TurboBike
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posted August 31, 2009 09:34 PM
Camshaft Havoc - Engine builders welcome!!
This is a question for the Pro and/or experienced engine builders.
Here are some factoids about the ZX12R build on my friend's bike. This started out as a Carpenter built 1290 that eventually put out 193hp on a DJ 150 on pump gas. Carpenter uses fairly big grinds in his builds and times them at 110int 112exh to get those big HP #'s at high rpms. Specs to something like 385int and 394exh or some thing like that. Anyhow, after about 14k miles my friends blows up his stock clutch basket which resulted in mild engine damage, therefore a full rebuild was in order. Before we started, the engine was split and the trans was dissassembled completely and every part was inspected. After many days of inspection, the build went forward. So we upped the compression with new JE pistons, new Falicon knife edge rods, lightened crank with no balancer, race cut built trans with billet basket and ceramic bearings in trans. All bearings were replaced in the engine of course. Kept the original cams as they showed absolutely no issues and utilized APE springs(not sure what psi) instead of the original Carpenter springs(not sure why he did that). After all this, the bike picked up 3-4mph in the qtr right off the bat. Bike runs and revs great.
Well, the bike has about 1500 street miles since the build, 1 full road race day and 5 passes down the qtr. We make another trek to the strip to lower some ETs with more gear and some mild enhancements. We didn't even get out of first before the bike suddenly lost power. Got back into the pits and the bike sounded like it was missing a cylinder. After getting it to the shop, immediately checked for heat from the header and the #1 cylinder is cold. Checked cold compression and the other 3 cylinders showed 180psi where #1 had 25psi. Uh oh!!
Pulled the valve cover and upon quick inspection........found this........hmmmmmm......How often do you see this happen?
Intake cam
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entropy
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posted August 31, 2009 09:53 PM
perhaps someone forgot to tq the cam cap?
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tcchin
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posted August 31, 2009 10:01 PM
The problem here is both obvious and easy to fix: Hostess Donettes are clearly inferior to VanDe Kamp's mini frosted donuts.
BTW, if you can provide a close-up image of the break planes, it would be a lot more informative. Initial impressions are that the failure was shear-related, not torsion-related, as the failure region is planar, not helical.
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TurboBike
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posted August 31, 2009 10:12 PM
quote:
The problem here is both obvious and easy to fix: Hostess Donettes are clearly inferior to VanDe Kamp's mini frosted donuts.
BTW, if you can provide a close-up image of the break planes, it would be a lot more informative. Initial impressions are that the failure was shear-related, not torsion-related, as the failure region is planar, not helical.
Yea. I didn't take these pics but I'll go over and take some detail macro shots and post them up tomorrow. We found the Donettes in the intake, so that may have been the reason for the mild heart attack.....LOL!
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entropy
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posted August 31, 2009 10:22 PM
please take pix of the journals on both sides of the area where it broke, and look at the cam cap.head for damage/discoloration in the area where the journals sit.
perhaps the cam was bent when it was installed???
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aliveagain
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posted September 01, 2009 04:17 AM
I did it when tightening the cam cap and didn't have the cam situated right.I tightened up the cap cover and heard a pop.
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osti33
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posted September 01, 2009 06:40 AM
 Edited By: osti33 on 1 Sep 2009 14:42
Aww Snap! Sorry couldn't resist.
Sorry about your busted cam. I've seen a couple broken cams like that and they both were broken from being installed improperly. The both ran for a little while then just like you described. Were all the buckets and shims still in place?
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KZScott
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posted September 01, 2009 01:25 PM
quote:
I did it when tightening the cam cap and didn't have the cam situated right.I tightened up the cap cover and heard a pop.
maybe a dowel pin wasnt lined up all the way?
Ive never seen damage like that(im kinda new to this stuff tho) wierd...
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01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
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aliveagain
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posted September 01, 2009 04:12 PM
Actually,I believe it was that round piece in the middle.I put the chain on an must not have had the middle part in the slots.The end of the cam was sticking up and I was just trying to pull it down.
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tcchin
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posted September 01, 2009 04:55 PM
quote:
Well, the bike has about 1500 street miles since the build, 1 full road race day and 5 passes down the qtr.
What roadracing class does this bike compete in? Is it competitive?
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TurboBike
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posted September 01, 2009 05:07 PM
Edited By: TurboBike on 2 Sep 2009 01:08
So I went down to the shop and had a look see. Without taking the head off as of yet, it simply looks like the cam failed at the end lobe. Once that broke then a few lobes over where now it no longer relies on the bearing support the other piece broke off as well probably shortly after the end fell out of the journal. The end piece broke off but was in it's place for bit and shows wear on the flat side of the lobe but no wear from there to the peak of the lobe.
Being that factory cams and regrinds are cast, it is hard to tell what kind of shear occurred. The journals are perfect except for where the lobe eventually scarred an edge once it broke and moved around. Otherwise the caps and buckets look fine, no spit out shims and nothing else I can see right now.
I believe that the cam simply failed. My guess is inevitably the weld and regrind process weakens the metal too much. Perhaps because the Kawis have thin castings. It appeared to us that the end broke off then the other section broke as it no longer had support at the bearing cap. Another thing is unless you can Xray the cams before and after, you never know what kind of internal stress cracks may have already been there.
Here are some more updated pics. You can see where the cam rubbed for awhile when the broken parts split. The end lobe though broke off cleanly and slid out of the cap eventually.
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chavcat
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posted September 01, 2009 05:54 PM
Kind of reminds me when my oil pump shaft snapped cleanly in two.
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tcchin
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posted September 01, 2009 07:10 PM
Definitely shear. It's hard to tell from the photos, but it doesn't look like a fatigue thing at all (no polishing of the mating surfaces on the #1 outboard segment). The second fracture looks like it was from cantilever bending shear, as its fracture is at a slight angle to the axis of the cam. The resulting high spot is probably responsible for polishing the middle segment.
Have you done a leakdown test yet?
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dougmeyer
Needs a job
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posted September 01, 2009 07:15 PM
Unless you tell me that the cap saddle bolts were absolutely still torqued, I'd say the cap was walking around a bit from loose bolts. Notice the burnished area around the bolt holes......
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TurboBike
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posted September 01, 2009 08:24 PM
quote:
Unless you tell me that the cap saddle bolts were absolutely still torqued, I'd say the cap was walking around a bit from loose bolts. Notice the burnished area around the bolt holes......
I'll have to ask the guy who took it apart to know for sure but I see what you are seeing. I'll go down there again and look at the other journal cap bolt holes for comparison.
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tcchin
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posted September 01, 2009 08:25 PM
Loose cap bolts would definitely allow stepwise shear loading of the camshaft. Nice catch, Doug!
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entropy
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posted September 01, 2009 10:41 PM
quote:
perhaps someone forgot to tq the cam cap?
I am happy when Doug backs me up 
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tcchin
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posted September 01, 2009 10:48 PM
Sorry Karl - nice catch, too!
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entropy
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posted September 01, 2009 11:34 PM
I am now careful about tq-ing cam cap bolts after i encountered weird PTV numbers when i had tightened, but not tq-ed the cam cap.
No doubt there is only one way for me to learn stuff, by making mistakes (usually several times)
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TRNorBRN6001
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posted September 02, 2009 08:26 AM
Ouch, that hurts!
Some of those cam cap bolts might have been fatigued when reinstalled and not caught.
I have had some evil ones that got a little stretchy. I think Karl might have experienced that as well.
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krexken
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posted September 02, 2009 11:05 AM
I'd be checking your old versus new valve spring pressure just to see.
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