Ace 100 cylinder head

[megawat]

Have a 1970 Ace 100 with cylinder head with two plug holes. Plug is in center hole and decompressor is in second hole canted toward rear. Is this standard or an option.
Thanks, Don

[RichardMott]

If there is a second spark plug hole, it might be a Webco head.

[RichardMott]

Here is the Webco on my Ace 100B+. Does his look like yours?

[MTRob]

Hi
It was an option you cold buy from different dealers back in the day (Head). The other hole is for a decompressor, we used them alot on cross country racing going down hills to slow down faster using both brakes. Find one on ebay a decompressor I liked how they worked, to slow down also to blow out water if we got stuck in a water hole during a race.
MTRob

[megawat]

Thanks for the help, guess I can assume the head is aftermarket but not Webco, has no lower fins. Decompressor is installed and works great.

[Gary G]

Could be a super rat head.

[junker2k]

It is a Compression release and we also put them in the stock heads before webco was around.
JK

[bchappy]

We also used the extra hole for a Compression Release on Flat Tracks where you could not have brakes. I also used them on Cross Country for an extra spark plug. If the plug fouled I just switched the plug wire to the other plug. Bailed me out a few times.

[dirtsquirt74]

This is a question. Built a custom trials bike and the head was bored for a compression release. How do you tell the difference between a webco head and a hodaka head that was bored ( after the fact ) for a compression release?

Richard S

[RichardMott]

Richard S,

The Webco head is a bit larger than the stock Ace/Rat head. You can see by the photo, the head is larger than the cylinder top. A Webco head is about 1 inch in diameter larger. You need to use a B8ES longer threaded spark plug rather than the standard B8HS.