notch the cam for midrange torque?

[79XS11F]

Originally posted by trbig
Anyone have any way of finding out just how many degrees one tooth would be? 360 degrees= 5 degrees 72 times. I am not around home right now, but I know the cam sprockets don't have 72 teeth. Not the sharpest pencil in the bunch, but one full tooth would seem to be way more than 5 degrees. Am I wrong? (Usually am... lol)

Tod

Even if one tooth was the correct change for 5 degrees I would not do ti that way. The idea is for it to be adjustable. No two bikes run the same and 5 degrees being great for him may not be great for you. go with the slots
Rob

[TopCatGr58]

Hey Posthuman,

Check your serial # against the thread in the misc. tech tips. They didn't make the XJ till 82. The 81 is an XS11. If it has curved spoked wheels, it could be a midnight special? But, if it has the MAXIM label, and YICS on the engine, then it's an XJ, and an 82 or later....in Canada till 84.

To keep the built in grunt, keep the air box, and stock pipes with the crossover. The cams swap was discussed quite a bit, if you do a search, you'll find.
T.C.

[trbig]

I know it's been discussed... but has anyone ever actually put '78 cams on a later big valve motor and done a dyno compared to what they got with the stock cams? There has been lots of speculation... but no actual proof that I have seen. This is the setup I am running, but I have nothing to compare it to... plus my clutches slip a bit, and I have the gear problem... but mine is only on 1st gear so far under hard accel... along with the crappy partsnmore pod filters... (The good ones should be at my house any day). I rode a buddies '80 Special a while back, and my XJ feels much stronger than his bike, but he's got a lot of miles on his.
I have been ALL OVER the top end of this motor this year. This winter, I want to get the tranny fixed up solid... run it hard a few days... then put the XJ cams back in and run it. All I'll be able to report is the way it feels to me.. nothing scientific.. no actual proof.... but will give you my completely biased opinion!!


Tod

[LoHo]

I know what they'd call my bike after I tried doing crap like this slotting-to-advance-the-cams to it:

Parts Bike


~LoHo~

[skids]

sCrap???

Originally posted by LoHo
I know what they'd call my bike after I tried doing crap like this slotting-to-advance-the-cams to it:

Parts Bike


~LoHo~

[randy]

LMAO

That's some funny **** right there!.

I've been following this thread 'cause it sound interesting, my having the '79 with the anemic bottom end. I was wondering, is the 5 degrees advance measured as crankshaft degrees or camshaft degrees? 'Cause we all know, one is half of the other! RIGHT?

[excess11]

One tooth???????/

My timing chain jumped one tooth and bent all the valves. I would think that one tooth is far to much!!!! This mod has top end destruction written all over it. Sounds to risky for the possible gain in torque. There are easier and less risky ways to gain power!

[trbig]

I would tend to think that 5 degrees would be measured at the cam since that's what you're notching. And I have never heard of counting 2 rotations as 360 degrees....
So in that chain of thought, since I am stuck in a frikkin hotel for the week, and I only had one picture of a cam to look at, I could see 14 teeth on a straight down shot. (Only seeing half of it) Give it the benefit of the doubt and call it 30 teeth on your cam sprocket. 360 degrees divided by 30... should come out to around 12 degrees per tooth.... a bit XSessive!

Tod

[MAXIMAN]

This is a very effective and safe mod if you know what you're doing. If you don't ...then don't try it. But for a quick and cheap boost in the bottom...especially for a big heavy touring bike like Zilla...this is a must mod.

Here's what my curves looked like after I did it:


The thing had MONDO bottom. Just look how it shifted the torque down low versus other 1100. And brother could you feel it by the seat of your pants.

Advancing the intake timing simply advances the opening and closing of the intake valve. The intake closing event is critical in maximizing chamber compression. This in turn helps bottom end power and torque. 5 degrees is optimal.

[MAXIMAN]

Originally posted by trbig
Anyone have any way of finding out just how many degrees one tooth would be? 360 degrees= 5 degrees 72 times. I am not around home right now, but I know the cam sprockets don't have 72 teeth. Not the sharpest pencil in the bunch, but one full tooth would seem to be way more than 5 degrees. Am I wrong? (Usually am... lol)

Tod

DON'T DO IT!!!

In the words of my 2 1/2 year old grand-daughter...

TOO MUCH! TOO MUCH!

I believe the Eleven cam sporckets have about 40 teeth. So one tooth would be roughly 9 or 10 degrees. Can you say "BENT VALVE"?

[skids]

Lets see... the cam sprockets rotate once as the crank sprocket rotates twice, right? The reference in degrees is to the crank, or the cam?

[LoserShoes]

When you degree in a cam the degree wheel goes on the crank.

Steve

[randy]

Thank you, Steve. I thought I was going senile. So the question still stands. What did your mechanic do, maximan? 5 more degrees BTDC crank? Or cam sprocket 5 degrees?

[excess11]

Ouch!!

It would seem that with the cam advanced you would have to watch the RPM'S alot closer. If you over reved the engine and floated the cam. The valves would hit the piston for sure. This modification decreases the valve to piston clearance by having the valves open sooner when piston is on TDC.

[MAXIMAN]

He slotted the cam sprockets and advanced the timing. The sprockets are slotted across the bolt hole where they can be advanced or retarded.

I don't think 5 degrees is anywhere near pushing the valve clearance. I believe you have to go well beyond that...like 10 degrees or so.

All I know is it wasn't real expensive and it WORKED. It resulted in a big bottom end.

I highly recommended the mod if you want much grunt for a heavy bike.

A 4 stroke engine is only at TDC twice in the cycle. The power stroke...both valves are closed. The exhaust stroke only the exhuast valve is open. During the intake stroke directly after the exhaust event the piston is long gone before the valve opens. Advancing 5 degrees should be dangerous. but 10 degrees might...not sure.