BritBike Forum logo
BritBike Sponsor BritBike Sponsor BritBike Sponsor
BritBike Sponsor

BritBike Sponsor

BritBike Sponsor
BritBike Sponsor BritBike Sponsor BritBike Sponsor
  JWood Auction  
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

Member Spotlight
Lancs Tiger
Lancs Tiger
Wigan, Lancs, England
Posts: 30
Joined: July 2008
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
213 registered members (57nortonmodel77), 1,710 guests, and 564 spiders.
Key: Admin, Global Mod, Mod
Newest Members
Gilly, XTINCT, Bruce Roberts, Brian Ellery, Jon Andrews
9958 Registered Users
Top Posters(30 Days)
btour 191
koan58 100
Stuart 84
NickL 72
Popular Topics(Views)
438,248 mail-order LSR
Forum Statistics
Forums33
Topics65,286
Posts632,373
Members9,958
Most Online3,995
Feb 13th, 2017
Like BritBike.com on Facebook

Previous Thread
Next Thread
Print Thread
Rate This Thread
Page 1 of 2 1 2
#424828 - 03/18/12 8:01 am Modified a65 keeps pinching up.  
Joined: Feb 2010
Posts: 394
markoz Offline
BritBike Forum member
markoz  Offline
BritBike Forum member

Joined: Feb 2010
Posts: 394
Au
Hi its been a while since last post but ive been busy restoring a pinball and some watches.
I am having some major issue with my BSA Firebird with SRM 750 conversion.
I cant get it passed the 500 mile mark without it pinching up the left side piston, 3 times now. the engine tightens up to the point of seizure leaving a flat spot on the lower back of the piston. I have two barrels both professionally bored and it has happened on both. Piston clearance is correct and have had two different piston manufactures SRM and JP. OIl pressure appears correct. Could this be a result of a slightly bent rod or any other ideas please.
Thanks Mark

The way things are going i too might have to sell for $50000 like the eBay T-Bolt

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
#424832 - 03/18/12 10:00 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Aug 2001
Posts: 6,897
triton thrasher Online content
BritBike Forum member
triton thrasher  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 6,897
scotland
Originally Posted By: markoz
Piston clearance is correct.


Sounds unlikely that the clearance is "correct,", but are you sure you have no possibility of a weak mixture, too-high compression ratio or dodgy ignition timing?

Are you even running the engine at decently high rpm?


Amateur Loctite enthusiast.
#424838 - 03/18/12 10:08 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Feb 2010
Posts: 394
markoz Offline
BritBike Forum member
markoz  Offline
BritBike Forum member

Joined: Feb 2010
Posts: 394
Au
Hi Allan Clearance is 5 thou bottom of the skirt, done by professional engineer with good reputation.
This has happened with 2 sets of barrels
Mark

Last edited by markoz; 03/18/12 10:38 am.
#424846 - 03/18/12 10:44 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Dec 2004
Posts: 8,889
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,889
Scotland
We are shooting in the dark unless you give more details, what ignition are you using, what work has been done if any on the carbs, what rejetting did you do to cater for it now being a 750.

#424851 - 03/18/12 11:10 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Mar 2011
Posts: 827
wak Offline
BritBike Forum member
wak  Offline
BritBike Forum member

Joined: Mar 2011
Posts: 827
derby england
i would give it more than 5 thou,i had a 500 triumph(69 bore ) and that needed 6 thou even with geniune powermax pistons,the bible tuning for speed says between 2 to 3 thou per inch of bore,sprint engines have as much as 20 thou so i would go about 6 1/2 with 79mm bores


BSA CYCLONE
BSA METISSE
TRIUMPH TR6C
BSA BUSHMAN
INDIAN WOODSMAN
#424854 - 03/18/12 11:29 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Feb 2010
Posts: 394
markoz Offline
BritBike Forum member
markoz  Offline
BritBike Forum member

