Raw water belt on Yanmar 3YM30

[EmeraldCoastSailor]

Before my 500 nm Gulf crossing I thought it wise to have a "pro" help look over my engine and do maintenance including new belts. I just assumed he'd bring the right type for my engine. I never did like the excessive play in the water pump">raw water pump belt even though it was bolted in the maximum "out" position. But it worked fine (until it didn't) and I know you want minimal pressure on the pump pulley to preserve bearings. A little over two years later, upon start up water didn't flow so I immediately looked at engine and notice belt was slipping and not turning pump. One touch down on the belt got it to working but obviously a change was needed.

I got out my 7 year old original belt that I saved as spare and noticed it was 19" when the replacement was 20". My guy at Marine Maintenance (PCB FL) who knows Yanmars like the back of his hand said it was a mistake he'd seen people make before. I installed a new 19" and now have a snug arrangement. I just hope it isn't too snug for the bearings as the pump is bolted in maximum "in" position currently. I get a bit of deflection so I think I am good. Maybe the belt will stretch a bit? What I really think this engine needs is a 19.5" belt.

[bobnlesley]

Originally Posted by EmeraldCoastSailor

...What I really think this engine needs is a 19.5" belt.

Your problem's perhaps in using a belt from the local/general supply line which in the USA, is Imperially sized as opposed to Europe and Japan which is metric? The correct (metric) belt size for that motor is I believe an 8 x 500mm, that 500mm length equating to about 19.60", so very close to your 19.5".

[SV Bacchus]

BnL, that is excellent information! I never would have thought to check for metric sizes on belts. Duhhhhh, I will now.

[Captsteve53]

Actually most modern and certainly all Japanese engines come out with Metric sized belts and yes they dont meet the same fitment specs as the US sized A belts or B belts , although numerous A SECTION BELTS are fitted to metric pulleys,

Metric size belts are available in a huge length range which makes getting the correct fitment easy,

Dont worry to much about having bearing issues (that takes a fair amount of tension to do that, a nice tight belt is better than a loose one,

The general rule is that the belt when tight should only deflect down no more than 1/2" inch max with your firm thumb/finger pressure , to get that sort of tension the alternator usually needs to be prized out with a spanner or piece of short wood , (so fairly tight)- New belts especially will stretch with in a short time so they usually require a re tighten after a week or so, This is especially true of lower quality belts- never scrimp when buying a belt,


Cheers Steve

[basssears]

Originally Posted by bobnlesley

Your problem's perhaps in using a belt from the local/general supply line which in the USA, is Imperially sized as opposed to Europe and Japan which is metric? The correct (metric) belt size for that motor is I believe an 8 x 500mm, that 500mm length equating to about 19.60", so very close to your 19.5".

Thanks Bob, I'll go SV Bacchus one better, I didn't even realize there were metric belts out there (I know I know, I'm a US-centric-uneducated-wanna-be-mechanic). I have very little adjustment on my alternator (Universal/Westerbeke M40) and am sitting between sizes on US belts (45.58" works but leaves no room for outward adjustment and I really think should be a tad tighter, 45.08" is too short to mount), I'm going to try a 1150mm that might just do the trick!

-- Bass

[01kiwijohn]

Uh oh! On those little pumps, run the belt a little looser than you'd expect. I have replaced a number of them where the bearings wore out quickly, destroying the seal retainer, the cover plate and the housing.

[macman4190]

Originally Posted by SV Bacchus

BnL, that is excellent information! I never would have thought to check for metric sizes on belts. Duhhhhh, I will now.

Yanmar3YM30 has two different belt sizes, depending on serial number.