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Old 06-24-2006, 07:35 PM   #1
ktmnate OP
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Hole in de piston 620

I finally took my 620 apart to see why there was no compression. The motor died right next to my work. I was hard on the gas shifted into second and it started to pull and then nothing! I must say that it was pulling real strong before it went.


Here is what I found:








My question is why? Is there any reason this would happen? The bike is a '97 620 with a Hi-flow head from an '03. Could it have been too much compression? Has this happened to anyone before? I'm still trying to decide what to do next. If I'll make it a 625 or keep it a 620. It's not about power. Because this thing had more power than any single I have ever riden. It once pulled the front up while spinning the rear and held it like that for 50'. It actually scared me.


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Old 06-24-2006, 07:37 PM   #2
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I have to add that everything else looked good. No marks on the cylinder. Just a hole in the piston poor KTM.
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Old 06-24-2006, 07:54 PM   #3
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Nate,

That's a strange way for a piston to fail. Not a hint of melting, just a fractured hole. And with the combustion traces around the underside of the failure, it looks like the breakdown took place over time, not immediately. Is this a detonation failure? If so it's not like any I've seen. Where did the chunk go from the piston crown?
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Old 06-24-2006, 08:13 PM   #4
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Quote:
Originally Posted by ChrisC
Nate,

That's a strange way for a piston to fail. Not a hint of melting, just a fractured hole. And with the combustion traces around the underside of the failure, it looks like the breakdown took place over time, not immediately. Is this a detonation failure? If so it's not like any I've seen. Where did the chunk go from the piston crown?
The chunk is in the case. I haven't tried to get it out yet. I don't even know if it's in hundreds of pieces or not. I sure hope I don't have to split the case. The bike never had any pre-detonation/pinging. I always ran premium grade gasoline. and it ran prety good. with the burn marks, it looks like it had been that way for several miles. It almost looks like something hit it or punched a hole. I thought it very wierd.


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Old 06-24-2006, 09:08 PM   #5
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A lot of modern high performance engines have oil jets under the piston to cool the center. Maybe the metal just fatigued due to too many heat cycles.

There was an Q&A in the last Cycle World about whether powder coating aluminum wheels (at between 400 and 525 degrees) would weaken the metal. IIRC, the answer seemed to be that damage is possible even if the wheel is heated to as low as 375 (depending on the quality of the aluminum). And damage is even more likely as the heat rises.
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Old 06-24-2006, 10:54 PM   #6
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So Nate, again I ask you...what strange force in this universe causes us to work on bikes at the same time? I was in the garage until 5:00 AM this morning tearing apart my 620 Adventure. Be glad. My piston shows seizing marks and tore up the bore.

Wanna' setup a group-buy on pistons and cylinders? I'm in for two of them (haven't torn down the 640 Adv yet).
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Old 06-25-2006, 02:56 AM   #7
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Quote:
Originally Posted by ktmnate
I have to add that everything else looked good. No marks on the cylinder. Just a hole in the piston poor KTM.
You could put the 80mm Rallye Crank in Nate . . . .

They are smoother . .
101mm bore X 80mm Stroke = 641cc (640 Rallye)
102mm bore X 80mm Stroke = 654cc (660 Rallye)
OR
103mm bore X 80mm Stroke = 667cc
105mm bore X 80mm Stroke = 693cc (Cases will need to be machined)

You will need to put a spacer on the base gasket, Shorten the camchain tensioner balde and deck your new head to suit . . . .

Below is my Good friend's KTM supermono. Runs on old 609cc Supercomp motor with Lots of tweaks. . . . . .
Name:  Servalloy KTM (Small).JPG
Views: 482
Size:  62.5 KB

Pezz :)
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Old 06-25-2006, 03:06 AM   #8
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Your evil Pezz

Putting idea's in everyones heads like that. There will be LC4 owners trying to stuff there engines up on purpose now, just so they have a valid excuse for going big.
Quote:
Originally Posted by Pezz_gs
You could put the 80mm Rallye Crank in Nate . . . .

They are smoother . .
101mm bore X 80mm Stroke = 641cc (640 Rallye)
102mm bore X 80mm Stroke = 654cc (660 Rallye)
OR
103mm bore X 80mm Stroke = 667cc
105mm bore X 80mm Stroke = 693cc (Cases will need to be machined)

You will need to put a spacer on the base gasket, Shorten the camchain tensioner balde and deck your new head to suit . . . .

Below is my Good friend's KTM supermono. Runs on old 609cc Supercomp motor with Lots of tweaks. . . . . .
Attachment 76453

Pezz :)
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Old 06-25-2006, 06:17 AM   #9
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Quote:
Originally Posted by Pezz_gs
You could put the 80mm Rallye Crank in Nate . . . .

They are smoother . .
101mm bore X 80mm Stroke = 641cc (640 Rallye)
102mm bore X 80mm Stroke = 654cc (660 Rallye)
OR
103mm bore X 80mm Stroke = 667cc
105mm bore X 80mm Stroke = 693cc (Cases will need to be machined)

You will need to put a spacer on the base gasket, Shorten the camchain tensioner balde and deck your new head to suit . . . .

