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Author Topic: Maximum allowable piston/cylinder wall clearance  (Read 238 times)

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dermohar

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Maximum allowable piston/cylinder wall clearance
« on: December 21, 2018, 19:26:59 »

Does anyone know the spec  (factory or otherwise) for the maximum allowable piston/cylinder wall clearance for a used engine?  I have a couple of used engines, want to determine which ones are really usable.

As an engine is used, the cylinders do not wear evenly - greater wear down lower due to the thrust of the piston against the sides of the cylinder.

In the area of maximum wear, what is the max spec before rebore/rering/new pistons are recommended?

I have cars with slant six engines but I'm sure the 318, etc are much the same specs.  (Have a dial bore indicator and caliper for pistons)

Thxs
« Last Edit: December 21, 2018, 19:28:06 by dermohar »
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M_Body_Coupe

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Re: Maximum allowable piston/cylinder wall clearance
« Reply #1 on: December 31, 2018, 09:37:39 »

Hi Dermot,

The 1980 FSM, in the Engine section (9-41) shows the following:

1) Cylinder Bore Inspecting
- Out-of-round measure of 0.005" max
- Taper measure of 0.010" max

My experience has been that the top of the bore is what usualy wears faster. This being primarily due to the piston ring loading against the bore during power stroke. That is not to say that bottom bore can see wear due to piston scruffing, etc...but in most cases the top is where the wear happens, right to the point of having that dreaded 'ridge'.
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