That ain't going to rub out.. (G5 content)

[Chuck in Indiana]

Austin and Jessica were loaded down headed to the Wisconsin rally on the G5. I got a text saying they were on I74 and it blew all the oil out. (!!)
The good thing is they didn't go down.
I texted back and said it sounded like he blew a hole in a piston or broke a ring.. but not good at any rate. 
He brought it back to the shop and I showed him how to do a leak down. Zip compression on that side, and blowing out the breather. Told him to pull the head off and have a look. Sure enough, the Snot dis side  cylinder was toast.
2019-08-02_05-57-22 by Charles Stottlemyer, on Flickr
I'd say it broke a ring, but I guess "what" happened isn't important exactly ..
The question is: Why did it happen? He had been complaining of poor fuel economy, so I had him pull the carbs and see what was in there. Stock jetting for a G5.. but.. the idle and mains had been drilled out. I told him to buy new idles and mains per Guzziology, and he installed them. Adjusted the carbs, checked timing, and it was retarded. Set it at the full advance mark @4000. He said it had never ran better until it didn't..  
When we were talking before the tuneup, he said he had been running regular in it. "It's just a tractor engine, isn't it?" "Uhh, no."
When I went to the shop after telling him how to set the timing, he had apparently been running it longer than he thought. I grabbed a big box fan and put it on the engine instead of the mechanic.  It was hot enough that you couldn't touch a valve cover..
That's about all I have. Fluke?

[bigbikerrick]

Holy Cow Chuck, no bueno! Do you think its possible to even figgure out what caused that?
Rick.

[acogoff]

     Shucks anyway!!! I would probably check that valve stems are not bent from the floating chunks just before stoppage. My T3 has never liked regular ever -seems to ping under the slightest acceleration or load.

[RinkRat II]

         With the way the top ring land is worn or melted away I might suspect a leaky exhaust valve perhaps. Looks like it took a while to do it, Glad they're okay.

             Paul B

[Antietam Classic Cycle]

    Never saw that before...

[Chuck in Indiana]

    Never saw that before...

Me, either. That's why I'm asking..

[Chuck in Indiana]

Hmmm, Jeff Parrish sent Austin a picture of a convert engine with the same damage, same cylinder. Timing? I/we only timed the right cylinder, and assumed the left would be ok..(?)

[Antietam Classic Cycle]

Combination of low octane and left cylinder timing off would be my guess.

[pete roper]

Pre-ignition would be my guess for the start of it. Given the position of the top ring I'd suggest that the poor and uneven burn made the piston go all sorts of queer shapes, (Note also the speckly damage to the deck and squish band.) and then with the rings not sealing oil was getting past the gap in the top ring and burning causing the initial melt. Shortly thereafter, with the structural integrity compromised and localised hot spot the piston went totally out of round and the seizure occurred with consequent mayhem. I'm assuming the G5 uses the same cast iron liners that the 'Vert and SP used? That also wouldn't help as the CoE of the material of the sleeve and piston differ making seizure almost an inevitability.

Service the heads, throw a new set of barrels (Nicasil) and pistons on it after cleaning it thoroughly. Service the distributor and give it new springs and ride it for another 200,000.

[bigbikerrick]

Well, if pre ignition due to timing too far advanced on the left caused that,nasty looking damage, that  IMHO is another reason to install a Dyna III ignition in these old bikes!
Rick.

[pete roper]

If it's not timed right or there are issues with the distributor it won't make any difference whether the spark is generated by points or Hall effect. It'll still melt itself.

[jacksonracingcomau]

Shame, but posting this is good tip for anyone setting timing
If it retards itself it is because points heel has worn, reset gap to fix
DO NOT TURN THE BODY
Hope no other damage, should be easy if exy day to fix
And keep wick lubed to prevent heel wearing again (I would replace worn set)

[Antietam Classic Cycle]

Shame, but posting this is good tip for anyone setting timing
If it retards itself it is because points heel has worn, reset gap to fix
DO NOT TURN THE BODY
Hope no other damage, should be easy if exy day to fix
And keep wick lubed to prevent heel wearing again (I would replace worn set)

The only "wick" on the big-block dual-point timer is the little felt square that is supposed to keep the advance mechanism lubricated. I use Bosch Distributor Grease to lube the cam and it's proven very effective - the points on my Convert are still at the same gap as when set them 14k miles ago.

[jacksonracingcomau]

The only "wick" on the big-block dual-point timer is the little felt square that is supposed to keep the advance mechanism lubricated. I use Bosch Distributor Grease to lube the cam and it's proven very effective - the points on my Convert are still at the same gap as when set them 14k miles ago.

Correct, little felt square, in 41 years, over 600k miles, have lubed it a bit ! Points last pretty much indefinitely
Centrifugal force lubes the heels, idiot proof system, if one maintains by the book
Not 14 k but often 50k between adjustments, even then only ever a thou or so..
Chain wax on cam and in adv retard unit pretty good too
But sure your german stuff won’t hurt, any lube is good lube.
Cos this is Chuck’s thread $ should be saved (Guzzi content),
If Bosch stuff free, I retract all

[Rough Edge racing]

 I say detonation damage, I've seen pistons like that before...Pre ignition always holes the center of the piston where it's  the most distant from the cylinder wall..An engine can go into detonation but you may not hear it...It takes a bit of time to do damage like that... Heavily loaded air cooled old tech deep hemi head bike on the highway is a good cadidiate....

