6V71 Two stroke into TK

[mylesdw]

I am restoring a Bedford TK and have the chance of a Detroit 6V71 and a nine speed. Extra power over the 466 engine would be great and I believe they used that engine in the KM series trucks. Any comments about this idea would be very welcome, especially about this engine.

[G-CPTN]

The DDAD engine was an SVO (Special Vehicle Option) in the Bedford KM but it was (at least initially) a 6V-53 rather than the 6V-71 so you might have to consider the torque-loading on the rear axle.

Australia did fit DDAD engines into KMs, but I don't know whether these were 53s or 71s and what rear axle specification they used.

SVOs were engineered by 'specialist' engineers (who considered the effect of such modifications from standard specification) and many SVOs were subsequently run down the production line (where multiple orders were involved such as twin-steer or small wheels for brewery use) rather than being modifications of vehicles pulled off the production line and converted in a dedicated area.

I'm not suggesting that your idea is flawed, merely to alert you to the possible weakness in the drive train. You might want to avoid full-throttle in the lower gear ratios (at least until you get used to the combination) and it depends on what sort of load (and gradients) that you intend to tackle.

Good luck!

[G-CPTN]

The DDAD engine is, of course, a two-stroke, and will 'happily' run backwards as well as forwards (for example if you muff-up a hill-start).

Be warned that once this happens it will not respond to the throttle-pedal, and, unless you 'pull the emergency' flap (which places a plate over the inlet) it will 'smoke' as it starts to consume the sump-oil and engine speed will increase until the engine overspeeds and destroys itself (and, possibly, you).

Under no circumstances should you ignore this advice (and make sure that any driver knows this) and make sure that you never drive the vehicle without the emergency flap being connected and operational.

It is surprisingly easy to twerk the engine into reverse (as stated, usually on hill-starting) and without the flap - you must get out and run!
The standard stop-control will have absolutely no effect.

If it smokes heavily it's about to blow!

You might be able to stall-it by selecting a gear and engaging the clutch (I never attempted that) but the big red handle is the only sure way.

[G-CPTN]

Another thing to look out for is if the sump level rises (especially if you have an intermittent 'miss'.
The injection pipes are 'internal' and if they crack and leak you will lose fuel into the sump (and the injector cam roller followers will wear flats on the rollers so the engine will miss - but when you check the gaps they will seem OK). The camshaft operates the injectors mechanically.

It might be worth doing a DDAD maintenance course as the engine is somewhat different to a conventional diesel with an injection pump.

Some marine applications use DDAD engines.

You might be able to buy a maintenance manual - or at least borrow one and read it.

[coastie]

Sounds scary!

A friend of mine used to have a CZ bike (Iron curtain bike) which, if started wrongly, would run backwards and gave him many surprises!

[mylesdw]

Originally Posted by G-CPTN

The DDAD engine is, of course, a two-stroke, and will 'happily' run backwards as well as forwards (for example if you muff-up a hill-start).

Be warned that once this happens it will not respond to the throttle-pedal, and, unless you 'pull the emergency' flap (which places a plate over the inlet) it will 'smoke' as it starts to consume the sump-oil and engine speed will increase until the engine overspeeds and destroys itself (and, possibly, you).

I've heard about them running away on the sump oil but not running backwards. Surely a flap on the inlet would be no help either in this situation because the inlet is now the exhaust?

[G-CPTN]

Now you've got me befuddled.

I only know that it worked for me when I did it.

Maybe it was catching it early?



I've just noticed that you are in New Zealand.

I suggest you find one of the Ozzie owners and see what axles they used for the Detroit.

IIRC the Bedford 22500 (single speed) axle was restricted to the Bedford 466/500 engine.
Detroits always had Eaton (or RABA or SOMA) axles. If you have (or get) a suitably-rated Eaton axle you should be OK.


See my correction for post #2 (KM for TM in the first line - sorry!)

[mylesdw]

What do you know about the two speed axle? I could probably lay hands on one of those without too much trouble. I guess using the matching TM axle would be problematic because the TMs are (probably) full air brakes.

[G-CPTN]

From your website:-

We have here a 1980 Bedford TK. Its model number is KGLC3 which I believe makes it a 300 cubic inch petrol model (4.9L) with 167" wheelbase (4.2m). Amazing that Bedford were still making petrol trucks as late as 1980. At some point it was converted to CNG (Compressed Natural Gas) and later a diesel fitted. When we bought the truck in around 2005 it came with a Bedford 466 diesel and five speed.

It really depends on what you intend using the vehicle for.

If it's just a 'show pony' then you might be able to use the existing axle (especially if it ran with the Bedford 466 engine).

The KG allowable maximum weight is probably 12 tonnes and if you intend fitting a living container (for use at shows) then you should be within the 12 tonnes.

I was basing my assumptions (and warnings about the axle) that you were starting with a model KM (and an artic tractor at that).
Normally the Detroit 6V-71 would be operated at 32 tonnes, and I assumed that you might be running at that weight.

The Bedford 22500 axle that I referred-to was standard fitment in the rigid (16 tonne) KM with the 466 engine and would have had air brakes and would also have been fitted to some TK KH with hydraulic brakes.

I don't know of any rigid 4-wheelers that have the 6V-71 engine (though, no doubt somebody might have done what you intend doing - however, probably not starting with a 12 tonner).

One reason is that the Detroit 6V sticks further out the back of the cab than the 466 engine (KM artics that were fitted with the Detroit engine were long-wheelbase KMB models rather than the standard KMA model). You would have to move the front of any body that you might have to accommodate the engine (and you might struggle to get a suitable engine-mounting rear crossmember into a KG).
I've never heard of anyone fitting a 6V-71 into a KG - but I suppose it depends on your ingenuity.
What do you intend doing about the parking brake?

I can't imagine that any axle fitted with hydraulic brakes would handle the load that would normally be pulled by a 6V-71.
As I've stated it depends what you intend for your vehicle.

For your information the Bedford 300 petrol engine was popular for its higher horsepower (than the 330 diesel) and was preferred by fire engine operators and regions where petrol was cheap (it was quite thirsty compared to the diesel option) and continued as an option right until Bedford closed down. Some TK KG fire engines were fitted with the Bedford 466 engine (as an SVO) - but they operated at weights below 16 tonnes of course (like yours).

[G-CPTN]

The Bedford 22500 axle was fitted to the KGTE site-tipper, which was powered by the 381 cu in version of the 466 engine:-
http://archive.commercialmotor.com/a...kg-site-tipper


It would have had hydraulic brakes of course but it only operated at 12 tonnes (or slightly less).

The TK KH (13/14.5 tonne) model also had hydraulic brakes and would have had either a Bedford 22500 single-speed axle or an Eaton two-speed - but it would also have 10-stud wheel-hubs!

http://archive.commercialmotor.com/a...w-four-wheeler

The KG and KH artics probably had Eaton two-speed axles (and would maybe operate up to 24 tonnes).