R100 cams

[mattcfish]

I think the 336 cam was advanced to make it more "streetable". An engine with a 336 is not really very happy below 3500 rpm or so if installed straight up. Other posters have implied that the stock 308 cam were advanced as well, is this true?

My bad George, I think I made an assumption due to the wording of the German article that the post 78 308's were also advanced, maybe it was just the 336. I'm hoping there is more bottom end power for tooling up the mountain roads.
Regardless my 1975 R90/6 now has a post 1978 advanced 336 cam, 1000cc 9.5+:1 pistons, a post 81 tranny and clutch, later and lightened valve gear, dual plugs, crank mounted ignition, and many other upgrades made previously. I'm almost ready for the first fire up and break in. I did everything myself with parts collected over the last 4 years except the valve pocket machining. God knows what I've created.

[Garnet]

According to my Haynes manual all 1978 bikes had their cams advanced 6 degrees. Since many specs in the book show a differance between US and UK bikes for other specs but not the cam timing I assume that the change was made for performance reasons rather than emissions.

[vanzen]

Cam timing was advanced in 78 to meet EPA emissions standards.
Many of the changes made at this time (and until the mid 80s, anyway)
were a mad scramble to present a bike to the market
that would meet ever more stringent regulations, could run on pump gas –
while trying their best to salvage previous performance specs.

Advance 6º for performance ?
Not a chance !
Back in the day an offset woodruff key was the means to return cam timing to pre-EPA specs –
and get the GO back ...

[mattcfish]

Cam timing was advanced in 78 to meet EPA emissions standards.
Many of the changes made at this time (and until the mid 80s, anyway)
were a mad scramble to present a bike to the market
that would meet ever more stringent regulations, could run on pump gas –
while trying their best to salvage previous performance specs.

Advance 6º for performance ?
Not a chance !
Back in the day an offset woodruff key was the means to return cam timing to pre-EPA specs –
and get the GO back ...

Thanks for that rain on my parade. We'll see if it will at least be an improvement over the 308. I'll give a full report after break in.

[vanzen]

...We'll see if it will at least be an improvement over the 308.

The 308, being the production cam, was advanced in 1978
as were the 336 sport cams.

~ from BMW:
Camshaft 0°–
Intake opens 32 BTDC Intake closes 52 ABDC
Exhaust opens 52 BBDC Exhaust closes 32 ATDC

Camshaft with 3° retarded slot –
Intake opens 38 BTDC Intake closes 46 ABDC
Exhaust opens 58 BBDC Exhaust closes 26 ATDC

...The sport camshaft, originally developed for the BMW R75/5 motor, has been retroactively
approved by the factory for all motors with the 40mm exhaust valves (R90/6, R90S and
R100/7 up to August 1978).

For the motors with the 44mm intake valves (R100S, T, RS, RT and R100/7 after model year
1979), there also exists the possibility of installation. However, because of the larger valves
additional work is necessary, as described in the installation instructions ...




Improvement is a pretty nebulous term that may be defined to any individual's preferences.
The 336 will deliver a seat of the pants difference at 5k, no mistaking it.
Attention to specs when building and proper tuning will be the determining factor.

Improper timing of dual plug bikes is often the fly in the proverbial performance ointment.

[mattcfish]

Improper timing of dual plug bikes is often the fly in the proverbial performance ointment.

I'm hoping that the adjustable curves on the Omega ignition will help with this. I spent 7 months obsessing over the details on this one. I hope it pays off.

[vanzen]

I'm hoping that the adjustable curves on the Omega ignition will help with this. I spent 7 month obsessing over the details on this one. I hope it pays off.

The option of adjustable curves is a best case scenario
and puts the ball in your hands, eh ?

[Garnet]

I suppose I should have said "change in performance rather than for emissions" in my post.

Emissions where not an issue in the EU market at the time that BMW advanced the cam timing on all their bikes while making specific emission changes for the NA only market. Perhaps someone at BMW wanted more low end grunt????

Matt, I feel that the 6 deg advance on the sport cam is a wise move for the street. You still have to ride in the real world traffic and you can't always be above 5 grand when running around town. You have put a lot of though and research (and money) into a package. Lots on complaints I have read about the 336 cam or dual plugs come from people who have just done one thing and expect a new bike.

[the quinner]

Cam timing was advanced in 78 to meet EPA emissions standards.
Many of the changes made at this time (and until the mid 80s, anyway)
were a mad scramble to present a bike to the market
that would meet ever more stringent regulations, could run on pump gas –
while trying their best to salvage previous performance specs.

Advance 6º for performance ?
Not a chance !
Back in the day an offset woodruff key was the means to return cam timing to pre-EPA specs –
and get the GO back ...

It really depends on what one calls "performance."

There are many versions of the stock profile "308" camshaft...1) 1970-75 small seal/points nose. 2) 1976-78 big seal/points nose. 3) R65 no seal/no nose. 4) 1979-95 no seal/no nose. ALL of the points nosed 308 cams (1970-78) have the same timing/specifications (read on...). This doesn't even get into square drive vs. key drive for the oil pump...

The stock valve timing was changed DURING the 1978 model year...and was done by moving the slot in the camshaft sprocket. The 1970 through early-78 sprockets are identified by the machined flat area where a tach drive gear can be pressed. The late 78 sprocket is unique to that year only and does not have the machined flat for the drive gear.

The 336 cam was available in 1) 1970-75 small seal/points nose. 2) 1976-78 version "A" big seal/points nose. 3) 1976-78 version "B" big seal/points nose. 4) 1979-95 no seal/no nose. There was not an R65 version of the 336 cam. Note that #2 and #3 fit the same bikes, but had different woodruff key locations...to account for the different camshaft sprockets. With the 1976-78 bikes, you MUST know what you have...assuming is expensive (and harder to tune).

Which is better? What is performance? I don't think there's one answer to the question...it's qualatative, not quantitative. The only way to approach something as radical as a camshaft change is to do a LOT of research and decide what is best for the situation. For the big bore bikes, a bit of torque at the expense of some power actually makes a lot of sense...98% of the time, one rides with partial throttle at some engine speed well below redline. Why worry about the peak power in this situation?

[mattcfish]

The 336 cam was available in 1) 1970-75 small seal/points nose. 2) 1976-78 version "A" big seal/points nose. 3) 1976-78 version "B" big seal/points nose. 4) 1979-95 no seal/no nose. There was not an R65 version of the 336 cam. Note that #2 and #3 fit the same bikes, but had different woodruff key locations...to account for the different camshaft sprockets. With the 1976-78 bikes, you MUST know what you have...assuming is expensive (and harder to tune).

I did something unique with my bike, I used the no seal 336 cam (#4) with a double sprocket and 1976 timing cover (points cam hole blocked off). The reason...I had a brand new double sprockets and chain set, I wanted to retain the mechanical tach, and the 336 fell into my lap for less than $30.00. When I put the double row sprocket on... did I do something to the timing? It appeared that the timing mark was in the same place on both the double row and single row sprocket relative to the key notch. I believe (I hope I'm not wrong) the notch on the camshaft was moved but the sprocket marking and notch remained the same on double and single sprockets regardless of the year.