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Simca Marmon SUMB - Diesel conversion

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Advice is required from anyone who has converted a V8 Simca SUMB to Diesel. I have a V8 Petrol version and need to change to a diesel engine, however the choice of engine is critical. Does anybody have any knowledge of this conversion? The vehicle has been used for the last 15 years every week in the winter but does under 1000 miles per year. I fear that the engine has been run on unleaded petrol for the duration and is now complaining by not being able to get it running. Carb has been rebuilt, new condenser, new spark plugs, points overhauled, coil replaced, gravity fuel tank installed as fuel pump diaphram knackered. Final straw is that the starter motor is on a go slow!

In advance, manyIMG_0198.jpg thanks.

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Hi

 

I owned one for a while which had a part complete conversion using the Volvo/Volkswagen D24T turbo diesel and automatic gearbox out of a Volvo 960 estate car. Unfortunately the previous owner stopped at what he needed for some off roading and farm use and never sorted out electrics etc, and I never got round to it before selling it as a spares unit together with my petrol SUMB.

 

Power wise it is a reasonable match (100 vs 110HP) although the gear ratios aren't quite right (so too fast in 1st and max speed about 40 in top, versus 50 with the V8). The engine is used in a similar military vehicle - I believe the British diesel Pinzgauers also have a D24 variant.

 

Mechanically it was fairly ok - the drive shafts from the gearbox and transfer box had each been cut 1/2 way and then joined; an extra pulley and belt were fitted at the front of the engine to drive the SUMB brake compressor. The new engine extended further back and the cab floor needed cutting away to fit (I think the French Renault engine official conversion also had a larger cover in the cab space, and moved the batteries out of the cab to compensate). The auto box helps because it has bowden cable controls so the gear lever location is flexible.

 

The previous owner had used it for several years like that - the main issue was that the D24T starter and generator are 12V and the conversion had been done without thought to preserving the wiring harness (the fuse box was in the way of the new engine) so it would have needed a complete new wiring harness to make road legal. Had it been done with a little more forethought I think it could have been quite easy to convert the whole lot to 12V.

 

One other issue which stopped me was that the previous owner did not retain any details of the donor vehicle - I was never able to sort out change of engine type with DVLA as a result - so it remained on SORN as a petrol unit all the time I had it. if you do this it is best to keep the donor vehicle details and get a receipt or engineer's report from a reputable garage (ideally MoT centre) - you may well need that for insurance too

 

 

Hope this helps

 

Regards

 

Iain

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Hi Iain,

Many thanks indeed for your reply. From what you say it is definitely a possibility. The mating of the gearbox to the transfer box is a simple way forward. If the 1st gear is too high, did you try it in low ratio?

I will start looking for an engine and gearbox. The volvo D24t is 6 cyl, so a 4 or 5 cylinder might be an option.

Again many thanks, James

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James

 

The high/low pushrod was disconnected from the transfer box when I got the diesel converted one - because i never got that far (separation, house moves, storage issues) I never reconnected it before it went to another SUMB owner as a spares donor.

 

I guess a 4 or 5 cylinder unit would be shorter, but I think anything less than 100HP would be underpowered on hills (my V8 SUMB was in fairly good condition but slowed quite a bit crossing the Orwell Bridge, so anything less powerful would be too slow uphill for trunk roads, I think!)

 

Regards

 

Iain

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Hi,

 

You could probably overhaul the existing engine for a fraction of the cost and effort of replacing it with a diesel. I've done a large number of diesel conversions so you can trust my judgement on this. There are masses of parts out there for Ford V8s. Starter motors can be rebuilt. Fuel pump replace with electric. If the engine won't start, bearings, rings or re-bore will still be far less cost and effort than engineering a diesel.

 

That said I can fully understand why you may want a diesel so you could have a look at what the French put in them here:

http://www.milweb.net/features/sumb.php

 

 

 

- MG

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