Topic: HD valve springs - change the gap?

[Patrick]

I've installed APE valve springs in my CB750. Do I still set the valve clearances at the stock settings?

Thanks.

[eurban]

Go with what it recommended for the camshaft that you are using.  Typically high performance camshafts require somewhat larger clearances.  If you are using the stock camshaft then stock clearances should be fine although I don't know why one would use HD springs with a stock camshaft . . . . .

[Patrick]

I have no idea if this is a stock cam for a K0, Eurban. I've posted a picture and been told it looks quite aggressive....

[754]

Try to get someone to measure the lift or diff in lobe dia, and mention any numbers on it..may help to id it..

[Patrick]

The only marking on it is "R7".

[736cc]

Earliest oem cams were marked R1

[Jerry Rxman Griffin aka MuthaF'er]

Eurban,

Wish I'd had heavy duty springs when I missed a power shift to 2nd, revved somewhere above 10K, floated and broke #2 intake valve and obliterated the engine back in '76. Insurance is the only reason for a stock engine I can think of. If they need replacement then why not go ahead and use HD other than consideration of potential increased cam/rocker arm wear?! I rev my bike to 10K fairly regularly since without worry now.

[MRieck]

Eurban,

Wish I'd had heavy duty springs when I missed a power shift to 2nd, revved somewhere above 10K, floated and broke #2 intake valve and obliterated the engine back in '76.

               You don't do things half ass do you Jerry.

[eurban]

Heavy duty springs will increase valve train component wear guaranteed.  The 750 engine in stock tune (or even in a mild performance state) will not make additional power at RPMs above the float limit of the springs.  I would guess that Honda chose the stock spring based both on the valve control requirements of the stock engines usefull RPM range and valve train longevity.  Having an extra cushion to missed shifts might be worth it, particularly for aggressive riding but there is certainly a down side.

[Patrick]

Well, they're in there and I'm not tearing down the top end again to put stock springs in. That brings me back to my original question: Do I adjust the valve clearances or are the stock settings appropriate?

Thanks.

[MRieck]

Well, they're in there and I'm not tearing down the top end again to put stock springs in. That brings me back to my original question: Do I adjust the valve clearances or are the stock settings appropriate?

Thanks.

Personally I'd set the lash at .003 and .004 (intakes/exhaust). That .002 /.003 is real tight. I've had great results setting 79-82 DOHC lash @ .006/.008 (especially with individual filters etc). That also calls for .002/.003

[754]

Try to measure lift and you can get a better anwer.

I will look at an engine today and see if I can make a plug to go in the tappet cover hole, and hold a dial indicator so you can measure lift...

[754]

Found more info on the 315 RC cam..
checking clearance.050
310 deg duration
lobe centers 104


 looks like i could build a threaded plug for tappet cover hole to hold indicatior to measure lift
.. even if your angle was not spot on it would be easy to say.. a stocker has .254 lift and the ? cam has.312.. ..woulld give some indication of mild or wild..

 I dont think springs in a stock motor are that bad an idea, you may only get 83 K outa the top end instead of 88K... but cheaper if you overrev to hang together than to break parts..in which case you wont be getting max mileage anyway..

[eurban]

754, I think you are pretty far off the mark with your example.  I have seen a couple of performance motors taken apart with less than 20k in part due to valve train wear issues.  Of course one typically rides these motors alot harder . . . .

[MRieck]

 Wear and longevity would be dependent on seat pressure and total lift of the cam. Unfortunately the higher the lift cam the more seat pressure you need. The engine also will rev higher with the high performance cam which also effects wear. You don't get anything for free....especially high performance. APE or Kibblewhite springs set to the highest installed height with a stock cam really wouldn't increase wear that much. It will a little but is 10% greater wear to much?