lazy (sticking) valves
 

2003 Miata purchased non-running. History unknown, but gas was varnished. No compression on cylinder 1...didn't check the others as I ASSUMED broken timing belt. Pulled valve cover and timing belt was there. Spun the engine over with starter (bad idea, VVT head poured oil everywhere) and noticed some intake valves took 20-30 seconds to close. This is only on cylinders 1 and 4. I can spin the cam followers by hand while the valves are taking their sweet time to close. I pulled the intake cam, and all cam followers come out easily. What can cause this, and how would you proceed? Trying to avoid pulling the intake, but that is my next step so I can see the valve stems.

Thanks for your help!

Galen

P.S. The valves are still slow, but are still taking 5-10 seconds to close after turning the camshaft over multiple times.

Bent?

I'd start with replacing the valve stem seals, which can be done with the head installed. Theres a walkthrough on here somewhere. My guess is they have turned very sticky and gummy over time and are preventing the valves closing smoothly. Old oil can sludge badly and cause this too in extreme cases. Could also have sat with those valves open for years and have rust on the valve stems, also causing/contributing to the problem.

I am going to pull the intake tomorrow morning to have a look at the valve stems. I feel bent valves would not close, no matter how slowly, and badly gummed up seals would just pop off instead of holding the full pressure of the spring. I have considered changing the seals anyway, asit isn't that much extra work.

I also considered that the springs could be weak from being held open for that long, but the two cylinders sticking are not open at the same time.

Thanks for helping me brainstorm!

Galen

You really need to pull the whole head off and remove all the valves and inspect them. I would not think the seals would be strong enough to slow down a valve like that because the springs have way way more pressure to overcome that. Maybe the stem seals went bad and let a bunch of oil down the guides and it hardened and now they stick like that. Pulling the head is not that hard and you can do the job properly and much easier with it off.

It is the old gas. When the gas turns to varnish, then gets in the guides, it is so thick the springs can't close the valves. Best to pull and clean. Also flush out the fuel system. I have seen this a lot over the years when vehicles sit.

There is always one in every group! While I knew what I needed to do, what you said was correct and I was resisting the inevitable.

And the winner/problem was......

VALVE SEALS!!!!

After pulling the spring off the first valve, I had to tap the valve out with a hammer and extension. I couldn't move the valve by hand until it was past the valve seal. I still can't believe it didn't just pull the valve seals off instead of holding the valves open.

I am willing to bet this is also the cause of a lot of the loud valve train tapping people hear.

Next week, I will pull every valve, clean up the head and put it back together with new valve seals...probably Felpro.

Thanks for everyone's help!

Galen

Good deal man, sounds like the stem seals are absolutely trashed. Felpro is good, OEM is better, Supertech is a NO NO NO. lol.

A lot of the BP valvetrain noise is from the HLA's which get gummed up over time and they dont adjust properly anymore and makes a CLACK CLACK especially when you run the car hard and they dont fill with oil properly. The BP4W and VVT used solid lifters and dont suffer from that issue but these engines even at their best sound a lot like a sewing machine. They are very simple engines but they are not the most advanced tech. However I absolutely love the BP engines and will continue to run one in my miata until the day I die. I have come to love these engines over the years because they are dead simple and when you build one and do it right they will make a ton of power and are still reliable. Good luck with yours, sounds like you know what you are doing. Keep us updated on how it goes.

When I made my initial diagnosis, I had only pulled one intake valve, and it slid in and out of the guide easy as pie. The other 7 intake valves are tight all the way until they are all the way out of the guide, regardless of the seal, so seals were NOT the problem. There is a very minor amount of corrosion on the intake valve stems that I think is the problem. The other option is varnish buildup inside the guide itself. Time to clean the valve stems with some fine abrasive and see if that corrects the issue. If not, I will have to get a reamer for the guides.

The exhaust valves operate smoothly as they should.

Galen

After cleaning with acetone, my problem was definitely caused by the fuel varnish inside the guide. A couple of minutes with an acetone soaked brush in a drill and all guides are tight and clear. Now to do a quick port/polish of the head and put it back together.

Galen