Do Guzzis' ever hole a piston?

[Rough Edge racing]

 I'm interested in gathering some info on air cooled engines... A 71 Triumph with about 500 miles on a rebuilt engine came into my shop of horrors with no compression on one cylinder. A hole in the piston..the cause was a blocked fuel vent, the engine went lean under load, unchecked preignition always burns a hole right in the middle...The rider should have backed off the throttle when the engine faltered....
 Old Brit bikes and two strokes have limited ability to deal with this.........How about a Guzzi?  They seem to have a decent cooling reserve....Anyone put a hole in a piston?


       
     

[boatdetective]

Detonation and preignition are rife in my business. Technically, preignition is caused by a spec of glowing debris imbedded in the crust of carbon on the piston crown. Although I see holes in the middle of the crown- I more often see a ring of worn away aluminum around the circumference of the piston crown.

In general, leaning out is the major culprit. consistently low octane gas and luging the engine under heavy load will also do it (driving an underpowered, overloaded RV up and down mountain rods). I'm sure it can happen to any gas engine given the right conditions.

I tend to doubt that any cooling reserve can prevent this. The internal temperature of the combustion chamber under detonation can reach 2500 degrees F.

If you're interested in the topic, you should look into early attempts to understand and combat the problem in aircraft engines.  The struggle to produce supercharged piston engines that could perform at high altitudes during WWII resulted in many advancements. The US was an early proponent of 100 octane av gas- an edge that the Germans did not have.  Sodium filled exhaust valves were also invented during the war as a better answer to internal cooling.

[Rough Edge racing]

 I'm somewhat informed on detonation and preigntion. I do have a several books on WW2 aircraft engine design and problems.  A  forged piston can be more tolerant than cast pistons  about detonation ..
  Waiting for photos of holed Guzzi pistons..

[John A]

I've been around these since '77 and it's not something that happens too often, I did once hear of a guy who said he heard of a guy's brother in law who heard of a feller who did it but there may have been whiskey and exaggeration going on so no pics....

[Sasquatch Jim]

 That mostly depends on what they are shot with.

[ajwood]

Can damage occur by running out of gas under heavy load?

[Tobit]

I don't have it at my fingertips but I have a neat picture of my holed V50 Monza piston.  Not because of preignition or detonation, just good old fashioned broken valve. 

Either it floated and the piston smacked the head off the valve, or some other argument, but the stem was jammed solid in the guide while the piston shows a very definitive hole shaped like the head of a valve going through edge first.  The head and piston crown were a complete mess, as was the cylinder.  Still have the piston in a box somewhere.

The argument took place before I bought the bike.  Stan Friduss gave me the option of rebuilding the stock engine or putting in a Lario powerplant.  I went with stock V50.

Tobit.

[wymple]

I've never seen nor heard of one with a Guzzi. Surely somebody has done it.

[Rough Edge racing]

Can damage occur by running out of gas under heavy load?

  Yes, like running hard and the fuel runs low and the rider doesn't back off while switching to reserve. Low octane can lead to detonation and  then if continued can lead to pre ignition. It's said that pre ignition can melt a hole in just a few seconds....
  I have never holed a piston despite running lean...And that would include horrible abuse of automotive engines.....Opps, I correct myself, had an Audi Fox  that lost a piston...

[cruzziguzzi]

Seems like Calvins were shipped pre-destined to hole their pistons... At least mine was.

Todd.

[rodekyll]

It's hard to hole a 2-pot engine because of lean burning.  They tend to die from leanness before the problem gets catastrophic.  More cylinders = more 'help' cycling the lean piston through the number of strokes needed to melt it down.

MOST of the holed/broken pistons I've seen on aircooled engines (and I've seen my share) have been from valve head launches (burned valve/two-piece valve braze failure) or oil failure at the rod little end.  Next would come timing, and down the line is the wrong heat range spark plug.  Somewhere below that are the few honestly melted crowns.

[cruzziguzzi]

It's hard to hole a 2-pot engine because of lean burning.  They tend to die from leanness before the problem gets catastrophic.  More cylinders = more 'help' cycling the lean piston through the number of strokes needed to melt it down.

MOST of the holed/broken pistons I've seen on aircooled engines (and I've seen my share) have been from valve head launches (burned valve/two-piece valve braze failure) or oil failure at the rod little end.  Next would come timing, and down the line is the wrong heat range spark plug.  Somewhere below that are the few honestly melted crowns.

Great - more support for procrastination in getting my ECU re-flashed.


Todd.

[rodekyll]

I didn't say it can't happen.   

[cruzziguzzi]

I didn't say it can't happen.   

Wait... what?.... Crap!
Well, in any case I have what passes for winter coming so the heat won't exacerbate the condition.

Todd.

[Hacksaw]

Okay. Since the search function turned up zilch I was forced to go out to the work bench and retrieve the evidence of my totally stupid, irresponsible act of negligence from some dozen or so years back.
Here is how it came to be:
One late Spring the Ambassarado was in need of new points & rotor button. I purchased them and since the symptoms had 'gone away' I tossed them, along with new plugs and condenser in the saddlebag.
Fast forward to a VERY HOT, late July afternoon. I left work on my 55+ mile commute home and needing to be home sooner than usual I decided to take the freeway. As I began the, what I hoped would be, quite fast romp down the freeway, those aforementioned ignition symptoms decided to return.
Not a problem I say as I exit the freeway at the Waco, Nebraska off ramp. I roll into the truckstop parking lot and begin my, by now can be done in my sleep, replacement of all ignition related items.
After a few burned finger incidents made better by the unleashing of long & loud strings of profanities I was ready to fire the Ol fella up.
Tossing everything back into the saddlebags I tossed a leg over, verified neutral and turned the key. "Man that fired REALLY EASY" I said to myself as I clunked into first gear. "Maybe too easy"? I asked myself as I found neutral and turned the key to the off position and began to 'ponder'....
Naw, I don't need the wife to bring me the timing light. It's close enough and besides, He'll let me know if he gets unhappy.
So, fired up and off we go.
Did I mention it was VERY HOT in late July?
Yes, the bike communicated to me things were awry and yes I ignored it.
AND
Yes, I should've listened and stopped,
 AND
Yes Virginia, Guzzis can "Hole a piston"