[pete roper]

I was always taught hole in the middle was likely detonation. Gnawed by rats at the edge was pre ignition. Mind you it's been so very long since I've seen either, (I killed a few Triumph pistons with both 'Back in the Day'!) I might of got it arse about.

[Rough Edge racing]

I was always taught hole in the middle was likely detonation. Gnawed by rats at the edge was pre ignition. Mind you it's been so very long since I've seen either, (I killed a few Triumph pistons with both 'Back in the Day'!) I might of got it arse about.

 Kevin Cameron is a known authority on abnormal combustion....You had it right, your memory was wrong...

        https://www.youtube.com/watch?v=aH-lDh3rVFQ

[AZach]

I will say i had been running premium for about 2 months or so now since chuck said something to me about it.
What was wild was we went about 90 miles before it let out but the only change was that we stopped for lunch and got on the interstate about a mile maybe two away and got up to 80. We were on the interstate for roughly 10 miles before it gave out.
So I wonder if the several months and many miles of regular gas and the very retarded timing weakened the rings and when I finally got on it with full power it just failed?
Also to note the work seemed to drastically increase my MPG haha I have about half a tank left at 90 miles where as before I was switching to reserve at 90.
So seems like the consensus is that baring any internal damage from shrapnel is replacing busted parts, clean very well, and the distributor springs we should be good to go? 
Also I'll go out on a limb and say if I'm doing one side do the other side?
Thank you for all the info and input by the way it's much appreciated.

[Chuck in Indiana]

Let's postulate that Austin doesn't have any money. The skinflint that pays him doesn't pay him what he's worth.  *Assuming* when we pull a rod cap off and it's ok, what would be the issues of getting a used cylinder for that side as a temporary fix to get him going the rest of the summer?

[AZach]

Ahh so just a used cylinder or piston/rings?  Like you said enough to get through summer and if it does it again it won't be a huge loss with used parts. Then this winter I can go through both sides.

[normzone]

I can hear the red suspenders snapping from here ...

[guzzimatic]

On my '76 Vert I have a used piston and cylinder I got from Handy Andy(thanks Andy!) but I still needed rings...Say how about the stock rings on the piston I have been using as an ashtray for my Parodi cigars! Many thousands of miles later they are still happily reciprocating!

[Old Jock]

I was always taught hole in the middle was likely detonation. Gnawed by rats at the edge was pre ignition. Mind you it's been so very long since I've seen either, (I killed a few Triumph pistons with both 'Back in the Day'!) I might of got it arse about.

Been there many times too Pete, was on the motorway once giving it the beans one day on my Trident, when the mirrors went all sorta blue.

Engine lost power

Looked around and could not see anything past the back of the bike, I was like a battleship making smoke

[Cdn850T5NT]

I never get it right: what is pre-ignition versus detonation versus pinging?

[Mike Harper]

Holy Cow Chuck, no bueno! Do you think its possible to even figgure out what caused that?
Rick.

Without a doubt , Lack of proper maintenance.
 
 When was the last time the heads were properly re torqued and valves reset, and the proper mixture checked to see it is not too lean. Also the ignition timing set at full advance they way it should be.

Mike

[Rough Edge racing]

I never get it right: what is pre-ignition versus detonation versus pinging?

    The video I posted in reply #16 gives the answers you are looking for. And this article is considered to be one of the best explanations...http://www.contactmagazine.com/Issue54/EngineBasics.html  Pinging is the sound you hear when the engine is detonationg,and while a  liquid cooled car engine will tolerate some detonation, older air cooled bikes will not....Detonation at high speeds often can't be heard...
  I became really aware of detonation when I got into land speed racing with vintage Triumphs..I found power using leaner fuel mixtures than the competition..I have to be vigilant and inspect spark plugs often with a doctor's otoscope looking for early signs of detonation...
  There are many misconceptions about detonation and how higher octane fuel limits it...The biggest myth is high octane fuel burns slower...This totally goes against what is really happening because detonation needs time to happen, so the faster the fuel/ combustion  burn, the less time there is for detonation to occur..Higher octane tends to limit spontanous ignition of the "end gases",the cause of detonation... this is discussed  in both links I posted...

[Groover]

How many miles are on the bike?

[Cdn850T5NT]

    The video I posted in reply #16 gives the answers you are looking for. And this article is considered to be one of the best explanations...http://www.contactmagazine.com/Issue54/EngineBasics.html ...

Many thx. I willl view☺.

[Chuck in Indiana]

Without a doubt , Lack of proper maintenance.

I feel much better now..

[Chuck in Indiana]

    The video I posted in reply #16 gives the answers you are looking for. And this article is considered to be one of the best explanations...http://www.contactmagazine.com/Issue54/EngineBasics.html  Pinging is the sound you hear when the engine is detonationg,and while a  liquid cooled car engine will tolerate some detonation, older air cooled bikes will not....Detonation at high speeds often can't be heard...
  I became really aware of detonation when I got into land speed racing with vintage Triumphs..I found power using leaner fuel mixtures than the competition..I have to be vigilant and inspect spark plugs often with a doctor's otoscope looking for early signs of detonation...
  There are many misconceptions about detonation and how higher octane fuel limits it...The biggest myth is high octane fuel burns slower...This totally goes against what is really happening because detonation needs time to happen, so the faster the fuel/ combustion  burn, the less time there is for detonation to occur..Higher octane tends to limit spontanous ignition of the "end gases",the cause of detonation... this is discussed  in both links I posted...

Thanks for that. The article is aimed toward guys that are converting automotive engines for aircraft use.