BritBike Forum

Home, Sponsors
Newsletter, Regalia
Calendar, Bike Project
BritBike Museum
Spiders Cartoons
"OLD" BritBike Forum

DVD- Manuals & Parts books
BritBike Stickers & Decals
Upgrade to:
Premium Membership Premium Life Membership
Vendor Membership Site Sponsor Membership

Photo posting tutorial

Sponsors campaign ads..
BritBike Sponsor
BritBike Sponsor
BritBike Sponsor
BritBike Sponsor
BritBike Sponsor
Shout Box

Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Member Spotlight
Member Since: 09/15/11
Posts: 673
Who's Online
77 registered (reverb, robcurrie, Jack Adams, Boomer, Triless, c caspary, KC in S.B., Paul Sammut, ken sak, ricochetrider, No Name Man, Ignoramus, bill50cal, TR6Ray, JoelH, jurbanec, KADUTZ, Jon W. Whitley, Kerry W, htown, Glen Breaks, enigmaT120, franko, Stein Roger, Mike W., royaloilfield, Mark Z, Tridentman, eezeetoo, Peter Quick, Allan, noisy norton, Tasman, Shane in Oz, bsalloyd, Gary E, mxman1, Richrd, Pender, Bob Buchanan, GrandPaul, Rich B, fettlefart, Zombie, JD, bon, Brody kolbeck, Mike P, Lannis, Randy Pigford, D.Bachtel, Jeff K., koncretekid, jfligg, skidog, mac, kurt fischer, Bola, Sam, konon, BeezaBryan, 68triton, MaaseyRacer, Mr Jazzbo, machico, Bodie, penna-john, GaleGorman, greg mack, DMiller, JBMorris, Mike, in Idaho, Fetch, Don Leaming, David in Atlanta, Ken Hosford, Tiger100), 456 Guests and 119 Spiders online.
Key: Admin, Global Mod, Mod
Newest Members
Johnvr, ChM, Sarge, Dave Shaw, T160red
8428 Registered Users
Top Posters (30 Days)
Lannis 211
kommando 90
Allan Gill 85
wadeschields 80
Stuart 77
NickL 75
KC in S.B. 75
triton thrasher 75
ricochetrider 67
Gordon Gray 65
Forum Stats
8,428 Registered Members
33 Forums
56,029 Topics
524,098 Posts

Most users ever online: 1,804 @ 03/01/11 6:54 pm
Manuals on DVD (Free shipping)
BritBike.com Decals & Stickers (Free shipping)
BritBike.com decals & stickers
Topic Options
Rate This Topic
#371542 - 05/04/11 2:30 pm piston cylinder clearance, A65
oleandreas Offline
BritBike Forum member

Registered: 05/31/06
Posts: 198
Loc: Tynset Norway

Bsa A65, 1969. old 750 kit. Devimead.

Anyone have any opinion on a piston - cylinder clearance on 0,25 mm = 0,0984 inches.

I have recently got a Devimead cylinder, seems to be almost newbored, bore 80,05mm. No edge on the top inside the cylinder from wear, the pistons that came with measures 79,80mm, 90 degrees on the writspin, down on the piston. (79,25 mm on the top).

Is it worth trying with this clearance ? I know Normally its reccomended around 0,11 mm. I have cast iron cylinder and as far as I know the pistons are forged.

Alternatively Im checking with Ed V if he migth have some suitable and lighter pistons to sell me. These pistons I have here with the Devimeade cylinder weights 430 g with writspins, the Ed V pistons (B44, JE) I have for another project in bore 79,5mm weights 385g included wristpin. I guess lighet is always better.. IM using stock A65 engine, stock crank, ported head and bigger valves

Top
Support Your #1 BritBike Forum!
Membership Type! Free
Member
Premium
Member
Premium Life
Member
Vendor
Member
Site
Sponsor
Recognition No Premium Member Premium Life member (5 years) Vendor Member Site Sponsor Membership
Post commercial threads No No No Yes Yes
Custom title No Yes Yes Yes Yes
Upload avatar & photos No Yes Yes Yes Yes
Link avatar & photos Yes Yes Yes Yes Yes
Private Message Storage: 10 100 100 100 100
Length of signatures 255 600 600 600 600
Removes this very advert island between post 1&2 No Yes Yes Yes Yes
Price Free $12.90/year $105.00 No End
$55.00/5 years
$210.00/year
($17.50/month)
Email
Click on button >>
  Premium Member Premium Life member Vendor Member Site Sponsor Membership
#371543 - 05/04/11 2:43 pm Re: piston cylinder clearance, A65 [Re: oleandreas]
wak Offline
BritBike Forum member

Registered: 03/29/11
Posts: 809
Loc: derby england
.010" sounds a bit big .005" is the norm and as worked well for me.
_________________________
BSA CYCLONE
BSA METISSE
TRIUMPH TR6C
BSA BUSHMAN
INDIAN WOODSMAN

Top
#371546 - 05/04/11 2:57 pm Re: piston cylinder clearance, A65 [Re: oleandreas]
kommando Offline


Registered: 12/31/04
Posts: 6358
Loc: Scotland
Clearance will depend on the pistons you fit, the material they are made of if a big factor plus if they are cast or forged.

