Lower end cap... check valve??

Grumpy Bear

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Aug 23, 2014
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'74 Merc 500 Thunderbolt. I noticed this hole when I took off the lower end cap -- nothing in it and light and air blows right through. Then I see on some diagram that there is supposed to be a tiny check valve in there?? What is the purpose of that? Is there supposed to be a check valve in there? And how do you install it? Thanks!

lower cap.jpg
 

racerone

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Dec 28, 2013
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Serial # of your engine ?-----Are you 100% sure a check valve should be in that hole ?----Did you look to see if there is a passage way to a check valve that is in the block ?-----The check valve is shown at the top on some schematics.------Check valve needs to be there somewhere along the hose to put oil to the top.--Can be an inline check valve as well.
 
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Grumpy Bear

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Thanks for your response. Serial # starts with 407 ('74 500). Pretty sure that schematic shows this tiny check valve going in that little hole...and when I look up the part on eBay, it is indeed quite small. I know about the check valves on the cylinder housing, but this one is apparently different. I'm just wondering if this thing is really necessary on this model -- there wasn't one in there when I took the end cap off.
 

racerone

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On ---mercrui***parts.com---Did you read the note concerning ----USA / Australia / Canadian serial #'s
 

Grumpy Bear

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Well, son of a gun... looks like it doesn't apply to my particular motor. I didn't even notice the serial # range for this item in the parts schematic. Thank you for cluing me in! Just a question, though: the hole goes through the housing to the inside...won't that cause needed 2-cycle oil to exit the lower cap? Or is the hole covered up by the crankcase cover when it's installed?
 

racerone

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Sorry, but you need to take a close look at how all this works.--------It is not hard to figure out how oil from the bottom is pumped back to the top !!!!
 
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