[dl.allen]

vintage triumphs are known for this.  It is recommended to run them a couple degrees retarded at 3500 rpm for protection

[56Pan]

The shape of that piston, the high dome, looks exactly like a pair of 12:1 pistons I had in a '56 Triumph T110.  This was in '72-'73.  The only thing it would run on without pinging was Sunoco 260. (Yes, I had it timed correctly). When I tore it down, I took the pistons to a local Triumph shop and they told me they were the 12:1 compression ratio.  If he ran it on 87 octane, I don't doubt he detonated and holed one of them. Just going by the picture and memory here. I'd like to know what fuel he was running.

[Tobit]

Here's the Monza piston I mentioned above....



V50 owners, don't miss a shift!

Tobit

[Rough Edge racing]

The shape of that piston, the high dome, looks exactly like a pair of 12:1 pistons I had in a '56 Triumph T110.  This was in '72-'73.  The only thing it would run on without pinging was Sunoco 260. (Yes, I had it timed correctly). When I tore it down, I took the pistons to a local Triumph shop and they told me they were the 12:1 compression ratio.  If he ran it on 87 octane, I don't doubt he detonated and holed one of them. Just going by the picture and memory here. I'd like to know what fuel he was running.

 It's a stock style 9-1 piston. The old style high compression Triumph pistons have a very peaked dome know to cause combustion problem ..9-1 compression Triumph will detonate on 87 octane...A careful rider with the engine tune up done properly can be ok 91 octane but 93 is best....
  Sunoco 260 would be 98-99 octane by today's rating system.

 The forged 10.5 compression pistons in my 650 race Triumph look like this.. The 1930's hemi design requires a big dome for high compression..The left side piston shows an intake valve witness mark from running the engine beyond the cam design...
       

[56Pan]

It's a stock style 9-1 piston. The old style high compression Triumph pistons have a very peaked dome know to cause combustion problem ..9-1 compression Triumph will detonate on 87 octane...A careful rider with the engine tune up done properly can be ok 91 octane but 93 is best....
  Sunoco 260 would be 98-99 octane by today's rating system.

 The forged 10.5 compression pistons in my 650 race Triumph look like this.. The 1930's hemi design requires a big dome for high compression..The left side piston shows an intake valve witness mark from running the engine beyond the cam design...
       

Thanks for the info and pictures.  I would have thought the holed piston in the picture was more than 9 to 1?  Your head has nine head bolts.  I believe my T110 only had eight.

[johnr]

Can damage occur by running out of gas under heavy load?

No. Because the engine stops working (producing heat) and while I expect it leans out as it runs out this wouldn't happen for long.

[Rough Edge racing]

No. Because the engine stops working (producing heat) and while I expect it leans out as it runs out this wouldn't happen for long.

 No.This is a cause of holed pistons in many situations...Under heavy load ( like wide open throttle) in the short time the engine leans out, detonation and or pre ignition happens instantly...Pre ignition can hole a piston in a second if the rider doesn't back off the throttle.
 

[John A]

Detonation and preignition are two different things. Pre ignition is caused by things like timing, a hot spot in the chamber, overheated plugs etc. the mixture is lit off early. Detonation is when the mixture is lit off instantly and is caused by things like preigniton, temp, load, power setting, wrong fuel etc. detonation will destroy an engine before the operator realizes it is happening.

[Guido Valvole]

@ Tobit above -- was that holed piston from a missed shift and over-revving or did the exhaust valve stretch? I replaced the exhaust valves in mine when clearance was going from .008 to .004 in 500 miles. Learned the hard way with a VW Bug… yep, #3 there, lousy ashtray and expensive paperweight. It ran fine right to the point it seized.
cr

[Rough Edge racing]

Detonation and preignition are two different things. Pre ignition is caused by things like timing, a hot spot in the chamber, overheated plugs etc. the mixture is lit off early. Detonation is when the mixture is lit off instantly and is caused by things like preigniton, temp, load, power setting, wrong fuel etc. detonation will destroy an engine before the operator realizes it is happening.

 Yes,  detonation occurs and many engines will tolerate some detonation. If detonation continues, hot spots can occur leading to pre ignition...

[LaGrasta]

rodekyll states "it's hard to hole a 2 pot engine" Somehow I did it to my Sportster years ago. I had a '98 883 that was built up for a HotBike Magazine story by an LA, CA dealer; 1200 big bore kit, hot electronics, SuperTrapps, etc. It was a beast. a few months afterward, doing about 120mph Saturday morning on Highway 74, white smoke bellowed out one pipe. Sure enough, holed one piston.

A year ago, I had my '10 V7 wide open and the same, white smoke out one pipe and I thought I holed the piston, but it still runs okay, no loss in performance, however now when riding it hard, it blows oil out the valve cover (air box over flow). As long as I keep the revs down, it doesn't leak a drop. I have yet to remove the jug and see what the rings and piston look like.