Subject:RE: RE: RE: RE: Need help with piston! Date:Fri May 24 21:47:48 2013
Response to:18506

Word of caution, if you bore .030 or more the walls of the
ccylinder will be very fragile at the bottom, handle with
What is the suggested piston / cylinder bore clearance on a
ST165 that is raced? I ordered a repair / service manual
from Al Lyons two weeks ago and havenít gotten it yet.

I was hoping to just get by with a quick hone job, but may
have to bore it to 0.030 over.

The old piston has a small ďchunkĒ missing between the ring
gaps. Probably usable but Iím going new.

Tom Van Beek has the bottom end of my engine, replacing all
the bearings. So I might as well put a new piston in it, and
not have to worry about it for a few years.

If your at 2.403 wouldn't your cylinder clean up for a .030
over stock piston bringing you to at least 2.405 plus
whatever the piston to bore clearance spec is or am I
missing something ? You also say in your message that you
can't find a .025 over piston anywhere, according to your
measurements it sounds like your piston's fine. All you may
need is a hone and re ring , now the question is have you
looked around for .025 over ring's ? You should try Mutt as
was brought up in an earlier message . That guy has more
knowledge locked in that brain of his than a friggin
Good luck ,enjoy the ride,half the fun's getting there.j.d.

It's my understanding the factory offered .010", .020" &
.030" oversize pistons. The aftermarket companies (like
Hepolite) offered .040" & .050" pistons for the brave of
heart. If you're running a race engine I'd overbore and add
a few thousands of an inch over suggested clearance to avoid
seizer. I'd check with Mutt on his recommendations.

Hello all, I am in need of some help finding a new
piston / rings for my 1956 ST165. I have been told the
standard piston for this bike is 2.375. The old piston out
of my bike measures 2.400, with a bore of 2.403. So I am
assuming my cylinder has been bored 0.025. Well, I canít
find a 0.025 over sized piston, anywhere. Harley
has over sized pistons in 0.020 increments, which is no help
to me. Anyone know where I can find a 0.025 over piston
w/rings? Need ASAP because Iím racing at Wauseon in 8 weeks.
Please email me as well as replying here so Iím sure to get
it. Thanks.