Ok guy`s i am sure you have seen this before but any comments would be appreciated
i have only owned it a short while and have not ridden it before this happened only did about 3miles but i`m guessing it may have something to do with a leaky head gasket note transfer at center pot ? the gasket was not visibly broke but the head bolts did seem to be not very tight
plan:
replace piston,rings etc to center new gaskets and torque to spec
thoroughly clean carbs
replace HT leads as per info found on here
have new plugs
just had timing set at classic bike mechanic dealers
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Looks just like my GT550 Right piston! Don't know if a head leak will cause the overheating, but that center head looks like its got some kind of blobs of metal in the 2-3 o'clock positions of the pix. Maybe that's evidence of a leak & molten metal trying to get out! That'll have to be cleaned off smooth to get it to seal right. Also, all that metal from the piston hole went somewhere! Typically will see some scoring on the cylinder walls that will at least require a good honing. Good time to do all three jugs! Usually some deposits to be cleaned from the head too (although I don't see much in the pix). While ya have the cylinder off, at least look down into the crank area to see what you can. May need some cleaning (which probably means the case will have to be split to do it right). That'll be your judgement call. Lots of work, but it's the only to be sure. The top end is easy.. the bottom -- Not so much!
Good Luck & keep us posted.
I really would check not only timing and plug heat rating, but carbs also. It might have been very lean and if so it may well burn through the next piston also
Mike
A compression leak is unlikely to cause a holed piston -- the cylinder with the leak should, if anything, run cooler because the mixture isn't burning as strongly (it isn't being compressed as much).
I would suspect the ignition timing was set too far advanced, or that it slipped while the engine was running, causing a localised hot-spot. It's not helped by the fact that Suzuki issued several different factory recommendations for ignition timing over the 380's life. My own 380M (1975 model) does not like the timing set at the factory recommendation, it pinks so I back it off a little.
Which model 380 is it that you have?
As mentioned, check what plugs were used -- they should be NGK B8 ES, EGV or EIX.
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
Thanks for the feedback guy`s i am starting from scratch really as i have no real history with this bike ,i heard it run before buying it but didn`t take it out for a ride although it sounded ok (i have a couple of other stroker`s )
when i got it home it started so put it in garage and started a refurb on most of the cycle parts but left the engine as is - why touch what isn`t broke
anyway ended up replacing clutch cover gasket then found my lack of dial gauge and ability to set up triple timing so sent it off to a classic bike mechanic locally
when collected it started easily sounded ok but he recommended cleaning the carbs but before i got home it started loosing power and running rough when i got home i noticed middle pot /exhaust was cold so i pulled the plug to see if it was firing and for some reason i decided to look into cylinder with a strong torch (you know that sixth sense thing crept in) and the rest is history
thanks craig380 yea the model i have is apparently a early A so yes i agree there seem to be a host of timing discrepancy between models my plugs are NGK B8 ES
Looks like the center cylinder was running super lean. Check the float height, check for air leaks at the intake boot etc...
If the cylinder bore is OK I'd look at these: http://www.ebay.co.uk/itm/72-77-Suzuki- ... 3cd3724f9b" onclick="window.open(this.href);return false;
The light color of the piston is from a layer of vaporized metal rather than a lean mixture.
Yes it has detonated to death and that was probably a slight air leak or too much ignition advance or simply a partially blocked jet. All it take is a layer of "fur" to significantly reduce the effective area of a jet and to change it from safely rich to dangerously leak.
The other problem on that cylinder is the head gasket. It is way too large and the gases in that annular ring will tend to detonate even when everything else is close to being spot on. I don't know if that's typical of a 380 but that's a problem that needs to be addressed.
tz375 wrote:The other problem on that cylinder is the head gasket. It is way too large and the gases in that annular ring will tend to detonate even when everything else is close to being spot on. I don't know if that's typical of a 380 but that's a problem that needs to be addressed.
@ TZ - that's common on the 380s, the inner ring of the gasket is always a couple of mm larger in diameter than the cylinder bore, even after being torqued down and 'settled in' from thousands of miles of running (the gasket design is a multi-layer 'crush' type, presumably to allow for slight differences in cylinder deck height because Suzi specified a 1-piece cylinder head across 3 separate cylinders).
Suzi only made one type of gasket, which was one-size-fits-all and had to account for peculiarities like the Italian-market 384cc triples (which had a 55mm bore as standard to get around some local insurance / tax laws). Suzi made 0.5 and 1mm oversize pistons for these too: Rocco 'Triplerocky' Garzone had a 401cc GT380 for this reason
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
My observation about the 380 (mine is a '74) is that the stock needles are way too lean at small throttle openings... about 025" too lean... raising the needle will make it way too rich at moderate throttle openings if you raise it to correct the lean condition.
A larger pilot only makes the idle too rich and still the lean spot remains in the #2 (std) position.
Couple advanced timing with the lean needle at extended cruising at small throttle openings and there's the holed piston.... it sucks when this happens.
