Timing belt?

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Mike k

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Thinking about replacing the timing (cam) belt as I once had a LWB landrover that split the belt and the cost was mega. It seems they are a crucial part of the whole engine mechanism which seems odd that such a cheap plastic belt can be so costly if it fails.

I checked all my maintenence manuals and nothing is jumping out to say replace at xx interval etc.No mention at all.

Been onto Keypart and apparently a belt is not a listed replacement part suggesting it doesn't have one.

Its a Mercruiser 4.2 D tronic 260hp diesel- does anybody know if it should have one and I have missed something ???

Cheers

Mike
 
cant comment on your engine but if it has one and its not been changed always better to change for piece of mind

we have a vw van that has snapped the cambelt in the garage at the moment it has bent all the vales and snapped a cam and damaged the head just goes to show how expensive it can be if it snaps
 
I have no idea on a boat engine but I'm a car tech myself.. It may not be listed as it could be a timing chain?
 
Mike k said:
Thinking about replacing the timing (cam) belt as I once had a LWB landrover that split the belt and the cost was mega. It seems they are a crucial part of the whole engine mechanism which seems odd that such a cheap plastic belt can be so costly if it fails.

I checked all my maintenence manuals and nothing is jumping out to say replace at xx interval etc.No mention at all.

Been onto Keypart and apparently a belt is not a listed replacement part suggesting it doesn't have one.

Its a Mercruiser 4.2 D tronic 260hp diesel- does anybody know if it should have one and I have missed something ???

Cheers

Mike
Click to expand...

Hi Mike,

no flimsy belt
no fiddly chain
2 inch thick crank shaft drives gears.

on the end of the crank under the raw water pump is your viscous damper which must be kept in balance.
I didnt bore you with the detail at the time but thats why I encouraged you to clean the rust off a couple of months ago.


your good to go mike :)
 
DAKA said:
Hi Mike,

no flimsy belt
no fiddly chain
2 inch thick crank shaft drives gears.

on the end of the crank under the raw water pump is your viscous damper which must be kept in balance.
I didnt bore you with the detail at the time but thats why I encouraged you to clean the rust off a couple of months ago.


your good to go mike :)
Click to expand...

Cheers Pete

good news - nah great news!! and I have sprayed the damper with that anti rusting spray you use for over wintering the engine.

As usual thanks for all replies

Mike
 
Low reving engines where weight of the unit is not really going to effect the end products performance ,like a diesel in a boat.( fuel/ water and cruising gear ,fouling and people are all variables )
Tend to use heavey gears to transfer drive up to the top of the engine, from the the crank to the camshaft (s)
Inertia is not an issue as they are revved up slowly and then held at a constant RPM
Contrast this with a high performance sports car , say a two seater,
Here any weight saving particular if it's mid engined is critical .
Now think of the rev range Ferraris V8, s redline @ 9000 rpm + and are ultra responsive - low inertia all the moving components are made of light weight materials , hollow valves , short Stroke titanium pistons and a cambelt to transfer the drive upto the camshafts .
These are time lifed to 3 years in the service schedule .
So I would have thought " boat diesels" designed from strach or adapted from HGV will have cam gears .Rev - up inertia is not an issue.
A cambelted boat diesel is a poor adaptation of poss an attempt to create some sort of high speed road diesel engine
In-between alternatively , cam chains can be used , it's the tensioner that goes here , all Porsches have chains a happy compromise -with inertia/ reliability
But not quite as revy as belted Ferrari.
 
Sensibly diesel engines fit into three categories.

LDA Light Duty Automotive (Cars Vans)
MD Mid Range Light/heavy trucks
HD Heavy Duty.

LDA motors tend to feature chain or belt to camshaft drive.
MD and HD motors straight cut or helical gear driven cams.

Comparing diesel engine design with gasoline engines forget it........Gasoline is for girls.

On LDA engines belts today should not be derided, Mercedes Srinters and Transit Duratorque engines are dogged with chain failures.

One HD engine exeption Gardner undoubted durability but timing chain a real nausiea, remember being shown how to do it when I was about 12. Later in life I was involved in testing a Cummins 855 with chain instead of gear driven cam to measure difference in parasitics.

Move to multi valve engines and overhead camshafts, Cat 3406 E onwards, Cummins ISX, Detroit S60, Volvo D12 etc etc. Driving cam in head with gears is a pain, getting a gear train to be able to drive a cam AND allow for head/block re-surfacing tolerance AND at the same time being reasonably quiet results in some complex solutions. All these forgoing heavy duty engines CAN be repaired if head gasket fails and torches the block. IVECO OHC cam Cursor motors they flunked out and have no rebuild tolerance with their engines if they need pulling down, it is a new block.

Volvo D4/6 was designed by clever guys at Deutz, darn good base motor but the only way of driving OHC and meeting noise parameters set down by Volvo was to go with a chain. In terms of durability in commercial applicaions this has to be the engines fuse. And as I remember Volvo insisted on their corporate standard of copper injector sleeves, real stone age thinking but that is another story.
 
As LS states, belts are OK, but need maintenance. On my Isuzu based Merc diesels, the belts need changing at 5 years. I've got this to look fwd to this winter on Raf's engines.

Belts can degrade more rapidly if you get water (condensation) in the belt cover. This can degrade the glue that is used to adhere the various elements of the belt during manufacture, causing premature failure. Should not be a problem in a boat, unless the bilge is so full that water can be drawn-in through the front cover or crank seal.

When I was at Land Rover, we had to pressurise the front cover on the Gemini 2/3, taking a positive feed from the turbo, so that when the vehicle was wading, and the engine drenched, the effect of the sudden cooling did not cause a drop in pressure in the front cover, sucking in water through the crank seal. The positive pressure cured this issue.

As LS states, most modern light duty diesels, based on Eu 4 and beyond, with 4 valves per cyl and very high pressure common rail injectors have chain driven cams.
 
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