Small Marine Diesel Belt Alignment

[Mike Banks]

You need to take off the belt and use a set square against one of the pulleys, set the square under the oulley and touching the side. If the pulleys are the same size, it should align perfectly with the other pulley.


If the pulleys are of different sizes, you need to put a string over the centre groove of each pulley and pull it tight. A large rubber band also works fine. Now take the set square and put the base on one of the pulleys. The string or rubber band should line up perfectly with the side of the square.

Adjust the pulleys until they do--and you should be in business.

[dfelsent]

Originally Posted by Cheechako

Try Gates Green Stripe belts. Alignment is hard to check for sure. Also, watch out for proper belt size, thickness , angle etc.
I had one Yanmar I never could get right no matter what I did.

I heartily second Gates green stripe belts. In my applications they have lasted and lasted. Including alternators on the hairy edge of the belt capacity.

I also have been careful about alignment and tension. I use a turnbuckle to hold alternator tension. Easy to over do it though but easy to set it up right.

[belizesailor]

So...I cleaned up the pulleys on both engines and that helped a lot. Port engine is doing fine now. Stb engine is maintaining good tension, but still has a bad chatter. I think its the alternator bearing. Alternator turns easy and smooth by hand, but once loaded starts to chatter.

Im going to rebuild the stb alternator (its original 20 years old anyway) and see if new bearings improve the situation. If not, maybe its the water pump. The chatter is variable and intermittent so hard to isolate for sure.

The only other option is the main shaft...hopefully its not that.

[slug]

Originally Posted by belizesailor

My twin Volvo MD2020s are chewing thru belts at an impractical rate (like requiring adjustment every 3 hours of run time). I suspect belt alignment issues. I recenty resolved an automobile belt alignment issue by pressing the power steering pump pulley further on to the shaft...a common problem/solution in automotive environments. However, Ive never made such an adjustment on a small marine diesel. The means of doing so are not obvious, are there any?

Hard to say don’t know your engine

Normally the only adjustment are shims on the bottom. ...alternator axle
To move forward and aft

[GordMay]

Originally Posted by Niall leslie

If ( lack of ) pulley alignment proves to be an issue then another useful method of checking is to remove the belt(s) then place a straight tube or rod of suitable diameter and length into one set of pulley grooves and, holding the rod or tube firmly against one pulley, see how it "sits into" the other pulleys. This method automatically compensates for differing 'belt centre line to edge of pulley' dimensions and is very accurate.
Sometimes a long 3/8" ratchet set extension may be used very easily.

Many ordinary belts are running at close to or above their design capability in marine applications these days therefore the little extra money for high quality Gates or similar belts is usually very well worth it.

Best regards,

Niall.

EXCELLENT advice, Nial.
Welcome aboard the CF.

[jimbunyard]

Originally Posted by belizesailor

So...I cleaned up the pulleys on both engines and that helped a lot. Port engine is doing fine now. Stb engine is maintaining good tension, but still has a bad chatter. I think its the alternator bearing. Alternator turns easy and smooth by hand, but once loaded starts to chatter.

Im going to rebuild the stb alternator (its original 20 years old anyway) and see if new bearings improve the situation. If not, maybe its the water pump. The chatter is variable and intermittent so hard to isolate for sure.

The only other option is the main shaft...hopefully its not that.

The old 'long screwdriver to the ear' trick is a good way to isolate brg noises in alternators or waterpumps...

[belizesailor]

Originally Posted by jimbunyard

The old 'long screwdriver to the ear' trick is a good way to isolate brg noises in alternators or waterpumps...

Yeah, Ive done the "long hose in the ear" trick and Im still not sure, but I figure a pre-emptive rebuild on a 20 y.o. alternator is not a bad idea anyway and it eliminates one possibility.

[belizesailor]

Pulled the alternator and tore it down. Rear bearing is fine, but the cover/shim/retainer it sits in is shot...crumbled in my hands. The bearing is probably fine because its just been slipping in this worn out retainer and not wearing! Seems like a bad design (plastic retainer). The front bearing rotates smoothly, but there is a lot of lateral play in the shaft.

Meeting mechanic this afternoon to pull and press in new front bearing.

Port engine will likely be due for same very soon...one of the joys of catamaran ownership...whatever happens on one side will soon happen on the other!