator tab on the shells will be at the back and the DIST on the piston will face the timing belt so it just looks like whoever built it put the pistons and rods together correctly but then put them in the block back to front

[mattbenselin 0]

Can someone clarify for me running my block with the pistons facing the wrong way (dist faces dizzy not timing belt) will be ok? I dont know how many miles the engine has done in this confirguration but I have driven it about 4k miles with no problems. I had the head off and noticed this but its all back together again now, I thought there would not be a problem. Just to add the pistons are from a DKZ block so have a dish but only partial not full like the 1.6 pistons:

 

 

Thanks, Matt

[DamirGTI 342]

Yes this ones are fitted the wrong way around .

 

By fitting them this way you've moved the piston crown squish area opposite to the cylinder head/combustion chamber squish area so the mixture will be pushed off the spark plug , which will result with uneven mixture burn , slowing down combustion , and some other bits and bobs (as it can be seen by the amount and position of carbon deposits on the piston crowns)

 

The squish area is very important and needs to be mirror image piston crowns + combustion chambers on this type of engine with such piston crown design . It's all there for purpose so better turn them the other way around towards the timing belt

 

Damir

[mattbenselin 0]

Easiest way to do this? Preferably without removing head please!

[DamirGTI 342]

Set the all the 4 pistons on the half a way position in the block (like when changing timing belt - "lock" the engine the same way using cam and crank pulley timing holes)

 

Remove :

 

Sump

Sump spacer

Oil pump

Undo and remove big end caps with the shells (but mark which cap goes where prior to refitting back on the conrod ! , can leave the top shells in place as they usually stick to conrod or the crank with the presence of oil as on the lower caps ... if they fall off note the position of each shell)

 

Now this might be a little bit tricky , you'll need to turn the crank as well in order to gain sufficient clearance to push the piston up and move the conrod (bolt threads) away from the crank so that you can swing the piston/conrod assembly the other way around .. try first , when you undo and discharge all the bearing caps , just by pushing each piston all the way up as far as it goes and then you'll see if it will swing around without the need for repositioning the crank , if not move/adjust the crank position so that you can do so without the conrod/bolts touching the crank (one pair of pistons will do a swing without the crank reposition but the other pair won't me thinks it's been ages since i've been doing this so i really can't recall the boys will know best ! )

 

Damir

Edited April 22, 2009 by DamirGTI

[Tom Fenton 1,541]

Its a difficult one for me whether you bother. Yes there are the advantages that Damir quite rightly points out, but turning the pistons means you may disturb the rings which is not preferable IMO.

[DamirGTI 342]

Yes quite right but i dunno if the ring gaps will be so much off position after the swinging job that it'll be noticeable they might be tight with the cylinder wall so the ring reposition will be , i dare to say , minimal .. they're moving a little bit on the piston while the engine runs anyway even when fitted (gaps arranged) the right way after rebuilding

 

Damir

[mattbenselin 0]

So...how much difference will it make turning them around regarding squish patterns? It seems like a difficult process to turn them 180 without disrupting the rings? I dont know who built this engine but they obviously didnt know what dist meant! Thanks for the help and info everyone, what would best thing to do now?

[Rom 0]

Id probably leave well alone if the engine has been running a while with them the wrong way. Unless your going to rehone and fit new rings.

 

Its quite a logical conclusion to assume DIST means distributor.... Aslong as your not working on Peugeots

[welshpug 1,657]

Shouldn't matter at all that you disturb the rings, just undo the cap bolts, push the piston up the bore, spin it round and re-attach the cap.

[mattbenselin 0]

That makes it sound a lot easier And the effort is outweighed by the improved squish pattern created? think I might have a go then, anything else worth doing whilst its apart, such as uprated oil pump spring...?