Timing with isky cam

[arcturus]

Hi, I have installed an isky cam part number 705171 which was described as "mild tuning"the inlet opens earlier at 26* btdc instead of 20*btdc Should I need to alter timing to compensate.?
I think 705161 is the standard B16b cam but could be wrong

[blueosprey90]

George, I can't offer much guidance as I have never been inside the B-16 engine. I don't know how the camshaft timing is set on the B-16 and I'm otherwise incompetent on the subject.

But there is a difference between camshaft timing and ignition timing; and I don't think they are inter related. In other words, you cannot fix or adjust camshaft timing with ignition timing.

I can't see the column labels/titles on your attachment. But I think the number you are looking at, 26*, affects duration - meaning that the valve opens up 6 degrees earlier than stock. That means that combustion gasses have longer to get into the engine, thus providing more power (in theory). I'm guessing that the 6 on the timing card is telling you to set your ignition timing 6 degrees before top dead center.

On the MGA engine that I've been working on, where the crankshaft and camshaft are connected via a timing chain, I set the camshaft timing at 102 degrees before top dead center. This was based on lobe separation distance in degrees, plus the cam manufacturer's recommended camshaft advance which was maybe 2 or 3 degrees. In other words the camshaft manufacturer recommend a camshaft advance on the timing card of 2 to 3 degrees. From memory, I'm pretty sure that my lobe separating distance was 101 degrees. I set the camshaft timing at 102 degrees rather than 103 or 104 degrees to give myself a more grunt at the lower end of the camshaft power curve. In other words, more torque coming out of the corners. If I had set camshaft timing at say 104 degrees, I'd have comparatively more power at the top end.

Normally, on the MGA camshaft timing is set based on the alignment of the camshaft sprocket gear (each tooth is worth 6 degrees, I think) and offset keys which move the sprocket teeth forward or back by maybe up to 3 degrees depending on the offset key you have/buy. In my case I used an adjustable sprocket which made precise adjustment quite easy without the need to fool around with offset keys. (But there was still a somewhat complicated procedure using a timing wheel and finding max lift at top dead center.)

My guess is that on the B-16 engine, cam timing is set once you set your timing gear and is not so easily adjusted. (But if the cam timing card says to advance the cam by say 3 degrees, my guess is that you would do that with an offset key).

Like the MGA sprocket, however, if you are one tooth off on the timing gear, your cam timing may be 6 to 8 degrees off depending on how many teeth are on the sprocket. So if you are having poor performance, e.g., no power, check to see that your cam sprocket (gear) is properly aligned with the crankshaft sprocket (gear).

Good luck, I hope my comments don't send you down the wrong rabbit hole.

[mocambique-amazone]

Everything like blueospray wrote George.
I'm doing the offset sprockets by my own.
102 (Isky will tell you the right number) overlap at before TDC is the important number.
Nothing else. I wouldn't dof anything now. You have to remove the timing gear cover to do this. And the cam gear....

Good luck, enjoy. Kay

[arcturus]

Received this answer from Richard. Now I know why I have been chasing my tail trying to get a decent tickover!
RICHARD ISKENDERIAN

Fri, Mar 27, 9:55 PM (11 hours ago)

to me
George.

Typically a normal idle speed with the VV71 would be around 800-850 RPM.

If you are trying to use STOCK ignition settings ( initial advance ) , it will need to be raised .

Usually about 12-14 deg. initial advance with 34-36 deg. total advance works about correct for this cam.
If you are using stock settings, it will definately idle too rough.

Regards;