Yanmar 3YM30 - Speedseal

[Bob_Ranft]

Been having overheating problems on Yanmar 3YM30. Overall volume of water coming out of exhaust seems down, plus zero water coming out of exhaust at tick over speed.

Been through system three times or more, no air leaks, no sign of any problems.

Decided to change seawater pump drive belt with new spare, an operation that would be straight forward if one had six elbows in each arm.

Same result after changing drive belt (new impeller fitted earlier) but noticed when changing belt that it took a lot of effort to turn the water pump over by hand and with a spanner.

Then began to wonder if the Speedseal cover was squashing the impeller and causing the drive delt to slip. Replaced Speedseal with original cover, loads more water coming through now, plus what looks to be normal amount of water at tick over speed.

But not really happy with the Yanmar seawater pump drive belts. They appear to be well down in the pulleys, possible that they are running on the bottom of the pulleys instead of the sides, hence easy for them to slip. Next job is to find better belts. With a better belt, might be able to put the Speedseal cover back, more I think about this the more I think the problem is belt related.

Lots of folks have commented in the past about Yanmar pumps not priming at start up etc., wonder how much of this is actually belt related, as apposed to other possible faults in the system. Also not keen on applying excess tension on the seawater pump drive belt, as excess side loads on the pump bearings appears to kill them off.

Replaced the alternator belt with a Gates belt two plus years back as the original was (being kind) not very good. So off to Gates belt supplier tomorrow to hunt for a better belt.

Things you have to do.

Bob

 

[Kwik Decision]

Thank you for posting - we also have a 3YM30, which is sometimes difficult to prime. We have the standard cover and drive belt; I'd be interested to hear if a better quality belt, which sits properly in the pulleys, is beneficial.

 

[No Regrets]

I doubt very much your issue is with the 'make of drive belt' or seal. Any well adjusted belt would do the same job....

This isn't rocket science!

Overheating engines are usually caused by partial blockages in the raw water circuit, once the usual thermostat and pump problems have been investigated.

 

[vyv_cox]

Your pump should not be at all difficult to turn by hand, accepting that there is some friction generated by the vanes. Are the bearings failing? The pump on my 3GM30 has done 2500 hours on the standard belts and cover, no problems at all. Sounds like you should be looking elsewhere.

 

[Hadenough]

Have you got the correct profile belt? They are supposed to bear on the the sides of the vee no it the bottom.

 

[RichardS]

Your pump should not be at all difficult to turn by hand, accepting that there is some friction generated by the vanes. Are the bearings failing? The pump on my 3GM30 has done 2500 hours on the standard belts and cover, no problems at all. Sounds like you should be looking elsewhere.

+1

I have two 3YM30's and the water pumps are easy to turn over by hand. I have my drive belts adjusted very loosely to avoid bearing wear and have loads of water spraying out even at tickover. The belts don't need to be tight because there should be little resistance.

Richard

 

[Bob_Ranft]

Pump turns over with no resistance when impeller is out and drive belt is off. So presume bearings are OK. Only 80 hours on this engine.

Original belt and new spare are both Yanmar supply - Mitsubishi. There is a feeling the belts are running on the bottom not the sides of the pulleys, as mentioned in original post.

Maybe a few days before I can get my hands on a Gates belt to compare against original. Will post findings and Gates part number later.

Meantime thanks to all for help.

Bob

 

[Sneaky Pete]

I have my drive belts adjusted very loosely.

Richard

Can you quantify loosely.
Loosely to one person could mean tight or slack to another. Usually a belt is tensioned by how much it can be pushed down and up in the middle of its longest length.

 

[john_q]

Let us know how you get on with Gates as I contacted them recently for belts for a Yanmar 3GM30, I gave them the Yanmar part numbers, they said they did not recognise these, so I gave them some cross reference numbers and their reply was contact the USA office

 

[KAM]

I found the poor pumping problem on my 3ym30 was due to corrosion and wear on the cover plate which only seems to last a season. I now polish the face at the start of every season and it's been fine for the last 10 years.