Below is my Good friend's KTM supermono. Runs on old 609cc Supercomp motor with Lots of tweaks. . . . . .
Attachment 76453

Pezz :)


damn you. now I want one...well I always did but now just wantit more.
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Old 06-25-2006, 09:30 AM   #10
ktmnate OP
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Quote:
Originally Posted by Pezz_gs
You could put the 80mm Rallye Crank in Nate . . . .

They are smoother . .
101mm bore X 80mm Stroke = 641cc (640 Rallye)
102mm bore X 80mm Stroke = 654cc (660 Rallye)
OR
103mm bore X 80mm Stroke = 667cc
105mm bore X 80mm Stroke = 693cc (Cases will need to be machined)

You will need to put a spacer on the base gasket, Shorten the camchain tensioner balde and deck your new head to suit . . . .

Below is my Good friend's KTM supermono. Runs on old 609cc Supercomp motor with Lots of tweaks. . . . . .
Attachment 76453

Pezz :)
I thought about doing that. Dirtrider has a 670 or 675 setup that he builds. I'm not sure I want to invest all the money in it. I think I'll just replace the piston and get her back on the road. With the FCR and the Hi-Flow head, she really had great power. Not to mention MotoChick is ready to kill me for the '06 640 ADV I bought.


Nate
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Old 06-25-2006, 09:41 AM   #11
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Look like detonation failure to me.

Judging by the piston condition, I take it the bike had not been in service long before this happened so I'd suspect you've got something going on with the 03 head and the pre-02 bottom end. Are the pistons the same between the 02 and 03?

- Mark
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Old 06-25-2006, 09:45 AM   #12
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Quote:
Originally Posted by GregCifu
So Nate, again I ask you...what strange force in this universe causes us to work on bikes at the same time? I was in the garage until 5:00 AM this morning tearing apart my 620 Adventure. Be glad. My piston shows seizing marks and tore up the bore.

Wanna' setup a group-buy on pistons and cylinders? I'm in for two of them (haven't torn down the 640 Adv yet).


Hello Greg,

I have needed to get to it for almost two months. I spend the last 12 days working. I even had to work on Fathers day. I did take a nice ride on Fathers day to Nevada. Just a quick breakfast and then road home through Lake Tahoe. It was a really nice ride.

Have you found a sorce for pistons yet. I talked to my local dealer. They can get them but they were like $320 (Part #58430007100 II). Does anyone make a forged piston for the 620? I spent half the night trying to figure out why it did that. The only reason that I could see is what Colorado mentioned. I think going with the Hi-Flow head and the very open exhaust caused it to run very lean. The exhaust is the factory supertrap. but the previous owner had something like 14 plates. I had never checkd the jetting and am regretting that. Poor KTM I need to get her fixed up and go chase some sportbikes in the hills. It really pisses them off when a thumper with knobs can keep up in the tight stuff.


Nate


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Old 06-25-2006, 09:52 AM   #13
ktmnate OP
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Quote:
Originally Posted by markjenn
Look like detonation failure to me.

Judging by the piston condition, I take it the bike had not been in service long before this happened so I'd suspect you've got something going on with the 03 head and the pre-02 bottom end. Are the pistons the same between the 02 and 03?

- Mark
They are now showing the same part numbers. The 620 had been replaced several times and now it's forged. The bike had under 500 miles since a valve adjust. It would start right up and run great. It did have some sputtering as it was warming up. It felt like jetting which I knew needed attention. I just didn't think it would lead to this.


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Old 06-25-2006, 10:26 AM   #14
Donkey Hotey
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Quote:
Originally Posted by ktmnate
Have you found a sorce for pistons yet. I talked to my local dealer. They can get them but they were like $320
Holy jeebus did they go up? When I checked Cyclehutt back in December, it was $211. Their server is down right now so I can't check.

Cast pistons really are okay and have their advantages. Forged pistons have to be setup looser than cast pistons because of different rates of expansion. That adds to the piston slap until fully warmed. They also tend to be heavier.

There's 102 & 103mm Wiseco 660 pistons on fleabay for about $180. If the $320 price is real, I might just end up going 102mm on this baby. Man, you've got me thinking now. I was just going to throw a stock piston at it and debate replating vs new cylinder.

102x76 would be 621cc. The motor is already wayyy oversquare and those pistons are 13:1. That means machining them to lower compression (something I don't have time for right now). Big bore is just the wrong way to go for what we want out of an engine (torque, not RPM).

Man, I hate spending a huge bucket of cash and not improving things while I'm at it. Which way are you leaning?
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Old 06-25-2006, 11:48 AM   #15
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Detonation is one reason the piston failed. You need to make sure the compression ratio isn't to high with the High Flow head. You also need to make sure and always run super unleaded fuel. Has it been pinging lately?
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