Top
#371547 - 05/04/11 2:57 pm Re: piston cylinder clearance, A65 [Re: oleandreas]
Alex Offline
BritBike Forum member

Registered: 09/05/02
Posts: 7702
Loc: NorCal
^^^What he said^^^^
_________________________
A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
sixtyseventy Lightboltrocket road racer...and many more.

Top
#371555 - 05/04/11 3:52 pm Re: piston cylinder clearance, A65 [Re: Alex]
oleandreas Offline
BritBike Forum member

Registered: 05/31/06
Posts: 198
Loc: Tynset Norway
If I understand you right, the clearance seems to big.

I have forged pistons, and cast iron sylinder. guess this set is from the 1970 or 1980s...

Top
#371556 - 05/04/11 3:58 pm Re: piston cylinder clearance, A65 [Re: oleandreas]
kommando Offline


Registered: 12/31/04
Posts: 6358
Loc: Scotland
According to this site

http://www.glmmarine.com/castvsforged.html

Pistons: Cast vs. Forged

GLM offers an extensive line of pistons for all major brands and models of outboard engines. GLM pistons, like OEM pistons, are cast as opposed to forged.

We have all heard the advantages of forged pistons. However, when you consider the disadvantages of forged pistons it becomes very clear why GLM cast pistons are the ultimate pistons for your rebuilding and repair projects.

The major disadvantages to forged pistons are actually a result of the forging process itself. Forging results in a piston that is considerably heavier, than cast pistons, and is limited in the aluminum alloys that can be used to produce the piston. Additionally, the forging process also limits the design configuration of the piston itself.

The forging process and its limited choice of aluminum alloys result in a dramatically higher expansion rate for the forged piston. This means that the set up characteristics are very different from the original engine manufacturers' and that break-in and warm up periods are crucial for the forged piston.

An example of the dramatic expansion of forged pistons is the piston skirt clearances in the cylinder. A typical forged piston has a skirt clearance of approximately .0007 to .0009. A cast piston has a skirt clearance of .005 to .007. The forged piston has 10 times more slop in the cylinder. This results in less ring stability against the cylinderical wall, more piston noise and extra blowby.

In all fairness, after the forged piston has reached operating temperature, its dramatic expansion makes up for these extra clearances. However, this should remind us of the typical customer that a dealer services. Can we expect the casual weekend boater to strictly observe the extended break in period and the critical warm up procedures required for a forged piston? Let your own experience answer this question.

Most forged pistons are quality products, but they are better suited to racing and professional applications.


Note only the manufacturer of the orginal pistons knows the recommended clearance, asking a forum with incomplete info (you don't say which brand pistons they are ) is asking for trouble.

Top
#371561 - 05/04/11 4:33 pm Re: piston cylinder clearance, A65 [Re: oleandreas]
Alex Offline
BritBike Forum member

Registered: 09/05/02
Posts: 7702
Loc: NorCal
When in doubt, 1.5 part/thousand clearance has not failed me once.
_________________________
A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
sixtyseventy Lightboltrocket road racer...and many more.

Top
#372055 - 05/08/11 2:23 am Re: piston cylinder clearance, A65 [Re: oleandreas]
jaycee Offline
BritBike Forum member

Registered: 09/17/08
Posts: 520
Loc: angeles city, rp
i read the post three times,as the link.im not the smartest fella in the world i admit,but i must respectfully submit that .0007-.0009''is significantly LESS than .005-009"

Top
#372104 - 05/08/11 1:16 pm Re: piston cylinder clearance, A65 [Re: oleandreas]
Mr Mike Offline

BritBike Forum member

Registered: 08/06/01
Posts: 3743
Loc: Cape Carteret, NC
I think what Alex is saying is a 3" diameter piston gets 3 x1.5/1000 equals .0045" clearance or .114mm. Alex, correct me if I am wrong. Ed V has bored a bunch of cylinders for me and not a smoker of slapper in the bunch. Send him your cylinder and he'll provide the piston and correctly fit them. If you wnat to use your piston send it also and he'll tell you what to do.

Mr Mike

Top

Moderator:  Mike Carter 


BritBike Forum

Home, Sponsors
Newsletter, Regalia
Calendar, Bike Project
BritBike Museum
Spiders Cartoons
"OLD" BritBike Forum

DVD- Manuals & Parts books
BritBike Stickers & Decals
Upgrade to:
Premium Membership Premium Life Membership
Vendor Membership Site Sponsor Membership