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Old 08-10-2020, 01:47 AM   #1
Brendan1959
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Default Piston orientation

Can anyone tell me which way the split in the piston faces, I marked the cap but not the rod (fool).
They must have had an issue finding piston rings at the last rebuild, Have a close look.
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Old 08-10-2020, 02:00 AM   #2
dave in australia
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Default Re: Piston orientation

Some, but not all, pistons are marked on the top which way is forward.
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Old 08-10-2020, 02:24 AM   #3
Richard in Anaheim CA
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Default Re: Piston orientation

1. Flat part up

2. Split toward cam
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Old 08-10-2020, 04:15 AM   #4
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Default Re: Piston orientation

Thanks
No stamps on the top
split to cam will hep
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Old 08-10-2020, 10:15 AM   #5
katy
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Default Re: Piston orientation

The split goes opposite to the thrust side.
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Old 08-10-2020, 11:06 AM   #6
Bob C
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Default Re: Piston orientation

I've seen that before where they run three rings on four groove pistons.
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Old 08-10-2020, 06:29 PM   #7
Brendan1959
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Default Re: Piston orientation

I count 11 piston rings
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Old 08-10-2020, 08:40 PM   #8
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Default Re: Piston orientation

If the pistons are supposed to have the split to the cam then they must have been in the wrong way round!
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Old 08-10-2020, 11:54 PM   #9
1930-Pickup
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Default Re: Piston orientation

Quote:
Originally Posted by Brendan1959 View Post
If the pistons are supposed to have the split to the cam then they must have been in the wrong way round!
A few years back I had a 1925 Dodge Brothers roadster. Someone in the past had put all the piston split skirts in the wrong direction.

I was driving to work one day and...KER-BLAM-tinkity-tink-tinkle! One piston disintegrated and it rained small crumbly bits as gravity sucked them into the bowels of the engine.

Too fun.
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Old 08-11-2020, 01:33 AM   #10
Dodge
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Default Re: Piston orientation

They probably cut the ring grooves and added spacers to save the pistons.
In any case those pistons have been more than once around the block.
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Old 08-11-2020, 01:57 AM   #11
Brendan1959
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Default Re: Piston orientation

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Originally Posted by Dodge View Post
They probably cut the ring grooves and added spacers to save the pistons.
In any case those pistons have been more than once around the block.
They will not be going around the block again, I wonder how well it ran with only one compression ring.
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Old 08-12-2020, 08:18 AM   #12
Kurt in NJ
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Default Re: Piston orientation

According to the service bulletins the split goes to the left side(left/right determined from drivers seat)
This makes the camshaft side the thrust side that has the solid skirt,
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Old 08-12-2020, 09:01 AM   #13
rotorwrench
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Default Re: Piston orientation

The direction of rotation sets the thrust side. When a connecting rod is going down on the power stroke in a clockwise rotating engine (as viewed from the front), the piston thrusts the opposite direction. In the case of the model A, the thrust side is toward the valve chamber. Split skirts are for piston expansion as they heat up but that spit is a weak point on the skirt so you don't want the split on the thrust side.
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Old 08-12-2020, 10:45 AM   #14
abachman3
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Default Re: Piston orientation

I recently took apart a motor at the museum and it had two pistons facing each way... guess they were doubling down that at least they would be half right!
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Old 08-12-2020, 02:37 PM   #15
Kurt in NJ
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Default Re: Piston orientation

For my smiths compresser I switched #2,3 because the thrust is on the upstroke for the 2 air compressing pistons
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