Camshaft valve timing 336

[mattcfish]

I just picked up a 336 cam on eBay for way less than I was willing to pay ($42.00) .
I think I caught everyone sleeping. Every 336 I've bid on in the past sold for more than the retail price. It isn't the right cam for my 75' R90'6, but I have a good plan to make it work.
This is a cam off a 77 R100, bean can ignition motor. I already use a crank mounted ignition, so I plan to plug the hole to the cam nose (weld it shut or thread in a plug) and put my double row cam gear on it. I know many will denounce me for not going single, but I have a brand new crank gear and I want to keep the mechanical tach drive. I know I need to get a new oil pump rotor.
I believe the other thing I need to do is change the smog valve timing from the 3 degree advance back to zero. I can use an offser woodruff key to do this. The offset keys are available from SJBMW http://www.sjbmw.com/parts.asp#s=store& ... =1&pid=989 #1104 at $24.95 each .
I found these Mercedes keys that come in different offsets http://www.autohausaz.com/search/produc ... 6219910267.
Does anybody know if Mercedes used the same size key?
I read that all the bean can cams have the 3 degree advance, is this true? Is the old "zero" setting the best setting? I'm going to be running 42 intake and 40 exhaust with dual plugs. compression is a little over 9:1, with Dellortos and a 2 into 1. I know I may or may not have to deepen the valve pockets. Does anyone know for sure with this model bike?

[gspd]

3 degrees cam timing is not a HUGE seat of the pants difference for 'normal' street riding.
It is for a race bike.
Anyone can immediately tell the difference between a 10 second and a 20 second 1/4 mile bike .
In real life, can anyone really tell the difference between a 12.9 and a 13.0?

Either will run well.
On a dyno, one would be a bit stronger in the upper ranges, the other would be a bit stronger in the lower and mid.

[mattcfish]

3 degrees cam timing is not a HUGE seat of the pants difference for 'normal' street riding.
It is for a race bike.
Anyone can immediately tell the difference between a 10 second and a 20 second 1/4 mile bike .
In real life, can anyone really tell the difference between a 12.9 and a 13.0?

Either will run well.
On a dyno, one would be a bit stronger in the upper ranges, the other would be a bit stronger in the lower and mid.

Would less advance = more valve clearance?

[Major Softie]

Oooo, good question. I'm not sure because one direction moves it toward where the exhaust is sticking out more, and the other moves it to where the intake is sticking out more, so it depends on which one is closer at whatever you are calling the "zero" point. Since intakes are bigger, my WAG would be that they create the greater clearance issue, but it all depends on the geometry of the valve angles and placement.

[gspd]

Valve clearance (lash) stays the same.

piston/valve clearance (cutout on piston).
On a stock engine the pistons won't hit the valves if the cam is out 3 degrees either way,
A worn out timing chain does that.
On your particular engine I don't know how much clearance there is to begin with.

[George Ryals]

Don't forget that the 336 cam has 1.28 mm more lift than the 308 cam and 2.06 mm more than the 284 cam.

[Garnet]

3 degrees either way.......that's a tough one.

Tell ya what, send me the cam and I'll do extensive testing and get back to you in a year or two and let you know what I think works best.

42 bucks!!!!!!!! How do you sleep at night

[mattcfish]

Oooo, good question. I'm not sure because one direction moves it toward where the exhaust is sticking out more, and the other moves it to where the intake is sticking out more, so it depends on which one is closer at whatever you are calling the "zero" point. Since intakes are bigger, my WAG would be that they create the greater clearance issue, but it all depends on the geometry of the valve angles and placement.

It seems to me that lift isn't the issue it's duration and overlap. With 3 degrees extra advance the exhaust valve is actually a little ahead of the piston on the exhaust stroke (for example), but the intake is opening earlier during the "scavenging" period before the piston reaches TDC on the same stroke. The intake valve is wider so the chance of it kissing the piston should be greater with more advance on the cam. Moving the cam back to the "old" setting and leaving the intake at 42mm should give me the most clearance. That's my theory anyway. I can see how bigvalve (44mm+ intake) bikes with 3 degrees advance would need deeper pockets, but a 42mm intake with regular valve timing........? Does anyone know for sure?
I'll be sure to check when I put it all together this winter.

[mattcfish]

3 degrees either way.......that's a tough one.

Tell ya what, send me the cam and I'll do extensive testing and get back to you in a year or two and let you know what I think works best.

42 bucks!!!!!!!! How do you sleep at night

Thanks for the offer.

[KenHawk]

I think that you're going to have to use some clay and check your actual clearances.

Thats the real-world way to get real info.