What camshaft 356 or spitfire cam?

[Tors]

Hi all,

I’m in the process of rebuilding the 1952 A7 engine. I got it rebored to fit new pistons (gandini +040, 7,5:1).
I’m reading up on the engine and came across a spitfire cam and wondered if that one would  work in my engine in combination with the 7,5:1 pistons.
I assume that the original cam is a 67 356 since the bike is a star twin.

Any thoughts/practical advice?

Regards Torsten



My intropost:
https://www.a7a10.net/forum/index.php?topic=18580.0

[Swarfcut]

  The early engine crankcase differs from later types with regard to the camshaft trough. The Spitfire cam will fit, bearing bush sizes etc are all the same, but the lobes may catch on the crankcase. Later engines have a wider trough.

 More important is attention to the crankshaft, the big end bearings are supplied with oil via a cross drilling, the so called sludge trap. This is accessed by removing the two screwed in plugs. No if's or buts, this is the most important aspect of ensuring a trouble free rebuild. Lots on the forum and YouTube. As we say they can be real bastards to get out. With the plugs removed the oilway needs to be cleared of accumulated carbon, sludge etc and given a good wash through. Another oilway leads up from the timing side journal, This can be cleared at the same time.

I reckon a copy of Roy Bacon's book "BSA Twin Restoration" will help identifying parts and time spent reading previous posts on engine building will save a lot of hassle.

The attached pictures tell the story....

 Swarfy.

[muskrat]

G'day Tors.
All of what Swarfy said.
I have number 53 off the production line of short stroke A7's (same as yours). I fitted the 357 cam without having to modify the cam trough. Castings being castings all have minor differences. Lucky mine were deep enough.
Trouble with going high comp (over 9:1) is the thin flange barrels and the small fins (50-54). (My A7 is a hot rod with big fins and 357 & A7SS head).
Best is to stay as close as possible to standard if you don't want to twist spanners too often.
Cheers

[Black Sheep]

I have a 357 cam in my Star Twin but I would suggest you are as well with the 356 unless you spend a lot of time above 4,000 rpm..

[Tors]

Thanks for all replies!

@ Swarfy..
Yes the sludgetrap is already taken care off, as are crank bearing and bushing (crank regrind on the bushing side).

I read about the making room bit regarding the spitfire cam. That is not a problem for me. But if as black sheep stated, the gain is in the above 4000 rpm range… i’ll stick with the 356. The comp is 7.5 : 1 according to gandini. Not 9:1 as in muskrats

[Bsalloyd]

I installed the 357 cam into my 1953 Super Flash. I had to set the cases up in a mill to remove the case interference. The bike runs great. There is a definite difference in the exhaust note.