Also a good opportunity to re-check your timing with the head off. RonHaven't cleaned off the soot yet as was going to discard that piston. If I remember last time I had head off think it was genuine piston. The one in my refurbed barrel has a genuine crossed rifles 1/2 mm oversize piston so will see how that runs. When I get it on. Then will see what I can do with the seized barrel. Need it checking and new piston.
Checking timing. Presume you mean measure the piston movement for spark to occur just before tdc.
I will give that a check.
Paul Crisp
email (option): bsa945@btinternet.com
We usually do. But went straight home this time.
Paul Crisp
email (option): bsa945@btinternet.com
Checking timing. Presume you mean measure the piston movement for spark to occur just before tdc.
I will give that a check.
Paul Crisp[:)
Yes Paul. As you are probably aware. Too retarded will cause it to run hotter. Near enough is not good enough
The piston should be at 7/16" BTDC with the handle bar lever at full advance....Points just breaking. So much easier to get right with the head off I had the same experience some years ago with my M20. It nipped up a few times even after 200+ miles of careful running in. Mixture good! Timing correct! and it buggered up my piston like yours. It just needed another 1 thou hone out. Ron
PS. I wonder if modern fuel has any issue?
email (option): ronpier@talk21.com
Paul,
I can give you some sound advice on your engine and how to run it, i even may be able to supply a genuine NOS piston depending on your size. I have run and worked on these things for years, also im only over at Huddersfield.
Just send me a direct mail and we can swap phone numbers.
Tim W
email (option): t.j.walker@btinternet.com
Also a good opportunity to re-check your timing with the head off. RonHaven't cleaned off the soot yet as was going to discard that piston. If I remember last time I had head off think it was genuine piston. The one in my refurbed barrel has a genuine crossed rifles 1/2 mm oversize piston so will see how that runs. When I get it on. Then will see what I can do with the seized barrel. Need it checking and new piston.
Checking timing. Presume you mean measure the piston movement for spark to occur just before tdc.
I will give that a check.
Paul Crisp
was a BSA 1/2mm oversize piston.
have a 1mm oversize and the one in my spare barrel ( the one I am going to now put on is a 1/2 mm oversize too.
Paul,
Looking at you pics again the piston looks to have been running in the linered cylinder for a while, It could be genuine as it looks to have a Welworthy oil ring not like the new ones. The piston also has burnt oil under the oil ring to suggest it had been in there a while. You did not say how long you have had the bike and what miles you have done on it.
So why did you have the seizure, could be a few things main ones as Ron says timing and tight bore but if you have had the bike and ridden it a lot the tight piston would have nipped up before now. Could be running weak on the main jet as you said you were on the Beverley bypass so would have been on the main jet, the blackness you have now could have come from a rich pilot jet as you said you had run in gently after the seizure so this could mask the weak main jet. Dual carriageways and long bypasses don't do out long stroke engines any good holding them at high revs on the main jet for long periods with this new fuel. These engines in their day never came across full throttle for long periods so if you are to use them like this check for weakness at full throttle and just shut off every now and then.
Your cylinder looks like it will clean up with a hone it looks to be only alloy from the piston stuck on the liner you can then check the piston clearance on the thrust face. There looks to be plenty of clean oil about so that was not the problem, also your valves look nice and proud so if it was mine i would use the cylinder fitted find a genuine piston, hone the cylinder and check the clearance and magneto timing, and check the magneto lever has enough friction to keep the cable on full advance when you are riding it, wet sumping is a other issue and nothing to do with your seizure.
Hope it gives you some ideas
Tim W
email (option): t.j.walker@btinternet.com
I think you may be right about the bore, it does look only superficial alloy, just surface laid. seems to be no scoring or tram lines anywhere so anti glazing, a little honing may do the trick.
I have had the bike some time, but only pottered about sorting out basic stuff like Carb, Magneto, replaced mag dyno oil seal, new tyres, repaired broken lug that holds on the rear stand. :-) normal stuff.
Only have done around 140 miles on it then seizure.
Could be slightly out like ron said when I set up timing after Mag refitted.
Will double check this timing.
Apparently came from Ireland and was in service there before I got it.
I do have a spare barrel which I have had refurbed to fit my spare NOS 1/2 mm OS piston. Used an RM11 Dragonfly Oil ring set and managed to source a nice oil ring from Cox and Turner Engineering. Otherwise would have needed to open wider the oil ring slot for the RM11 oil ring.
So now two choices, hone up the old Barrel, fit new spare piston. After checking rings for for correct gaps of course.
Or
Fit valve springs to new Barrel. (Just need to get a spring compressor to fit valve springs.) Then fit new refurbed/painted spare Barrel.
Got my New gasket sealing stuff now.
My old Hylomar tube had gone solid in my tool box.
So now fresh tube.
when I get to put exhaust back hope you guys use the same stuff as this HOLTS firegum.
Decided to put recon spare Barrel onto bike. New springs fitted to new valves all nicely relapped in.
New piston fitted.
Gasket on barrel fitted.
Now to check out the points opening while piston easy to measure.
Paul Crisp
Tims point about weakness at the top end is very relevant...Check the main jet size is correct, needle is straight and that it's clip is in the correct groove for base settings..
Also check you have the correct throttle cutaway...
I'd recommend fitting a solid copper head gasket as well..If that is annealed fully no gasket sealant is needed on the head joint assuming the faces are good...Check the cylinder head gasket face is flat with a straight edge...
Ensure you have an annealed copper gasket under the cylinder head timing access bolt and check that the carb mounting flange is flat..Fit new gaskets to the carb joint as required...
Check the settings of the valve lifter carefully to ensure it is clear of the tappet head with the ex. valve fully closed...
Be ABSOLUTELY sure you have the timing set correctly..It is critical you avoid setting it at all retarded...There is a lengthy piece on the subject in the 'technical section' of the forum....
Retarded timing settings and mixture weakness are the two enemies of these engines, both of which can increase running temperatures to the point where damage is done......Ian
email (option): ian@wright52.plus.com