compression releases for sporties - Harley Forum

garysdad · #1 06-09-2009, 02:33 PM

I have "modified" my old '86 evo sporty,to the point that Ineed to reduce the compression for starting ,I have a Spyke starter installed and its still a beast ,I have releases from Vulcan but cant find any info on installation jigs or even pics on where they should be installed,as I have access to machining tools and am willing to tackle the job myself , the local HD shop is more interested in selling me a bigger machine, and have limited knowledge if it ain't stock. any input would be appreciated, pics would be great , dimensions perfect!!! thanks,Bob

JCourneyaP · #2 06-09-2009, 09:11 PM

I am sitting on the fence waiting on replies on this. Interested.

In the past before my motor was broken in I use to put the bike in second and rock it back and forth to relieve the pressure.

I do not believe it causes any harm. I no longer need to do that.

frisco-rigid · #3 06-10-2009, 12:37 AM

Hi Dad

I have 2 motors with similar Comp Releases..
This photo shows a dedicated "pad" on the head where the releases were factory installed..
You will have to be very careful to drill & tap Dead Square to the head surface, as I'm sure you're aware..

These C-R's are .780" C to C to the spark plug.. I advise more like the .900" C - C on my other motor cuz this 780" is a wee too close to comfortably slip a Plug wrench on the plug,, I had to grind down a plug wrench end to fit in..

OK,,, if the CR's close tooo soon,,, before the motor starts,, which they often do thus hanging up the starter,, you can drill more relief holes in the HEX head of the CR's..
I had to drill 2 more relief holes in the 127" motor CR's to assure that the motor could spin enough to start.. Each of those releases Now have a .116" (a size 32 number drill) hole drilled in 4 outa 5 flats on their Hex heads..
Care must be taken to NOT drill into the shaft, a nick is OK just Do Not drill through the shaft..

Upon starting the CR's still close up tighter than a Bulls Ass in fly season so don't worry about that..

unclepsycho · #4 06-10-2009, 12:52 AM

Frisco
When I bought compression releases for my 100" Revtech, EVO based motor, I was told I would hafta take them out every so often to clean them.
Is this true???
so far they seem to work flawlessly. over 20k miles on the stock starter.
( a guy with a bike like mine was on his 3rd starter in 4500 miles)

I got lucky, the heads were pre-drilled for dual plugs, so all I had to do was remove the allen head plug behind the push rod tubes .3and install the CR's.

garysdad · #5 06-10-2009, 01:48 AM

Ya, I borrowed a set of heads for a twin cam that are drilled and tapped , gives me a good Idea of where to start, have to make my own jig so as to get them as close to the same as possible ,,the old "eye ball "routine don't work as good as it did 30 or so yrs. ago!!! Bob.

unclepsycho · #6 06-10-2009, 01:51 AM

good point....
these bike engines are a bit more precision than the ones a few years ago..... A jig is a great way to do it.

Good Luck.

frisco-rigid · #7 06-10-2009, 01:54 AM

Hey Unc

20K and NO probs---- ah, you kinda answered your own question huh..

I've never heard that piece of advise before..
I've never felt the need to do it so I figure it's the kinda thing a guy will do if he feels he should..
If you do remove them always be sure to keep a wee NeverSeize on the threads..

The units on the 127" motor I installed in my LiL Suction Cups sickle work flawlessly too cuz I drilled those extra holes..
I never use the CR's on the above 120" motor cuz I kick it..

Jeeeze,, that guy you know needs a set huh..!!

unclepsycho · #8 06-10-2009, 01:59 AM

frisco
I think he did install them with the 3rd starter.....

thanks for the reply.... I was just gonna watch the plugs and if they looked carboned up for any reason...then I would take alook at the cr's too.

garysdad · #9 06-10-2009, 02:04 AM

Thanks for the pics and measurements ! the clearances will be tight fer sure,,, won't be the first time I've had to modify tools to work.On my heads , I think I may have to go in at an angle to make them work . I got the shortest realeases with .360 " thread length, so as not to have to remove as much aluminum. Tested right after break in at 205 lbs. compression, could damn near run diesel!!!!! Wisco pistons (1200), 883 heads ,Evans v8 cams ,ya know the story I'm sure. thanks , Bob.