What on Earth?!

Message

who_gives_a6 · #1 Post by **who_gives_a6** » Thu Jan 16, 2014 3:15 am

Continuation from fuel pump woes thread..

2nd gear near redline, shifted to 3rd and it locked up. Here's the results.

Brand new exhaust cam is no good. Billet decomp looks good. Cylinder was undamaged and the piston moves freely with the head removed. Haven't torn the bottom end down yet but will for inspection. Even though it spins freely, I'm curious of the rod/bearing condition. Head has some gouging and seat damage.

What would cause this? Valve float? 3 of 4 valves snapped off at the heads. I keep good logs of riding and after looking this engine has an estimated 17hrs on it, including engine break in/heat cycling. Changed oil 3 times on it; Amsoil. My other quad setup 100% identical has roughly 55hrs and my identical but 478cc has nearly 20. All ridden the same way and maintained alike.

Tim did everything on it. Head job/porting, stroker crank, CP 97MM piston.

who_gives_a6 · #2 Post by **who_gives_a6** » Thu Jan 16, 2014 3:16 am

What I saw when I pulled the head.

who_gives_a6 · #3 Post by **who_gives_a6** » Thu Jan 16, 2014 3:18 am

After removing the snapped valve heads.

who_gives_a6 · #4 Post by **who_gives_a6** » Thu Jan 16, 2014 3:19 am

Bottom of the head. One valve left.

ScramblerXLE · #5 Post by **ScramblerXLE** » Thu Jan 16, 2014 5:44 am

If you look at your second pic, you can see the witness marks that show one of your exhaust valves (the one with the flat lobe) had been hitting the piston for "a while" not sure how long it would take to see those witness marks, depends if it's just polished up or if it's actually 'machined' down a bit. I've seen issues with that on my KTM engines when using SUPER long duration cams with old / fatigued valve springs from float. Not sure if float caused that or if your valve was sticking and not shutting all the way. Either way, I'd guess that valve finally broke off and wound up near the middle of the piston, whereupon the next stroke, the intake valves found something in their way, and their heads snapped off. Sucks for sure...

kdeal · #6 Post by **kdeal** » Thu Jan 16, 2014 11:45 pm

Truth...... Your exhaust cam lobe wore down fast, floated that one exhaust valve, exhaust valve snapped off and did the rest of the damage to the intake valves by bouncing around and being crushed into the intake valves.

Unfortunately, this is one of the last problems with a Cannondale motor. The cams are well designed but usually paired up with a crappy set of valve buckets that cause extreme wear in some cases. Personally for all of my motors built for myself, I have been biting the bullet and putting in DLC coated valve buckets at close to $100 each. This will usually cure any and all problems unless the cams are worn to begin with. I also like to hoard FX400 cams because they are of the best quality and hardness and were manufactured by Megacyle Cams originally. Send the head back to Tim to see if he can clean it up by polishing and possibly some welding to avoid the cost of porting another head.

Ken

Canniboomer · #7 Post by **Canniboomer** » Fri Jan 17, 2014 12:27 am

The more common "sticky-bucket" right lobe of the exhaust cam appears to be the indicator. The wear at that lobe is MUCH greater and squared off compared to the decomp lobe and the intakes lobes. It might have been a sticky bucket issue that was still causing trouble.

Happyboy · #8 Post by **Happyboy** » Fri Jan 17, 2014 1:29 am

QUOTE (Canniboomer @ Jan 16 2014, 07:27 PM) <{POST_SNAPBACK}>

The more common "sticky-bucket" right lobe of the exhaust cam appears to be the indicator. The wear at that lobe is MUCH greater and squared off compared to the decomp lobe and the intakes lobes. It might have been a sticky bucket issue that was still causing trouble.

sticky bucket

who_gives_a6 · #9 Post by **who_gives_a6** » Fri Jan 17, 2014 2:12 am

Tim redid the head for me before so probably gonna send it back to him and see if we can salvage the head since I spent quite a bit for the porting on it already.

Now I need cams though. I already needed one for another build and now I need a new one for this one. Are there any sources of good exhaust cams left?

So what would be the best solution to never let this happen again? Money aside that is. Well, to a point. This trashed the piston too, so I'd gladly throw some extra cash into better parts to prevent this again.

omegas · #10 Post by **omegas** » Fri Jan 17, 2014 3:29 am

I don't have much time on mine, but went with KDeal's suggestion on the supper buckets

Ken, are those FX cams best for power also or just durability?