CAm TIming SNag

[Guest]

OK,
gs1100/1260, 1mm over valves

bought some 190 grind Web cams 370 lift. Cam timing of IN: 10* btdc / 52* abdc, EX: 50* bbdc / 12*atdc. Lobe centers are IN: 111 / EX: 109
I am using slotted cam sprockets. The ex cam is set at 50* @ 0.050" lift but it is closing at 4* not 10*

With the intake cam I have run out of slot to adjust it and I am only at 104.5*. The slotted cam cogs are APE and came off a set of webs out of an 1166 gs1100. I am missing something here but can't seem to see it.

20 pins distance between punch marks that are @ 12 O'clock, cam timing slots parallel with cam cover. Valve lift is taken from valve keeper @ 0.050" with zero valve lash, as listed in cam info.

What am I missing???

 

[GregT]

IMO lobe centers are more important than the actual open/close figures you see. So long as your figures are repeatable the lobe center calculations will be correct.
I've several times had to go to 21 pins for the inlet and go to the other end of the slot...So long as this information is noted for future use there's usually no problem.

Others may have different opinions.

 

[trippivot]

I've several times had to go to 21 pins for the inlet and go to the other end of the slot..

Others may have different opinions.

Me Too. open the slot or jump a tooth and reverse ends of slot.

"Lost" 6 degrees on closing?? yeah well there is still some mystery in doing this. you aren't missing anything

make sure your dial indicator is in perfect line with the angle of the valve stem/ spring retainer. a little off angle and there will be a variance but nothing is perfect.

Just take the individual number readings from the TDC pointer and run the formula..

When you get the LOBE CENTER formula readings to repeat after turning the engine thru multiple 720 deg cycles then believe what you have for a L/C.

make the adjustment changes from the opening degree number. don't worry- about the exact closing being what the mfg says. nothing is perfect- close maybe but not perfect

as long as valves don't hit and everything is tight you'll be fine.

it pays to repeat and check clearances

 

[Guest]

I installed a set of 348 lift webs with stock gs1100 cam cogs (the ones stamped 470) lobe centers on the stock cogs are EX 94, IN 102.5. Interesting.

Here are the rest of the numbers:
EX: open 51* bbdc; close 26* ATDC
IN: open 42* BTDC; close 34* ABDC

I don't have a set of stock cams though to measure. ran the numbers from the manual and come up with LC of 109/110

 

[biker66]

As stated earlier: move your intake cam on the chain to get the proper numbers.
When you're timing the cams with slotted gears you don't have to bother with the pin count, that's only useful for bone stock motors.
My personal note for my present cam timing goes something like this:
"Ex cam 9 o clock, Int cam 2 o clock, 21 pins."
This is just an example, the numbers will vary depending on how the slots are done.

Also, try measuring on another lobe.
When I checked the lobes on my 190 Web cams I found the no4 exhaust has different numbers, it's got about 5 degrees shorter duration than all the other lobes !!

 

[Guest]

As stated earlier: move your intake cam on the chain to get the proper numbers.
When you're timing the cams with slotted gears you don't have to bother with the pin count, that's only useful for bone stock motors.
My personal note for my present cam timing goes something like this:
"Ex cam 9 o clock, Int cam 2 o clock, 21 pins."
This is just an example, the numbers will vary depending on how the slots are done.

Also, try measuring on another lobe.
When I checked the lobes on my 190 Web cams I found the no4 exhaust has different numbers, it's got about 5 degrees shorter duration than all the other lobes !!

I here ya thanks. I am wondering why the stock cam cogs are not right either though.

 

[GregT]

Depends if the cams are regrinds on a stock core or done from blanks...
Even using a hardfacing buildup it's sometimes neccessary to juggle the lobe positioning to achieve a full lobe profile without going back to the buildup bench.
Personally I would never expect aftermarket cams to time up correctly on standard sprockets....if they do it's a pleasant surprise.

As for the cam quoted here with different lobes on the same stick - the first purchaser should have returned that one for attention.
I've had a standing arrangement for years with my local cam grinder - Kelford Camtech of Christchurch NZ - if I find a cam out more than 2 degrees from their specs it's coming back and going where the sun don't shine as reward for wasting my time....never had to do it LOL.

 

[rapidray]

Rob, unless you specify HARDWELD cams, you are getting billets that Web has. That is why you are having issues with them not coming out like the stock cams. Forget the pin count if it is what you have to do to get the numbers to come out correct. Sorry I didn't get back to you sooner but have been crazy busy. Ray.

 

[Guest]

Thanks guys. still working on it. Talked to Web today about my missing 8* of duration.

 

[RacingJake]

I don't even look at those numbers any more.

I just go by my P to V clearance now, it's easier and faster for me.

 

[trippivot]

I don't even look at those numbers any more.

I just go by my P to V clearance now, it's easier and faster for me.

AMEN !! set cams to the very minimum clearances; valve to valve, and valve to piston. So what if you have to up the idle speed -- it's fast!!

who makes a fuss over 2 degrees tolerance in a cam lobe???

you want perfect? well you aren't going to get it. :hand:

Did you ever consider the flank portion of the lobe is made for full running speed along with the interaction of the valve spring harmonics?? Gently opening and closing the valve when spinning at full speed is one thing and measuring it at a standstill another thing all together. the "lost degrees" can be found at 8K RPMs' as the valve is bouncing and bobbing in a semi controlled event, not with a dial indicator.