Cam question.

[Mekanix]

On the 750 and 1100 cams what is the distance for X and for Y




I'm looking into what I have for options for the twin by cutting off the extra lobes.
the 1100 has the same journal and lobe size (according to the manuals) I'm not sure about the width of the cam or if the sprockets are different in size Or if I could use a set of actual slotted sprockets.

I'm just looking for options.

Thanks for looking.

[gearhead13]

I dont have a set of cams here to measure, but are the stock ones any hotter than yours? Or are you going to buy aftermarket?
What cam sprocket you use depends on the amount of teeth on your crankshaft.
I used a dremel to slot out my stock sprockets, works well.
Are you porting your head as well? I have a set of 27 and 28mm intake valves and some exhaust valves here. I dont know what your stock valve size is.

[Mekanix]

I was going for aftermarket cams unless some stock ones are hotter than mine.

The stock 1100 and 750 are the same lobe height(34mm) and journal size (22mm) as my 400 according to the 3 manuals. I don't know about duration though.


I'm working on the sprockets right now, filing by hand but the dremel is coming out soon

The sprockets have 30 teeth on them. I'm assuming the crank has 15.
I just wasn't sure if I bought new cams that My sprockets would fit.


I'm not porting the head yet, Its something I'll look into soon.

My stock intake valves are 23mm
The 1100 has 27mm
The 750 has 23mm


My stock exhaust valves are 20mm
The 1100 has 23mm
The 750 has 20mm


I have a spare head that has cracks between the plug hole and exhaust seats on all 4 and I'm worried that going too big might cause this on my good head. What causes this anyway?



How will the seats cope with cutting them to the stock 1100 size or 27,23?

[gearhead13]

You cant go anymore than 1mm oversize without getting bigger seats installed.
Cracks between the valve and plug can be caused by overheating/high temp or so I have read.
I was thinking that yours might have 1100 sized valves.
I have never seen aftermarket o/s valves for the 400/750. But I think a good machine shop could cut down 1100 valves to 24 in 21ex.

[TeamDar]

Will not work. The two middle pistons on an inline four move up and down at the same time that is why the lobes are spaced 180 degrees apart for the pair. A twin has one piston at top dead center when the other is at bottom dead center. Do you see the problem? Only one cylinder will have the lobes where you need them if you saw off a four cylinder cam.

[gearhead13]

Will not work. The two middle pistons on an inline four move up and down at the same time that is why the lobes are spaced 180 degrees apart for the pair. A twin has one piston at top dead center when the other is at bottom dead center. Do you see the problem? Only one cylinder will have the lobes where you need them if you saw off a four cylinder cam.

Hmm didnt think of that.
Another thought, having four lobes of the stock cams would be half the cost of a 4 to have welded and reground. Might be cheaper than a set of web cams.

[Mekanix]

Will not work. The two middle pistons on an inline four move up and down at the same time that is why the lobes are spaced 180 degrees apart for the pair. A twin has one piston at top dead center when the other is at bottom dead center. Do you see the problem? Only one cylinder will have the lobes where you need them if you saw off a four cylinder cam.

Awesome !! that's the kind of thing I needed to know Its right there but I never even looked closely at the cams

Another thought, having four lobes of the stock cams would be half the cost of a 4 to have welded and reground. Might be cheaper than a set of web cams.

That might be the only way to go now. I'd have to contact someone.

Who should I try?

Comp ?
Web?

[platinum2]

mine seem to be the same length 6"11/16 hope this helps , and i do have some 1100 cams i am not using, ill let them go cheap if you need'em, 30shipped? i can give pics as well just holla ok,

[Mekanix]

Thanks Platinum2. That helps but it looks like it wont work as TeamDar Pointed out, The middle cylinders of a 4 move together.

I would need a cam that was ground to look like the two outside lobes of that camshaft.

[platinum2]

Thanks Platinum2. That helps but it looks like it wont work as TeamDar Pointed out, The middle cylinders of a 4 move together.

I would need a cam that was ground to look like the two outside lobes of that camshaft.

it will give me a headache to think about it so -
the middle 2 are 180 apart,therefore one is top dead center, other is bottom dead center, degrees,overlap,duration, gear teeth, crank teeth i dont know, i starting to get a headche im stopping here lol

[Mekanix]

it will give me a headache to think about it so -
the middle 2 are 180 apart,therefore one is top dead center, other is bottom dead center, degrees,overlap,duration, gear teeth, crank teeth i dont know, i starting to get a headche im stopping here lol

I hear ya.


From what I can see, It would be easy to set up one side or the other.

but when one is going down and the other is heading back up its going to hit the valves because they are on the way down.



The stock camshafts are set up 90' apart on the lobes. So if you can think of one side as just finishing a compression stroke the lobes should should be up and out of the way of the valves.

The other cylinder though is going to have a piston going up and valves going down at the same time because of lobes pointing down instead of being 90' out of the way.

[sk843143]

Some auto cams are hollow and the lobes are pressed on.......are the gs cams like this.....if so a good shop could press them off and reinstall them 180 off

[Mekanix]

Some auto cams are hollow and the lobes are pressed on.......are the gs cams like this.....if so a good shop could press them off and reinstall them 180 off

That would be great but these are cast as one piece and ground to size.


I am thinking in the back of my mind to hollow one out then cut the lobe off, move it 90' and weld it using a tube in the center to keep in straight.

[platinum2]

I hear ya.


From what I can see, It would be easy to set up one side or the other.

but when one is going down and the other is heading back up its going to hit the valves because they are on the way down.



The stock camshafts are set up 90' apart on the lobes. So if you can think of one side as just finishing a compression stroke the lobes should should be up and out of the way of the valves.

The other cylinder though is going to have a piston going up and valves going down at the same time because of lobes pointing down instead of being 90' out of the way.

yea thats all in the timing and sprocket sizes to keep that from happening lots of tech involved there

[sk843143]

Oh......ok.....and just an fyi.....when you measure can lobes......its the base circle (not pointy ) that gives you the lift......two cams can have the same lobe height......and diff valve lift numbers