change engines petrols to diesel

liamo

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11 Nov 2006
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Hi I have a boat with two volvo AQ 140 petrols on 280 out drives I wish to fit two VOLVO TAMB40B diesils to the 280 out drives ? would the gearing on the out drives be ok or would it need to be changed as it may leave the diesils over revving or would changing the props help I also need two bell housing to fit 40B to the 280 o drives ( thank you for any help .. Liamo )
 

ms1

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I believe it would be normal for the 280's to have a different ratio more suited to the diesels if diesels were fitted as original.
I changed twin petrol AQ145 on 280 leg for diesels and upped the 15x17 props to 16 x 21. It resolves over revving probs. however the 16x21's are a bit brutal for slow manouevering.
Incidentally I bought the props mail order from USA and got a pair for the price of one in the UK.
 

Ifraser

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I'm just removing a pair of AQ140's with 280 drives... the engineer who knows the boat said that before I got her she was not performing because she had diesel ratios on her legs not petrol so I guess it does make a difference. I've splashed out and bought the whole mercruiser 1.7 packages so i don't know exactly too much about the volvo ratio's.. cheers Iain
 

ms1

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I think the 280 ratios are
petrol 2.15:1
diesel 1.61:1

to answer your original questions
Yes you can do it
yes you need to be aware of over revv possibility and control this with prop changes or some other limiter to stop throttle opening. You need to get a machine shop to make you some adaptor plates to fit the bell housing and your new engines.
Depending on actual positioning of things you may find that you need to grind away an aperture in the bell housing to accommodate the starter shaft/dog which may not be in the same position as at present. Someone like Lancing Marine would be able to make you an adaptor plate to marry up engine and existing bell housing.
Alternatively you might get some suitable used bell housings that will fit directly from Coastal Rides.
I presume you already checked that existing bell housing will not accept the new engine.
If you want to spend lots of money you could get your outdrive ratio changed of course.
It would be prudent to check leg condition to ensure that your 280's are generally sound enough to take the extra grunt of diesels.
 
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