ET: Engine (Twin) valve timing for Gary Robinson 105 cams

[Restoration Man]

I have looked through the past comments on valve timing on twins but can't seem to find a definitive answer on valve timings for Robinson 105 cams. Please can any one who has fitted these cams to their bikes let me know what opening / closing points (degrees) they have used, or did they go for equal lift method?
The cam pinions are marked and using a DTI , I've obtained the following: IVO 50 BTDC, IVC 85 ABDC, EVO 68 BBDC, EVC 48 ATDC .

Many thanks, Restoration Man

 

[greg brillus]

You certainly wouldn't want the inlet closing any later than that........Does this bike have an electric starter fitted.........?

 

[Martyn Goodwin]

Back in 2006 Brian Hill observed the following about Gary Robinsin 105 cams: "These cams have Mk II profiles but modified overlap, around 95 degrees instead of 105. They are 'timed' by setting the inlet valve at maximum lift 105 dgrees after TDC. This gives a balanced overlap with the inlet opening 47 degrees BTDC and the exhaust closing 47 degrees ATDC."

 

[Restoration Man]

You certainly wouldn't want the inlet closing any later than that........Does this bike have an electric starter fitted.........?

Thanks for comment on IVC... does seem rather late!...No the bike has not been fitted with an electric starter.

 

[Restoration Man]

Back in 2006 Brian Hill observed the following about Gary Robinsin 105 cams: "These cams have Mk II profiles but modified overlap, around 95 degrees instead of 105. They are 'timed' by setting the inlet valve at maximum lift 105 dgrees after TDC. This gives a balanced overlap with the inlet opening 47 degrees BTDC and the exhaust closing 47 degrees ATDC."

Many thanks for this info... I will now check IV max lift to see if it's @ 105 degrees ATDC.....As to my original message, I Realise I made silly error in stating ......"EVO 68 BBDC, IVC 48 ATDC",
Should have read EVO 68 BBDC, EVC 48 ATDC ......thanks once again.

 

[Restoration Man]

Back in 2006 Brian Hill observed the following about Gary Robinsin 105 cams: "These cams have Mk II profiles but modified overlap, around 95 degrees instead of 105. They are 'timed' by setting the inlet valve at maximum lift 105 dgrees after TDC. This gives a balanced overlap with the inlet opening 47 degrees BTDC and the exhaust closing 47 degrees ATDC."

Hi Martyn, I Have had another go at setting up my Cams. This time checked IVO @ max LIFT, I got 105 degrees ATDC! Also checked both IVO & EVO @ 4 degrees BTDC and got equal lift of 0.130", and final valve timings of: IVO 50 BTDC, IVC 80 ABDC, EVO 70 BBDC, EVC 48 ATDC.

So I am happy with these results.. Hopefully all will be well when I come to start the bike up in a couple of months after completing a long restoration!

Many thanks again for you info.

 

[Martyn Goodwin]

Hi Martyn, I Have had another go at setting up my Cams. This time checked IVO @ max LIFT, I got 105 degrees ATDC! Also checked both IVO & EVO @ 4 degrees BTDC and got equal lift of 0.130", and final valve timings of: IVO 50 BTDC, IVC 80 ABDC, EVO 70 BBDC, EVC 48 ATDC.

So I am happy with these results.. Hopefully all will be well when I come to start the bike up in a couple of months after completing a long restoration!

Many thanks again for you info.

4 degrees is the magic number. Set the valves at 4 BTDC and set the ignition timing, fully retarded at 4 BTDC as well. Fully advanced should be around 34 BTDC

 

[youngjohn]

My 105's hold the inlet at maximum lift for about 7-8 degrees rotation of the crank. Is it the middle of this range which is set at 105 degrees?

 

[davidd]

My 105's hold the inlet at maximum lift for about 7-8 degrees rotation of the crank. Is it the middle of this range which is set at 105 degrees?

Youngjohn,

If I had that much dwell at 105 I think I would choose to set the cam using the equal lift method. Once you have set the cam timing with that method you can then see where in degrees maximum lift occurs. If you are near the spectrum of maximum lift I would be happy.

I never understood why it was called a 105 cam because max lift is not something that is important for understanding the cam events or timing. It is important to performance, but not timing. Considering there is no mention of where the measurement is taking place, I would assume measurement was at .005" and the 105 was based on a MK2, so it is a 55-68-73-50 target measurement. I did degree a 105, but I have misplaced the data, so I am not much help!

David

 

[roy the mechanic]

Six cylinder Rover cars cam timing is set at 107 early ones and 110 later. No other timing figures are given, they run strong and near silent.