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Old 12-05-2018, 18:50   #1
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Replacing a sheave in a snatch block

Has anyone ever replaced the sheave in a snatch block before? I have these:
https://www.westmarine.com/buy/ronst...14?recordNum=1
and the sheave is cracked badly. I figured that if I could drill out the rivet and change the sheave, then replace the axle with a bolt or something. Doable?
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Old 12-05-2018, 19:02   #2
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Re: Replacing a sheave in a snatch block

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Originally Posted by Laskadog View Post
Has anyone ever replaced the sheave in a snatch block before? I have these:
https://www.westmarine.com/buy/ronst...14?recordNum=1
and the sheave is cracked badly. I figured that if I could drill out the rivet and change the sheave, then replace the axle with a bolt or something. Doable?
Hi, of course it is doable, been there done that! I used a stainless bolt with a small round head with a hex socket in it and a thin nylock nut. Has been good for years now.
Just be sure to use a bolt that has a smooth section, not one that is threaded all the way to the head.
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Old 12-05-2018, 19:08   #3
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Re: Replacing a sheave in a snatch block

Cool. Thanks for the quick reply! Did you do it on this model specifically? If so, where did you find the sheaves?

Thanks
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Old 12-05-2018, 19:20   #4
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Re: Replacing a sheave in a snatch block

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Originally Posted by Laskadog View Post
Cool. Thanks for the quick reply! Did you do it on this model specifically? If so, where did you find the sheaves?

Thanks
Not that block specifically, the sheave was purchased at the local chandlery.
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Old 13-05-2018, 03:47   #5
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Re: Replacing a sheave in a snatch block

I have done a number of Ronston blocks by drilling the rivetted heads off, replacing the sheaves and using a bolt. I machine the heads of the bolts down to about half thickness and the same with the nuts. I punch the nuts in three places to ensure they don't loosen. I'd rather repair the old stainless cheek plate blocks than replace them with the plastic rubbish they're manufacturing now. Have not had to machine up any sheaves yet but being a plastic this should be quiet easily done and would consider doing them in alloy if I had to.
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Old 13-05-2018, 08:54   #6
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Re: Replacing a sheave in a snatch block

How do stop the original rivet or bolt spinning as you drill it out? When answering please consider I am on a yacht not in a machine shop!
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Old 13-05-2018, 10:33   #7
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Re: Replacing a sheave in a snatch block

Done it. Use a dremel tool and cut off wheel, carelfully. You can get a shoulder bolt of the proper length which will have no threads, try www.mcmaster.com
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Old 14-05-2018, 04:31   #8
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Re: Replacing a sheave in a snatch block

Thanks for the replies! Unfortunately I can't tell without taking the block apart, but does anyone know what are the specs of the sheave inside this model of block? I need the blocks to sail, so I can't take them apart unless I have what it takes to rebuild them first. The next question would be if anyone knows a good place to buy the replacement sheaves?
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Old 14-05-2018, 07:59   #9
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Re: Replacing a sheave in a snatch block

Was told that it is a 64mm sheave with a 10mm inner bore.
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Old 14-05-2018, 10:01   #10
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Re: Replacing a sheave in a snatch block

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Originally Posted by Mark Thurlow View Post
How do stop the original rivet or bolt spinning as you drill it out? When answering please consider I am on a yacht not in a machine shop!
I don't recall it being a problem but may have carefully used a grinder rather than drilled the peened out section off. I vaguely recall removing most of the protrusion then punching the shaft through thereby shearing off the thin peened section remaining without damaging the two stainless cheek plates. It's a few years since I have had to repair one.
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