Valve spring coil bind question?

Al Weyman · 13 Jul 2009, 07:47 (Ref:2500578)

I have been checking the coil spring clearance on a new engine I am building with a .645" inlet valve lift with 1.5 rockers (quite a stout roller cam). The springs are well up to the job with titanium retainers so I am not expecting any float however searching the net its obvious some people are getting their lines crossed with how much clearance you should have before the spring goes close to bound. On the Iskaderian site for example they say as long as you can get 10 thou feeler between the coils with the valve fully open which if stacked up would give a total of 60thou clearance then you are OK others seem to think its 60 thou between coils.

Can anyone throw any light on this as I have calulated I have about 100 thou before it binds but can only get a 25 thou feeler between the coils. I feel this is about right especially with the very stout springs and light titanium retainers but would appreciate an opinion.

ian_w · 13 Jul 2009, 09:19 (Ref:2500638)

1 to 1.5 mm total clearance is the minimum you would aim for. Your 100 thou ( 2.5mm ) will be fine.

Al Weyman · 13 Jul 2009, 09:23 (Ref:2500644)

Thanks Ian, I can get on installing the thing now, I thought it seemed OK but it was the conflicting comments I found on the net that were confusing.

GORDON STREETER · 15 Jul 2009, 16:15 (Ref:2502326)

Because I was forever breaking valve springs until I found the right ones I was always changing them in the pits. As we didn't have time to shim them to length I made a tool to lever the rocker arm down when it was on full lift. As long as it had a gnats knob more travel in that position it was OK and I never had a problem.

Al Weyman · 15 Jul 2009, 18:31 (Ref:2502407)

No this has a lot more than a knats knobs worth I would say conservatively 100 thou probably more like 120.

GORDON STREETER · 15 Jul 2009, 20:09 (Ref:2502449)

Its always best to have more clearance and if your engine isn't a high rever they don't need to be that close to coil binding. About 90lbs on the seat is what I use.
Also Al it depends how big the gnat is !

Al Weyman · 15 Jul 2009, 22:42 (Ref:2502513)

I will limit it to about 7500 but its probably good for 8000 it should make power up there as well as its quite a stout roller cam.

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