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Cracked YZ250 Cylinder

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I noticed coolant leaking from one of the cylinder studs of my '92 YZ250 and upon pulling the head off, and much to my dismay, I found a crack.

What recommendations are there? I cannot find any cylinders to replace this one. Thank you in advance for the help!

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You can try using some sealant on that bolt.  Many cars have engines where the head bolts go through the water jacket, and you just have to make sure you use some sealant on those bolts.

 

My biggest concern would be why it cracked there and what the overall condition of the jug is.  Probably worth it to replace with another one.

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MXRider72, would the cylinder you're referencing still be compatible despite the difference in design? Compare original 1992 YZ250: http://www.motosport.com/dirtbike/oem-parts/YAMAHA/1992/YZ250/CYLINDER-HEAD to 2011 YZ250: http://www.boats.net...HEAD/parts.html.

 

USED YZ426F, would utilizing Ultra Copper RTV be suitable? My thought with that idea is to fill the stud hole half-way with sealant and to coat the stud threads with sealant as well, then insert the stud and allow some excess silicone to bead around the edge of the stud and stud hole so that it will seal against the cylinder head when installed.
 

As for the cause of the crack, I attribute it to heat. The bike is a gift, and the PO had overheated the engine multiple times, partially melting the forward lip of the piston, and running without water in the radiators due to a leaking water pump seal. All of those issues have been addressed, with the exception of a hanging idle issue causing higher than normal temperatures. I was about to change the old carb intake boot and noticed the coolant leak. I think I was simply just the straw that broke the camel's back.

Edited by RussTheRush

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Do you have cap nuts on your head? I don't think it would matter if it's cracked or not as long as you have cap nuts and good copper washers it should not leak.

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As far as what cylinders interchange someone posted this link - http://www.oem-cycle.com/YAMAHAYZ250BIKEID.shtml

 

Lists 1992 YZ250 cylinder as: 4DA - FITS 92 YZ250, 92-93 WR250 - 4DA-11311-00-00

 

Doesn't mean other years wouldn't work but only that the cylinder PN is unique to 92 YZ and 92-93 WR...but looking at other parts on that site looks like there were lots of changes for the 1993 YZ250.

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As a matter of fact, the leak was coming out of the tip of the cap nut specific to that stud where the crack is located. I think what I'll try is the band-aid option first: Copper RTV Silicone sealant and new cap nuts. The copper washers are recent so I wont worry about those. Thank you very much everyone for the inputs!

As for the air leak, here is a reference URL to where I'm at with that gripe: http://www.thumpertalk.com/index.php?/topic/1064391-YZ250-Fuel-Knock?

Thanks again for the advice.

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Looks like that cylinder is sleeved, correct? The crack could even be from the sleeve being pressed in.

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As far as what cylinders interchange someone posted this link - http://www.oem-cycle.com/YAMAHAYZ250BIKEID.shtml

Lists 1992 YZ250 cylinder as:

4DA - FITS 92 YZ250, 92-93 WR250 - 4DA-11311-00-00

Doesn't mean other years wouldn't work but only that the cylinder PN is unique to 92 YZ and 92-93 WR...but looking at other parts on that site looks like there were lots of changes for the 1993 YZ250.

the cylinders are Indeed different, in several ways, including the whole powervalve setup/mechanism
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So, to give closure to this topic, I did the silicone sealant in the stud hole and put a slight bead around the stud once inserted. Once I installed the cylinder head, I put on all-new cap nuts with the result of no leaks before and after running the bike. Problem solved.

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