Point bounce RPM

35fordtn

35fordtn

Well-known member
My Sun machine set a record today with a distributor. A customer sent in a distributor and he had previously purchased the parts elsewhere (Mac Van Pelt). I installed his supplied points, bushings, rotor, etc. This was a typical 1937-40 68 series distributor.

I had previously run three other distributors tonight, with most having the points start to bounce at around 5300-5850 rpm's. This one ran all the way up to 7870 RPM's before the points started to bounce. While a flathead will never see those RPM numbers, that is a record for me. Hats off to Mac Van Pelt for selling quality points! They appeared to be the same points I have used but this set exceeded the norm.. Many "larger" vendors are selling crap points that make setting the dwell a nightmare if even possible and can rarely exceed 2600 rpm's before point bounce starts.
 
I commonly get > 5000 with NOS Ford points on my Sun machine. I usually back off as that is unreasonable territory for most flatheads, valves will float before then on stockers. I commonly take my avatar to 5500 when pulling onto the freeway. On that car I have 200 lbs pressure going over the nose of the cam.
 
Yes, I agree, I do however out of curiosity run all of them to the point of seeing what they will actual handle. Our results differ, is the MOST I have ever gotten from a NOS set is 4400 rpm's (crank). The newer quality points seem to have quite a bit more spring tension thus likely why they will handle more RPM's, however I am also aware that too much spring tension will cause the rubbing block to wear much sooner.

Regardless it is all irrelevant as 99% of the flatheads out there will never see these rpm's
 
Nice new record Mike . . . thanks Mac for good quality points! Most of the ignitions I tend to screw with have magneto points - so they tend to spin up pretty damn high.

This is one situation where "More is Better'! LOL
 
Don said:
What’s the solution to prevent bounce???? Increase spring tension???
Click to expand...

Higher spring tension will increase the RPM's before point float, BUT..... Higher spring tension wears out the rubbing blocks and pivot post on the breaker plate at a much quicker rate. In my opinion if they can hit 5000 Rpms they are good to go as a flathead would in the real world hardly see those numbers. The tension springs can be bent by hand to manipulate this as well. I have to do this on all the Early distributors (32-36).
 
Spring tension is one factor, the other is the type/characteristics of the actual distributor cam. Many performance distributors/magnetos use more of a "ramp" to lift the points, than a super-sharp peak. Makes sense that the ramp is less susceptible to causing point float.
 
Bored,

That is correct, however I can only speak in context to original Ford designs. The Lincoln V-12's have a much more subtle cam design with a more rounded cam lobe.
 
What are these "points" you speak of?
These are the only points I'll put in a distributor....
 

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The SBC dist dist is good for 6500. Works well on 6 volts, set it forget it. The stock crab worked well on the stock car up to 5K
 
I set them all at 2500 to 5000....lube well and let them run for a few minutes at 5,000 .plus.

Also soak every fiber block in marvel mystery oil , found out years ago that will extend the life of the point a ton......(and i like the smell)))
 
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I did not know you were in the hospital. Good to hear that your out. I need to stop by the shop and give you and Terry a hand soon.
I have been so dammed busy at home I think I need to step back and approach from another angle.
 
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