| Author | Message | ||
     Reepicheep |
I cracked the mounts on my rear head doing a stoppie into a Corolla, and a kind Badwebber helped me out by making me a good deal on a lightly damaged used rear head. The head has some light gouging on the mating surface (head gasket side, not rocker box side). The worst of the gouges is, unfortunately, right where the steel ring part of the head gasket resides. It is NOT the full width of the gasket, much less than that. But it probably will span the whole steel ring bit. I'm starting to clean up the head now (23k miles on it) to install. I'm doing my normal 800 then 1200 grit paper on the table saw machined deck (the flatest thing I can find in my house, flatter than glass even). It does a great job of taking old gasket gunk and raised aluminum spots off cleanly, leaving a nice flat surface. At least that's been my experience in the past (KLR head). Feel free to tell me if this is a mistake. I'm guessing that with 800 and 1200 grit paper, unless I spent a solid month doing little figure 8's, Ill never remove enough material to be significant. So the next question is how sensitive are these heads to leaks? Were it a water cooled bike, I'd be really worried. But it's not. The gouge spans the steel ring, but most of the fiber part of the head gasket sealing surface is just fine. I'm assuming the steel ring is a mechanical / temperature / erosion control element... and that the entire head gasket is what actually forms the seal. And I'm guessing that long before the whole fiber gasket can be eroded through a very small valley in that gouge... it'll just carbon up and create it's own barrier anyway. If it even manages to get through the copper head gasket spray in the first place... So the current plan is to "deck" that head with the 800 then 1200 grit paper until it's all clean, then hit the new head gasket with a fairly generous layer of copper head gasket spray, and put it back together and see how she holds. For some important context... this is a Uly that was already totaled out and paid for by the insurance company, so it has a salvage title and 20k+ miles. It is also a VIN that is squarely in the middle of a nasty little cluster of crank failures, so there is arguably a 10% or so chance that the motor will be toast before it hits 50k miles anyway. So this isn't the bike to be hyper conservative with (all new valves front and back, nothing but premium perfect parts, etc). I'll do that when I replace the crank (if and when it goes... and if and when I bother to reuse this same motor... as opposed to just getting a different salvage one). If this head doesn't work, and I have to rotate the motor down again anyway, I'm just out two gaskets, a cheap head, and a couple hours work. No weeping or whining on my part, I'm happy to take that gamble in this situation. So, my first question is if anyone has any other ideas about if it will work, or any other tricks I could use. My second question, is that I notice as I do my "table saw head decking" job, is that the squish plate seems to be ever so slightly recessed relative to the cylinder mating surface. I can tell, because that carbon has not come off yet, while everything else has been nicely polished. Is this recess important to maintain a squish band? Or did it just end up like this from the factory, and it's the head gasket that really creates the squish? Given I am reducing the depth of my gouges as I polish my way down, and cleaning up the carbon nicely, I'd like to patiently keep working at it until the whole surface is nice and smooth and carbon free... its not much further. But not if that will mess up my squish band in some significant way. Thanks for any help from people that understand all the voodoo of how that head really works, and how the squish band is actually created. And from people that have had success (or interesting failures) using less than perfect heads. | ||
| Buelliedan |
I would strongly recommend you pull both heads off and send them to a reputable head porting shop to have them deck them properly. You are just asking for head gasket leaks with what you are thinking of doing. This is what I do for a living so I really do know what I am talking about. | ||
| Reepicheep |
 Thanks Dan. | ||
| Reepicheep |
OK, just an update... Buelliedan has forgotten more than I will ever know about heads. And the wise course of action here is to take his advice. It would be irresponsible for him to say anything else, and thanks for your help Dan. I'm going to ignore his wise council... but not because I think he is wrong. I suspect he is right. I'm going to do it because my curiousity is greater than my fear of buying a new base and head gasket and tearing the bike down again.  I sit here with a 2007 Uly that has 23k miles and has been totaled out and paid for by an insurance company. I have inspected it pretty carefully, but the cracked head was a surprise, and there may be other surprises lurking. Plus, I am *right* in the middle of a pretty nasty cluster of VIN's with bad cranks. So there is a non trivial chance this motor will need a full rebuild before 50k anyway. Plus, (God bless BadWeb) somebody gave me a very fair deal on a head with almost the exact same miles as is on my bike (and the front head). They are "worn out" the same amount. The rub, as mentioned, is that the head has some nicks on the mating surface. I'll post pictures later. On one hand, my experience with a water cooled KLR-250 shows that head mating surfaces are stupidly sensitive. So I think Dan is right. But where the nick is, and with copper gasket spray, I can't stop wondering if it would hold on an air cooled motor or not. Would it fail? How would it fail? What would it look like after it failed? At this point, my desire to satisfy my curiosity is greater than my fear of spending 3 hours and $40 in gaskets. Even if it goes wrong, I kinda want to know! Helping me decide is the fact that both heads are in the same shape. So if I re-do one head, I should re-do both heads. Which is fine... Dan or Wes would do great things for me. So I think I'm gonna slap the thing together as is, and see how it holds, and post it as a data point. When it leaks (as it probably will), I'll post pictures of what the symptoms were and what it looked like. Then, if my crank is still holding, I'll pull both heads and ship 'em to Wes or Dan. How clean should I be getting those pistons? I cleaned off quite a bit, and all the really crusty stuff, but I'm getting bored poking at them. I'm assuming it doesn't matter that much... particularly since I am not planning on pulling the front head right now, so that piston is still "it is what it is". (Message edited by reepicheep on February 03, 2012) | ||
| Blake |
Bill, I'd suggest using nothing more fine than 600 grit, skip the 800 and 1200 grit, that is polishing. Leaving a more mechanically tactile surface for the gasket to adhere to is preferable. Fill the gouge with a good metal infused epoxy that is rated for high temp service? | ||
| Reepicheep |
Thanks! Good tip. I'll hit it with 600 grit. It's way polished now. I was looking to the copper gasket spray to try and help seal the gap. I thought about epoxy, but figured by the time it was applied I might be creating more problems then I am fixing, and because the tip of it will be in the combustion chamber. I'm thinking the copper will pack in and carbon up pretty quickly regardless. I'll post pictures tonight, that will make it clearer. And for the record, I still think Dan is right! | ||
| Reepicheep |
Still have to pull the pictures from the camera, but it went back together and passed the first real hurdle.. On Saturday and Sunday, it did maybe 5 heat cycles, one of which was probably a 50 mile ride, with no signs of leaking (or other mechanic induced problems). The latest top end kit includes valve guides (if anyone was wondering), and is getting pretty complicated on that inner rocker box square opening. Some kind of semi-rigid spacer, with a silicone gasket that is difficult to keep in place). I won't really trust it until I have maybe 100 heat cycles on it... But it already lasted longer than that disaster of a copper head gasket on my KLR-250. | ||
| Reepicheep |
Maybe 10 more heat cycles, and no leaks yet. A gamble for sure, and I would not recommend it. But so far so good. |
