KPMI beehive spring pressures

acadian · Nov 1, 2020

Confirmed the set up figures for the beehive springs from KPMI, seated and lift pressures all check out, but I'm wondering about the recommended pressures which, for these beehives, are 90 lbs seated and 189 at .350 lift. Stock dual spring pressures are 68 lbs seated and 140 or so nose pressure.

Does the 90 lbs seem a bit excessive for a street bike?

Fast Eddie · Nov 2, 2020

That’s disappointing. I thought the whole point of beehive springs was that they gave better control and didn’t need as much pressure as conventional springs in a like for like situation?

I wouldn’t be happy fitting springs heavier than stock. The stock springs, without any lightening of the rockers, or hollow adjusters, or dural nuts, are still safe to WELL over 7,000rpm.

acadian · Nov 2, 2020

My thinking as well. I've pinged KPMI to get their thoughts, but will have to see where I'm at with installed pressure once I finish cutting the new seats. I have a feeling I'll be below 90lbs without any shims, I'd be happy to install them at 75lbs seated. If not possible I will go with the OEM replacements from KPMI which are dialed in at factory specs.

Fast Eddie · Nov 2, 2020

Please keep us in the loop re their reply...

acadian · Nov 2, 2020

No issues with dropping the pressure to 70 lbs:

"I don’t see a problem dropping the pressure to about 70#, the question is, how do you plan on getting there?

The spring rate is about 282#/inch.

You want to drop the pressure about 20#.

You’re going to have to increase the installed height by about 0.080”
(0.080” x 282# = 22.56#)"

Fast Eddie · Nov 2, 2020

Interesting.

So, where are you gonna get the .080” from?

I gotta ask though, if it’s “no problem” running them at 70lbs, why do they make ‘em at 90lbs? I assume you didn’t intentionally buy race springs?

acadian · Nov 3, 2020

I bought the spring kit and valves etc from F&G, they are marketed as a 'performance' spring that's also suitable for street... maybe I got suckered by the marketing, maybe I wasn't thinking straight when I hit 'buy now' at 3am

but I think I can get close by omitting the shims I would have needed to hit the stated seat pressure

Tornado · Nov 3, 2020

Check out David Vizard's discussion of different spring designs I linked in a different thread:

David Vizard Discusses K&N

Found this segment on K&N air filteration by David Vizard in his video on how to improve Series A Mini Cooper engines from back in the 1970's. Relevant to all engines.

www.accessnorton.com

Hillbilly Bike · Dec 16, 2020

An older thread.....I have Kibblewhite Beehive springs in my dual Triumph 650 engine land speed racer...At the recomended installed height , 87 seated, 207 open...This compared to the KW standard dual "racing spring" pressures of 90 and 220 on my single engine racer..
KW sells springs as listed for stock engines....I don't believe the beehives are necessarily intended for stock engines.

jan nelder · Dec 17, 2020

acadian said:
I bought the spring kit and valves etc from F&G, they are marketed as a 'performance' spring that's also suitable for street... maybe I got suckered by the marketing, maybe I wasn't thinking straight when I hit 'buy now' at 3am.

so what other spring ratings are available?

acadian · Dec 17, 2020

Hillbilly Bike said:
An older thread.....I have Kibblewhite Beehive springs in my dual Triumph 650 engine land speed racer...At the recomended installed height , 87 seated, 207 open...This compared to the KW standard dual "racing spring" pressures of 90 and 220 on my single engine racer..
KW sells springs as listed for stock engines....I don't believe the beehives are necessarily intended for stock engines.

Jury is still out on the beehives, I'm having new seats installed in the head right now, when I get it back and cut them I'll see where I'm at with seat pressure, if I can get them to 80lbs I'll run them, if not possible I'll sell them and run stock springs.

T140 inlet cam and T120 exhaust cam with R followers at both ends

Hillbilly Bike · Dec 18, 2020

I have the T140 and T120 cams and R's in my T140 with stock replacement made in UK springs.It runs up to an indicated 7000 rpm with no noticable problems .I cannot say if 90 psi closed is too much for stock nitrided cams. And what is 90 on initial build can fall off some pressure after being run for a time.
I know car engine builders who shy away from Beehives because they believe a dual spring won't be as likely to drop a valve if one spring breaks.
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KPMI beehive spring pressures

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