Joined: Feb 2010
Posts: 394
Au
Boyer ignition 32 deg btdc, 32mm Concentric carbs, slide 3,needle jet 106, needle bottom notch, main jet 190 i think, we were having trouble with fuel and sooting up plugs, flowed head, 9-1 comp, 43.5 mm inlet valves, high output oil pump, roller bearing conversion, srm pressure release valve

#424855 - 03/18/12 11:54 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Apr 2005
Posts: 2,332
Mark Parker Offline
BritBike Forum member
Mark Parker  Offline
BritBike Forum member

Joined: Apr 2005
Posts: 2,332
Bega NSW Australia
What part of NSW Mark? Anywhere near me?
When you say lower back of the piston your talking about the skirt where it runs on the centre of the bore facing the rear I expect? If the rod is bent one would expect the wear to be on the side.
If your motor has a roller conversion check that the position of the crank puts the rods central in the bores.
What did JP recommend for piston clearence in an iron cyl?
I've used JP B44 pistons in an alloy block and they were fine. The best pistons and rings I've used are JE forged B44 from Ed V. They can run quite tight even in an iron cyl.


mark
#424857 - 03/18/12 11:59 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Aug 2001
Posts: 6,897
triton thrasher Online content
BritBike Forum member
triton thrasher  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 6,897
scotland
Ok- a genuine measured 9:1 is highish on a 750 Brit twin nowadays, but maybe ok. Measuring compression ratio with a burette is the sort of thing you have to do if you build a a tuned oversize special, which is what you have done, no matter what "bolt-on" claims you may have heard from sellers of big bore kits, etc.

I'm assuming it's an iron barrel. Wak has gone to the trouble of looking up Irving's recommendations and it looks like you're well under his minimum. I'm using 5 thou clearance on an iron headed Triumph with 72.5 mm bore. It seems to work well, but it's no racer although it runs hot as bloody Hell. Once again, you have a souped-up bike which may need to be on the loose side of recommended clearance.

At the end of the day, you used up all the clearance you had, when it seized. Honing one of your barrels out sounds like it's worth a try.

Last edited by triton thrasher; 03/29/12 11:44 am.

Amateur Loctite enthusiast.
#424890 - 03/18/12 3:19 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Sep 2004
Posts: 269
EWebster Offline
BritBike Forum member
EWebster  Offline
BritBike Forum member

Joined: Sep 2004
Posts: 269
Are the oil spray holes present in the LH rod? Some seem to get away without them - others cannot.

#424903 - 03/18/12 4:18 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Dec 2004
Posts: 8,889
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,889
Scotland
190 seems too small for a main jet, based on using a bigger carb and incresing the bore I would have started at 230 to get it running rich and then worked my way down. Just because the plugs are fouling just says at one particular throttle opening you are too rich. So you could be too rich just at 1/4 throttle, ok at 1/2 and lean from 1/2 upwards.

#424906 - 03/18/12 4:21 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Aug 2001
Posts: 6,897
triton thrasher Online content
BritBike Forum member
triton thrasher  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 6,897
scotland
You've to credit him with enough sense to use carburettor settings derived from his own road or dyno testing.


Amateur Loctite enthusiast.
#424911 - 03/18/12 4:32 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Dec 2004
Posts: 8,889
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,889
Scotland
You've to credit him with enough sense to use carburettor settings derived from his own road or dyno testing.

Why?

When doing trouble shooting leave no stone unturned, I always look at what I did or did not do which I should first as I am normally the culprit. Realising it was my cock up is preferable to not finding the problem. Its not a blame game.

#424914 - 03/18/12 5:36 pm Re: Modified a65 keeps pinching up. [Re: kommando]  
Joined: Jul 2009
Posts: 3,549
Pete R - R.I.P. Offline
In Remembrance
Pete R - R.I.P.  Offline
In Remembrance

Joined: Jul 2009
Posts: 3,549
Vic. Australia
I'd expect to use a main jet somewhere between 220 and 250 with a 932 carb.
If it 8-stroked with the 250,I'd work down from there until it ran better.

