Alternatives for 250 ED and SL heads

[gregg_floren]

It's well know that the heads on the 250 Hodakas do a poor job of dissipating heat because there just aren't enough full size cooling fins - half of them are missing on one side to allow clearance for the pipe. As the engine heats up the power drops noticeably.

I've see people use a different pipe and attach fins from a donor head to improve cooling, but has anyone ever successfully modified a head from a completely different bike for a Hodaka 250? Somewhat like Zundapp radial heads have been modified to be used on the Hodaka 125s.

[Darrell]

I can't find a picture of an ED head, but I think only the 250SL has the "cutaway head feature".

Strictly Hodaka was supplying oversized head gaskets, which theoretically function as an additional cooling fin between the cylinder and head.

I'm using one of these gaskets on a 250SL; regardless after parking the bike at a gas station during one hot day passersby commented that they could feel heat from the bike while at least three feet away. Since then I went up one size on the main jet and one tooth on the countershaft, which seems to offer some heat relief during highway rides.

[gregg_floren]

As far as I can tell the ED has the same profile - and missing fins - as the SL. See sample ED engine below.

The only difference I can tell (aside from the original colors) is the combustion chamber shape. The SL has an "egg shaped" combustion chamber with the the pug mounted at a slant from the rear. The ED has a more traditional symmetrical shape with the plug mounted straight down in the middle. See below.

[Darrell]

The 250SL head has an offset combustion chamber toward the intake side of the piston. The SL model was released a year after the ED and Hodaka rethought a couple of issues from the ED to the SL. Gear spacing was another one, I think.

Anyway, since the exhaust side of the piston runs hottest then offsetting the combustion chamber rearward should/might/maybe/hopefully help keep the overall piston temperatures more even and uniform.

I wonder if the redesigned combustion chamber for the SL was a bulletin for Hodaka from PABATCO.

I've also stepped down the spark plug heat range one step on my SL. Overall, my SL gets the job done and I'm not worried except when it down to long highway grades in hot weather.

[Darrell]

Regarding your question about adapting heads from other bikes. I recall that a long-distance 250SL rider (Mike Perret) modified a Suzuki 250 head (TM? TS?). It didn't sound like a piece-of-cake kind of project though.