BritBike Forum logo
BritBike Sponsor BritBike Sponsor BritBike Sponsor
BritBike Sponsor

BritBike Sponsor

BritBike Sponsor
BritBike Sponsor BritBike Sponsor BritBike Sponsor
The Bonneville Shop JRC Engineering dealers
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
Member Spotlight
Mike Austin
Mike Austin
Murrieta California
Posts: 26
Joined: September 2017
Show All Member Profiles 
Shout Box
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Who's Online Now
41 registered members (Alan_nc), 278 guests, and 392 spiders.
Key: Admin, Global Mod, Mod
Newest Members
Tim Pedder, blayde54, Davenz13, Sean65, Rerock
10478 Registered Users
Top Posters(30 Days)
NickL 89
franko 78
Triless 69
Popular Topics(Views)
748,756 mail-order LSR
Forum Statistics
Forums34
Topics68,848
Posts670,637
Members10,478
Most Online3,995
Feb 13th, 2017
Like BritBike.com on Facebook

Previous Thread
Next Thread
Print Thread
Rate Thread
PistonRings #758209
12/05/18 11:52 am
12/05/18 11:52 am
Joined: Feb 2012
Posts: 211
UK Tyne & Wear
P
photobob Offline OP
BritBike Forum member
photobob  Offline OP
BritBike Forum member
P

Joined: Feb 2012
Posts: 211
UK Tyne & Wear
I have a 1963 A65 Star Twin I have the barrels off at the moment to check if they need a rebore. The barrels at present are standard, I have carefully measured the wear in the bore and the maximum wear which is at the top is.003"this is the difference between the bottom unworn part of the bore and the top. The manual states that if wear is over.005" then a rebore is required, as mine are under that it should not need a rebore at present. I have also checked the piston clearances top middle and bottom this also confirms .003" maximum wear. I have a new set of standard piston rings but on trying them in the bore I find that in the unworn part of the bore I have a piston gap .015" and in the worn part of the bore it is .018". The manual states that the piston gap should be.008" to .013" so the new rings are above that recommendation is this normal. I have also measured the cylinder bore in the unworn part and it measures 2.9525" the manual standard bore size states 2.9521"-2.953"
Just to give some background on this bike, the pistons that are in now are the original pistons that it left the factory with in October 1962 it is a 1963 model and was not first registered until June 1963 these pistons have BSA cast into recess where the gudgeon pins go and the number on the otherside is 68-251. The bike has done approx 13,500 miles from new. when I bought it some 6 years ago it had stood dismantled for over 30 years,it only did 4,000 miles in the first 12 years of it's life.


Last edited by photobob; 12/05/18 12:14 pm.
Support your #1 BSA Forum and our favorite sponsors

Check out BSA on e-bay: BSA Parts in UK, BSA Motorcycles in UK, BSA Parts in North America, BSA Motorcycles in North America

 
Re: PistonRings [Re: photobob] #758210
12/05/18 11:54 am
12/05/18 11:54 am
Joined: Dec 2004
Posts: 9,667
Scotland
kommando Offline
BritBike Forum member
kommando  Offline
BritBike Forum member

Joined: Dec 2004
Posts: 9,667
Scotland
You can get away with larger than allowed ring gaps, much better than too tight a gap.

Re: PistonRings [Re: photobob] #758212
12/05/18 12:12 pm
12/05/18 12:12 pm
Joined: Aug 2001
Posts: 7,671
scotland
triton thrasher Online content
BritBike Forum member
triton thrasher  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 7,671
scotland
Your ring gap is not too big. Don’t worry about it.

Making the gap in the second ring 30% bigger than the top ring gap improves sealing.


Amateur Loctite enthusiast.
Re: PistonRings [Re: photobob] #758215
12/05/18 1:20 pm
12/05/18 1:20 pm
Joined: Feb 2018
Posts: 100
Oklahoma
T
Tracey Spear Offline
BritBike Forum member
Tracey Spear  Offline
BritBike Forum member
T

Joined: Feb 2018
Posts: 100
Oklahoma
Is there a risk of metal fatigue in the rings from squeezing and releasing .003 on every stroke?

Re: PistonRings [Re: photobob] #758219
12/05/18 2:11 pm
12/05/18 2:11 pm
Joined: Dec 2004
Posts: 9,667
Scotland
kommando Offline
BritBike Forum member
kommando  Offline
BritBike Forum member

Joined: Dec 2004
Posts: 9,667
Scotland
No, if they did then I suspect all my engines would need re boring and they are currently fine and most on second set of rings from worn rings not broken rings, the wear limit is 5 thou over original top limit so 3 thou is well within.

Re: PistonRings [Re: kommando] #758236
12/05/18 5:15 pm
12/05/18 5:15 pm
Joined: Feb 2012
Posts: 211
UK Tyne & Wear
P
photobob Offline OP
BritBike Forum member
photobob  Offline OP
BritBike Forum member
P

Joined: Feb 2012
Posts: 211
UK Tyne & Wear
Thanks for those comments it puts my mind at rest.This all started because I was convinced that I was hearing piston slap but I doubt it now.

