Forum

[Edward]

I completely agree with Les and Pauls advice is very well worth a try. Just a point to mention if you try to clean things up. Emery is fine on cast iron but not the alloy piston, minute particles of the abrasive can embed in the alloy, a very fine file is better.

[Alan R]

Hi Matey----- for God's sake please don't re-use that piston !! I have a used Std. bore piston, rings, pin & clips which is surplus to requirements (forged piston fitted). The piston brought me from Farnborough, Hants. to Telford, Shrops. recently with no probs. You can have it for FREE !! just pay for the P&P ?? Does that help any ??

[Dennis C]

I have to agree with the consensus of opinion, the problem has not been caused by lack of oil, it has been caused by excessive heat, double check your timing, check you have the correct main jet fitted and raise the needle a notch or two if it runs rich at this it's far better than another seizure you can always try lowering it again after running in, but take great care if you feel the slightest loss of power whilst riding stop immediately and let it cool down raise the needle again before riding on. ------- the bore should be OK with just a hone, you can buy a hone which fits an electric drill cheaply and do it your self, don't forget to clean the bore thoroughly before reassembly, the piston, you may be able to re use it but is it worth the risk?, it has been badly stressed and the crowns have been known to detach they are not all that expensive, put a new one in.

[simon]

I agree that piston is an ash tray now. They aren't that expensive that you'd want to re use that one. I had endless troubles with seizing with my old 51 bullet. I went through pistons and relined bores ( before I discovered that our hosts make a replacement at considerably less cost than a re line) . I couldn't work out why it continued to nip up even when I ran it in for a full 1000 miles at under 50 mph. As soon as I opened it up it would grind to an overheated halt. I'd always assumed that if the big end feed was an issue the white metal bearing would be the first thing to go but on finally pulling it all apart I discovered it had been replaced with a roller bearing and that the oil way was totally blocked. Amazing that the rollers hadn't packed a sad but although there was slight signs of over heating the bearing was fine. The point of this story is check that you are getting decent oil flow to the big end which you should be able to do by pumping oil into the hole that the quill goes into. Seeing it ooze out of the big end will at least let you know that it isn't oil starvation from a blocked big end journal.

[m1ks]

Alan, that would be greatly appreciated, thanks, let me know the costs and I'll gladly have that and will feel far happier knowing the old one isn't going back in.
I have a new set of rings in the way with the new head gasket anyway and was pondering one of our hosts high comp piston sets.
The hot running I don't understand as I had it running a good mixture, (don't know also how discoloured it was previously but i know there had been messing with the jetting etc), it's currently on stock settings, 90 main, needle at second clip from top and showing very slightly rich at idle and midrange on the colourtune.
(will have tea caddy and Shorty stainless silencer on rebuild so will change the main to a 95 and start from there)
Unless the few bursts of revs for the odd overtake of slow tourists and holding put at the slightly higher indicated speed combined with the lower oil just pushed the heat that bit further and enough to get it catching?
I'll take a look at the oil pump too though it seemed to be throwing through a good dollop when kicked over with the sump plug removed.

[Dennis C]

Hi Again, Great that Alan has a piston for you, when running in forget stock settings, raise the needle and let the extra petrol do it's cooling work, put the Colourtune back in it's box and forget it, we do not live in a perfect world with these old style engines and a degree of common sense needs to be applied, petrol has changed over the years and now burns hotter, better a bit rich than seized again, I have seen far too many pistons and bores damaged in this way by people insisting that stock is correct, IT IS NOT IT IS ONLY A GUIDE AND ALWAYS HAS BEEN.

[Norm]

Even the gudgeon pin looks like it has been cooked

[m1ks]

Norm, the gudgeon pin is barely coloured, the lighting in the pic makes it look more so, it was taken last night under kitchen spots with a phone camera and led flash so not the midst accurate colour representation.
Colin, to clarify on the colourtune, I've used this many times on many vehicles and never take the first reading as the final answer to carb settings, I use this as a baseline to get the pilot and midrange in the ballpark then compare this to setting the pilot by ear the old fashioned way and go for a compromise erring towards richer, after thus I rely on plug chops to tweak as necessary, if you see my previous posts the plug was giving a good reading with a nice rich chocolate brown colour.
The plug after the incident was showing no signs of running leaner either.
I'll rebuild with the larger main specifically due to fitting the less restrictive silencer and can always adjust after further checks and bedding in the new rings.

[m1ks]

No idea who Colin is, I meant Dennis,

[m1ks]

Thanks for the quill feed tip Simon, will try that before I rebuild.