Adjustable timing sprockets

[SJ Lambert]

The QED vernier sprockets I'm installing have 6mil diameter, grade 12.9 cap head locking screws - I imagine that they could be tightened to a much lower figure than a lubed 116 inch pounds?

[englishmaninwales]

I shall consider fitting adjustable sprockets when my cylinder head comes back from the machine shop. The timing marks were significantly off at TDC and no doubt will be worse if the head gets a facing/skim.
My preferred method of set up is going by in/ex valve lift at TDC.
Interestingly, before lifting the head, I compared the front cover TDC marker with a TDC dial gauge and found they match up accurately, makes a change from my K series engine in the Caterham with its poorly fitting belt cover and TDC marker!!
Can anybody give some lift at TDC detail for standard cams, for road use, giving good mid range torque without making the idle unbearably lumpy?
Malcolm

[512BB]

So who have you decided to use to carry out the work on your head Malky?

Leslie

[oldchieft]

The normal maximum for that bolt would be 14.5 n/m or 128 inch/pounds

116 inch/pounds seems about right at 90%

Jon the Chief

[SJ Lambert]

Thanks Jon

Just wanna make sure I don't squash the alloy centres.....

[types26/36]

Can anybody give some lift at TDC detail for standard cams, for road use, giving good mid range torque without making the idle unbearably lumpy?Malcolm

I am not sure what you mean by standard cams, I presume you mean standard Sprint type cams so I dont know if these Piper cam specs are of any use to you but they do show full lift @ TDC .
I think the 270 is equivalent to the standard sprint cam.

[englishmaninwales]

Can anybody give some lift at TDC detail for standard cams, for road use, giving good mid range torque without making the idle unbearably lumpy?Malcolm

I am not sure what you mean by standard cams, I presume you mean standard Sprint type cams so I dont know if these Piper cam specs are of any use to you but they do show full lift @ TDC .
I think the 270 is equivalent to the standard sprint cam.

Thanks, Brian.
I think I've correctly identified the cams as the Standard B type cams (no groove on cam drive flange) rather than the sprint or s/e cams. I will be cross checking the total lift against the detail in Miles' book, to ensure some other after market re profiled cams are not fitted.

So who have you decided to use to carry out the work on your head Malky?

Leslie

Leslie
I'm taking the Head to Cylinderhead Services in Northampton .

[512BB]

Crikey Malcolm, you are travelling a distance, but worth it to CHS. Its a shame the timing was not a little better, as I am coming down to Wales this week, I could have collected it for you and brought it with me.

Let us know what you have done and what you think, as I have a couple of heads that need work, and shall also be taking them to CHS. But based on the recommendations that I have received from friends, they should be fine there.

Leslie

[englishmaninwales]

Leslie
I have relatives close by so I can take in a visit to them too. I spoke to 5 companies in all and TBH it was difficult as they all seemed to be speaking from a position of experience and knowledge. Also one company also failed to return my call so they didn't pass the start line! CHS gave me the most confidence....we shall see!

[rgh0]

Thanks, Brian.
I think I've correctly identified the cams as the Standard B type cams (no groove on cam drive flange) rather than the sprint or s/e cams. I will be cross checking the total lift against the detail in Miles' book, to ensure some other after market re profiled cams are not fitted.

.

Standard Lotus "B" cams specification I believe are as follows. Never measured one up myself so this is specs reported by others only

Lift 0.35 inch
Duration Seat to Seat 248 degrees
Timing 15/53/53/15
MOP 109 degrees
Base Circle 1.20 inch

cheers
Rohan

[englishmaninwales]

Hi Rohan
I measured the lift as 0.35" ....but Miles' book states lift for the B type as 0.375" and timing as 22/62/62/22.The lift is greater than he quotes for C (s/e) D (sprint). Maybe a typo in the book?

I'm not sure now what I've got.

Malcolm

[types26/36]

deleated

[rgh0]

Lots of inconsistent data out there including in Miles book but my belief is as follows. I have never specifically measured a standard B cam but the progression in the data below is consistent with the progression in the performance of the engines. I would love to get actual data from a known original B cam. Unfortunately the ones that came in my Elan I had reground about 30 years ago into a higher lift spec and I did not bother measuring them first!

B cam "standard" - .35 lift 15/53/53/15 timing
C cam "S/E - .35 lift 22/62/62/22 timing
D cam "Super S/E or Sprint or Big valve" .36 lift and 26/66/66/26 timing.


cheers
Rohan