Re: PistonRings [Re: photobob] #758240
12/05/18 5:59 pm
12/05/18 5:59 pm
Joined: Aug 2001
Posts: 7,671
scotland
triton thrasher Online content
BritBike Forum member
triton thrasher  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 7,671
scotland
Piston slap?

Racing clearances, mate!


Amateur Loctite enthusiast.
Re: PistonRings [Re: photobob] #758245
12/05/18 6:44 pm
12/05/18 6:44 pm
Joined: Sep 2004
Posts: 900
Farnham, Surrey, UK
gunner Offline
BritBike Forum member
gunner  Offline
BritBike Forum member

Joined: Sep 2004
Posts: 900
Farnham, Surrey, UK
What make are the new rings you are using? Many of the replacement rings available including Hepolite are actually manufactured in the far east these days, the fit may not be as accurate as the originals.

If your'e seriously concerned about the ring gap It may be worth shopping around and trying a set from another maker.

Don't forget to de-glaze the bore and run the engine hard for the first few miles to get the rings to seat.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: PistonRings [Re: gunner] #758247
12/05/18 7:11 pm
12/05/18 7:11 pm
Joined: Aug 2001
Posts: 7,671
scotland
triton thrasher Online content
BritBike Forum member
triton thrasher  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 7,671
scotland
Originally Posted by gunner
What make are the new rings you are using? Many of the replacement rings available including Hepolite are actually manufactured in the far east these days, the fit may not be as accurate as the originals.

If your'e seriously concerned about the ring gap It may be worth shopping around and trying a set from another maker.


There is nothing wrong with his ring gap. New British Hepolite rings in a new bore often had gaps about 18 thou in a bore that size. And he’s got used bores.


Amateur Loctite enthusiast.
Re: PistonRings [Re: photobob] #758253
12/05/18 8:21 pm
12/05/18 8:21 pm
Joined: Dec 2002
Posts: 3,279
arkansas
L
leon bee Online content
BritBike Forum member
leon bee  Online Content
BritBike Forum member
L

Joined: Dec 2002
Posts: 3,279
arkansas
I suppose one of the scientists could come along and argue, but I agree with all the above. .018 is fine. In fact, ever since reading a John H. post about too close gaps popping the heads off new asian pistons, I do about .018 anyway. I know you have original pistons, but it'll be fine.

Re: PistonRings [Re: photobob] #758262
12/05/18 9:19 pm
12/05/18 9:19 pm
Joined: Aug 2001
Posts: 7,671
scotland
triton thrasher Online content
BritBike Forum member
triton thrasher  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 7,671
scotland
If your hot ring gap attempts to go less than zero, your engine’s top end will meet its doom.

Like wives and sweethearts, ring ends should never meet.


Amateur Loctite enthusiast.
Re: PistonRings [Re: triton thrasher] #758338
12/06/18 11:47 am
12/06/18 11:47 am
Joined: Feb 2012
Posts: 211
UK Tyne & Wear
P
photobob Offline OP
BritBike Forum member
photobob  Offline OP
BritBike Forum member
P

Joined: Feb 2012
Posts: 211
UK Tyne & Wear
They are the new style Hepolite rings have been hearing some adverse comments about these so I think I will buy some from a different maker and compare but most of the main dealers in the UK are supplying these Hepolite rings so are they really that bad.

Re: PistonRings [Re: photobob] #758339
12/06/18 11:50 am
12/06/18 11:50 am
Joined: Sep 2004
Posts: 900
Farnham, Surrey, UK
gunner Offline
BritBike Forum member
gunner  Offline
BritBike Forum member

Joined: Sep 2004
Posts: 900
Farnham, Surrey, UK
You can get Hastings rings for the A65 which are excellent quality and also use a three piece oil control ring which helps.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: PistonRings [Re: photobob] #758382
12/06/18 10:44 pm
12/06/18 10:44 pm
Joined: Jan 2014
Posts: 4,171
Aus
N
NickL Offline
BritBike Forum member
NickL  Offline
BritBike Forum member
N

Joined: Jan 2014
Posts: 4,171
Aus
Those new hepolite rings are ok, It's the prep that needs to be correct, nice coarse hone.
As for gaps I've taken motors apart that had bigger than 30 thou on the rings and they didn't smoke.
The book says 8-12 thou from memory but 15-20 is fine. (TT mentioned a slightly larger 2nd gap which can help.)
Not everyone has had great results with Hastings rings, a few blokes here have had a few out-of-round ones.
They also use a chrome top ring on some a65 kits which tends to take a lot of bedding in.
H+G sold by SRM are good, On a65 +0.040 and upwards i tend to use Harris T140 rings, i like the 2 piece oil ring they use.
Everyone has their favourites, like chocolate bars eh?


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: PistonRings [Re: photobob] #758386
12/06/18 11:01 pm
12/06/18 11:01 pm
Joined: Aug 2001
Posts: 7,671
scotland
triton thrasher Online content
BritBike Forum member
triton thrasher  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 7,671
scotland
I can vouch first-hand that 30 thou ring gaps don’t cause problems on another popular marque of Brit twin.


Amateur Loctite enthusiast.

Moderated by  Allan Gill, Jon W. Whitley 


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
Powered by UBB.threads™ PHP Forum Software 7.6.2