A10 Engine in a A7 Frame!

[wayne]

Doing a custom build using either a 49' A-7 frame or a 51 A-10 frame (BOTH are plungers) and im looking to drop in a 60's A-10 engine....so here are my questions:

are there compatibility issues with a7/a10 frames and their engines?

do i need to track down a "plunger" or "rigid"  engine or will a later swing-arm engine work?


basically I want put a newer a series engine in an older frame. Before i receive a flood of nasty emails i want to clarify its a period correct custom with all bsa components and NO frames will but cut/chopped! Promise.

[muskrat]

 G'day Wayne, welcome to the forum.
                                                   You will need a plunger type motor & g/box, they bolt together. Later type internals, barrels, head etc will fit. I have a '57 A7SS topend on my '51 plunger.
 Not sure if it's possible to fit an A65 motor in.
Cheers

[beezermacc]

I know two people who have plunger engines in swinging arm frames but you'd need to do a lot of 'surgery' to fit a swinging arm engine in a plunger frame!

[wayne]

I probably wont try to fit an A65 engine, I'd like to run a late 50's or early 60's A10 engine which i think are all of the "swing arm" variety. Could you elaborated on the "surgery" required to fit a swing arm engine into a plunger frame?

If I have to run a plunger engine do you know the year range and serial prefixes for either a7 or a10 engines?

[beezermacc]

Hi. A Swinging arm engine has an independent gearbox, consequently it is much longer than the plunger engine and gearbox. Fitting a swinging arm engine into a plunger frame is a non-starter without somehow stretching the frame. The plunger engine, in my opinion, is just as good. In fact my A10 plunger with original mag and carb absolutely flies, has loads of grunt and is easily my most pleasurable bike to ride (I have five A7/A10's). The last A10 plunger engine was built in 1957. I would not recommend fitting one of the early 'longstroke' A7 engines though they would fit, as parts are getting scarce and the later engines had some significant design improvements. I would recommend looking for an engine with prefix ZA10 or BA10 or BA7 but make sure the crankcases have the four large threaded bosses and rectangular rib to accommodate the gearbox studs and casting.

[wayne]

ive heard the earlier a10 engines have main bearing problems. could you post a picture of the portion of the engine cases you mentioned i think i know what you're talking but id like to be sure before i fork over alot of money on ebay.

so there's no practical way to fit a swing arm engine in a plunger, there's just so much easier to come by and seem to have many design improvements.

id prefer to run a mag i didnt think those were fitted on a10 until they transitioned to the swing arm engine...am i wrong? if so which years/prefixes had mags?

got a spare plunger engine lying around????

[trevinoz]

Wayne,
                All A7/10 engines used a magneto.
The A7/10 used the same main bearings from start of production until finish but the timing side was originally "white metal" and was changed to a copper alloy in the mid fifties.
The long stroke engine had a ball bearing drive side main and the others a roller.

  Trev.

[beezermacc]

The plunger engine also has the the primary chaincase inner cast integrally with the left hand crankcase. The swinging arm engine has an independent two-piece primary chaincase. Look for BSA A10 engines on Google images where there are lots of examples. If you see one on ebay post the listing on the forum, anybody here will identify what's there. These are swinging arm ones http://www.ebay.co.uk/itm/BSA-A7-A10-PRE-UNIT-CRANKCASES-SWINGING-ARM-FRAME-/220988196326?pt=UK_Motorcycle_Parts&hash=item3373ec45e6

[cosmikdebriis]

Few words from my current experiences of fitting my plunger engine back in the (plunger) frame

Haynes manual is next to useless...

Don't fit the engine and then try and fit the front engine plates or you will end up taking the engine out again... Grrr...

Fit the oil pipe union/thingy to the crank cases before you bolt the gearbox on or you will be taking the box off again... Grrr... (Luckily I found out before I fitted the engine or I would have been taking the engine out as well...

Top piston ring goes one way up. Has "TOP" marked on it. (luckily I checked first)

Mine's still not finished so no doubt I will turn up some more...