I am using cast types, and the machine shop measured each piston and bored
the corresponding cylinder to .002 clearance. The pistons are standard cast,
and there was a 2 thou variation between the biggest and smallest.
I am considering throwing this scored motor back together as is, to give me
time to build another engine with the care that is required. The oil ring
scores are only deep at the extremeties of the stroke, and the engine was
actually running fine still except for the oil consumption and pinging which
would have been caused when the ring finally broke. As the compression rings
are further up the piston they will still be sealing completely when nearing
maximum stroke, which is when it is needed most
If I swap pistons creatively, and hone to .004 or .005 clearance I think I
can remove all but the deepest parts of the gouge, which would leave 4 areas
only a 1/4 inch long and maybe 1/16 wide by 4 or 5 thou deep.
Otherwise I could get another block, rebore to my pistons and just transfer
the whole lot, but if I can save the block it would be preferrable.
I measure .0025 clearance in the big ends, which seems OK as you say, but as
my oil pump was standard and not overhauled, it would explain why my oil
pressure was on the low side (30lb hot at 4000rpm using 10W40 semi
synthetic)
Greg
----- Original Message -----
From: Jarrid Gross <JGross@econolite.com>
To: Greg Locke <glocke@ihug.co.nz>; Alpine list <alpines@autox.team.net>
Sent: Wednesday, 14 March 2001 10:09
Subject: RE: engine clearances
> Greg wrote,
>
>
> >What is an ideal piston to bore clearance, and a maximum acceptable
> >clearance for .080" standard type pistons in a reasonably tuned (110hp)
> >engine revving to 6500 (noise is not a worry).
>
> Depends upon the type of piston that you are using.
> Cast types tent to run tight, and forged tend to run looser.
> When an internal strut is designed into the piston, they tend
> to run very loose so as to provide for controlled expansion.
>
> Clearances run from 2 to 6 thousanths, and are typically dictated
> by the piston manufacturer.
>
> Stock pistons are at the lower end of the chart.
>
> The next issue as far as piston noise is concerned would be
> pin thrust.
>
>
>
> >Also, what would the ideal and max big end clearances be.
>
> For race, 2 to 3 thousanths is typical.
> For stock, 1 to 2 (1.5 typ).
>
> the larger clearances like more oil pump volume.
>
>
> Jarrid Gross
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