After running in for bit, as I stated, the engine felt like it nearly siezed, due to my poor riding, but it never did.
I striped it apart with much reluctance but bloody glad I did.
The 3rd down piston ring has seized in the groove, I need to replace the piston but thankfully the bore is perfect and polished with no scoring, I have caught this in time as it would of worn the bore unevenly if left.

Due to my recent job loss, has anyone got a +020 piston complete with rings at a reasonable price, I had a Gandini 4 piston ring piston, but now I have it apart would ideally like to replace with a Hepolite piston.

Julian.

email (option): 79aust@sky.com

Hi Julian...Sorry to hear the bike has expired...You need to be absolutely sure that the ignition timing is correctly set, the mixture is OK and there are no air leaks before you run the motor again...Do you have a solid copper head gasket fitted...?

It may be that slightly over exuberant use has caused your problem but if it wasn't that, you have to be careful not to simply repeat the process with another piston.....Ian

email (option): ian@wright52.plus.com

When rebuilding the engine double check the piston skirt clearances. Mine had been built (not by me) with the clearance just 2 thou on the tight side and at the mere sight of a hill would nip up. A 2 thou hone of the bore at the engine shop and all was fine but like you I had to put a new piston in.

I just took a look on ebay and see the Indians are listing +.050" piston rings ..... ....BSA pistons only went to +.040 and the next size up in a pattern piston such as Hepolite is +.060"....Ian

email (option): ian@wright52.plus.com

I have been following your rebuild with interest and must congratulate you on a job well done. Sorry to hear about your mishap.
A modern Hepolite piston is not the same as an original "Made in England" Part No 11957 Hepolite piston with split skirt. Unless you can get the real thing, a piston from any reputable manufacturer is probably fine. I am getting good service from an Italian "Kolben" piston.
I filed about 10 thou off the sides of the piston in the gudgeon pin area before fitting as this is where they are most likely to nip up.
If the scored surfaces are on the side and not on the front or back, you may be able to salvage your piston by careful filing and just fit new rings.
One final consideration is that so far, you are just guessing at the cause. If it is due to a bent con rod, or restricted axial float, rather discover this with a salvaged piston than damage a new piston. (see Ian's comment above).
Check that the piston is running concentric in the cylinder and not forced to one side. You should be able to gauge this using a feeler at TDC and at BDC.
The book gives a clearance of 4 to 6 thou. Try and get close to 6 thou.

email (option): pvlietstra@gmail.com

Hi Julian...Peters comments are very valid...Perhaps you should post a couple of good photos of the damaged piston so we can see where and in what form the damage is..It may be possible to deduce some useful information from this....You are safe with a Hepolite piston if you find one...Currently there isn't an M20 piston marketed under the 'new' Hepolite name....

If there was I wouldn't have any qualms about using one either...So far I have heard only good reports about the new 'Hepolite' Triumph pistons from a friend who has fitted quite a few...Ian

email (option): ian@wright52.plus.com

Thank you all for your comments, you all have it right.
At the time the engine tightened up was when the mixture was to weak and it was climbing up a hill, I remember when the bore was finished that it was 5 thou undersize and I honed it but it was still left probably 1-2thou undersize, so I always had this in the back of my mind.
After the initial seizure, I tweaked the mixture and rode the bike without loading it and it ran superbly.
It was only that the base gasket was a thin paper thing that started leaking a bit of oil and I wanted to replace it with a thicker more substantial version to stop any oil leaks, that prompted me to strip it apart. The engine has only run 20 miles since the seizure and as you can see the bore is okay and started to get it's mirror finish, but I have the rub on the side of the piston that has pinched the 3rd down piston ring.









Thankfully I have a hone, so if I can get a new piston then I could if needs be hone the bore a little to ensure perfection with fit.



Is it worth sticking with this Italian 4 ringed piston or change for the standard 3 ring version?

Julian

email (option): 79aust@sky.com

Having 2 oil control rings, maybe it's doing to good a job and removing to much oil.

