Datsun Roadster Forum-311s.org

Hi everybody, I have a question for the stroker people out there. A fellow roadster owner has a stroker motor with U20 S/U's and has been told he needs better valve springs to solve his valve popping and floating problem, that's how he describes it over the phone. Basically the engine goes flat and starts missing. I'm not sure if he has larger valves installed or what cam either. He says it has a stock 1600 valve train and things are floating at 5000 RPM. Is there any other springs available that will keep this from happening? Could he have things adjusted a little tight or is this a common stroker issue. Stroker issues are new to me so any input would be very welcome. Thanks... Bill Cole

Sounds like a valve timing adjustment more than a case of weak springs.
There was a post titled "R16 Adjstable cam gear" a few months ago from a member which had a stroker.
He might have some insight on the valve problem and may have had the same condition and solved it.

Ray B.

You could try some valve springs from Dean at Fairlady Products. I have them on my U20 with a big cam and I have wound it to almost 7000 rpm (on the old engine), and didn't have any issues that I could tell.

Will

I have small block chevy valves and springs in my stroker. That will not help you much though. I would try the NISMO competition valve springs. They are the same for the R and the U motor. The part number is 99996-B1061. I am not sure NISMO still carries them but Dean definitely does. Good luck.

Steve

Stock springs should work fine on a "big valve" 1600 valvetrain, up to 6000 rpm. If you have valve float before 6000 rpm, you might have weak valve springs. To be best of my knowledge, the stock nissan springs are pretty good, and tend to lose their preload less than their domestic counterparts.

Steve is right, though. The comp springs (the ones used for the "A" series engine) were still available from NISMO. All the 1600's that I'm aware of that get raced use these springs, and run 8000+ rpm.

I've had problems with race motors where they "run flat" at 5500 rpm. Some other causes could be: wrong cam profile for the valve diameter and/or compression ratio, or the wrong needle/jet combination for your setup. Point "bounce" also comes mine as well.

Regards,
Chris Coker

I thought I'd weigh in here. My valve train is stock and I don't seem to have any issues of valve float although I believe I need more carburetion now that I have driven mine a while. It'll pull 6500 in 1-2, then falls off and will no way pull 6000 or more in 4th-5th. I have not noticed any missing or float, just "breathlessness". Running an EI dizzy too.

Scott

I would suggest checking the springs for any damage/installed height/seat pressure, that sort of stuff. I had an engine with one broken inner spring that would poop out at 7250 everytime on the dyno, replaced the spring and the motor went to 8000 no problems. It acted just like a rev limiter. Just another idea to keep in mind.
Good luck.

Mark