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Yes. That is the main difference.

clean, new, oiled fasteners. ... because that's all they have at the factory. Makes sense to me. Thanks for helping me clear that up!

Hello All, I've been building engines for 20 years (motorcycle engines, mostly 2T race bikes). I've always known about the difference between wet and dry torque. But in all my service manuals there's a range given for torqueing fasteners, but never a mention of whether this is wet or dry...

I'm still picking away at this project in my spare time. So please post up any suggestions you have for aluminum alloys that would be good for this application. Thanks!

Those are great suggestions. I've got a bunch of heads designed in solidworks, but I'm trying to stay in the spirit of old school engine building because I race Vintage MX. I do have a friend right down the street who could easily SLA my designs and I could have them cast. Or go directly to...

Thanks for the tip! I will look it up.

I've finally gotten back to this project. Old School pattern making in process. Wood, bondo, spot putty and a lot of massaging to go. Here's what it looks like now. I'm building up the truncated fins, then extending all the fins and adding mass over the combustion chamber and flowing it out...

My YZ490 is the same way. I don't let anyone ride it. The YZ125 is a great bike and it has a lot of untapped potential in the porting and combustion chamber design. In vintage MX racing, we're not classed by displacement, only by year and technology: The EVO class around here is for drum...

Agreed 100%. This is what I aim to "fix" before casting. In the terrible paint pic below, if you use your imagination and patience with my bad "art". I've tried to show where I'm adding material to the top side of the chamber, especially as it loses altitude going away from the sparkplug...

Before: First steps. Clean and cut the webs out. Parting line will be centered behind the middle remaining webs and over the spark plug area. These webs may be continued across the entire head.

The Montesa fins look pretty "trick". I do recall that during testing, the magazines mentioned that the fin design was superior in collecting and holding dirt and mud. (not good) :) I'm intrigued by the cuts in the fins on the TZ cylinders. It appears to be more of a mechanical resonance...

Aha, Yes now I remember. Hypereutectic meaning the alloy has a high melting point... It's beyond the eutectoid football shape on the graph. It's been a while but I remember the graph! Time to start gathering up all my doorstops. :)

Thanks for all the replies! I've contacted the foundry foreman and asked about hard wax and also the possibility of melting down some heads and cylinders that I have. I'm wondering if melting down pistons would be a good choice of material, assuming that pistons would be a different alloy than...

Wow, Excellent thoughts from all! I don't post much, but really cherish all the great minds that frequent this forum! This application is a "free air" design in which the air passing by the engine is not forced by a fan or directed by any shrouding. Average Speed is somewhere around 20mph...

Welp... Because I don't fully understand why this material has a bad rating for "leak tight and pressure type applications" maybe I should ask: Why is it so bad? I don't want voids in the casting which would make hot spots. And I'm a little worried about the heat cycle + Pressure from...

Background: I'm modifying a vintage 2T race engine (porting, intake, combustion chamber etc..) In stock trim, this motor needs better cooling. I've found a cylinder head (sunburst style fins) that has more mass and more fin surface area, which I want to modify and duplicate in a casting. I've...