Possible seizure!!!

[Shark]

https://www.a7a10.net/forum/index.php?topic=10874.0

 My possible seizure, I hope you have better luck than me. Cheers.

[BagONails]

Sharky, I read through your thread and just wondered what you replaced those high compression pistons with in the end? How has it been since and is there much difference in performance now its all run in?
Cheers Bagga

[Shark]

Hi Bagga, flat top pistons with new rings and a light hone did the trick. Starts first kick, idles as it should and is as smooth as a 360 twin can be. From memory compression is about 8:1. Cheers.

[Minto]

OK, well I poked the endescope down the plug holes today and sadly both of the bores are scored , it’s difficult to tell quite how badly with the images I was getting but worthy of further investigation I think.
TT, where should I be measuring the fuel flow from? On a 276 pre monobloc is the plug used for checking float level an ok for this purpose?
Lurgy and work have got in the way of doing anything important over the last couple of weeks.

[Triton Thrasher]

Sorry I don’t know about 276 carbs.

[RDfella]

Beginning to despair of this thread. I get the impression Minto wants to strip the engine down, no matter what. Well, if that's what he wants to do, fine, go ahead. But it won't diagnose anything and what if, after a hone and new pistons, the bike does the same again?
As I said a while ago, if it ain't knocking or smoking then the engine, whilst pistons / bores may indeed be not pristine, is never the less perfectly OK for now. If the problem was too tight a bore, it would have seized 'properly' ie, pistons would be damaged to the extent rings are trapped with consequential knocking and smoke. It didn't, it tightened up gradually as a result of overheat. So the problem is either timing or fuel. As for checking fuel flow, how difficult is that? Take the fuel pipe off the carb and turn the tap on. Does it drip, dribble or flow? If the latter, that's fine. Now - the fuel filler air vent. Does it have a clear 1/16" vent hole or not? Easy enough to determine. After that, carry out a plug chop. Job done.

[Kickaha]

if it ain't knocking or smoking then the engine, whilst pistons / bores may indeed be not pristine, is never the less perfectly OK for now. If the problem was too tight a bore, it would have seized 'properly' ie, pistons would be damaged to the extent rings are trapped with consequential knocking and smoke. It didn't, it tightened up gradually as a result of overheat.

I had a similar thing with my A10 with the same symptoms as Minto, pulled over, let it cool for a few minutes started it and carried on, did another few thousand km before the top came off as the valves weren't sealing found evidence of a slight  "four corner" seize, bike still ran fine, it didn't do it again and I couldn't find what happened to cause it

I'd be doing a compression test and if that was in spec I wouldn't bother stripping it (which was what I did because I'm a lazy bastard)

[Minto]

Beginning to despair of this thread. I get the impression Minto wants to strip the engine down, no matter what. Well, if that's what he wants to do, fine, go ahead. But it won't diagnose anything and what if, after a hone and new pistons, the bike does the same again?
As I said a while ago, if it ain't knocking or smoking then the engine, whilst pistons / bores may indeed be not pristine, is never the less perfectly OK for now. If the problem was too tight a bore, it would have seized 'properly' ie, pistons would be damaged to the extent rings are trapped with consequential knocking and smoke. It didn't, it tightened up gradually as a result of overheat. So the problem is either timing or fuel. As for checking fuel flow, how difficult is that? Take the fuel pipe off the carb and turn the tap on. Does it drip, dribble or flow? If the latter, that's fine. Now - the fuel filler air vent. Does it have a clear 1/16" vent hole or not? Easy enough to determine. After that, carry out a plug chop. Job done.

Ok so I’m being a nob then. Thing is I’m not an expert in these things, this is the first engine I’ve rebuilt in over 30 years, and really I just want it to be the best it can be.
My apparent insistence on stripping the top end is due to my (maybe naive and unfounded) concerns over the possibility of the rings being stuck in the grooves or possibly broken (scoring seen on endescope pics).
All of the advice I’ve gratefully received on this thread will be heeded and looked at as soon as I feel fit enough to fight my way into the garage, and obviously checked in a sensible order, hopefully today.
But at some point (maybe after a few hundred more miles, maybe sooner depending on how it sounds n goes) the head and barrels will be coming off for an inspection, as to be honest it ain’t that big a deal to do is it!
Anyhow’s over n out.

[muskrat]

G'day Minto.
I remember back in the early 80's and new to my 51 A7 I rode from Sydney to Ulladulla the first time. Got about 1/2 way on the freeway and she nipped up. Waited 15 minutes and did the return trip no worries. About a year later stripped he down to find a few marks on the pistons and bore but she was still running well.
These days if I feel a nip it's straight down. Go your own way BUT you have been advised! 
Cheers

[JulianS]

Given the same problem I would not hesitate to strip my A10 and fully investigate the cause. I would not want an unexplained problem to cause me to worry about a recurrence each time I took the bike out.

Over the last 49 years of ownership I have had 2 cases of engine slowing as described. Both oil related.

The first time, about 1976/77, it started again after cooling and the cause was a recently installed very poor quality oil pump gasket which reduced oil flow and hence the bike overheating. New gasket no further problems.

The second time, about 4/5 years back, a hot day, bike running hot and refusing to pull up hills. Cause was an obstruction in oil tank to engine armoured oil feed pipe reducing oil flow and hence causing overheating. New pipe no further problems.

[berger]

hey minto stop being a nob there's only room for one nob on here and that's MEEE  so get orfff of my cloud . pub today on it

[Minto]

Ok, managed to get out to it today, first check fuel flow from taps, both flowing freely, over 500ml in a minute. Need to check this again from the carb, also need to get the carb off to make sure there’s nowt blocking a jet and to check there’s no grit or shit grabbing the slide.
Checked points, gap closed up from the 12 thou I’d set them at to 8 thou, possibly retarding the ignition too far so reset to 12.
Oil return is strong and I have one of those Triumph type pressure relief valves fitted, on which the button pops out on start up and moves in and out with revs and settles down as the oil warms up which seems to me to be indicating good pressure.
Going to drop the oil and flush out the tank and lines as it’s due now anyway. Then if there’s time I’ll take it for a run round see what’s occurring.
Holding off with stripping it for a bit.
Thanks everyone.
Jase

[RDfella]

Apologies if I was a bit blunt, Jase. Wasn't mean to be an admonishment, more a worry that you'd strip it, see marked pistons and then replace them without having diagnosed the problem. As Julian says, there can be other causes too. As a matter of interest, when I was modifying my auto advance unit prior to electric starter fitting, I found a thou difference in points gap gave almost a two degree difference in timing. So with points closed up .004" your timing could have been up to 8* retarded from full advance. That's not insignificant - around a quarter of the total advance. Could well have been the cause.

[Minto]

RDFELLA, no worries, I just didn’t want anyone thinking I was disregarding the very valuable and appreciated advice given.
Just putting the carb back on now, there was a tiny amount of fine muck in the bottom of the union and again in the coupling between the float bowl and carb body. All jets blown through and cleaned but think I’ll order some bigger main and needle jets to experiment with later, might improve things up that end.
Not wanting to “fix” more than one issue at a time without testing between. Replacing fuel filters as well, obviously.
Thank again.
Jase

[Minto]

Damn it, I’ve just spent an hour n arf looking for the oil filter I bought a while back, had to give up as I was loosing the plot and something is going to get broke if I carry on. So it’s all back in the garage til I remember where I put it or another one turns up in the post.
Consequently, no testing today.