belts and stretch

[Mark Nooney]

HI all
I replaced my belts on a yanmar 2GMF.
After about 15 hours the over heat alarm sounded.
I checked the path and found the belt had some play.
I figured that I had not torqued the set nut enough.
Reset the raw water pump and off we went.

fast forward 15 hours the overheat alarm sounds and the
I check the belt and it has play in it.

Do belts stretch that much in 15 hours?
Or is there a setting for torque that I am missing on the set nut?
Your input will be great.

Mark
Dream Too

 

[Allan Frey]

Two possibilities:
New belts normally stretch. You should always retighten to specified belt tension after 15 minutes of running. You might also need to do so again after several more hours. Also, you may have persisting problems if you do not have a hi quality belt like a Gates.

Second, the adjusting bolt can slip on its bar even if tight. Put a star washer between the bar and nut; this will dig in and prevent slip.

allan

 

[Ralph Johnstone]

Good Quality New Belts ..........................

Do belts stretch that much in 15 hours?

....................... such as Gates and Goodyear do not stretch. That's why you pay extra for them as opposed to the cheap offshore crap.

However, from what you are describing, I would suspect something is not holding on your water pump to allow that much slack to appear in 15 hours ......... twice . Either that or you've got your hands on the world's cheapest v-belts.

If it is the belt that's stretching, do yourself a favour and buy industrial name brand V-belts as opposed to Yanmar belts. You'll pay less than half the price and you'll know you have quality material.

 

[RichH]

Gates top quality ('top cog') are probably the best remedy vs. 'stretch'.

Another possibility, a specific recurring / common problem with most Yanmar engines, is rust pitting & developed roughness on the belt sheave 'faces' - especially the 'pressed steel' sheaves that drive the engine FWC pump.
Two solutions and One remedy:
1. remove the sheave(s) and 'reface' them ... best done in a machine shop (but dont get carried away with the amount of vee-groove face removal as the belt can/will then ride too deep in the sheave). If youre 'handy', the V-groove faces 'can' be 'rotary sanded' back to 'flat'.
2. replace the sheaves ... sometimes even the sheave on the crankshaft 'nose'.

Remedy: When long term storing the boat (more than several weeks) always spray the sheaves with a 'rust preventative' such as "Boeshield T9®"

This is a VERY common problem with Yanmar sheaves.

 

[Benny17441]

Recheck the belt size. Besides length, check width and depth of the wedge. Manufacturers try to make a single belt fit as many applications as possible but sometimes they overstrech their recommendations.

 

[Mike Culik]

Mark, my new Yanmar belt is doing exactly the same thing

 

[mr c]

I second richH. Same thing happened to me. I thought the belt was stretching. It turned out it was the beginning of the season so I thought I would start fresh with new belts. Over heat alarm went off checked belts they were loose. Tightened and little while later same thing. By then belt was already too big. Read some posts on this forum and someone said rust in the groove of the pulley. Sand with scotch brite and my problem has gone away. I repeat this at the start of every season.

 

[Mark Nooney]

Quick update for all - I overheated again this past weekend. I dove the boat to clear the thru hull if there was an obstruction. Changed the impeller - finally got friend to tow us in.
I am now changing the thermostat. I feel that is better to do then tear apart the heat exchanger. I'll let you know how that works out.

 

[mr c]

Checking the heat exchanger is not as hard as u think. Drain the coolant a little and take the 4 bolts off the front of the heat exchanger. Most of it is visual. Mine engine was only overheating at full throttle. Several of the tubes in the heat exchanger were clogged. But, for the most part it was my exhaust elbow.

 

[Mark Nooney]

Is the exchanger easy to pull out? From the drawings it should slide right out.

 

[mr c]

Mine does not slide out. Stuck? I was still able to remove the blockage with long pipe cleaners. I replaced the gaskets on both sides and refilled.

 

[kloudie1]

The tube bundle should slide right out with a little "persuasion".. Mark everything carefully and get new gaskets.. for both ends.. Pull both caps after draining the coolant.. if it is stuck, bump with a wood block or a soft faced mallet.. A brass pistol cleaning brush of about 38 caliber works really great for brushing out the tubes ..

 

[Mark Nooney]

Hi all,
Well I open the heat exchanger with little issue - the tubes were all clear - but I ran a clearing rod down them anyway. A .22 cal is the size for mine. Then, I changed
the thermostat. Found the thermostat that was in the engine didn't match the one
from the service manual. So I installed the new and buttoned it all back up and got the heat sensor gun out.

I ran the motor no load for 50 minutes through most of the RPM ranges.
I followed the temps from the switch to the pump out put to the heat exchanger input and
to the output of the heat exchanger. The temp never exceeded 183F.
It was interesting to see how the temps change as the thermostat opens and the flow returns from the heat exchanger. There was a good 50F drop coming from the output.

So in conclusion I think the both loops are performing as expected.
Bottom line I feel it was a thermostat issue.
Thanks for all the input

 

[mark porter]

Good final report, closing the loop. Thanks

 

[Mark Nooney]

Lessons Learned

OK here is the scoop - the thermostat change did not give me the desired
results. As we over heated again after 30 minutes.
So it was back to the drawing board.

I connected a hose to the push side of the raw water pump and ran the
engine for 1 minute. I measured less than a gallon of water. I should of
had 4 gallons/min at 1000 rpm.

Open the raw water filter and nothing was coming from the through hull hose. So took off the hose to the through hull and got a dribble of water.

Now to the wire coat hanger - ran that down and got a 4" spout of water.
After I got the little pieces of wood cleared I connected the through hull
hose, I performed the same test - 4 gallons / min as expected!

Lesson learned - KISS - look at the most obvious first before messing with the rest of the system.

The value in all this is that I completely know the cooling system for fresh and raw water.

Thanks for all the input.
MN