Topic: CB550 valve seat pressure

[bwaller]

I have discussed this with Mike Rieck before and he felt around 75lbs was probably a good number. Not second quessing and I expect Mike you'll see this and I wanted a final thought from you and anyone else with insight.

To help with the decision I assembled a valve (stock) in the head with stock springs then after with Kibblewhite springs.

With stock shims & springs the installed spring height was 1.430" and the spring pressure was 42lbs. Mind you these are thrity-two year old springs but all Honda offers is a free length fiqure and these are within range.

HD springs at that 1.430" was 62lbs.

KPMI recommends an installed height of 1.380-1.400. At 1.390 the pressure was 70lbs. I didn't pursue further without different shims but @ 1.380 should be close to 75lbs.

The cam I'll use in this race engine is Megacycles 12620 so certainly increased lift over stock, but these are small fairly light valves, the rockers are somewhat lighter than stock, and Ti retainers.

With the above info is 75lbs still a reasonable target?

Here's a picture of the oldie but goldie spring gauge, sorry I didn't realize the head was out of the pic.

[Bill/BentON Racing]

Brent ,when I read your question the first # came to mind was 70lbs. on the Yoshi kitted CB590.As usual Mike right on the money! ,Bill

[bwaller]

Yea Bill, Mike knows his stuff.  It's probably better to err on the side of too much spring than not enough unless one has a dyno and lots of time to fiqure all this out. There surely is a point though where all that will happen is too much spring pounds the seats & valvetrain unnecessarily.

I wondered if there was a majical number like for every extra thousand rpm's add so much extra spring pressure. I'm going to pick up shims and set-up by pressure anyway. From stock 42 to 70-75lbs ought to be plenty.

I should have just shut-up & followed some good advice....would have been done by now.   

[MRieck]

 Considering that engine is going to be raced Brent I'd stick to 75lbs. Remember....that pressure will always be falling back the more you use the engine. I was watching some YouTube video of slow motion valve spring movement at redline (automotive) and at valve float. That spring is going in 10 directions at once, the retainer is spinning like mad and the valve is wobbling around as it hits the seat. Pretty violent. Now imagine doing that for 30 minutes or so.

[bwaller]

Done, thanks Mike.

[Bill/BentON Racing]

Brent ,that extra 5 lbs might save your a$$! It's not going to hurt anything.Bill

[Queeg]

Considering that engine is going to be raced Brent I'd stick to 75lbs. Remember....that pressure will always be falling back the more you use the engine. I was watching some YouTube video of slow motion valve spring movement at redline (automotive) and at valve float. That spring is going in 10 directions at once, the retainer is spinning like mad and the valve is wobbling around as it hits the seat. Pretty violent. Now imagine doing that for 30 minutes or so.

can you link that video. i would love to check it out. send it to my pm box if you would like!
 thanks

[kos]

75lbs of valve seat pressure on small SOHC fours...

I agree...Mike is on the money.

I never run KPMI springs higher than 85-90 lbs on CB750 engines and the valves on that engine are bigger and heavier. That is on race engines at 762cc and with a 11,000 RPM limit.


KOS