motorcycle engined 7 disadvantages

[Peter Pennyfarthing]

Ladies and gentlemen, my first post. I am considering fitting a motorcycle engine to my 7 rolling chassis. Can people offer kindly advice on how it will affect the kinds of events/gatherings/competitions I can be involved in? I do want to feel included in the community but don't want to be constricted in my imagination with regards to my project build. I think that the VSCC and the 750 mc will not allow me to take part in competition events. Do those organisations do non competitive events that I would be able to be involved in? Will there be any other events (competition or otherwise) which I could take part in? Or should I just discreetly go into the hall with my service Webley for even suggesting such a thing? Thanks, Peter

[andrew34ruby]

Peter, I can understand you wanting more power but I'm not sure you'll be happy with a motorbike engine.

The car will no longer be mot exempt.

The axle ratio might not suit an engine that likes to rev.

The axle might not be strong enough.

It might be easy to go a bit too fast for the cornering ability and you end up through a hedge.

At faster speeds you would soon find the brakes to be not good enough.

It will sound all wrong!

It might be difficult/expensive to insure.

Put your bike engine into a Morris Minor (and fit disc brakes) and put the Minor engine into the seven.

[Steve kay]

Cammy Minor engine? SV Minor engine?

[Ivor Hawkins]

Personally, I don’t think you need to retire to the library with your service pistol because there are many Sevenists here who have made engine swaps with varying levels of success.

Andrew has made some valuable observations, but the real question is what do you want out of your Seven special? Will it be street driven or simply a bit of fun that goes on a trailer?

If it is the former, perhaps an engine more in keeping with the age of your chassis might be worth considering, such as an old vee twin out of a Y type BSA ( if you can find one!) a JAP twin would be great but it would probably put the rest of the running gear under so much strain, you might as well scratch build something. Perhaps a big single might be an option like a 500 Norton...

Odgy built a special with a maggot vee twin (Honda CX if I remember correctly, it’s on the old forum here so you can have a look) and being a cooking 500 it didn’t put to much strain on the original seven running gear.

If it’s a trailer car for competition, I’m not sure a bike engined Seven would be a bit restricted as to what you could compete in and there are already some very quick Seven engined cars out there already.

Have a look at Odgy’s car and see if that gives you some inspiration.

[Alan]

There are, if you look hard enough some really nice, small, pre war aero engines to be had. Together with old Harley and JAP stuff these would almost certainly be VSCC eligible. Go for it.

[Austin in the Shed]

I know a couple of people who have tried Harley engines in cars without much success.Jap engines also fitted,one still trialled now and a "dog "eard sprinted but they're a bit expensive at 15k? new.
How about a Ford A engine big and lazy and relatively light but you would have to set it back a bit to get between the rails .
Junk the heavy flywheel connect to a 3 speed 7 box,40 brake with some tuning 70-80 bhp.
I sort of think it's a bit of a cop out fitting a modern engine,going to that you might as well go for a more modern chassis.

[Peter Pennyfarthing]

Peter, I can understand you wanting more power but I'm not sure you'll be happy with a motorbike engine.

The car will no longer be mot exempt.

The axle ratio might not suit an engine that likes to rev.

The axle might not be strong enough.

It might be easy to go a bit too fast for the cornering ability and you end up through a hedge.

At faster speeds you would soon find the brakes to be not good enough.

It will sound all wrong!

It might be difficult/expensive to insure.

Put your bike engine into a Morris Minor (and fit disc brakes) and put the Minor engine into the seven.

Thank you Andrew, you make some valuable observations. Lack of MOT exemption was a bit of a hit I have to say; I suppose my next job would be to look into ease (or otherwise) of actually getting it MOT'd. (any further advice here welcome). As far as power goes (strength of 7 drivetrain, ending up in fields etc), I am pretty conservative with the right foot generally and would be very (overly) conscious of these concerns but I take your points; it would probably be quite easy to forget limitations in moments of exuberance. Lastly, it will sound fantastic!

---

Personally, I don’t think you need to retire to the library with your service pistol because there are many Sevenists here who have made engine swaps with varying levels of success.

