Removing and Fitting Chevrolet Piston
This article is ONLY FOR CHEVROLET OLD CARS ( ANTIQUE MODELS )
Raise the piston ring and insert a table knife or hack saw blade. As the knife is slipped back of the ring and guided around the piston with one hand, the ring is forced out of the groove with the other hand.
Remove the piston rings over the top of the piston and it will be found easier to remove the top ring first, then the center and lastly the bottom.
The piston and connecting rod may either be held in a vise or supported on a bench.
If held in a vise, rest the bottom of the piston on the top of the vise and tighten jaws against connecting rod.
Be careful in handling a piston its walls are light, and may be easily sprung, causing the piston to be out of round.
Removing Piston from Connecting Rod
To remove the piston from the connecting rod loosen the clamp screw and push out the piston pin.
Fitting new pistons is often resorted to where the compression is weak or the pistons and valves carbonize readily, when in reality the difficulty is due to improperly fitted or worn piston rings.
Roughly speaking, the pistons should not be replaced until the motor has been in service a long time, and the cylinder walls have worn so that the pistons slap badly when ascending grades, or on hard pulls.
Do not confuse “carbon knocks” with “piston slaps;” remember that on a cold motor there is usually a slight metallic clicking which will disappear as soon as the motor heats up.
With a clean motor, that is, carbon removed from piston heads and valves and properly fitted piston rings, there is little need to consider replacement of pistons until after the cylinder walls have become worn to a considerable extent.
If it is necessary to replace the pistons on account of piston slaps due to excess clearance and it is found that by fitting to a proper clearance at the upper part of the cylinder where the piston rings bear on the wall and the wear is the greatest, that the piston binds or does not have sufficient clearance at the lower part of the cylinder, the cylinder should be reground or reamed.
To determine the condition of the cylinders, use a piston and a thickness gauge of sufficient thickness to fill up the space between the cylinder wall and piston. Insert the piston and gauge at the top and bottom of the cylinder bore. If the piston binds at the bottom of cylinder and is free at the top, you will know the cylinder is tapered and should be reground or reamed.
To determine if cylinder walls are out of round, insert piston with gauge into cylinder bore, noting the clearance. Remove piston and turn “one quarter turn” with the gauge in same position on the piston, and again insert in the cylinder. If the clearance is not the same, the cylinder is out of round and should be reamed or reground and oversize pistons fitted. For that purpose we carry a stock of pistons, three, five, ten and fifteen thousandths oversize.
Inside micrometers, if available, may be used to determine the condition of the cylinder bore.
Chevrolet pistons are made oval, that is, the diameter through the piston pin hole is less than the diameter at right angles to the hole.
This is done to prevent the pistons from scoring, as the greatest expansion takes place through the piston pin bosses.
In measuring the clearance between the piston and cylinder walls, always do it at right angles to the piston pin and on a line with it.
The Models Four-Ninety Superior and G are equipped with cast iron pistons and the clearance should be from 2M to 3 thousandths of an inch.
The Models FA, FB and T are equipped with lynite pistons and the clearance should be about 3 thousandths of an inch.
To measure the clearance remove the rings from the piston and it slip it into the cylinder.
Secure a narrow strip of sheet brass or steel three thousandths thick.
Insert this between the piston and the cylinder, sliding the piston well into the cylinder bore.Then remove the gauge. For a properly fitted piston, some resistance should be felt, that is, you should feel the gauge” binding” on the piston and cylinder. •
Do not attempt to fit the pistons closer than this, as some room for expansion must be provided, and our experience has shown this to be the inside limit.
Powdered emery, glass or other abrasives should never be used to “grind in” an oversize piston, for three reasons.
FIRST : A piston which is made oval cannot be ground true, except on a special grinding fixture.
SECOND: The grinding takes place Steel Gauge on both the piston and cylinder walls, therefore, as the piston is oval the cylinders will be made” out of round.”
THIRD: The compound works into the pores of the cylinders, and no amount of washing or brushing will remove it. Therefore, it stays there and continues its job of grinding, making an early renewal of the piston and cylinder a certainty.
In almost every locality there are machine shops equipped to regrind or rebore cylinders and we recommend that when an operation of this kind is necessary, the work be instructed to them, providing you do not have such equipment in your shop.
Removing and Fitting Chevrolet Piston Article Source : This article courtesy should goes to : Chevrolet Repair Guide of 1923 by Chevrolet Motor Company.