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Old 14-04-2023, 16:09   #1
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What Coating on Yanmar Head Gasket?

Hi All,


So I'm replacing the head gasket on my Yanmar Diesel and the service manual from early 1980's says to coat both sides of the gasket with "Three Bond 50". The manual doesn't say what this coating is or what it's supposed to do. I contacted ThreeBond, but they couldn't tell me anything about formula "50" (they tell me their records don't go back that far). I have no idea what any such coating might attempt to accomplish in addition to a new gasket. Any ideas? Thanks in advance.
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Old 14-04-2023, 16:13   #2
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Re: What Coating on Yanmar Head Gasket?

Possibly A copper gasket sealant?
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Old 14-04-2023, 16:36   #3
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Re: What Coating on Yanmar Head Gasket?

Quote:
Originally Posted by AKA-None View Post
Possibly A copper gasket sealant?

Thanks for your quick input. The gasket doesn't appear to have copper in it. I don't know what it's made of (it consists of a few different layers), but it seems more like a soft lead or some such more than anything. I noticed that the gasket I removed, though it had less than an hour runtime on it, needed to be scraped away from the case mating surface (using plastic scraper and scotch-brite pad). Perhaps the coating is to allow an old gasket to be more easily removed (I'm hoping).
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Old 14-04-2023, 16:47   #4
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Re: What Coating on Yanmar Head Gasket?

Ideally loctite NS 5540 but it is expensive (IMO). High temperature / high pressure temperature curing sealant.

I (and others) have found Loctite 515 (& 518) suitable on old Yanmar head gaskets. It is only recommended up to 300F (150C) but I have never had a head gasket failure on old raw water Yanmars as they should run much cooler than a newer coolant cooled engine. It can even allow for a used head gasket to be reused if necessary.
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Old 14-04-2023, 16:56   #5
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Re: What Coating on Yanmar Head Gasket?

MLS gaskets don’t need to be coated. That was for the old fiberboard stuff
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Old 14-04-2023, 17:55   #6
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Re: What Coating on Yanmar Head Gasket?

Put it on clean and dry, as you pointed out the gasket has a tendency to adhere to the surface straight out of the wrapper. My service manual makes no mention of any sealant at all on the head gasket and the only time I’ve ever seen a GM gasket fail was after the owner used a sealant on his 3GM....10 minutes after its first start with a new gasket.
The introduction of “ monotorque” gaskets changed the game with head gasket sealants.
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Old 14-04-2023, 18:15   #7
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Re: What Coating on Yanmar Head Gasket?

Quote:
Originally Posted by skipperpete View Post
…the only time I’ve ever seen a GM gasket fail was after the owner used a sealant on his 3GM....10 minutes after its first start with a new gasket.
The introduction of “ monotorque” gaskets changed the game with head gasket sealants.
Thanks everyone! When I installed and used the last gasket “dry”, I didn’t encounter any trouble for the ~35 minutes the engine ran before opening things up again. I don’t recall seeing any updated part numbers for the gasket that might indicate a change (I’ll look again), but I don’t need to overthink this either. I’ll have a look at the Loctite products mentioned and make a decision based on skipperpete’s response and what I learn about the Loctite products.
Thanks again!
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Old 14-04-2023, 18:21   #8
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Re: What Coating on Yanmar Head Gasket?

Quote:
Originally Posted by svonadym View Post
Thanks everyone! When I installed and used the last gasket “dry”, I didn’t encounter any trouble for the ~35 minutes the engine ran before opening things up again. I don’t recall seeing any updated part numbers for the gasket that might indicate a change (I’ll look again), but I don’t need to overthink this either. I’ll have a look at the Loctite products mentioned and make a decision based on skipperpete’s response and what I learn about the Loctite products.
Thanks again!
Did a head gasket failure cause you to open the engine again?
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Old 14-04-2023, 19:04   #9
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Re: What Coating on Yanmar Head Gasket?

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Did a head gasket failure cause you to open the engine again?
No. I was tackling another issue when I first opened it up, but decided I should do some pre-service inspections before getting too deep. So in went a “sacrificial” head gasket for a bit and then its removal. I’ve never had an issue with head gaskets on this engine. I only ask the original question because the manual stipulates the use of “Three Bond 50” and I don’t know what that is or why it might be used.
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Old 14-04-2023, 19:48   #10
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Re: What Coating on Yanmar Head Gasket?

Some information about Three Bond 50 from the Yanmar YSM service manual and some information about the gaskets and necessary sealants from the Yanmar 3QM30 service manual.

These engines will be the same vintage as your engine but I dunno about the head gaskets available today, they might be made from more modern materials.

As posted above, I have not had a problem using Loctite 515 / 518.
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Old 14-04-2023, 20:07   #11
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Re: What Coating on Yanmar Head Gasket?

Quote:
Originally Posted by Wotname View Post
Some information about Three Bond 50 from the Yanmar YSM service manual and some information about the gaskets and necessary sealants.
As posted above, I have not had a problem using Loctite 515 / 518.
This is much appreciated. I can’t see it clearly on my phone, but hope to see it when I’m next at a real computer.
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Old 15-04-2023, 15:28   #12
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Re: What Coating on Yanmar Head Gasket?

Quote:
Originally Posted by SY Harmony View Post
MLS gaskets don’t need to be coated. That was for the old fiberboard stuff


Thanks for the update
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