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Top End Rebuild - Coolant Leak


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I was just completing my first top end rebuild ('05 525 MXC) and filling up fluids when I noticed a leak at the head gasket (front and right side).  I figured there was no reason to continue and fill up the oil, so I haven't done that.

 

I was using the top end gasket kit from Moose Racing.  I couldn't find a distinguishable side on the head gasket to indicate up or down.

 

Obviously I've got to break the engine down again. (Bummer)

 

Question/Help: How do I stop it from happening again? 

 

I don't want to repeat the mistake.  It's too much work.

 

Any advice would be appreciated.  Thanks!

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Make sure there is no old gasket material left, and DO NOT clean it off with a rotary tool like a dremmel or brush on a drill. Instead use gasket remover and a scraper, or sandpaper on a sheet of glass, etc.. Get a strait edge and make sure the top of the cylinder and bottom of the head are perfectly flat. Should be some videos on you tube showing how to measure it up. Clean the threads on the head bolts with a tap and die and lubricate them, then use a good torque wrench to install them following the pattern in the manual. Use a radiator pressure tester before filling with coolant if you want to check first.

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Thanks.  Yeah, I sent the valves and the cylinder to the machine shop and had that part of the top end done.  the surfaces where definitely clean.  I used a normal torq wrench on the four main bolts (50nm).  I couldn't fit the torq wrench in the tight spots for the three bolts that connect the cylinder to the head.  I ended up using a torq wrench I had for my spokes and it seemed to work fine.

 

I'm mostly wondering if I there was any secret step I may have left out.  I put the head gasket on dry.  I wasn't suppose to add three bond or anything was I?

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The gasket manufacturer instructions will tell you if you need any added stuff on it. If you got OEM gaskets then follow the KTM manual. In my experience most go on dry.

If it was leaking when you're just pouring in coolant then something was really wrong. Maybe the head wasn't seated all the way or something. Make sure it seats flat before you put any bolts in. Get a proper torque wrench on all the bolts. You might need to get an adapter or two, but make it happen. The torque wrench manual will tell you how to adjust the torque values for any extensions that add length to the wrench, such as crows feet, etc..

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I appreciate the response.  Yeah, felt like something was wrong alright.  If I can spring for the KTM cam chain riveting tool, I certainly can fork out the money for a torq wrench that will fit.  Live and learn.

 

It must have just not been seated correctly.  It's my first time, so I guess I chock this up to experience and hope to do it right the next time...

 

Thanks again.

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All good decisions come from experience, and all experience comes from bad decisions. 😉  The first time I learned the importance of a good torque wrench I was in middle school and my buddies 1984 YZ 80 needed a new top end.  We did the work ourselves and didn't torque the head down enough and it blew all the coolant out on the way down the driveway.  I think it quit before he even got it into top gear.  Just that quick it overheated and damaged the piston and cylinder and had zero compression.  So we got to repeat the entire rebuild.  But we gained "experience", and nailed it on the second attempt!  :banghead:

 

The most important thing is to try to figure out what went wrong the first time, and I bet you'll never make the same mistake again.   

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I had an additional observation.  The two different dowels that are between the cylinder and the head don't come out.  They are completely fixed in place.  One is on the head and the other is on the cylinder.  It was that way when I tore the engine apart the first time.  I didn't do anything with them, just left them in place.

 

Is that normal?  If not, how do I remove them?  They are really stuck in place and I don't want to damage them or the respective head and cylinder.

 

I tore the engine down again last night.  I couldn't see anything out of the ordinary.  I was kind of hoping I would find something obvious that would have contributed to the issue.  Now I'm left with guessing.  I don't want to just repeat the steps and hope for a different result.

 

The dowels are the only piece that stands out to me.  It makes it harder to clean the surface around them.

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So, I have worked on that particular engine, but those dowels should come out... And they need to come out to properly prepare the head and cylinder mating surfaces ("decking")

You said you knew the surfaces were clean because you sent the head to the shop... Was the surface milled or checked for warpage? Anytime I pull a head, I clean the mating surfaces with 400 grit wet on a surface plate. This cleans any residue and will show any areas that are perfectly flat. Most of the time, any minor warpage can be sanded out with 10-15 minutes on the plate

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