Thermostat Case O-Ring 91303-634-010


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dmoxley49
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Joined: Thu Oct 02, 2014 8:41 pm
Location: Bells, TN
Motorcycle: 1978 GL1000, 2014 Can Am Spyder, 2016 Slingshot

Thermostat Case O-Ring 91303-634-010

Post by dmoxley49 » Wed Feb 28, 2018 9:23 am



Perhaps somebody can help me out with this issue.

Recently I was working on a 1978 Gl1000 and during the project that refreshed the seals on the cooling system. I found that the O-Ring located in/on the thermostat case (91303-634-010) was missing, however, no coolant leak was seen there prior to the project. Since I was refreshing the seals, I bought an O-Ring and installed it. I thought it odd that there was no seat for the O-Ring. There is a collar located there, therefore the only place to install the O-Ring is around the collar. When installing the case, this point mates to a coolant passage in the motor case.

Everything went back together and ran fine (no leaks from that location), but a couple of days went by and a leak started. Tracing it back to the source, I found that the O-Ring had broken apart and chunks of it was coming out from around the collar location. I have no idea why the O-Ring was not there prior to the seal refresh project (I am not the first owner) or why the O-Ring failed. The nearest bolt to that point was torqued and or course the O-Ring was compressed, but not overly so based on what I saw. It may be that the source where I got the O-Ring had this part sitting around for a long time . . . it is just speculation on my part.

My question . . . has anybody replaced this O-Ring before? If so, what were your results? I am not sure why, with no seat at that point, a flat rubber gasket would not have been used, if one is needed at all given there was none there before.

Thanks in advance for any help provided. A part diagram is included to help identify the seal location I am referring to. It is item 15, and is located in the area behind the bolt location (the diagram is a little misleading)





kndw
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Re: Thermostat Case O-Ring 91303-634-010

Post by kndw » Fri Mar 02, 2018 10:13 am

The o-ring goes around the 12*10 collar, and there is a little room left open for it in the upper part, I believe. It definitely needs to be installed.

Sounds to me you had bad luck.

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dmoxley49
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Re: Thermostat Case O-Ring 91303-634-010

Post by dmoxley49 » Fri Mar 02, 2018 11:01 am

Thanks for the reply. I agree . . . bad luck and perhaps an old O-Ring. This time I will be obtaining one from the local dealer instead of online ordering. Other than draining the coolant, I am hoping for just a three bolt loosening/removal and getting enough room to insert the new part. I may end up removing the thermostat cover as well if all else fails. I am trying to get this done without removing the carb rack if possible. Here is where the good luck needs to happen.

I'll post the results, hopefully successful, when done.

Don

kndw
Posts: 90
Joined: Sat Jun 19, 2010 2:56 am
Location: Driebergen, Utrecht
Motorcycle: 1976 GL1000 Plempbak

Re: Thermostat Case O-Ring 91303-634-010

Post by kndw » Fri Mar 02, 2018 2:19 pm

Sounds tricky, you may need to loosen the bolt at the back too, to lift the center part of the external tubing...

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dmoxley49
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Re: Thermostat Case O-Ring 91303-634-010

Post by dmoxley49 » Fri Mar 02, 2018 10:23 pm

Thanks for the heads up. I agree with you.

The pain I may run into might be the motor shroud that straddles the thermostat case. Without moving that, there is only about 1/4 inch to play with.

The interesting thing I found while looking at cases being sold on ebay is, that on every one I looked at that had a gasket still installed, they were all flat O-Rings. The one I received when I ordered, was/is round. When I researched the part number online, I kept bumping into a round O-Ring. Something to talk over with the Honda dealer parts folks.

What I found through ebay is shown below. Perhaps I am seeing the solution others have found or the O-Ring I am getting is wrong. I'll know more when I go to Honda.



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dmoxley49
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Re: Thermostat Case O-Ring 91303-634-010

Post by dmoxley49 » Sun Mar 11, 2018 10:54 am

I thought I would update this thread to include what the status is, on the O-Ring mystery. So far it is still a mystery. What form an O-Ring will take if I buy/order one will take, is up in the air.

However, I believe I have found a solution. JB Weld makes a silicone gasket maker that is good up to 500 degrees and can stand up to chemicals (gas, coolant, oil). If it comes to that, I will lift the thermostat case up enough to clear out the remains of the current O-Ring from around the collar and fill the space left with the gasket maker. Once cured, it will form seal that can withstand the tightening/torque of the thermostat case bolts and will not break apart.

There is only one thing stopping me from doing this. The leak has stopped. I don't know how, so any theory is good for now. I am just chalking this up to FM (Friggin Magic). But that is okay . . . I now have a slight leak on the left side valve cover gasket. The cover bolts have worked themselves loose over time, so perhaps the little snugging up I did will cure that. If not, new gaskets (the current ones are over three years old).

Never a dull moment.

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redbug
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Re: Thermostat Case O-Ring 91303-634-010

Post by redbug » Sun Mar 11, 2018 12:42 pm

yes I see the problem. The o-ring fits in a counter sink around the tube. The old o-ring still might be in the groove. It will be smashed flat and hard as a rock, look up in there, might need a dental pick to get it out. be sure the mating surface is smooth and clean. OEM on the O-rings and thermostat. Oh you know those valve cover bolts bottom out, fresh gaskets and proper torque on every thing you do.
" Ridin on Tulsa Time "

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dmoxley49
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Re: Thermostat Case O-Ring 91303-634-010

Post by dmoxley49 » Sun Mar 11, 2018 2:14 pm

I think you are absolutely right. I do remember seeing a darker area around the collar but passed it off as a discoloration from the mating of the two parts (engine case to the thermostat case). Your description fits "hard as a rock". That makes perfect sense. No wonder I thought there was no gasket/O-Ring there before. Learned something new. If the leak starts up again, It appears I will have my work cut out for me.

Regarding the valve cover bolts, so far I have just snugged them up and keeping an eye on the leak area. If it starts up again, I am going down the new gasket set path.

Great info . . . thanks.



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