The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: spyke on 12.01. 2010 20:23

Title: Engine spec suggestions?
Post by: spyke on 12.01. 2010 20:23
Hi Chaps,

Almost finished the rolling chassis of my Spitfire inspired  A10.  Next will be a gearbox rebuild and get that bolted in, ( hopefully shouldnt take too long , famous last words, I seem to be able to remember uttering when I started the rolling chassis but still!)
But after that  I need to start on the motor. I have most of it including large journal crank, thick flange barrels and an ali head. Despite it being a Spitfire I would like to build the motor "soft" with lowish comp pistons, mild cam, so my questions are what comp ratio, what camshaft number and  will this be ok with the ali head. I dont want to use one of my iron ones even painted silver so please dont suggest that. Im tempted to ask SRM to refurb and assemble the bottom end and ill take it from there or get T and L to refurbish the components and Ill reassemble, any feelings on these options.
Look forward to your opinions as always.
Cheers Spyke
Title: Re: Engine spec suggestions?
Post by: rocket man on 12.01. 2010 21:51
good idea srm on bottom end have you thort of needle roller conversion had mine done
also had stronger con rods put in i have the 375 cam fitted also had it dynamically balanced
it make a difference less vibes heres a short vid of my bike with my princess on it

Title: Re: Engine spec suggestions?
Post by: spyke on 12.01. 2010 22:04
bike sounds great and some good engine mods but my budget wont stretch quite that far
Title: Re: Engine spec suggestions?
Post by: Brian on 12.01. 2010 23:11
I would suggest the 356 cam with 7.25-1 compression if you want a nice "rideable" motor still with adequate performance to enjoy the bike.

My plunger A10 has this set up and it is perfect for everyday riding, cruises comfortably at 65 mph with plenty left for overtaking etc but still easy to start, idles well etc etc.

In contrast my 61' A10 has the 357 cam with 8.5-1 and although it goes harder it is not so "useable" when it comes to riding in rallies or riding with friends at slower speeds etc. The cam is quite noticeable and it does take a much heftier swing on the kickstart to start it.
Title: Re: Engine spec suggestions?
Post by: trevinoz on 13.01. 2010 02:32
I agree with Brian, that is what I am running in my Flash.
But I still love those 357 cams!
Title: Re: Engine spec suggestions?
Post by: MG on 13.01. 2010 08:55
Hello Spyke!

I'm running the GF (iron head) with a 356 cam, 9:1 forged Wiseco pistons and a 30mm Concentric (also opened the ports to match). It has loads of torque in the low and mid rpm range, compared to the 357 cam power is cut at high revs, but that's ok, as it is a tourer.
When done properly, the timing side bush is good for at least 30.000 miles, I personally don't see the need for a roller conversion. It is important that the timing side bush is machined properly with the crankcases assembled and alligned with the roller bearing on the drive side with a clearance to the crankshaft of 2 thou. To avoid any distortion in the crankcases when clamped it even is advisable to mount the cylinder when machining the bearing.
Another thing I would recommend is having the crankshaft (+camshaft and cam followers) nitrogen hardened and I fitted an oil filter in the return line.