Hi Julian...Assuming you have contact marks all the way round the piston above the rings you need to get this piston measured to determine how much 'side relief' it has...
Pistons are not round as you might imagine...They are at the largest diameter measured across the thrust faces (on the front and back of the piston)...
The sides are 'relieved' or reduced in diameter, to reduce the amount of friction generated during running...I recently had a pattern piston through my hands that had no side relief at all and was completely round...
If the side relief on this one is the same, or insufficient, you may be able to apply this by hand and at the same time reduce the amount of damage to useable levels...
When removing material from a piston always use a smooth file...Not emery cloth, as the abrasive grit can get embedded in the piston surface...
Use a sharp, smooth file and apply some French chalk to it before commencing work...This will cut down its tendency to pick up aluminium and scratch the piston surface...Also clean it frequently with a file card and reapply the chalk as you go....
The 4th. ring isn't an issue..some M21 pistons had this feature as standard and performed pretty much as the 3 ringed versions...
First though, get it accurately measured to see what you have...Ian

email (option): ian@wright52.plus.com

Ian,

I do need to change the piston as the 3rd piston ring has snapped when I tried to free it from the pinch and I can't find replacement rings only for this Gandini piston.
Have you any experience with JP Pistons (Australia), I've just seen this link:

http://www.classicmotorcyclespares.com/index.php/default/dynamo-brushes-large-type-1-2x1-4-pair-92.html#Pistons,_Rings,_Liners

Also seen a NOS piston advertised:
http://britishbikebits.com/genuine-nos-piston-ass-std-4-9-1-bsa-m20-1#.UlMw_hDMYzc

I'm not sure what Draganfly supply, but they do have a premium price at £108?

Julian

email (option): 79aust@sky.com

Clean up the ring groove and find another oil ring. Get your bore professionally honed out to 4 or 5 thou. It's just a slogger! Is the bottom ring the same as the upper oil ring? If so just use that.

Hi Julian,

Just an idea:
First of all, almost any professional piston shop or engine rebuild shop can have a custom oil ring made for your piston.
Secondly, I think that in the worst case- you can check the relief on the sides,
And if your piston is still up to specs, remove the bottom oil ring and re-fit it upstairs and leave the bottom one free..

Noam.

email (option): noam10@gmail.com

Ian Wright

....When removing material from a piston always use a smooth file...Not emery cloth, as the abrasive grit can get embedded in the piston surface...
Use a sharp, smooth file and apply some French chalk to it before commencing work...

email (option): viaconsu [at] planet'dot'nl

I've just had a closer inspection and the base oil ring is the same width as the top oil ring (3.17mm), I have also emailed Gandini to see if they have are able to supply a replacement.
When it comes to the piston, I can get a single cut mill file and will possibly give a little extra side relief.
I suppose if would be best to ensure the bore is spot on, even though it has smoothed out. I have a bore gauge and from what has been said I assume it is best I hone it again and ensure the size is spot on, there is a very slight step at the top, but I think this is just an oil deposit at this early stage.

Julian

email (option): 79aust@sky.com

Julian try F W Thornton they supplied a set of rings for my 1937 HM21 contact details are

Orleton Lane, Wellington, Telford, TF1 2BG, Shropshire, ENGLAND

Ph: +44 (0)1952 252892 Fax: +44 (0)1952 246082

e-MAIL: enquiries@fwthornton.co.uk

good luck. Dave

Hi Keith,

I measured the bore at it came in at 82.49mm, I've just run the hone through it and now have it at a spot on 82.50mm.
I have put my hand into a very deep pocket and ordered a new piston and will await it's arrival before rebuilding or honing any further. I fully have taken on board what Ian, Hans and Peter have said and I'm still a little unsure on the relief of the piston, but I would much prefer to see a clean piston inside, instead of the heavly scored version like I currently have.
It will be ridden in now with allot of due care and I'm very glad that I caught it when I did as the scoring was minimal in the bore, the hone has wiped all clean and removed any prior linear marks.
I also know that the polished bore had opened a little from when it was originally honed. As I stated in some earlier posts, the engine was freeing up and running allot easier after the initial rides, but if this had of been left then tragedy would of been imminent.
I can only say to anyone else who does this for the first time, don't get carried away with labouring or racing the engine, they really do need to be handled with allot of care after this sort of rebuild.
I hope I've learn't my lesson and really hope that this never happens again.

