Okay lets cover another side note on this one...
The rings need to be down in the hole about .100 as a minimum when your
through... ( they will likey be Much farther then that )
A common mistake at Bonneville is to try and get the last degree of
compression by moving the upper compression ring within .50 to the top of
the piston... and since there is this little combustion process going on
above it ... well the rings get a little hot... and well they Melt stuff....
be it bores... pistons.. or themselves...
I guess the one thing I've learned out of all my efforts is that it's real
easy to out trick yourself... keep it simple... built power by builting in
reliability.... buy the good Valves.. seats.. pistons...rods and especially
spend good money on the best bolts you can get... torque them correctly to
properly machined surfaces.. and enjoy the damn thing...
I am Very guilty of using what I have on hand even if it's not the best when
rebuilding my Healey motors... it's dumb... just how many 100 blocks are
there lying around?
Just some food for thought.
Keith ( I'm going down to work on my hot rod... Bonneville is just around
the corner and I've got another 100hp....684hp and the record in C Gas
Modified Sports is 223mph.... since I went 246 with the old motor there is a
slight chance my wife is going to set a record this year )
----- Original Message -----
From: "Chris Dimmock" <cd3000@bigpond.net.au>
To: <healeys@autox.team.net>
Sent: Monday, June 14, 2004 5:36 AM
Subject: Re: how much can you take off the top of a piston?
> Hi All,
>
> Keith Said:
>
> " The edges of the pistons are going to have Huge quanity's of material...
> so
> I just don't think that's a factor... Having the wrong compression ration
> on the other hand can be ugly..."
>
> I totally agree.
>
> Pison Crown thickness is different to piston shoulder (outside diameter)
> thickness on a dished piston.
>
> i.e. a picture paints a thousand words - so here is an attempt at an asci
> art example of a dished piston...
>
> ____ ____
> l \ / l
> l \_________________________/ l
> l l
> l l
> ^
> l _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ l crown thickness ^
> l l
> l l
> =============================== top ring
> l l
>
> i.e on a dished piston, - "machining the top of the piston" - actually
means
> "machining the outside 'shoulder' of the piston - as Keith rightly said -
> and it only affects the compression ratio and piston/ head clearance. It
> generally has NO effect on piston strength
>
> I just checked the depth of the dish in an old piston from a 100/4 engine
in
> the garage - with a RULER - it was nearly 3/8in deep (.375 in) ..... so
> machining the shoulder by .030 will not affect the strength of the
> piston..... Check you own pistons more scientifically before
> proceeding......
|