Cam choice r60/5

[chasbmw]

Has anyone fitted a 308 degree cam to a 600 and if so what was the results?

Cheers

[barryh]

No experience with changinging cams but if you get no response and want to do a temporary experiment to change the cam timing a couple of degrees in the general direction of a 308, tighten up the valve clearances by a couple of thou or as much as you dare. I've only ever done it the other way. Widening the clearances to 6 & 10 thou will soften cam timing a few degrees. I did once try to calculate how many degrees but it's impossible without a cam chart. I think in the end I estimated roughly 1 or 2 degrees per thou.

So it's a very small effect but I found it noticeable (which is why we are always told to set the valve clearances before tuning the carbs). The most noticable effect from widening the clearances was higher idle speed and richer mixture which is to be expected from reducing valve overlap. In your direction you would be increasing overlap (if a 284 has any) and might have to screw in the throttle stops and richen up the idle mixture a touch.

[Garnet]

It should, in theory, reduce the pinking problem that R60s suffer from. It is a far better solution than reducing compresion or retarding timing, both of which are a loss of power and fuel economy.

An R60 really starts to run out of breath at around 6000 rpms where as a 308 cammed engine gets up to 6500+ before tapering off. From that I would expect that the start of the bottom end grunt would move up from the low 3000s to mid to upper 3000s.

If I still had an R60/5 I would try it.

[Motorhead]

MEASURE THE LIFT if similer the cam fits an operates smooth

the big? IS WILL THE MOTER RUN WITH MORE OPEN VALVE fill/exhaust TIMES WITH LITTLE bores

will a R60 improve performace with a 308 what is in a stock R60/ 5 anyway

[mattcfish]

Haven't tried it, but I have a 60/5 block and I can confirm that a 308 fits nicely in it. The reason I say that is, I tried inserting a 336 in it and found that the lobes interfere with the the aluminum at the base of the lifter bosses. A little grinding and it too would work. Just thought I'd put that out there.

[hal]

So it's a very small effect but I found it noticeable (which is why we are always told to set the valve clearances before tuning the carbs).

Thanks, you enlghtened my day! (learned something, and then for me it's a good day )

[StephenB]

No experience with changinging cams but if you get no response and want to do a temporary experiment to change the cam timing a couple of degrees in the general direction of a 308, tighten up the valve clearances by a couple of thou or as much as you dare. I've only ever done it the other way. Widening the clearances to 6 & 10 thou will soften cam timing a few degrees. I did once try to calculate how many degrees but it's impossible without a cam chart. I think in the end I estimated roughly 1 or 2 degrees per thou.

So it's a very small effect but I found it noticeable (which is why we are always told to set the valve clearances before tuning the carbs). The most noticeable effect from widening the clearances was higher idle speed and richer mixture which is to be expected from reducing valve overlap. In your direction you would be increasing overlap (if a 284 has any) and might have to screw in the throttle stops and richen up the idle mixture a touch.

Can you run that by me again in slow motion? I have a 600c engine with the stock cam (the one with the 10 47 47 10 deg or whatever it was). I would like to run the engine with points and am planning stock 9.2 compression, retarding the ignition to 3deg BTDC static, adding a DynaBooster to extend points life and a later R100 advance unit (-012) to push max advance out to 3600rpm or so. Now what is the effect of widening the valve clearances in this case? Does it help or does it counteract my measures? What is with tightening those clearance ?

The engine isn't together yet, so I don't know whether it is pinking or not. But the above measures combined should be sufficient. I can always use an electronic ignition to reduce/avoid pinking but where's the fun in that?

Stephen

[barryh]

I did say the effects were small but they are real and I found them readily detectable.

Widen the clearances and the valves must open a couple of degrees later as well as having slightly less lift. So wider clearances reduce the cam duration and therefore reduce valve overlap. On a 308 cam wider clearances will give the 'effect' of richening the mixture at low revs and raising the idle speed because the reduced overlap means less reversion and less mixture going straight out the exhaust. I was able to turn in the mixture screws and turn out the throttle stops to bring the idle speed back down. That's my real experience with a 308. You wouldn't want to do this with a 284 beacause it's moving you in the wrong direction and it would make any pinging potentialy worse.

R60's can ping because the shorter duration of a 284 cam closes the inlet valve earlier than a 308 and therefore it increases the effective compression ratio. I was speculating that if on a temporary basis you were to tighten up the valve clearances that would have the effect of adding a couple of degrees to your 284 cam duration. Opening the valves a couple of degrees sooner would reduce the effective compression and might help with any potential pinging. It would move your valve timing a small way in the direction of a 308 cam. I stress again the effects are small but real.

[StephenB]

I was speculating that if on a temporary basis you were to tighten up the valve clearances that would have the effect of adding a couple of degrees to your 284 cam duration. Opening the valves a couple of degrees sooner would reduce the effective compression and might help with any potential pinging.

So, there's the dare: how much can you reduce valve clearance on a permanent basis? You mentioned temporary basis which equates to a race application?

I believe that running zero clearance on a hot engine is the "normal"mode of operation and a result of the temperature coefficients of the various material used in the valve train when the engine is at its operation temperature.

I have heard (no first had experience) that even running zero clearance adjusted on a cold engine is possible. And now I begin to understand why that is.

Zero clearance adjusted on a cold engine would be the dare ... ?

Would 0.002" IN and 0.004" exhaust be doable without detrimental effects on the valve train, even long-term?


Great thread, thanks!

Stephen

[Garnet]

Check your valve clearance hot, then let the engine cool and check them again. That will tell you how much they tighten with temp. I bet you find little difference.

Manufactures usually give a bit wider spec than needed as a safety margin and to increase adjustment intervals. You can safely run your valves tighter, you just need to check them more often.

How tight? You will figure that out for your self after a few checks. Get some gloves that you can handle wrenchs with, and check them hot, that is how your valves spend their working life, and that is what you want to know.