Need some technical help with leaky valves and seats.
I have an aluminum head vtwin engine that I sent both heads to a machine shop for new valves and fresh cut of the seats. They finished them and said that they held 22in of vacuum and sealed perfectly.
I got them home and decided to check them anyway. Filled the combustion chambers full of water and blew air into all the ports and not one bubble came out of any of the 8 valves. Thought to myself that was confirmation that the machine shop did the job right.
Bolted them on the engine, and before I mounted the carbs or even turned the crank, I decided to do a leakdown test. Got 10% leakage on both cylinders, but the real bad news was that the leaking was mostly coming from the intake valves on both cylinders!
Called the shop and they said they guarantee that the valves and seats were perfect, and that maybe the springs were causing the leaks because the valves now sit further in the head, and the springs were more relaxed. But I don't buy that because the pistons were at top dead center for the install of the heads, and with the proper valve lash and both intakes and exhausts closed, the rocker arms never touched anything. In other words, the heads were in the same state on the engine as they were sitting on my bench 30 minutes earlier. It held water on the bench, but won't hold air on the engine.
So my question is which one of the following would you do?
1. Shim up or replace the springs to get these to seal.
2. Take heads to a different shop and double check the work.
3. Just run it a few hundred miles and see if the valves "hammer" in with rpms and heat cycles.
Thank you.
I have an aluminum head vtwin engine that I sent both heads to a machine shop for new valves and fresh cut of the seats. They finished them and said that they held 22in of vacuum and sealed perfectly.
I got them home and decided to check them anyway. Filled the combustion chambers full of water and blew air into all the ports and not one bubble came out of any of the 8 valves. Thought to myself that was confirmation that the machine shop did the job right.
Bolted them on the engine, and before I mounted the carbs or even turned the crank, I decided to do a leakdown test. Got 10% leakage on both cylinders, but the real bad news was that the leaking was mostly coming from the intake valves on both cylinders!
Called the shop and they said they guarantee that the valves and seats were perfect, and that maybe the springs were causing the leaks because the valves now sit further in the head, and the springs were more relaxed. But I don't buy that because the pistons were at top dead center for the install of the heads, and with the proper valve lash and both intakes and exhausts closed, the rocker arms never touched anything. In other words, the heads were in the same state on the engine as they were sitting on my bench 30 minutes earlier. It held water on the bench, but won't hold air on the engine.
So my question is which one of the following would you do?
1. Shim up or replace the springs to get these to seal.
2. Take heads to a different shop and double check the work.
3. Just run it a few hundred miles and see if the valves "hammer" in with rpms and heat cycles.
Thank you.
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