jotacorsa
Hero member
- Location
- between Santa Fe and Taos
cam, you missed the part where patrick slotted the wheels removing any threads
Valve timing redux
- Thread starter triumphguy
- Start date
Dellortoman
Hero member
- Location
- Tasmania, Australia
No, I saw that. It's what alerted me to the fact that the sprockets weren't tapped. Seems a better arrangement to me doing it that way. There's more room to make slots in the sprockets than in the narrow little ears on the flanges. If the slots are long enough to cover one tooth pitch, then you can put the timing anywhere you like.
I would have done it that way myself but it looked like there wasn't enough clearance room for nuts or bolt heads in the cam chain tunnel.
Cheers,
Cam
I would have done it that way myself but it looked like there wasn't enough clearance room for nuts or bolt heads in the cam chain tunnel.
Cheers,
Cam
mcnicol
Hero member
- Location
- Safety Harbor, Florida, USA
Why not just drill and tap the holes in the camshafts to the next inch (or whatever) size that's just a little bit bigger, slot the sprocket, and Loctite the bolts to be safe? BSF 9/32" has a major diameter of 7.142mm, 26 tpi, almost the same pitch as M7. Unfortunately I'll bet the hole in the camshaft is a just a bit bigger, and the next inch size up is 5/16" which is a lot bigger, not much different from M8. But it seems to make sense, if you're going to file slots in anything, why not do it in the much easier to replace sprockets? Assuming the flange on the camshaft is thick enough for a usable tapped thread, and if there's a suitable sized thread standard.
Ken
Ken
triumphguy
Junior member
There was some reason I decided to use a nut and bolt rather than just tapping the camshaft flange to the next oversize, but for the life of me I cannot remember it now. There is room in the cam chain tunnel for a short bolt and nut, and the countersunk heads of the bolts sit barely proud of the sprocket surface so they clear on that side as well. Tapping the camshaft flange would be a cleaner installation and I see no reason why it wouldn't work. Wish I could remember why I didn't do it.
I rechecked the timing a couple times last night and I am consistently getting max lift on intake at 104.5 to 105.5 degrees and on exhaust at 108 using the 'stop-start-divide by two' method. The span between stop and start averages 7.92 deg on intake (13 tries) and 7.18 deg on exhaust (11 tries). I am also consistently getting intake opening 25 deg BTDC, closing 50 deg ABDC, and exhaust opening 56-57 deg BBDC and closing 14.5-15 ATDC.
Scott, your calculation assumes the cam lobe is symmetrical on both the opening and closing ramps, does it not? It seems to me that if the lobe is asymmetrical, then simply positioning the cam halfway between the opening and closing points would not ensure the point of highest lift is where it should be. I know that with these specific cams, at the calculated centerline the pointer on the dial indicator is still moving. You can see by the attached chart that these cams do not open and close the valves at the same rate; the data points on the chart are all 10 deg apart. Do not rely on the chart for actual opening and closing points; I clocked these in my lathe so the exact position of TDC compression was just a guess. However, the lobe shape is accurate. This has been a very educational and occasionally frustrating experience for me and I could not have done it without the assistance of this group.
Cheers,
Patrick Cherry
Ojai, CA USA
I rechecked the timing a couple times last night and I am consistently getting max lift on intake at 104.5 to 105.5 degrees and on exhaust at 108 using the 'stop-start-divide by two' method. The span between stop and start averages 7.92 deg on intake (13 tries) and 7.18 deg on exhaust (11 tries). I am also consistently getting intake opening 25 deg BTDC, closing 50 deg ABDC, and exhaust opening 56-57 deg BBDC and closing 14.5-15 ATDC.
Scott, your calculation assumes the cam lobe is symmetrical on both the opening and closing ramps, does it not? It seems to me that if the lobe is asymmetrical, then simply positioning the cam halfway between the opening and closing points would not ensure the point of highest lift is where it should be. I know that with these specific cams, at the calculated centerline the pointer on the dial indicator is still moving. You can see by the attached chart that these cams do not open and close the valves at the same rate; the data points on the chart are all 10 deg apart. Do not rely on the chart for actual opening and closing points; I clocked these in my lathe so the exact position of TDC compression was just a guess. However, the lobe shape is accurate. This has been a very educational and occasionally frustrating experience for me and I could not have done it without the assistance of this group.
Cheers,
Patrick Cherry
Ojai, CA USA