Originally Posted by Davezilla
I've been considering the jake's Diamond head for my next build too since it has the different combustion chamber design to see how that works out. Another one I'm keeping a close eye on is VMB's Shark head he's still designing and perfecting at the moment.
I just picked up a Super Rat bottom end from BGF Motors on ebay last night that I'll do my next build on. I know these have ignition issues but I got a few ideas to hopefully work around that issue, and now that I can get those ignitions fairly easily I'll take the risk. First thing I'll need to do with it is check the geometry and change out all the bearings for the good stuff. I'll also check, true, and balance the crank while I got it apart since it could just as easily be engine vibes that's killing the CDI units in these as well as the heat with not enough opening in the covers to let it escape out quick enough. My other thoughts here are that other magnetos might work better with the type of rotor this engine uses.... We'll soon find out.
I also saw that the same seller has the jugs with the straight intakes installed on them so I bought one of his to see if it has the bigger flat transfers, if so that'll be great, but if not, I got other sources for these jugs. The Super Rat bottom ends he sells also come with a piston installed so that'll take the initial guess work out of piston selection too.
I'm hoping I can get one of these to work reliably because these will make for a very clean looking install on future builds.
I think you'll like the design of the diamond head Dave, Im not gonna claim it to do a better job than the Fred head or similar, but a.016 gasket used on each one will cleary raise compressjon more if the Jakes diamond head is on that same engine because of how the squish band area will actually be down in the hole just a little, the lack of me considering this fact is how I ended up with a tight squish than I was aiming for on the newest "Taffy" build, I was looking for twice the squish that I ended up with, so Its possible that I will need add a thin base gasket to what I already have or make me a thicker head gasket or just make a thin one from some of the 8mil aluminum I have, Im concerned about not having but slightly over 1/4 of a mm squish clearance, compression is gonna be through the roof with that setup and may just be way to high, but of course I have to try it first to see how it acts.
Im a little concerned about continued gasket compression as the engine runs a while, I sure dont want it getting to the point that the piston starts to strike the head.
Ive looked at those SR engine BGF has listed, if the engine atually is a SR it will be 40mm stroke and use the low pin piston, best wishes on the build, Im looking forward to hearing about it and how well it runs.