Okay this is a which came first question.

I'm on the chassis dyno the other day running an F20C with a ported head, some killer camshafts and individual throttle bodies. We make a first pass and are making 280+RWHP on a crappy tune NA on gas. The engine seems to want to run so I go back into the computer and bump the rev limiter to 10,200.

We make another pass and hold it against the limiter a few seconds to see how the limiter behaves. Still running crappy but still 280+ RWHP. Make a few mixture changes, light the engine for another pull and about 6800 all Hell breaks loose and the engine just winds down. It still spins but no compression. We pull the cam cover and about 2/3rds of the cam follower rollers are shattered and there are needle bearings all over the place (Hmm, so that's how they're constructed). Suddenly I see the bolt that holds the timing chain sprocket/gear in place lying in the floor pan of the car (it's a race car not a stock S2K so it has a floor pan). Except it's not an entire bolt, just the part from the threads out, like the threads are still in the head and it has just sheared off.

I haven't taken it apart just yet but I've read some posts about that little bolt coming out. Except that it appears thay mine didn't since it sheared off.

So the question... did the valves hit the pistons which jammed everything together and caused the bolt to snap, or did the high lift cam and heavier valve springs over stress the bolt which snapped causing all the valves the "interact" with the pistons? I.e., has anyone ever snapped one of these bolts before?

Thanks,

Jim

P.S. does anyone make some decent exhaust rockers that have some extra clearance so they don't hit the exhaust cam lobes? I have to grind all my exhaust rockers to clear the lobes. And no, I don't run VTEC.

 

Pictures?

 

You'll know whether the valves hit the pistons when you get a look at the piston crowns. Until then, it's hard to know whether there was contact or not. Too many variables and too many unknowns.

LOL, and yea, how about some pictures. Not that they'll help, but I wanna see.

 

I don't see how the cams could have overstressed the bolt at 6500 and there was no sign of it at 10500. It may have been loosened at that point but I think you would have noticed a whining noise first. There is a rubber piece that sits flat with the head where did that end up?? How much actually came out and what was left inside of the case?? is the rest of the bolt still in place?? Maybe the threads failed??

 

The cam sprocket bolt breaking while the engine was running at any speed would cause some pretty nasty damage, including the compression loss. My bet is the bolt broke. At this point it doesn't matter, as you now have a paperweight.

 

Yeah, I'm assuming that ALL the valves hit the pistons as the engine wound down from the failure with the cams not turning. So I don't know what that will tell me.

Chefj what little rubber piece where are you talking about?

No pics yet as I am on the road a few hundred miles from the motor.

And paper weight? Hardly. Just an excuse to sleave it, put some < 300 gram 13.0 to 1 J & E pistons in it, probably some Ferrera Ti valves, and a custom chromoly bolt (With a safety wire hole) for the timing chain sprocket/gear and see if we can spin it to 11,000 and 320+ RWHP (What the computer says we need for 300 mph).

It never stops.

Keep smilin'

Jim

 

It's in paperweight mode until you do all of that.

 

[QUOTE=jimknapp,Nov 14 2007, 10:30 PM] Yeah, I'm assuming that ALL the valves hit the pistons as the engine wound down from the failure with the cams not turning.

 

"Wall of shame", Red? More like a dumpster of shame. A crank, couple of engine blocks, set of pistons. Oh yeah and a credit card/checkbook combination too.

Hey, but it's still the fastest Honda powered vehicle on Planet Earth, okay?

Okay?

Oka...

Oh never mind.

By the way, I set my top speeds with a basically stock F20C. I did all the destructo stuff after I started "thinking" about it more :-(

Keep the shiny side up,

Jim

 

Okay, I got pics of some of the destruction. So how do I post them in a message?

Thanks,

Jim