Mariner Magnum 40 Powerhead

paul325i · 25 June 2008, 23:16

Quick question about my 96' Magnum 40.

It seems to have died a death internally, sounds like a push rod or something fairly large has broken inside. The engine is free for about 45 degrees of crank turn then solidly locked in both directions.

It was running fine and actually stalled itself to a dead stop.

Question is, is it worth taking the engine to bits to investigate or are you still able to purchase replacement complete power head blocks? A rather large piece of sheared machined alloy made it out of the bottom carb...

I don't really want to replace the whole thing as the rest of the outboard is in perfect condition.

thanks,
Paul

Downhilldai · 26 June 2008, 00:11

Sounds serious/terminal.

A rebuild or replacement powerhead is likely to cost a lot more than the value of the motor. As it's 12 years old now, you're probably better off getting a newer replacement motor (ex-RNLI Mariner 40 for example), or look out for a used motor with a knackered lower unit, which you can pinch the powerhead off/fit your lower unit to.

PS
No pushrods in 2-strokes - could be a con-rod, piston or crankshaft, none of which is good to break

paul325i · 26 June 2008, 22:32

Are new complete blocks still available for engines of this age or is it only a case of having it reconditioned?

It's currently fitted to a chinook 4m with console and power trim so if it has to be replaced i'd like to fit something that will almost bolt right on in place of it.

What are my best options for replacement as far as brand and 2/4 stroke go? And is 40hp as large as anybody would go on a 4m?

PS sorry i meant con rod!

Downhilldai · 27 June 2008, 01:34

I reckon a replacement powerhead would cost a lot of money - best to ask a Mariner dealer about that, but a s/h outboard 2-3 years old may not cost a lot more.
I'm not sure about the max power rating on a Chinook 4m, but Avon Searider 4m is rated to 50hp, so this may give you something to work from.
IIRC, your 'Magnum' is a 'heavy duty' version of the Yamaha based 2-cylinder Mariner 40, suited to workboats and commercial applications. There are loads of Yam/Mariner 40s around and you should be able to source a good used powerhead from one of these, if you fancy keeping the remains of your original motor. Bear in mind that the rest of it may be getting a bit long in the tooth now though.......

Markyboyo · 27 June 2008, 14:01

I'm pretty sure that a 1996 Magnum 40 is a 4 cylinder, not 2 like the yamaha based 40hp engines.

Downhilldai · 27 June 2008, 22:24

Yep, think you're right on that one Markyboyo - just checked a '95 Merc brochure and it shows an XR40 as a 4-cyl, based on the old Merc 50, so the '96 Mariner Magnum 40 is probably the same motor.
In that case, while there's loads of these around, they'll all be ancient

Nos4r2 · 27 June 2008, 22:49

Quote:

Originally Posted by Downhilldai

Yep, think you're right on that one Markyboyo - just checked a '95 Merc brochure and it shows an XR40 as a 4-cyl, based on the old Merc 50, so the '96 Mariner Magnum 40 is probably the same motor.
In that case, while there's loads of these around, they'll all be ancient

Yep-but there's loads around with good powerheads still and they can be had for £100 if you look.

Downhilldai · 27 June 2008, 22:59

Quote:

Originally Posted by Nos4r2

Yep-but there's loads around with good powerheads still and they can be had for £100 if you look.

Yep - may take a bit of searching out to find the right one, but if all the ancills on Paul's Magnum are ok, it could end up being a cheap fix

Nos4r2 · 28 June 2008, 00:04

Quote:

Originally Posted by Downhilldai

Yep - may take a bit of searching out to find the right one, but if all the ancills on Paul's Magnum are ok, it could end up being a cheap fix

Yes, very cheap-last good 4 cyl merc 50 powerhead I bought cost me more to ship than to buy.

From memory the powerhead/leg interface is identical on all of them from the very early 1970s red bands (earlier red bands had a different driveshaft) right up to the end of the production run. It's only the ignition system (and the places on the powerhead the ignition system bolted to-make sure you check that!) and carbs that were different.

(Note if you ever do it, for the gearbox to work properly you have to use the shift shaft from a powerhead with the same type of carbs as the ones you're using or you can't engage forward gear)

paul325i · 28 June 2008, 18:50

Thanks guys,

Yes it's 4 cylinder, twin carb.

I'll spend some time searching down the used power head route then, so basically any 50hp Mer/Mariner block from around the same period should be a near enough fit?

Would there be any implications to fitting a 50hp powerhead with the magnum's carbs?

Nos4r2 · 28 June 2008, 20:13

Quote:

Originally Posted by paul325i

Thanks guys,

Yes it's 4 cylinder, twin carb.

I'll spend some time searching down the used power head route then, so basically any 50hp Mer/Mariner block from around the same period should be a near enough fit?

Would there be any implications to fitting a 50hp powerhead with the magnum's carbs?

I'd just use the whole lot-50hp carbs as well. They were crankshaft rated so you'll only get a gain of around 4-5hp anyway.

paul325i · 30 June 2008, 18:12

Had a bit of a breakthrough with the engine. It seems it's sheared part of the reed casing which apparently is normally quite easy to weld up.....