Do Model A Engine Valves Rotate?

BButturff

BButturff

Senior Member
I'm curious, have searched the forum and the internet but didn't find an answer. But I would think Model A engine builders would know.


Do Model A engine valves, either stock or modern valves with adjustable tappets, rotate as they're operating? If not, what prevents them from doing so?
 
Generally no. In theory they could move a little over time but not actually rotate. The way the valve springs and keepers work the parts are locked together. In heavy duty applications there are "free" valve keepers assemblies that allow the valve to rotate. The lifters are a different situation. If the cam is ground correctly the lifters will rotate as the lobe centerline and lifter centerline are slightly offset which causes the lifter to rotate each time it is contacted but the cam.
 
The following is from the "Builders Guide" for the new engine, but applies to original engines using Snyder's modern valve set (A-6505-M).

If you wish to extend exhaust valve life, consider using valve rotators. Valve rotators rotate the valve slightly during each cycle and are used on engines subject to high loads like performance Corvettes or truck engines. Valve rotators take the place of modern valve spring retainers and are compatible with Snyder’s Modern valve set (Part number A-6505-M). The part number for valve rotators is GM 14042575, SBI 161-1012, or Federal Mogul RC157S. For high-performance engines, stronger valve springs will be needed to compensate for the added inertia of the valve rotators.
 
I'm pretty sure my Ron Kelley engine from the late 1990's had rotators on the exhaust valves. He said it keeps the hard-working exhaust valves from seating in the same place every time. It's supposed to keep the valve from getting too hot, although I'm not sure how that is effected. I don't recall if Ron installed stronger springs with the rotators.
Marshall
 
Marshall V. Daut said:
I'm pretty sure my Ron Kelley engine from the late 1990's had rotators on the exhaust valves. He said it keeps the hard-working exhaust valves from seating in the same place every time. It's supposed to keep the valve from getting too hot, although I'm not sure how that is effected. I don't recall if Ron installed stronger springs with the rotators.
Marshall
Click to expand...


I understand why they would have them on the exhaust valves as the valves run hotter on the side closest to the flame path. But for the minor cost of 4 more, I would think it beneficial to have them on the intake valves as well. Even today they can be had for about $10 USD each.
 
Ford started using rotator assemblies on V8 engines in 1951. They were discontinuing hardened valve seats so the rotators were used to aid in seat longevity.
 
You must log in or register to reply here.
Back
Top