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[m1ks]

If you want someone to run in that 500 motor I'll volunteer BTW,

[MadMike]

Hmmmmmmm. "1/2 arsed mechanics" somebody said. Frankly I wouldn't trust a mechanic to make me a cup of tes, it would probably come out tasting of coffee. So I understand that you can rebore to +080! So a +060 rebore should solve the problem. Then somebody suggests that Enfield 350's are prone to seizing??????? Why would you put up with that if it were true? Would you buy a washing machne or a dishwasher and accept that it seized up as a matter of course, even though it only cost about £300? Well you might but I bet your collective wives wouldn't. For goodness sake it is the 21st century and people have no right to put up with machines that are accepted as "nipping up because all 350's do that" particularly after parting with several thousand ponds of hard earned cash. Shakes head in bewilderment and assumes the position with the corkscrew and another bottle of Merlot.

[Dennis C]

For some strange reason this thread is only one of many relating to the same problem and I for one have given up trying to trace them all. ------- As you say Mike, why on earth would anyone put up with a design fault (IE 350s seizing up). --------- be sensible guys it just doesn't happen, the original post and pictures tell the story, the bike was seized due to over heating, timing wrong?, running lean?. possibly both but almost certainly the second. ------- An old style engine like this requires carefully running in to prevent this problem, you can help by letting it run rich to increase the cooling from the slight increase in fuel, then lean it off again after running in is complete. having seen that the piston is a good quality JP I would be tempted to inspect it carefully clean it up and refit with new ring if all appears OK.

[m1ks]

There's a specific reason there are a few threads relating to the same problem, that being, with the format of this forum, adding to the end of an older thread with a new query, everything gets lost and the new query goes UN observed in the main.
If you check all the threads relating to this you'll bore each separate one relates to a different question, (excepting one alone which the forum duplicated and the duplicate had only one respondee, (which I would have edited or deleted if the option were available!)
To be fair to the seizing comment, the poster states that the 350 is more PRONE! To seizing, not 'they all do that sir' and another commented that the JP pistons are also more prone to this phenomenon.
I'm merely collecting, (where possible), real world experience to try and ascertain the cause of the problem and ensure it's less likely to re-occur.
If you check my other threads, (again, this is where the forum format is lacking, every other forum allows the user to be clickable then search user started threads!), you'll note the mixture wasn't lean, out was in fact bang on with a very slight erring towards slightly rich showing a chocolate, (rather than biscuit), brown in the plug chip tests, there was also no evidence of pinking. The only difference being this was a slightly longer run, (5-6 miles), on constant throttle, (1/2-3/4), at a slightly higher indicated speed, (55-60)

[Dennis C]

m1ks, I am not trying to be clever here, I am calling on many years experience and I have seen far too many nearly new pistons damaged in this way, you keep insisting that the mixture was "spot on", this may well be the case and I wouldn't dispute it, the fact remains that when you gave the engine some real work to do the piston seized. ------------ I have told you what the answer is obviously you do not agree, that is your right, please try and remember that although you have mechanical experience there are others on here who know far more about these old style engines than you, sometimes it pays to listen to them.

[Presto]

Hi m1ks, in my experience, running at constant throttle for 5 to 6 miles is an engine killer on a 350 in certain circumstances. Nothing places more heat related stress on such an engine.

[Bullet Whisperer]

Just to make it perfectly clear, I said the 350 [meaning Indian Iron Barrel type] is more prone to seizing than the 500. How do I know? Well, I have had four of the buggers do it, one when a 40 ton truck was right on my arse, so don't anyone tell me it doesn't happen !!! As to why, well I reckon the standard pistons are made from total s**t that expands too suddenly once a certain temparature is reached and unless you are quick on the clutch and backing off the throttle [like I now am] it will seize. I didn't immagine it the other day when one tightened up, but got off the throttle and clutched it so quick, it was idling within a few yards. Am I riding them too hard - is 60 mph on the flat too much too expect for a few hundred yards? - NO it isn't. Perhaps in India they survive the heat because they may be ridden more slowly due to the bumpy roads. Perhaps most over here don't exceed 50 mph. I am not particularly rough with them [except my own] but they shouldn't be doing this. Remember these words when someone goes under an artic on one. It could well happen.
Paul.

