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Radius the corners of the piston and you won’t have that problem. Standard fuel should then be fine, you could always use an octane booster if you feel it needs it, but I’ve never found much gain.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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Picked up an SRM 90 degree race cam, and it arrived the other day. I took it out and looked it over today. It looks like a nice piece. However, my biggest issue is that it has no marking or identification marks on it at all. It also did not come with a cam card, I reached out to SRM to get the specs so when it comes time to install I can degree it in.


1960 - BSA Gold Star
1966 - Triumph T120TT
1970 - Triumph T120
1975 - Norton 850 Electric Start
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SRM 'Race'cam info

High quality made camshaft to suit the BSA A50 and A65 models fitted with a big bore kit , this is a high lift sports camshaft profile and is suitable for use with high compression engines and for tuned engines. Use our valve spring set SRM part number SRMSP5-RACE

Gives good mid range torque and high RPM power , for standard stroke engines is suitable up to 7,500 RPM

When fitting new camshafts and followers , cover with cam assembly lube; always check fitted valve spring length, most camshaft and follower failures are caused by over stressed valve springs Check valve springs at full lift and make sure they are not coil bound and can be compressed at least another 0.080 inch ( 2.0mm).

Use standard BSA cam timing gear positions

Tappet gap set @ 0.020 inch for cam timing/duration check only for the figures below

Inlet opens 45 degees BTDC Closes 78 degrees ABDC = duration 303 deg
Exhaust Opens 81 degrees BBDC Closes 45 degrees ATDC = duration 306 deg

Set running clearance to 0.008 inch inlet 0.010 inch exhaust ( 0.20mm and 0.25mm )

Cam lobe lift on cam is 0.372 inch over base circle 9.45mm


Overlap 90°
Intake Duration 303°
Intake Lobe Centre 106.5° ATDC
Exhaust Duration 306°
Exhaust Lobe Centre 108° BTDC
Lobe Separation 107.3° (Cam°)

The only way to 'degree' is to either broach new keyway or make up stepped keys.
Of course you are stuck with lobe centres.

Last edited by NickL; 04/29/22 2:13 am.
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