At what rpm aproximately did you feel the most power increase?

I've got a delkevic shorty muffler (with baffle) which sounds amazing but makes my ears ring.

I've also got the vm36 with ufo so that accounts for some differing jetting.

I have sold hundreds of cams and pistons over the past 15 years without any interference issues.  That includes my own Savage which has had 0.025” taken off the cylinder and 0.015” from the head, for 0.040” total, a 97mm Wiseco and used with all the cam profiles I’ve had, the Stage 1, 2 & 3.
Like DBM my engine has been to 7500 several times and 8000 once with no damage.  It starts and runs just fine.

Your particular case is the first I’ve heard of.

You did not choose the wrong cam.  The Stage III cam is pretty mild.  When combined with the high-compression piston you will not lose much, if any, low-end torque.  Explaining all the ins & outs of camshaft design and selection is way too much to go over here in this post.  Just rest assured that your camshaft selection was reasonable & proper. 

"Unfortunately, the shop has been the ones to do the work from the beginning.  When I initially took it in to get all the parts installed they told me that on the first test run of the parts installed along the first block or so they heard the shattering and took it back. They then replaced the gear, chain, guides, and tensioner"

This nugget of gold may hold the answer to what happened to your engine.  These cam chain drive sprockets don't just fail out of the blue. As I mentioned earlier, the cam drive sprockets are known to fail in the manner you described.  These sprocket failures can be attributed to over-torqueing the primary drive gear nut.  In your case, there's a lot of "IFs" involved.

IF the shop over-torqued the nut, it may have resulted in the sprocket failure.

IF the sprocket failure resulted in the sprocket separating and falling apart, the drive chain would have jumped time.

IF the chain jumped time, or fell off altogether, it could have altered cam timing enough to cause the piston to run into the intake valves.

All of those IFs would explain why the piston hit the valves.

IF the valves were extended just the right amount when the piston made contact...and...IF the rocker arms were at just the right angle there may have been sufficient side loads to result in the guide fractures.  They fractured right at the weakest point (circlip grooves).

Right now, the burning question should be what caused this failure?  Your failure is not attributed to your cam selection.  Your failure is not attributed to wear & tear.  I think your failure is the result of an assembly error.

Sometimes you just have to lick your wounds and move on.  Pick up the pieces.  Make the most of the situation and see what you can learn.

As long as the shop has your engine in their possession you aren't going to learn anything about your engine, why it failed, how to properly assemble it, etc., etc.  Based on what you have said so far, it seems highly unlikely that the shop will share anything with you that might reveal any errors on their part.  

Get it out of there.  Bring it home where you can see it, feel it, smell it, take pictures of it.  BTW, do you have any pictures of that cam chain drive sprocket?  Pictures of the left-hand nut that secures the primary drive gear would also be insightful.

LANCER wrote on 12/28/20 at 06:34:49:


Here's the only picture I have of the sprocket failure and the subsequent engine disassembly they say they did.

I would hope that since they claim they disassembled the engine after the sprocket failure that they would have seen if the valves or guides were astray. Besides wouldn't it have demonstrated the problem immediately afterwards? I really don't know.

As an tangential question, do you think it's fair to request that the shop pay for the costs associated with these repairs? I can't directly prove that it was their fault for the failure, however since they were put in charge of the whole process I feel they should take responsibility for the cost of replacement parts/repair? What do you think? I already paid for all the repair costs associated with the sprocket failure on top of the cost of the modifications for which I had already paid them. Am I being reasonable?

Does anyone else think that broken gear looks just like the one a couple months ago from the guy whose counter balancer went out of sync?
I thought we pointed at someone not knowing the nut was left hand thread and over torqued it trying to get it off the wrong way crushing the gear.
Those gears don't ''JUST BREAK''

Might be the same cause this time with a different result.

Torque spec for that nut is 65-80 ft.# That's not all that tight.

I can do that easily with an 8'' or 10 " ratchet handle  and socket and I'm not real strong.

If the shop used a 1/2 in. drive air wrench to take the nut off, and put it back on with the same tool, it's very likely they broke the sprocket when reinstalling the primary drive gear and nut.

I think even one of the newer 20V or more battery powered impact wrenches are probably strong enough to do it.

I also wanted to share this with you.  This is a picture of a primary drive gear nut.  It has obviously been grossly over-tightened.  My guess on this screw up is that someone was working on the engine and they were not aware that the nut has left-hand threads.  They tried to remove the nut and just kept reefing on it until the corners folded over.  I suspect the drive sprocket on this engine was toast by the time they figured out the nut is left-hand.  You can actually see the "L" stamped on the face of the nut indicating its left-hand.

Good luck with the project.  Maybe your next lecture presentation will be on proper engine assembly.  Keep us in the loop.  Your valve guide failure is unique.  Figuring out what happened will help us all.