Topic: Distorted/leaking thermostat covers – Antique Outboard Motor Club,Inc

This topic has 14 replies, 9 voices, and was last updated 9 years, 6 months ago by chinewalker.

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May 11, 2015 at 10:12 pm #1464
johnyrude200
Participant
I have been running into a lot of these situations, but of course don’t find out until after I’ve replaced the thermostat and gasket, only to see water start gushing out of the 0.5mm gap.

Any recommendations/tips to help reuse the same cover. I have been seeing many of them distorted and try sanding/lapping them down, but that doesn’t seem to work very well.
May 11, 2015 at 10:26 pm #15731
chinewalker
Participant
US Member
Double up the gaskets?
May 11, 2015 at 10:39 pm #15732
chris-p
Participant
Any particular motor? Are you using gasket sealing compound? As stated, worst case, double em up.
May 11, 2015 at 10:56 pm #15733
legendre
Participant
quote johnyrude200:

I have been seeing many of them distorted and try sanding/lapping them down, but that doesn’t seem to work very well.

Are these housings steel stampings or aluminum / zinc castings? Warped steel can be a headache, trying to re-form a precision surface.

But if they’re cast, then you must have some flaw in your lapping process. Either you’re not going far enough, and they still have excessive warping – or a flaw in your tools / technique isn’t producing the desired flat and uniform surface.

As you’re lapping, do you follow your progress, checking with feeler gauges?
May 12, 2015 at 12:00 am #15745
Mumbles
Participant
This problem is common with the three bolt cast aluminum housings. Since they can’t be lapped or machined because of a protrusion on them, I have resorted to mounting them in the press and VERY LIGHTLY apply some pressure to coax them back to their original shape. Being cast, they will break in a heart beat so light pressure is the key here.
May 12, 2015 at 12:14 am #15749
johnyrude200
Participant
Thanks Mumbles, they seem to be common on the 6, 10, and 18-20-25 thermostat covers. They distort at the ‘thin’ side (starboard side), and those 3 screws really don’t do that great of a job of tightening the cover down.

Legendre – I am using a straight edge and holding it across the surface of the cover to see where the warp is. Just one of those deals that when you disturb something that has been set for 40 years, you trigger 3 other issues in the process. Better me I guess than the next guy.
May 12, 2015 at 12:28 am #15750
legendre
Participant
quote Mumbles:

This problem is common with the three bolt cast aluminum housings. Since they can’t be lapped or machined because of a protrusion on them (…)

You can’t even mill them true? How was it done at the factory?

Could someone please provide a photo or drawing of this part, I’m curious what feature prevents a straightforward lapping..?
May 12, 2015 at 12:40 am #15753
Mumbles
Participant
May 12, 2015 at 12:20 pm #15782
david-bartlett
Participant
I have seen this where people store their motor lying down in freezing temps. A bit of left over water can freeze and cause the cover to deform. Another good reason not to lie the motors down during unheated storage.
May 12, 2015 at 12:52 pm #15785
dan-in-tn
Participant
US Member
The way I remember this working is the part sticking out of the casting holds the thermostat down in place. The OEM gasket is already very thick. Doubling the gasket makes the thermostat loose and leaky. Now if you are removing the thermostat then it doesn’t matter, but that is another discussion. Removing material around the outside surface only will make the casting dig into the thermostat and warp it at the screws. Just something else to think about when you are dealing with this irritating part.

Dan in TN
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