Britbike forum Forums British motorcycles in general British modified/specials BSA A65 Stroker Questions

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.

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.

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.

Your twin plug question, no real advantage to it, the a65 head is pretty good
and although i've seen it done a few times, they didn't win so never bothered.

https://imgur.com/a/pZJbCmW

That is a good looking install, I have seen some that look less finished than that. What ignition is this setup running?

You can run 2 x 6v double ended coils with any EI that has wasted spark.
So all the usual suspects conform, Boyer Pazon Sparx Trispark etc.
With the micro based types you'll need suppressed plug caps or leads.
Trust me, on an a65 it's a load of work for negligible gain unless you are
going to run dope at about 15-1 CR.