Andrew has made some valuable observations, but the real question is what do you want out of your Seven special? Will it be street driven or simply a bit of fun that goes on a trailer?

If it is the former, perhaps an engine more in keeping with the age of your chassis might be worth considering, such as an old vee twin out of a Y type BSA ( if you can find one!) a JAP twin would be great but it would probably put the rest of the running gear under so much strain, you might as well scratch build something. Perhaps a big single might be an option like a 500 Norton...

Odgy built a special with a maggot vee twin (Honda CX if I remember correctly, it’s on the old forum here so you can have a look) and being a cooking 500 it didn’t put to much strain on the original seven running gear.

If it’s a trailer car for competition, I’m not sure a bike engined Seven would be a bit restricted as to what you could compete in and there are already some very quick Seven engined cars out there already.

Have a look at Odgy’s car and see if that gives you some inspiration.

Thanks for your comments Ivor, I saw images of the one with the CX 500 engine (what is a "maggot" vee twin btw?) after I had begun to get excited about the idea of a motorcycle engine. I had thought of single cylinder engines but just happened upon a fore/aft vee twin Honda from slightly after the CX era (hardly vintage with respect to the 7). I got one for £95 so not going to break the bank if I don't use it. Anyway, perhaps I'll keep a look out for something more in keeping with the era. I'm definitely not interested in winning hill climbs/races etc, perhaps just taking part, if possible, in fun gatherings, trials and group drive outs. I wouldn't want to find myself excluded from the social aspects of ownership if you see what I mean. Thanks again for your encouragement!

---

There are, if you look hard enough some really nice, small, pre war aero engines to be had. Together with old Harley and JAP stuff these would almost certainly be VSCC eligible. Go for it.

Thanks Alan, that's interesting to know and encouraging. The important thing is that I wouldn't find my car entirely ineligible for gatherings although I understand it might not be to everybody's taste.

[Stuart Giles]

From the little I've seen of the marketplace, any period larger capacity motorbike engine is going to be seriously expensive. If you just want to have fun with your car, a Honda CX500 or the 650 version shouldn't break the bank. IIRC correctly, back when they were new, the CX was known as 'the plastic maggot' due to their (lack of) styling. Having said that, they were one of the most popular bikes with motorcycle couriers; so they were clearly reliable over high mileages. Is your 'fore and aft' twin shaft drive? if it's chain drive, sorting out the driveline could involve a lot of work.

If you're looking an alternative car engine, I have seen a Riley 9 motor fitted in an A7 special; probably won't be easy to find a good one at a sensible price though. Way back when, Austin 7 specials were just home built sports cars that happened to use a lot of A7 running gear. The 1172cc Ford 10 engine was a popular swap then. Although they were made until the early 60's this motor dates back to the 1930s, so could be considered 'period' although the VSCC will probably spurn them forever. The earlier E93A unit has just under 30 BHP with the original 'lawnmower' carb and iron exhaust manifold. A bit of simple tuning will bring the power up to 40 BHP+

A fair few recently built A7 specials have used the 750/850 OHV Reliant motor -obviously not 'period' but it's a light, compact (relatively) high revving motor that easily fits in an A7 chassis and will work well with the A7 factory final drive ratio.

[Malcolm Parker]

The all aluminium Reliant OHV engine works very well in an Austin 7 or Big 7 chassis and the gearbox has nicely spaced ratios.  My Big 7 special with an OHV Reliant engine did 20, 40, 60 and 80 mph in the gears and was a lot of fun.  I believe that the Reliant OHV engine is sought after for use in Trikes and is getting rather scarce.

I would stick to an Austin 7 engine.  Mildly tuned 25 to 30bhp will provide plenty of fun, especially if you can keep the weight right down.   Have a look at Colin McLachlan's 'Moose' hillclimb car, a good example to follow I would have thought.  Also, possibly not relevant, the value of the finished article is likely to be higher if it has an Austin 7 engine.  No problems with the DVLA or insurance companies (hopefully!)

[Terry McGrath]

Regarding the strength of the transmission, I use a 4.9 Austin 7 CWP in my Riley-engined Amilcar and it has coped with 77 BHP and competition starts for years.