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Author Topic: Destroyed Engine  (Read 2886 times)

Offline WestonHorner

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Destroyed Engine
« on: June 06, 2016, 08:22:51 PM »
So I decided to start a new topic since my previous topic is no longer relevant to the problem I now have.

Anyone ever have a valve head break off? At around 5,000 rpm...... Anyone got a good explanation for why this would randomly happen?......... Current mood: ticked off...

So anyone have a spare engine they want to sell for really really cheap?? ......or free?... Maybe a good running 720?.... lol

Offline Dragon

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Re: Destroyed Engine
« Reply #1 on: June 06, 2016, 10:16:49 PM »
That is some serious damage.   I feel for you.  I'm in the midst of trying to get a couple running and having lots of issues.   Sounds like you were close to having everything ironed out.   

DS650 stock bore.  She just looks slow. 
DS730 Big Bore.  Being built now

Offline BigRay800

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Re: Destroyed Engine
« Reply #2 on: June 06, 2016, 10:22:50 PM »
WOW!!!  That brings back nightmares from my 800 turbo days.

  Dragon good to hear your alive!
Ds650 powered by Suzuki GSXR 1000 [sold]
Girl made me buy a damn RZR

Offline Dragon

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Re: Destroyed Engine
« Reply #3 on: June 07, 2016, 08:18:08 AM »
I was thinking about what may have happened and it is possible that the timing slipped.  I am guessing you have a hydraulic cam chain tensioner.  I am betting it failed and the chain skipped putting cams out of alignment.  When that happened the valve and piston would have had a catastrophic meeting. 

I had this happen on a rebuild I did and while we just trying to get it to start the damage was enough.  Bent valves and wiped out the piston. 

And thanks Ray.  Missed everyone
« Last Edit: June 07, 2016, 08:24:52 AM by Dragon »
DS650 stock bore.  She just looks slow. 
DS730 Big Bore.  Being built now

Offline WestonHorner

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Re: Destroyed Engine
« Reply #4 on: June 07, 2016, 01:33:42 PM »
Dragon,

I check the cam chain and it was perfect. No slack in it. Or VERY very little. Not enough to slip a tooth by far. It's just a stock DS650 Rotax motor. Has the normal bolt holding the cam chain tensioner in. Everything was perfectly fine in the top on. Cams looked great and everything was securely tightened. The cams were also still aligned with each other when I opened it up.

I was maybe about 5 to AT MOST 7,000 rpm when it happend. I was thinking maybe it had a valve float which cause it to strike the piston and break off? but I doubt it would have valve float at 7k?... It has stock everything, 100mm piston, stock cams, stock springs, stock valves.

Could the valve just fail from fatigue overtime? They are 15 years old afterall ?  :-\

I was so close to having it running great and just bought my ORV stickers the day it happend...... great....

Offline Dragon

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Re: Destroyed Engine
« Reply #5 on: June 07, 2016, 02:20:17 PM »
It was a theory.  Guess not.  When it happened to me, the tensioner frozen in the compressed position and allowed slack on the timing chain a cam jumped just enough to have the piston slap the valves. 

You just mad me realize mine is 11 years old   YIKES!!!  Not much left stock though.

Anyway, that was the only thing I can come up with based on my experiences.  I am sure someone far more knowledgeable than I will speak up. 
DS650 stock bore.  She just looks slow. 
DS730 Big Bore.  Being built now

Offline ACEISBACK

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Re: Destroyed Engine
« Reply #6 on: June 07, 2016, 08:33:42 PM »
Cams were aligned but did you happen to check your valve gap? You still may have floated a shim and not caught it if it's a shim under. If it's the OEM bucket system then it would have been apparent.
I don't "think" a valve would have just snapped or broken without slapping the piston or some out of the ordinary force acting upon it.
If you can read this, thank a Teacher. If you can read this in English, thank a Marine.

Offline WestonHorner

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Re: Destroyed Engine
« Reply #7 on: June 08, 2016, 07:11:42 AM »
Well, I had a valve adjustment done from a shop back in February. When I opened it up after the damage the valves and shims looked fine. Brand new shims which tells me they did in fact do the work and changed them. They are the OEM bucket style. And everything was well seated and didn't look like it had moved or even had the possibility of moving. I've since pulled the cams out so I can't take any pictures to show unfortunately.

If what you're saying is correct in that it would not fail from regular heating/cooling fatigue then I am assuming it hit the piston and that is what caused it to break off. But if that's true then, it floated? I have a rev limit at 8,500 rpm with the big gun CDI. I was going somewhere between 5,000 and 7,000 RPM but really no more than 7,000 rpm when it happend. I wouldn't think it could float the valves at 7,000? Even with stock springs?

Offline Oldmanracing

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Re: Destroyed Engine
« Reply #8 on: June 09, 2016, 04:18:13 PM »
Could be a lack of oil to the top end.
When was the last time you cleaned the oil strainer, bottom of oil tank?
If the strainer gets plugged, the oil to the head gets reduced.
My guess if the the valve had lack of oil, valve galled(hung up) long enough in guide for the piston to hit the valve.
Check the strainer for contamination.
Let us know what you find.

OMR

Offline WestonHorner

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Re: Destroyed Engine
« Reply #9 on: June 10, 2016, 03:11:58 PM »
Well I just actually replaced the strainer with a brand new oem one just before this. I did an oil change and replaced the hose/strainer since it was leaking before.

Could have been low oil since I did the oil change? Maybe didn't top it off completely? That sounds like the best answer so far.

Offline BigRay800

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Re: Destroyed Engine
« Reply #10 on: June 10, 2016, 05:38:11 PM »
New Theory,  Damn thing just broke!
Ds650 powered by Suzuki GSXR 1000 [sold]
Girl made me buy a damn RZR

Offline WestonHorner

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Re: Destroyed Engine
« Reply #11 on: June 10, 2016, 05:51:06 PM »
Lol BigRay...... Agree'd.

Offline pugs

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Re: Destroyed Engine
« Reply #12 on: January 12, 2018, 07:02:36 AM »
keeper let go and you dropped a valve* this is due to an improper shim or just oil maintenance*  just a quick guess :)  any pro would find your answer in couple hours.

 

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