#424915 - 03/18/12 5:47 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Feb 2010
Posts: 394
markoz Offline
BritBike Forum member
markoz  Offline
BritBike Forum member

Joined: Feb 2010
Posts: 394
Au
Thanks guys for the input. The 190 main do seem low but we worked down from 220 (Road). As for the oil hole in the rod i cant remember, i do have a set of new rods somewhere in the shed and i know one has the oilway.

#424922 - 03/18/12 6:04 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Aug 2001
Posts: 3,403
gavin eisler Online content
BritBike Forum member
gavin eisler  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 3,403
argyll. scotland, uk
Needle clip in lowest groove will give rich running this may have confused main jet selection by making the midrange over rich and helped wash oil off the bores leading to the nip ups.
What oil are you using?

Last edited by gavin eisler; 03/18/12 6:05 pm.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#425003 - 03/18/12 11:24 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Aug 2001
Posts: 3,348
BONZO R.I.P. Offline
In Remembrance
BONZO R.I.P.  Offline
In Remembrance

Joined: Aug 2001
Posts: 3,348
Michigan, USA
Here's a total shot in the fark but I haven't seeen it mentioned .Is it possible the piston skirts need to be clearanced ?Are there any witness marks in this area on the bad pistons?as the engine is assembled this can look fine but with revs the crank can flex and do some silly stuff .

FWIW-BONZO

#425016 - 03/19/12 1:08 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Mar 2005
Posts: 9,968
John Healy Online content
John Healy  Online Content


Joined: Mar 2005
Posts: 9,968
Boston, Massachusetts
Marl: The piston and wrist pin will often give up a lot of information about the cause of the seizure. We are not 16 again, "Working on mysteries without any clue."

The question is, did the piston seize from:

A Lack of Lubrication.
Area of piston seizure is constrained to the bottom edge of the thrust faces of the piston. Melted aluminum will be smeared UP across the thrust face. A little bit of pin discoloration. No burnt carbon underneath piston dome.

Lack of Clearance.
Area of seizure constrained to area just under oil ring. Melted aluminum smeared DOWN the thrust face of the piston. Very little pin discoloration. No burnt carbon underneath piston dome. Area under opposite side of seizure show signs of polishing - aluminum has started to melt.

Too much heat.
Dome of pistons show signs of detonation - aluminum pistons sparkles through burnt on carbon. Carbon burnt on under piston dome often flaking. Pin discolored from dark blue to purple. Seizure on four corners of piston just for and aft pin hole. Often seizure continues to area under oil ring.

The pin is telling!!!


#425043 - 03/19/12 5:32 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Feb 2010
Posts: 394
markoz Offline
BritBike Forum member
markoz  Offline
BritBike Forum member

Joined: Feb 2010
Posts: 394
Au
and the prize goes to............................
LACK OF CLEARANCE
Area of seizure constrained to area just under oil ring. Melted aluminum smeared DOWN the thrust face of the piston. Very little pin discoloration.

#425096 - 03/19/12 4:04 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Sep 2002
Posts: 7,812
Alex Offline
BritBike Forum member
Alex  Offline

BritBike Forum member

Joined: Sep 2002
Posts: 7,812
Seattle
Unless you are 100% certain of your mixture, particularly on the needle and main, you're asking for trouble. Particularly the needle mixture is oft ignored, despite the fact that this is where you spend most of your time. If you're lean on the needle, it will run hot and it will seize. Ask me how I know...


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#425146 - 03/19/12 9:23 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Sep 2008
Posts: 710
Blown Income Online content
BritBike Forum member
Blown Income  Online Content

BritBike Forum member

Joined: Sep 2008
Posts: 710
Edgewater, Md
If the sludge trap is clogged the left piston will seize. I'm running 6 thous. clearance on MC pistons in my a10. Your piston manufacturer should be able to tell you what clearance is needed.


