The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: 900triple on 14.10. 2008 22:08

Title: Can an A10 top end go on an A7 bottom end?
Post by: 900triple on 14.10. 2008 22:08

Hi,

New to this site (excellent first impressions BTW).

I am putting together a non standard 1953 ish plunger A7 and am trying to find out if its possible to put an A10 top end on the engine...and if so whats involved.
This has probably been covered many times but any advice would be welcome.
Cheers
Alan

Title: Re: Can an A10 top end go on an A7 bottom end?
Post by: trevinoz on 14.10. 2008 22:37

Only if you strip down and replace the crank and rods, so I guess the answer is no.
                                                     Trev.

Title: Re: Can an A10 top end go on an A7 bottom end?
Post by: a10 gf on 15.10. 2008 21:11

Welcome onboard Alan, I hope you will find all the help you may need. Post any stories and pictures about your ongoing restoration.

e

Title: Re: Can an A10 top end go on an A7 bottom end?
Post by: fido on 16.10. 2008 09:06

If you want a bit more power I suggest you build the engine to A7SS spec. with higher comp. pistons etc.

Title: Re: Can an A10 top end go on an A7 bottom end?
Post by: 900triple on 16.10. 2008 10:32

Quote from: fido on 16.10. 2008 09:06

If you want a bit more power I suggest you build the engine to A7SS spec. with higher comp. pistons etc.

Thanks for all of the posts - I am after more grunt rather than power and revs plus the engineering challenge (however slight) of a conversion....

So far it sounds as if a crank/rod plus top end change may suffice?

Title: Re: Can an A10 top end go on an A7 bottom end?
Post by: trevinoz on 16.10. 2008 21:44

Alan, what you are intending is building an A10 engine in A7 crankcases which is no trouble as the cases are the same. Use a 356 or 357 camshaft, you may have to ease the cam tunnel to fit.
I would go for the 356 cam which is what the Super Flash used and would develop as much power as a plunger frame can handle, unless you are a thrill seeker.
                     Trev.

Title: Re: Can an A10 top end go on an A7 bottom end?
Post by: Brian on 16.10. 2008 22:26

I would totally agree with Trevinoz. Use the 356 cam and go for around 7.5-1 compression and you will have a very nice motor to suit the plunger frame.

I have this setup in my plunger A10. I run standard gearing and the bike will cruise all day at 60-65mph.

Title: Re: Can an A10 top end go on an A7 bottom end?
Post by: olev on 17.10. 2008 11:21

Gday Alan,
recently read (on the internet) about an early american racer who stuck an a10 top end on an a7 by machining the top fin off a set of a10 barrels to match the shorter conrods. He was apparently quite successful in the 500cc division for a while. I looked again but can't find the site. lets face it, you can't beat cubes.
good luck, tom

Title: Re: Can an A10 top end go on an A7 bottom end?
Post by: beezalex on 24.10. 2008 21:15

Quote from: trevinoz on 16.10. 2008 21:44

I would go for the 356 cam which is what the Super Flash used and would develop as much power as a plunger frame can handle,

Is there a power limit to the plunger frames?  Do they have a particular weakness?  I'm planning on racing one so some info or experience would be appreciated here.

Title: Re: Can an A10 top end go on an A7 bottom end?
Post by: jfligg on 26.10. 2008 14:21

Hi Alex  Can you tell us more aout your plunger race bike?  Got any pictures.  Jeff