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Discussion Starter · #1 ·
I have a 2004 Suzuki ltz 400. It had been upgraded to a 440 big bore by the previous owner. I just rebuilt the engine. I put a hot rods bottom end kit in it and Vertex big bore piston in it. I replaced one valve that was questionable and put all new valve seals in it. I replaced all bearings and seals/gaskets. I rebuilt the carb and rejetted it.

I originally started it up and had issues getting it above half idle without popping and backfiring. With help from this forum I eventually figured out that the cdi box was bad. I replaced that and was finally ready to test ride it. I noticed before taking it out that the oil was extremely low. I thought this was odd since I hadn't even ridden it yet. It had taken me a few weeks to figure out the cdi issue so I just thought that maybe I forgot to fill the oil up all the way or something. When I took the bike out for a ride it made a loud pop sound and started smoking and puking oil into the airbox. A lot of oil!.

During tear down I dropped the oil and it was full of Coolant. When I pulled the head I found a head bolt that had bad threads and looked liked it might have lifted a little. The gasket between the cylinder and block was clearly leaking oil at the corner where that bolt was located. I thoroughly inspected everything else and found no issues. The bottom end still looks great as well as the piston and rings. I inspected the head and found no issues but I did not have it pressure tested.

I got new gaskets and reassembled everything. It started up and ran great. I ran around the block a few times and it had awesome power. The next day I went to take it out again and noticed it was low on oil again. I added more oil and went for a ride. I got about 100 feet away and it started smoking and puking oil from the air box again. This is identical to what happened the first time.

Any ideas on what's causing this? The only thing I can figure is that maybe the head is cracked. I'm becoming a bit frustrated with this project. Any help would be greatly appreciated. Thanks
 

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The oil may be draining from the tank into the case when it sits for awhile. This is nothing to be alarmed about. You have to get it warm, shut it off and check the oil level within a minute or so to get an accurate oil level, since it’s a dry sump system. You may be over-filling it.
The head studs are only good for 1 rebuild and should be replaced after that as they tend to stretch. It’s also important to note that the threads should be soaked in oil before torquing the head on. This changes the torque and may result in a blown head gasket if installed dry. I retorque them after a couple of heat cycles once they cool off. You can reuse the base gasket, but never reuse a head gasket.
 

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By the way, there have been a few instances of cylinder decks not being flat right out of the box. If I remember right, they were a certain batch of Cylinder Works kits bought off EBay. I imagine there were very few of them, but it’s possible they are still out there. If it keeps blowing head gaskets, you might want to get it checked at a machine shop.
 

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Check that the head is flat as well..
 

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Discussion Starter · #5 ·
Thanks everyone for your help. I was definitely overfilling the oil. I think the head studs failed the first time letting Coolant into the oil. I replaced with new ones. No Coolant in the oil this go round. I drained the oil refilled to spec and everything is perfect. Seems like a poor design having to warm the engine up to get an accurate oil level but oh well. Now I know. Thanks a lot.
 

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Yeah, it’s a dry-sump thing. It works well, but sometimes leaks back into the case if it sits. Jet engines do the same once in awhile. Check valve just doesn’t seat perfectly sometimes. No failed parts, just fire it up and it’s fine for another year. 😂
 
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