[m1ks]

Dennis,
I understand your comments are well intentioned and I truly do appreciate anyone taking the time to read and respond to my queries. (If you take the time to look at the previous posts and responses you'll note this)
It does seem however that you are making a few assumptions along the way probably due to not having followed the previous threads, which hopefully i'll clarify here in case there was any confusion.
First of all, I'm a little miffed that in one sentence you're saying that I keep 'insisting' the mixture is spot on and that you wouldn't dispute it, yet you do that very thing shortly afterwards when you say, open quote-I have told you what the answer is obviously you do not agree-close quote.
As above, if you read my previous posts, you'll note, I set the bike back to stock, set initial carb with a Gunson colourtune, (used successfully many times on many bikes), then performed plug chops to tweak the midrange, a picture of the final setting spark plug colour is shown and this tells you the mixture was good erring to slightly rich, as it also did on removal after the seizure), I haven't worried over the top end yet as it has yet to go beyond 3/4 throttle.
I too have several years of mechanical experience and my first 'proper' garage job was cutting my teeth on aircooled VW flat fours when I worked for a VW specialist, (those beetle engines aren't all they're cracked up to be incidentally, i've rebuilt more than a few with holed pistons and burnt valves), I am willing to admit that whilst I have a very good grounding in mechanical works, theres always more to know about specialist one make machines, hence the reason I like forums like this, it allows me to draw upon the experience of those who have owned, ridden and maintained them for years and enables me to make my decisions based upon those experiences hopefully avoiding problems and in the long run helping new owners in the future.
Moving on from that one niggle and looking at other comments i'll hopefully be able to give you enough of a background to the problems.
1-You refer to nearly new pistons, I take it from this that you believe I fitted this, or it was otherwise recently fitted, this is not the case, the piston has been in the bike to my knowledge at least a full year, (much of which it was used little), if not longer, I merely decoked the whole thing and re-assembled after getting it and then primarily because I had the head off to helicoil the spark plug thread.
It displayed minor scuffing to the front of the piston when I removed it for decoke before i'd ridden it and was certainly well covered in carbon indicating it had been in use for some time.
2-You state, when I gave the engine some real work to do!, This I disagree wholeheartedly with, a cool evening, solo rider, (i'm not a big fella), very slight incline and an indicated consistent throttle and speed of 55-60mph I do not consider loading the engine excessively, in fact, in the week prior it traversed much steeper inclines in 3rd and 2nd gear on the way to and from the MOT test, (25 miles each way), during a hot day with me and rucksack, a much heavier load though less consistent throttle and not exceeding an indicated 55 on the clock as I was running it warily being the first proper ride.
Believe me when I say, I wish it were as straightforward as, 'oh yes, it's clearly running lean' that would set my mind at ease and be an easy fix for the rebuild.
As BW says, is 60 on the flat (for even a few miles) too much to ask, i don't think so, it certainly shouldn't be on a 350cc motorbike
(Today I stopped to chat to a young french fella wild camping as I was curious about his bike, i'd passed him earlier and seen what I thought was a heavily laden Yamaha SR500, not such a common sight and a nice looking bike, it turns out, it was a very heavily laden Yamaha SR125, so much so that you couldn't tell what it was under the tank bag, panniers, travel pack and other bits of random luggage bungeed to it, he'd travelled from France, through Switzerland and umpteen other places before hitting the UK and heading to the Scottish highlands, so if him and all that luggage can travel that distance at a good 50-55 average covering long distances at a go on a 125 4 stroke single, then, definitely no, a short burst of 60 unladen on a 350 single is not asking too much).
3-As said, I didn't take BW's statement as a blanket, 'they all do that' statement, and took it in the meaning I believe he intended, that being that in his experience they are more prone to it than the 500.
Thanks to all who've responded so far including yourself Dennis and I certainly don't want to upset anyone or fall out with anyone, I know there are things I can learn about these machines yet and am happy to provide further info on any problem for help diagnosing if anyone wishes, i'm not here to dispute anyones knowledge or experience, ultimately, I want to get my bike running again and enjoy it before the summer is over.

[grunda 12]

siezing 350,s ? i,ve riden mine as hard as i can from purchase at 75 miles on clock never run in properly just to see if i could blow it up and guess what its done 10,000 miles and never siezed up,although there was a fault on the origional ignition coil that fiened siezing i.e engine cut clutch in at 60mph anyway just get the barrel bored happy days

[Bullet Whisperer]

I'm just glad I didn't have one of those dodgy snapping clutch cables on each occassion, or I would have been done for by now! I have never had a rebored one tighten up, by the way, all were std bore Indian barrel and piston, one set that tightened [in front of the truck] was fitted on a Redditch machine. Paul.