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Replacing the engine (repowering)

Written July 2008

Some information for those considering replacing the engine and gearbox on an older motorhome.


The information presented here is based on our own experience. In 2005 we replaced the engine in our Bedford Bus with an Isuzu 6BD1-T.


Why change the engine?

In our case, we were faced with only two options. Our existing engine (a Bedford 466ci) was in a sorry state and was not maintaining oil pressure at low revs. It was not performing well and generally lacked power. Our two options we :

a) Recondition the existing engine 


b) Replace the old 466 with a more modern engine


We were living in Perth (Western Australia) at the time.

The old Bedford 466 removed and ready to be stripped - [Click for a Larger Image]
The old Bedford 466 removed and
ready to be stripped


We had the old engine removed from the bus and stripped down to see what the issues were with it. For all we knew, it may have been a simple and relatively cheap repair job. Once the engine had been stripped down the engine rebuilders completed an assessment and the news was not good. It would require a complete rebuild. They also recommended that the fuel pump be rebuilt at the same time.


It is my opinion that most engine rebuilders will suggest that you replace or recondition everything - wheather it needs it or not. I suspect that this is to protect them from the possibility of an older part failing unexpectedly and causing damage to new parts during the warrantee period. 


The cost estimate to rebuild and refit the old Bedford 466 engine was $7,500, plus another $1000 to rebuild the fuel pump. We had already spent $1500 in getting the engine out and having it stripped and assessed.


We were very much undecided about the course of action from this point. The old Bedford engine had performed well - it was a well respected engine with a good reputation for toughness and longevity. There was no reason to believe that once reconditioned it would not continue to faithfully propel the bus for many years.

Among the people we spoke to about the engine, we found the comments and advice from Adrian (who sources and supply's parts for Bedford's) the most compelling. He said ...

"The Bedford 466 engine is rated to deliver 140 horse power - even when brand new, half of those horses had broken legs and the other half were old drays! An engine built on 1950's technology can not compete with a more modern engine."

Adrian recommended we replace the old 466 with an Isuzu 6BD1-T and a 6 speed overdrive Isuzu gearbox. He said that it would perform better, run quieter and be more economical.  


Armed with this advice we set about trying to find a second hand Isuzu 6BD1-T and transmission. It turns out that these are very popular engines with a great reputation - and thus quite well sought after. We finally found an engine and gearbox at National Truck Spares on the east coast. I negotiated a price for the engine, gearbox, freight across the country and everything we would need to fit the engine. This was basically everything from the radiator to (and including) the tail shaft. The price quoted was $7500. The engine had done less than 100,000km and would be guaranteed for 6 months or 50,000km from fitting. All that remained was to find somebody to fit the new engine.

We also found out that we needed to apply to the WA Land Transport dpt for approval to fit the new engine. This turned out to be little more than a formality - just some forms to complete and the work would have to be inspected by an engineer (we also needed to transfer the bus registration to WA).



In phoning around mechanics in the area, we received responses ranging from a polite "No thanks" to "yea mate, bring her round, I should be able to look at it in about 3 months". Some quoted as much as $12,000 over the phone!

The new Isuzu 6BD1-T still on the shipping pallet - [Click for a Larger Image]
The new Isuzu 6BD1-T still on the
shipping pallet

We finally found an older man who owned a tiny bus company running mainly Bedford buses. Ian was an English born mechanic and had worked on Bedford buses most of his life. Ian estimated $3500 to fit the new engine.


We paid for the new engine and arranged to have it delivered to Ian's workshop.