Anyone seeing issues with premature valve leakage and power loss on LO206?
My son is complaining of power loss after just a few race weekends. When I perform a leakdown I am seeing an increase of a few percent from the last top end. Usually the exhaust valve, occasionally some on the intake valve. Seeing 4-5% when he complains.
I have now started checking the motors every 3 Club weekends and before any big race. I lap valves, if necessary cut seats, and last resort drop in and lap a new valve. I target 1 to 1-1/2% leakdown installed on the block, with no audible leakage on the valves. Only ever hear air around the lifters. Sometimes I am seeing valve warpage, and no we don’t run crazy lean on our motors.
So couple questions:
- Can a driver really feel a difference between a 1-1/2 leakdown motor and a 4-5 leakdown motor?
- Is 1-1/2 leakdown a good number for an assembled motor?
- Why would we be seeing such rapid loss of valve sealing?
You really should not be needing to lap vales every 3 races! From the guys I’ve talked to in the pits, they do it maybe once a season if that.
One thing that I’ve had recommended to me from my mechanic is to pull the engine to TDC as soon as you come off the track. Is your son doing that? This ensures that as the head cools, the seats and valves cool down together.
Also, I would recommend checking your head gasket. I recently had a huge amount of leakage and thought it was the valves. Turns out there were two channels blown through the head gasket.
That is about the extent of my knowledge but hope that helps!
No, you can’t feel the difference between 1% and 5%. It’s gotta be way higher than that for any noticable power difference.
There’s no reason you should need to check and redo the valves that offen… Last time I did mine it was at around 35 hours and had 6% on a blockoff plate. I don’t notice a laptime difference until it’s in double digits and even then, it’s not something that’s felt, it’s only on a stop watch.
I get 0% on a block off plate and 1-4% on a block generally with a fresh head on a used engine.
The longer you run a head the less you will have to do it.