Julian

email (option): 79aust@sky.com

Hi Julian
Thanks for that reply. I'm afraid its just all part of the learning curve, but very satisfying when it all comes right!
If you can, get hold of a copy of Phil Irving's "Tuning for Speed" first published in 1948. Ignore the "speed bit" its the bible on how to rebuild an old engine, Phil was the chief designer for Vincent, He also designed the Velocette rear suspension and the Repco engine that won the 1966 F1 so knew his stuff!
Regards
Keith H

Thanks Keith,
Just downloaded a PDF version of Tuning For Speed, saved me the £161 from Amazon?

Julian

email (option): 79aust@sky.com

Hi Julian,Russell motors are listing complete piston, rings, clips and pin at £60
got to be worth a call
cheers Rick
ps if you dont get lucky mail me off forum,i may have another supplier

email (option): richardholt@rocketmail.com

Phil Irving's Tuning for Speed

Free e-Book

http://tuningforspeed.com/

Noam.

email (option): noam10@gmail.com

Thanks Richard, but I have already paid and awaiting the replacement Gandini piston @ £89.
Gutted now, seeing the Russell motors price at £60.

Many thanks any way.

Julian

email (option): 79aust@sky.com

Just rebuilt the engine and the movement of the piston is now fine and the valve clearances have been set to accomodate the thicker base gasket that I've just fitted. However, ever since I've had the bike running there's a clicking noise from deep down and I've just been turning the engine slowly and can hear a light "click" every time I get to the point when the exhaust valve is at it's highest lifted point and is just about to start to lower down.

What is the cause and what is the solution?


Kind regards,

Julian

email (option): 79aust@sky.com

Hi Julian,that is the backlash in the cam gears,as the valve spring pushes the
cam over the top.The cogs on the cam jump forward slightly and a click can be audible as it hits the next tooth.
cheers Rick

email (option): richardholt@rocketmail.com

Hi Julian..If this is just caused by wear of the gear teeth on the cam and/or crank pinion, the solution is new components...

If it is caused by the crank running outside its .002" (measured at the mainshafts) concentricity limit there is nothing you can do without a full engine strip down (though it will run OK like that, if a little noisily, as long as it is only slightly out of tolerance.)

If you turn the engine over and test the backlash between the gears at various points it will be constant if gear wear is the problem...
If, however, the problem is crankshaft concentricity you will find a marked variation in clearance at different crankshaft positions...Ian

It's amazing the diffference after a bit more TLC.
just re-built the engine and using my gauge, I've set the 7/16" BTDC and got the gap spot on with the magneto. First kick and it started a treat.
sounds so much quieter and the click is just wear in the cam gears.
Hoggin the Bridge is on Sunday at Aust Service Station (M48) and I hope I can get my bike there to join the 3000 plus bikes to do part of the run and give it a bit of a ride.
Really happy with how it now sounds as the engine is really smooth, will ride in with real care and low loading.

Thanks for your assitance as always.

Julian

email (option): 79aust@sky.com

Just done a 32 mile ride with the new piston and it went brilliantly, however!

When I stop and leave the bike for a few minutes it just won't start straight away, the timing is spot on.

As a newby to riding these old classics, should I switch off the taps and let the carb run dry before parking, as I think it's flooding if left?

Julian

email (option): 79aust@sky.com

May I thank Naom Zehavi for giving the link to "Tuning for Speed", the book by Phil Irving? I lost my copy decades ago and now find I can't afford a replacement.
And anyone who hasn't read it - well , you should! Mike Nash.