A few of you might remember that I was having engine issues a few weeks ago and it was discovered that my head gasket was blown. The engine was leaking down 30%+ and TDC was almost impossible to feel on the pull cord. My engine guy showed me the telltail sign of a 206 blown head gasket: black soot marks on the block just above the head gasket seam on the top of the head directly above the header.
Well last race weekend, the engine was running better and had great compression. However, yesterday half way through the race day, my engine felt dead on power, was surging while idling on the stand and behaving exactly like it did when the head gasket was blown…I could still find TDC but only when it cooled down which indicated compression was being lost. I looked for those black soot marks and sure enough…it is blown again.
I talked to my engine guy at the track and he said this is almost certainly because the head is warped and because it is a 206, he can’t machine the head back to flat. I guess he sees 206 heads warping at the top near the header fairly often because of the heat that gets focused here from the header.
I know there are some of you here with LO206 building experience and I was just curious if this tracks with what you have seen? The engine only had 1.5 race days and maybe ~6 individual practice sessions on it since the head gasket was replaced.
Overall, I have been a bit annoyed with this engine to be honest. For an engine that is supposed to be super reliable, I’ve had constant issues with it. It is definitely older (came with the used kart when I bought it) but is a previous series and race winning engine. Compression feels amazing when the head gasket isnt leaking lol. Just trying to feel out if it would be better to pick up a brand new stock engine or replace the head on this one.
Yes, it is normal, unfortunately. If the head is warped, it will keep happening.
I dont believe head deck surface is a tech item anymore. This allows you to “true up” some if they are not warped too badly. If your engine guy is not doing that when he checks a blown head gasket, I would ask him to start.
If it is beyond flattening, you can buy another head and throw it on there. That would be cheaper than a new engine if you are happy with this engine’s performance. Or, you can buy a new engine.
I’ve got the Canadian briggs rulebook open on my computer. As far as cylinder head goes, it calls for a minimum head thickness of 2.431" and states that the gasket surface is not a tech item. I would take this to imply that if the head is thicker than the minimum, id go ahead and cut as little as possible to get the gasket surface trued up.
I’d check the US rules and bring that up with your builder.
Interesting, I’ll ask him about the deck surface not being tech! Though honestly, paying for labor to true the surface up is probably going to cost just as much as buying a new head…
I think my performance issues have been related to this head being warped and I’m not sure how I would get a read on the bottom end’s performance. I’ve read that engines with a lot of use can sometimes outperform new engines.
Leaning towards buying a new head as that is something I could order and install myself rather than spending just as much to “save” this problematic head.
I am assuming you are suggesting to adhere the 500 grit sandpaper to the flat plate, remove the head and slightly “plane” the head deck surface?
Bingo. The glass is a flat surface so glue the sandpaper down and make sure it’s pressed flat while it dries. Then knock the 2 dowel pins our of the head from the top side and true up the surface
If you go the lapping route, use lubricant on the sandpaper, and lap in figure 8 pattern, rotating the head 90 degrees every couple of figure 8s. That will help avoid uniform gouging.
Also, get a wide tip Sharpie and black up the gasket surface, check every few passes to see if you’re getting closer to a full cleanup.
I’d follow what people like James, TJ, or Derek suggest, none of them have let me down yet.
If you go the route of lapping the head, can you take pictures of the head through the glass plate so we can see the high spots, then a few along the way and then, when you are done, please?
Really curious to see the process and then how it turns out.
So I wanted to read the rule book again before going down the lapping road. I do see the minimum thickness spec but I also read, “Cylinder head must be “as cast”.”
Wouldnt that prohibit doing the lapping to true it up? This language is too vague IMO. Technically, now that the head is warped, one could argue that it isnt “as cast” either…
I am new to my local club and don’t want to be accused of cheating over this!
It does say as cast, but it also says the gasket surface is non tech, so i take that as permission to true that surface up.
If it doesn’t say you can, you can’t… But if you do, don’t tell anyone.
A few years ago there was a rule about the surface finish of the head being as machined. They removed that because any gasket cleanup would change that surface finish. It opens up the door to allow you to clean up the surface by machining it slightly just keep it within the total height. Most all heads are within .001" - .002" of that spec anyway so there isnt much room at all to remove material but it’s enough to true up warped heads that like to pop head gaskets
In my experience the newer heads with the exhaust side head bolt heat dissipator thing warp worse than the heads that didn’t use them. Counterintuitive, but that’s my experience.
Interestingly, this head is the older style head without the heat dissipator!
They still warped over time, but I always saw less warp.
Disassembled my engine to have a better look. Yup…head gasket is blown.
One thing I can’t figure out is how to knock the dowel pins out. The flanges of the valve cover are in the way. Any tips?
Yeah that is what I figured. Wasn’t wanting to deal with the springs and all that if it could avoid it haha.