Piston installation

[TK in LA]

OK Barner's here we go. I'm in the process of re-ringing a '29 motor. On tear down I noticed all the pistons have the arrow to the rear which is normally to the front. On removal, the rod is in the correct orientation for the slinger and the expansion slot is away from the cam in this configuration, that is all but one. On it, the arrow was facing to the rear like the others but the slot was on the cam side. Where do I go from here? Reverse the pistons so the arrow is to the front and the expansion slot is towards the cam or leave it alone. What about the odd piston?
Thanks for any thoughts you may have on this. Always fun and interesting!

[katy]

IMHO I would put the pistons back in the way they came out.

Your mileage may vary.

[Jim Brierley]

I would reverse all but the odd piston. The expansion slot should be away from the thrust (power) side.

[TK in LA]

Thanks Katy and Jim for your input. After more research I'm going with Jim's reply. Though in the long run it probably won't make a large difference, at least I know it will be the best it can be to start with. Thanks again for taking the time to respond.

[Barber31]

I would also say to replace them as they were. If you're doing a re ring job then it obviously has some miles on it and that means the parts are worn into each other already. Switching things up might cause more problems down the road. I would at least call a engine rebuilder to get their opinion.

[Mike V. Florida]

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Originally Posted by Barber31

I would also say to replace them as they were. If you're doing a re ring job then it obviously has some miles on it and that means the parts are worn into each other already. Switching things up might cause more problems down the road. I would at least call a engine rebuilder to get their opinion.

Jim Brierley is an engine rebuilder.

[Barber31]

Haha. Well that settles it then!

[Jim Brierley]

The items where wear pattern is important are the rings, which you are replacing.

[TK in LA]

Correct Jim. Who ever worked on the motor previously did a lot of strange things. My main concern that started this was the excessive oil in two of the cylinders and lower compression. Looks like they had a couple of pistons with the rings almost in line and the oil rings were all the single ring type. I've gone to the Grant rings with the three piece oil ring. The motor isn't that great but this should improve over it's previous condition. Thanks again!

[Tom Wesenberg]

Do you have any pictures of the pistons?

The cam side is the thrust side, so the slots should be against the driver's side (left side). Also look at the skirts and see if the thrust side doesn't have more contact area, as many pistons do.

[Glenn Thoreson]

An old thread for sure but it solved my problem. I'm currently doing a ring and vavlve job on my hillbillt parade jalopy. All the piston skirt slots faced the cam but number one. It was facing the opposite. Having not remembered which way was right, my brain was boiling over. So, I decided to ask you guys. Problem solved! Many thanks!
Glenn in Wyoming

[Bob Bidonde]

Confusion re thrust side of a cylinder?? I believe the following to be the correct logic.
In the Model "A," the cylinders are offset 0.125 to the left (driver's side) of the crankshaft's rotational axis. So the thrust side of a cylinder is its left side. As such, the expansion slot in a piston should be to the left (driver's side) of the engine.

[Jim Brierley]

The thrust is on the left side. With the piston going downward on the power stroke, the rod is angled to the right, putting the thrust on the left, the cam side, as Tom stated.