How bout some cam timing?

[TADracer]

All this talk about exhaust scavenging and valve overlap on another thread made something pop into my mind (I know, that can be dangerous).

With cam chain stretch, head gasket changes, etc. it is possible (maybe even probable) that cam timing could be off by a degree or two across the board. Advancing the cams as little as one or two degrees can affect the low end torque quite a bit and chain stretch could possibly retard cam timing.

Does anyone have the factory blueprint specification for the stock cam timing, checking height, base circle, overlap, etc? And, has anyone ever strapped on the old degree wheel and dial indicator to check any of this out?

[81xsproject]

When Maximan did his rebuild, he had the intake spocket slotted to advance the timing 5 degrees.

[trbig]

If your cam chain is properly adjusted, it shouldn't change your timing at all. The only way for that to happen, would be for you to have slack in the chain.... enough that it would probably jump teeth on the sprockets. You could have the chain 5 feet long, running on a sprocket outside the bike... but as long as it was tight, it still wouldn't change the timing. There will be a miniscule amount of actual stretch to each link, but nothing that I would think would be measurable. These chains aren't rock solid tight anyway Even when properly set, there's a tiny bit of play back and forth.

I was talking to Maximan this weekend, and he said that if you slotted the cam sprockets so you could advance the timing 4 degrees, it would help the low end tremendously. He did that first to his motor without changing anything else and said it made a huge difference.

Tod

[prometheus578]

You "Slacker"!

but nothing that I would think would be measurable

Friend TRBIG...
A worn cam chain will stretch, same as any chain. Those with chain driven wheels will attest to this, as the chain must periodically have the slack adjusted out.
On brand new bikes, or an older one with a new cam chain, when it's at TDC the timing marks on the cam gears will line up perfectly. On models with some mileage, the chain has stretched so much, that when lining up the cam gears, the marks rarely point exactly where they should. Sometimes, they're so far askew that I have to double check everything to ensure I'm not a tooth off!
As TADracer intoned, a stretched chain will retard the timing, but only a few degrees.
Back when I was in school, there were these two guys. I called them "The Timing Brothers". One was advanced and the other retarded...

[mro]

but nothing

Originally posted by P rom
Back when I was in school, there were these two guys. I called them "The Timing Brothers". One was advanced and the other retarded...

Hey P rom,
was the "advanced" guy named Slugo???


Sorry, just could not keep my fingers from typing that.


mro
btw, would not a little "retard" help with fuel we have to use now?

[MAXIMAN]

The stock cams are dialed in at 108 degrees...I THINK. My intake (a Web Stage 2) is now advanced 6+. My exhaust (OEM late cam profile) has been retarded 3 degrees. Next week I'll swap the stock exhaust cam with the late profile (short duration high lift) for A '79 EXHAUST CAM (long duration short lift). Just itching to see what happens . In theory I should loose mid range and gain top end. But Dan thinks since my intake is pretty rad I may loose nothing in the mid range and gain in the top. We let ya know how it gels.

However for stock cam timing...to be absolutely sure...PM Dan Hodges. The guy is a friggin walking service manual on the tech specs of these old bikes. He'll be glad to answer.

[MAXIMAN]

Re: but nothing

Originally posted by mro
btw, would not a little "retard" help with fuel we have to use now?

Retard where? Exhaust...no Intake...maybe. Or are you thinking ignition timing?

[prometheus578]

Ahhh... MRO, that was very good!
How astute of you to catch that.

would not a little "retard" help with fuel

With all the "self-serve" gas stations in the area and their low-paid employees, I can't get the little retards to help with anything!
What's happened to service in this country?

[Pat Kelly]

Ahhhh... the good old days when a clean-cut attendant pumped your gas, checked your oil, checked the air in the tires, checked belts and hoses, tranny fluid, brake fluid, and washed your windshield. Plus you got dishes or silverware just for buying gas for 32 cents per gallon.
Back then a truck came around and bought the barrels of used oil to recycle it. Now the station owners have to pay to have it hauled-off to be recycled.

Times have changed and it's retarded (lame attempt at getting back on topic)

[MAXIMAN]

OMG! Hahahaha Now I feel like the retard!

[TADracer]

Thanks Guys.

Sent a PM to Dan and will let you all know what he comes back with.

[pggg]

Well you can bet your bottom dollar it wasn't a fluke the eleven was the fastest production motorbike in the world straight off the showroom floor back in 78'. It's power curve is pretty much perfect as is. The yamaha crowd had the cam timing on the eleven sussed 29 years ago. Leave it alone!

All dialing in cams does is shift the power curve around, gain grunt in one area of the rev range - and immediately lose grunt in another. Waste of time. Just replace the worn camchain.

[MAXIMAN]

Hey Patrick...why don'tcha tell us wht ya really think?

[pggg]

Cody, as ya know, I'm too nice a guy to do that...

[MAXIMAN]

You?...