Would you notice a 50% power reduction?

[AZrider]

Carver,

It's not unusual to burn intake valves but with lean running engines (thanks to CARB) as these are I would have thought an exhaust valve would have gone first as the intake charge of fuel and air usually protect the intake side. These engines are truly amazing that they can run such low fuel to air ratios and get away with it.

Did the shop have any comments?

AZ

 

[dcarver]

The cylinders were not totally dead...just a little weak. Unlikey you would notice it especially if it degraded over time. There is such a small window of time during the compression and power strokes for "leakage" to occur (no matter where it leaks to) that the leak becomes much less apparent to the power the engine is making compared to the relatively long time interval (slow RPM) during a compression check and the constant pressure of a leakdown test. The cylinders were still making compression and the leakdown wasn't totally zero (like with a hole in a piston) so those cylinders were far from dead.
My guess, off the cuff, based on the compression comparisons and leakdown is that the motor might have been down 5 or 10 % on power not 50% or more.

That is not a bad idea on the bent valve thought. Hadn't really considered that a valve might have tagged a piston on a severe overrev at some point. Certainly possible I would guess particularily if you happened to remember such an event. Since the tech mentioned that the intakes seemed to be leaking on the leakdown test it adds more credence to that idea. Usually the valve train on overhead cam engines like the FJR are pretty tolerant for overrevs so it might not be the first thing you would suspect. The engine is protected by the rev limiter on upshifts and missed shifts but if the transmission were downshifted too far at too high a speed the engine can be mechanically overreved and the rev limiter will not be able to prevent it. If I think about it long enough I might change my bet to a bent valve instead of the head gasket.......

Thanks everyone for the responses.. Regarding a bent valve, I'd be really surprised. I know I've NEVER overreved the bike.. ever. No missed shifts or downshifts too early. I'm embarassed to admit this, but the bike has never even seen the rev limiter, and only twice has it been near that zone. I just don't go upstairs all that often.. Only one other person, outside the tech at the shop, has ridden the bike. That guy, I was with during the ride and didn't hear any missed shifts so I'm still sticking with the gasket leak theory. Back to thread topic, it's nice to know that the performance degradation wasn't has severe as I originally thought; I was really wondering why I hadn't noticed the power loss... Guess my CBA colors bleed through to CSA too (chicken shit association..)

 

[sleddoc]

My 23k 06 A model is now in the shop with cylinders 3&4 at 60/80 psig. 1 and 2 at 180/190. Leak down test indicates leakage through intake valves through throttle bodies.

The head gasket sounds like the best guess. Intake valves usually dont burn because they run much cooler than the exaust valves. The only way I have ever burned a valve ( on a SB Chevy ) is by over-reving and ( floating ) the valve, because the valve springs cant close the exaust valve fast enough and my foot is heavy, the valve seat burns. Make sure you let us know what the shop thinks the cause was, I am thinking it might have been that way since it was new but if a TB sync was done prior to this visit to the shop this condition would have made a sync impossible.

 

[Graham Downunder]

Sounds to me like a split in the head gasket between 3 & 4 cylinder. This starts a small leak and becomes worse over time. You would not notice it generally because it can take months to become bad.

Look forward to great engine when you get it back.