haven't started on the gear yet. just busy with other things going on right now. i did have little down time to play with another head and motor that i will be installing on my thunderbolt.
head was originally a 5hp-ohh small chamber style head that i modified couple years ago with some briggs stock flathead valves and seats i stoled out of a briggs block. 1.125 intake and 1.00 exhaust. for you clone guys that would be a 28.5mm intake and 25.4mm exhaust.
head is also modified with dual springs and dyno flathead briggs retainers/keepers. yes dual springs. i will be running a 255 dnyo cam with some clone 1.3 ratio rockers. total lift will be .331+
head was on a big bore cylinder(2.835)
now it is going back on a stock bore with a factory steel sleeve engine.
so the first thing i need to do is mill little more off the head.
my goal was to try to get the compression into the 11's +
here is where it sits now...in the pall bark.
now here is what i am trying to accomplish. as everybody knows when building any type of Tecumseh ohh or flathead hs-40 or hs-50 the racing cam you get from dyno or even isky does not have a compression relief on it. well for the flatheads with the 245 cam and maybe the 255 too there not bad to pull over once you learn how to pull them over,but for the overhead valve engines. you better have it spot on when you pull it over or your arm will be coming off. i know in the pass with a overhead engine with 30 degrees advance, heavy springs and high compression it's game on when pulling it over. doing little research i found some parts that just might work.
first i had to find a spot on the head if i could install a remote spot for a external compression relief unit that was originally made for a small chain saw.
here is the spot i pick and the only spot...lol
casting hole that was aready in the head.
next was to see if i could drill a hole through the side of the head and all the way through into the chamber right above the intake valve seat.
next was to machine a .075 aluminum plug. i will need to go back and plug the outer hole area and after tapping out the threads.
the compression unit/threads will keep the plug from ever coming out again.
tap i needed to run through was a 10mm.
i will also need to run a small washer spacer so the compression unit will clear fully when open.
completely installed.
OPEN
CLOSE
nice thing about installing it on the intake side. it doesn't really build up
carbon and when it might i should be able to spray some
carb cleaner down through the vent hole on the compression relief unit if indeed it ever plugs up.