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#114645 - 04/23/07 7:23 pm Pinking on a 78 Bonnie  
Joined: Jan 2006
Posts: 28
Bonnieboy Offline
BritBike Forum
Bonnieboy  Offline
BritBike Forum

Joined: Jan 2006
Posts: 28
Epsom Surrey
Just had my beloved Bonnie rebuilt at vast expense.Ran it in for 500miles, and on first trip out taking to 3500revs she seized, top of Piston disintegrated. Mr Mechanic says did this coz' of my abuse!! But it was pinking & no way I would abuse my Bonnie(owned since new)He put new Pistons in-but it is still Pinking and I am worried same thing will happen again. Using Leaded/SuperU as before-Timing spot on. My mate recons I should retard couple of degrees and should solve problem ANY IDEAS PLEASE

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#114646 - 04/23/07 9:15 pm Re: Pinking on a 78 Bonnie  
Joined: Dec 2004
Posts: 8,896
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,896
Scotland
1. If the said mechanic timed the bike then get a new mechanic.

2. If you were running the bike in at low revs and it was pinking you should have stopped running the bike.

3. As your mate says retard the timing and run on highest octane fuel available eg Shell Optimax. If it pinks retard some more until it doesn't.

4. Check the piston to bore clearance before running again.

5. Read John Healy's posts on lugging Triumphs.

#114647 - 04/23/07 11:37 pm Re: Pinking on a 78 Bonnie  
Joined: Mar 2005
Posts: 9,971
John Healy Online content
John Healy  Online Content



Joined: Mar 2005
Posts: 9,971
Boston, Massachusetts
While the "book" states you should time the T140 motor to 39 degrees, Brian Jones, Triumph's engineer found in extensive tests with gasoline provided by MIRA (English automotive testing grounds) that emulated what was available in the US at the time, that the bike would ping less if timed to 37 degrees.

While T140's are prone to pinging, they are most vunerable to detonation damage during the break-in period. There are two things working against you: 1. the rings are not broken in with reduce capacity to transfer heat out of the piston and 2. The oil that is getting by the rings into the combustion chamber reduces the effective octane rating of even the best gas available.

Further, there is a trend in the vintage trade to emulate a lot of cylinder preparation techniques used with modern cars and motorcycles that use steel or ductile iron rings. These rings are pre-lapped round at the factory and do not require the break-in of grey cast iron rings.

Grey cast iron rings are lapped in situ during break-in. Thus using a modern 300 plus grit surface finish, made worse by planar honing techniques, reduce the ability for rings to hone themselves round.

The old rings of the damaged pistons, if not roughed up too much during the seizure, can often tell the tale. Look at the ring there should be a shiny silver wear mark 360 degrees around the BOTTOM of the two compression rings. If it is not there or intermittent the bore was too "smooth" and the rings didn't get "honed" or broken in.

Also the wrist pin can give you a lot of information as to the piston's temperature during the seizure. For example: if the wrist pin is still silver colored, as it came out of the box, the seizure would NOT have been heat related and I would check the piston clearance.

There are other basic assembly techniques that will toughen a motor to detonation. Being sure the head gasket doesn’t stick into the bore, the valve seats aren’t narrowed to racing spec’s ( we like .075 inch or wider for the street). Remove all of the sharp edges from the piston. Be sure the valve’s exterior margin isn’t too thin, etc…
Good luck… John


#114648 - 04/24/07 3:17 am Re: Pinking on a 78 Bonnie  
Joined: Jan 2007
Posts: 57
Floss Offline
BritBike Forum member
Floss  Offline
BritBike Forum member

Joined: Jan 2007
Posts: 57
Queensland Australia
Hi all
another possible cause is that if you had the cylinder barrels nicely powder coated during the rebuild, you would have drastically reduced the effectiveness if the fins to disapate heat. All the minute pore in the casting are filled in and greately reduces the fin surface area.

I have seen a bike sieze after two rebuilds as a result of this.

good luck

Floss


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