Topic: Wiseco piston failure w/pics

[scondon]

   Two years ago I threw a rod and busted up an 836cc engine pretty good. Fortunately only 1 cylinder was destroyed so I took the remaining three pistons/sleeves, and using a spare piston and sleeve from another block I was able to transfer parts into spare cases and cobble together another running engine.

   Six months ago I was on my way to work when the cobbled engine lost power and started blowing smoke. I pulled to the side of the freeway, and realized that something bad had happened to the #1 cylinder due to all the smoke and cold exhaust pipe. I was closer to work than I was to home so I limped to work on 3 cylinders. After work I limped  25 miles home in the slow lane, and parked the bike where it has sat until this weekend.

  Today I pulled the head off to inspect the damage, and found that the outer edge of the piston top that defines the intake valve relief broke away on #1 AND #2 piston. #1 piston melted away through all three rings, and a cloud of smoke ensued. #2 piston must have blown the shrapnel out the exhaust, and kept on running as if nothing at all had happened, even though the top ring is now exposed.

  Now I'm guessing that heat and fatigue caused these failures, rather than some inherent flaw in the Wiseco 836 piston. The bore on the cylinders was sloppy loose, and the ring gaps were HUGE when I put this engine together. Thinking that combustion gasses were overheating the top ring, and the aluminum piston failed at its thinnest point where the valve relief is.

  Any guesses as to what can cause this type of failure are welcome. I would rather not repeat it any time soon.

[GammaFlat]

friggin bummer.  What were your use patterns?  Did you detect any pinging?  What is the shape of your combustion chamber (modified)?  My gut says it's not the pistons (especially since 2 failed). 

Yer scarin' me.  I'm about to put together an engine for "the ride". 

[Old Scrambler]

Could you show us the valves and the head gasket?

[bollingball]

The bore was sloppy and the ring gaps were huge. Why did you put it together that way? Got any more specs or measurements when you built this motor. A little loose here a little tight there all adds up to something that may be doomed to failure would have to know all the specs.

[scondon]

friggin bummer.  What were your use patterns?  Did you detect any pinging?  What is the shape of your combustion chamber (modified)?  My gut says it's not the pistons (especially since 2 failed). 

Yer scarin' me.  I'm about to put together an engine for "the ride". 

I didn't detect any pinging at the time of failure, but over the life of these pistons I have had some issues with it. Hot cams, porting, big bore, etc.. I have had a bear of a time getting rid of it at 3/4 throttle when the engine is hot and under load(going uphill, or against heavy wind). Glad you brought it up.

Chamber shape was not modified except to fit larger intake valves. There is no evidence of any valve to piston contact.

I'm trying to get an engine together for "the ride" too, but am experiencing some....speed bumps.

The bore was sloppy and the ring gaps were huge. Why did you put it together that way? Got any more specs or measurements when you built this motor. A little loose here a little tight there all adds up to something that may be doomed to failure would have to know all the specs.

Short story is that I needed transportation to a new job, and I had two blown engines of which I cobbled together a "runner" from. I didn't expect it to last forever.

The sloppy bore and big gaps were because of a local "pro" machinest  who did the boring and assured me that it was ok. This was years back, and it was the first engine I ever did.

I know it won't make sense to most to not "do it right as long as your in there," and I would agree. But the fact that I've had little to no income the past couple of years means I gotta just play with what I have.

[scondon]

Could you show us the valves and the head gasket?

They look surprisingly fine. No damage, no combustion leaks on the fire rings. Just a bit of aluminum from the piston, and burnt oil in #1. Exhaust valves are tan in color, not white from over heating.

[scottly]

I don't see any severe scoring on the piston skirts, so I would guess pinging, also.

[Jerry Rxman Griffin aka MuthaF'er]

Were you running lean?

[dave500]

they dont look to have gone lean,if the piston to bore clearance was that sloppy allowing the piston to rock over and put pressure on the top forward edge of the piston causing the break?continuing to use the motor has caused more damage such as the melting we can see,i lay money on carbon build up with a too close piston edge clearance to the combustion chamber edge,have a look at the piston on the right,how the carbon is disturbed around the outer edge,how does the chamber look in this area?pics?
http://forums.sohc4.net/index.php?action=dlattach;topic=84902.0;attach=142000

[shino]

Now i'm getting scared too. I just had an 836 kit installed on my bike. Hope we can figure out what happened so we can prevent it happening in the future on other rides.

[scondon]

Now i'm getting scared too. I just had an 836 kit installed on my bike. Hope we can figure out what happened so we can prevent it happening in the future on other rides.

I wouldn't get too worried about having yours fail like mine, shino. Lots of people running Wiseco's, and this is the first I've seen of this type of failure.

...i lay money on carbon build up with a too close piston edge clearance to the combustion chamber edge.

This sounds like a very plausible explanation. Carbon build-up is very hard and repeated tapping at 6,000rpm could easily break that thin bridge. I'll take a closer look at the pistons and head in the morning.

I have another engine with Cycle-x 850 pistons that had some sort of catastrophe in the #1 bore. Limped it home 1.5 miles, and when i pulled the spark plug I saw that the electrode had been smashed. Obvious that something "cut loose." I haven't pulled that engine apart yet, but I'm expecting to find something similar to this failed Wiseco engine.

I'm beginning to believe that California gasoline is utter crap to use in an old, bored out bike. No science, just opinion based on the ungodly amount of hard carbon that I've found when I pull these engines apart after 20,000 miles.