1955 BSA Bantam D1 Plunger
1956 BSA A10RR Street and LSR Bike
1961 BSA C15S
1966 BSA spitfire
1969 Triumph T100C
1970 Triumph TR6R
1972 BSA Lightning LSR Bike
1974 Triumph T150V
#425169 - 03/19/12 11:46 pm Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Mar 2005
Posts: 9,968
John Healy Online content
John Healy  Online Content


Joined: Mar 2005
Posts: 9,968
Boston, Massachusetts
Alex: When you have that kind of heat seizure the oil will bake underneath the piston dome. The heat will migrate down the piston pin support casting on either side heating the pin. The temperature the pin reached, that caused the seizure, will be recorded in the color of the pin: Light Straw through dark purple into black.

Seizures, where the pin is still silver as it came out of the box and there is no burnt on carbon under the piston dome, is telling you the piston was within normal operating temperature and regular piston expansion caused the seizure.

Income: The lack of oil seizure is distinctive in that the seizing is at the bottom of the bore. Yes, if the crank is plugged with crap and oil isn't flowing, you can get a piston seizure.

Reading pistons for failure analysis is a bit subjective. Especially because a lot of references are for diesel, two stroke and water cooled engines. But there is a lot to see in a damaged piston and with a little common sense you should be able to sort out the cause. A lot of heat can only come from combustion. Gotta go... more later...


#426827 - 03/29/12 7:15 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Feb 2010
Posts: 394
markoz Offline
BritBike Forum member
markoz  Offline
BritBike Forum member

Joined: Feb 2010
Posts: 394
Au
Pistons out with evidence of pinching up


What do people think of these cut away pistons they do seem heavy with thick walls they are from JP pistons AU, should i clean them up and reuse or full replace. Cheers Mark
The blue color around the pins is a reflection

Last edited by markoz; 03/29/12 7:27 am.
#426828 - 03/29/12 7:41 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Mar 2011
Posts: 827
wak Offline
BritBike Forum member
wak  Offline
BritBike Forum member

Joined: Mar 2011
Posts: 827
derby england
Take the score marks off with a medium file cutting across ways hone a couple of thou out the bores and imho it will be fine


BSA CYCLONE
BSA METISSE
TRIUMPH TR6C
BSA BUSHMAN
INDIAN WOODSMAN
#426834 - 03/29/12 9:02 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: Apr 2005
Posts: 2,332
Mark Parker Offline
BritBike Forum member
Mark Parker  Offline
BritBike Forum member

Joined: Apr 2005
Posts: 2,332
Bega NSW Australia
Mark, just for interests sake, what do the pistons with pins weigh?
A +040" A65 piston and pin is 425G
A +020 JP B44 full skirt + pin 405.4G
A +020 JE B44 " " " " 375G


mark
#426835 - 03/29/12 9:06 am Re: Modified a65 keeps pinching up. [Re: markoz]  
Joined: May 2004
Posts: 3,548
BSA_WM20 Online content
BritBike Forum member
BSA_WM20  Online Content
BritBike Forum member

Joined: May 2004
Posts: 3,548
Sydney Australia
Yes, clean them up.
However I would go one further and machine the siezed piston so that it is back to the same profile as the other ( might be oval & not round ).
Take some better photos.
Turn off the flash, put your camera on a stand of some sort, measure the distance from the piston to the lens so that it is in clean focus then send them to JP asking politely for their recommendations.
They are usually more than willing to help when asked nicely.
JP's usually run with a big clearance.
Also carefully check your bore.
Easiest way is with a ring sitting on the bottom of an upturned piston to keep it square in the bore.
Light it from underneath and look for a consistent ring gap @ 1/4" intervals and also for light any where between the ring & the cylinder wall.
Ignore this if you have a lathe or mill and a good tickler gauge to check the bore with.
A lot of machine shops mount the cylinder from the head ( because that is the way cars are done ) in stead of the flange so you end up with a bore that is true to the sloping head and skewed to the crank.


Bike Beesa
Trevor
Page 1 of 2 1 2

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
UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.795s Queries: 16 (0.018s) Memory: 0.9969 MB (Peak: 1.3462 MB) Zlib disabled. Server Time: 2017-11-22 20:17:34 UTC