Pistons

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monzadon
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Joined: Fri Aug 11, 2017 3:35 am

Pistons

Post by monzadon »

I have a 65 Monza with the140 motor, i am putting in new piston rings .and i.need to.file the gap, what should the ideal gap be, the.specs are 13 to 23, and another question i had to replace two pistons and i.had a machine shop put them on the rods and i just noticed that the top notch is on the wrong side, how much of a problem is this?

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terribleted
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Re: Pistons

Post by terribleted »

You do not want to put the engine together with a piston upside down. This must be fixed. According to the 65 Shop manual ring gap should be .015-.055 on the oil rings and .010-.025 on the piston rings. Unless the piston rings specify a different gap this is what you should use. Toward the bottom of the range on both is ideal, but, as long as they are within the range no issues.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia

66vairguy
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Re: Pistons

Post by 66vairguy »

monzadon wrote:
Wed Aug 26, 2020 10:18 am
I have a 65 Monza with the140 motor, i am putting in new piston rings .and i.need to.file the gap, what should the ideal gap be, the.specs are 13 to 23, and another question i had to replace two pistons and i.had a machine shop put them on the rods and i just noticed that the top notch is on the wrong side, how much of a problem is this?
Piston wrist pin holes are slightly off center to minimize piston slap during the power stroke. The offset position depends on engine rotation. The notch (or other mark) on a Corvair piston goes toward the flywheel side. Note people often confuse the front and back of a Corvair engine, best to say flywheel or oil pump side. So if your piston mark is NOT TOWARD THE FLYWHEEL side you'll have a noisy engine and eventually cracked piston skirts.

I've learned there are few truly good machine shops now - you have to tell them everything or they guess at it.

The last thing you want is piston rings expanding to the point they touch ends at high engine temperatures, especially on turbo engines. This is one case were a small gap is not better. Just me, but I use the middle of the spec. Most of use don't put that many miles on a Corvair engine, you don't have to build it to go over a 100,000 miles like a modern engine will go. Just my point of view.

66vairguy
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Re: Pistons

Post by 66vairguy »

BTW -- DO NOT redo the wrist pins. AFAIK you can install the rods so the piston marks face the flywheel end. The rods are symmetrical to the best of my knowledge so you don't have to have the side with the numbers facing the same direction as the factory did it. I've seen more than one set of rods with the numbers facing the other way because of how the pistons were installed.

If I'm incorrect others can comment.

monzadon
Posts: 116
Joined: Fri Aug 11, 2017 3:35 am

Re: Pistons

Post by monzadon »

You said the numbers on the rods don't have to face the way the factory did it so can i just take the pistons that the machine shop did wrong and just turn them the opposite way to what the factory did, would. This possibly throw the crank out of ballance? or should have the machine shop.put them the right way?

66vairguy
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Re: Pistons

Post by 66vairguy »

You can go to the Corvair Center Forum and ask. There has been some debate about which way the numbers should face. Some were concerned about the large end bearing tang location, but others said it varies even when all the numbers are correctly orientated.

Just me but I would not re-use a piston after the wrist pin is pressed out. Others can comment.

If you didn't instruct the machine shop how to orient the piston with respect to the stamped rod number, then I doubt you can hold them responsible.

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terribleted
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Re: Pistons

Post by terribleted »

66vairguy wrote:
Wed Aug 26, 2020 5:07 pm
BTW -- DO NOT redo the wrist pins. AFAIK you can install the rods so the piston marks face the flywheel end. The rods are symmetrical to the best of my knowledge so you don't have to have the side with the numbers facing the same direction as the factory did it. I've seen more than one set of rods with the numbers facing the other way because of how the pistons were installed.

If I'm incorrect others can comment.
This sounds right to me. Never really thought about it as I make sure the pistons are mounted the correct way.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia

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