Ironhead Compression Release

[iamdouglas1]

Hi All. . .

I'm putting a 1969 XLCH together and I'm interested in a compression release or two for the Old Girl. I'm getting to the age that I need to negotiate a compromise for my knee.

Like what kind release, how many, and especially, where to install in head.

Is there a sparkplug drill and tap that is preferred?

. . . and finally, what's it like to start the bike with them installed? does it puke oil and soot out of the release?

[JW113]

No, they don't puke oil and soot. I have them on a twin cam, and you need to get the motor spinning pretty good to get it to fire with the comp releases pressed. Not sure how well that would work with a kicker, though I'm sure it's been done.

The releases I have are not spark plug thread, much smaller. I want to say 3/8-24 maybe?

If your knee is the concern, is fitting it with an electric starter completely out of the question?

-JW

[iamdouglas1]

On the question of adding an electric starter. The engine cases wouldn't accommodate a starter.

Also, an electric starter would change the character of an XLCH.

Does your compression releases make any noise when the bike starts? How does that work?

Thanks JW

[garyajaz]

I have a couple on my 1974 ironhead.
its high compression , stroked and a bear to kick.
a trick I had to do is thread one of the holes on releases. plug them.
then will have enough compression to kick it over.
which as you know happens much slower than a elect foot.
if not you may bleed off the needed compression to start.

there was a thread here with pix a while back.  I will try to find it and post link

[garyajaz]

http://harleytechtalk.com/htt/index.php/topic,38971.0.html

[JW113]

Dang Gary, the pix are not there. Would have loved to see how it turned out.

Doug, yeah it makes noise. Psst psst psst psst psst psst Braruuuum snap snap put-put, put-put. But, without them, it does too.

Either Rrr Rrr KLANK.

or

Rrr.....................Rrr Rrr Rrr Rrr BraROOOM, put put put put put put.

These big inch high compression motors are real pain to get started. Like using a motor cyclestarter to fire up a car engine.

-JW

[garyajaz]

yeah, I had them turned on to private in photo buckett.
just now changed it to public so pix should come up when they change files.

[garyajaz]

[garyajaz]

old pix not coming up. oh well, here are a few.
as old thread says I used Vulcan 10 mm releases.

[JW113]

Thanks Gary, nice job with it. About the same location as my 2'nd plugs.

So, with these comp releases you can kick start it OK?

-JW

[garyajaz]

lol  without them I can stand on kick start lever and just stand there.
with them I can start it.
like I mentioned 80 cubic inches and 12.5:1 compression.

*have to plug one release hole or bleeds off too much compression on kick start..

[JW113]

Ah! Indeed. As was my chopper, same thing. Like trying to kick a passenger peg.

So I'm wondering how the OP, Douglass, will fare with compression releases on a stock 900cc. Sounds like some "tuning" will be required to find the right balance of compression bleed off, and still have enough to fire up.

I have SE heads on my twin cam, which came with comp releases. There is just a real small hole into the combustion chamber, maybe .050" ?? If that. And even with that, it bleeds enough compression off that sometimes it won't start with both comp releases pressed, so I have gotten into the habit of only using the front one.

-JW

[iamdouglas1]

Hey, thanks guys. Those pictures are perfect Gary. 'gives me the location that works. and the way the comp release fits between the fins. Perfect.

. . .and JW, what kind of adjustment are you talking about as far as the amount of bleed off. I was under the impression that the little poppet valve opens full into the combustion chamber. I didn't know there is an optimum opening amount, otherwise the bike won't start. What you're saying is I'll have to adjust that poppet valve within a tight range; won't work if too much release and too little comp release and ouchie.

JW said:
"a trick I had to do is thread one of the holes on releases. plug them.
then will have enough compression to kick it over".

JW . . . why do you have to plug one of the holes for the compression release. If the rear c r is closed it shouldn't leak down? it sounds like you removed one c r and filled the hole so no more c r for that cyl. why wouldn't you just keep that c r closed? 

[JW113]

JW said:
"a trick I had to do is thread one of the holes on releases. plug them.
then will have enough compression to kick it over".

Actually, it was GARY that said that. And I'm not exactly clear what that means either.

So what I meant by "tuning", was that you might need a way to "jet" the compression releases. i.e., be able to start with a small bleed hole, and enlarge it little by little to find the right balance of compression bleed off, but not too much so it will still start with the slow cranking speed of a kicker.

good luck,
JW

[garyajaz]

ok, let me esplain lucy

with the Vulcan release in hand one will notice 2 ports. these are holes that the internal release vents compression out of.
I threaded one of the two holes and plugged it.
without doing so too much compression was lost due to slow kick speed.

So what I meant by "tuning", was that you might need a way to "jet" the compression releases. i.e., be able to start with a small bleed hole, and enlarge it little by little to find the right balance of compression bleed off, but not too much so it will still start with the slow cranking speed of a kicker.

JW called it right.  with my motor just plugging one side on each did it.
on your motor maybe plug both of them and start drilling out one plug for each release till it works.  that is your "jet"

[JW113]

Good x'splainin' there Desi!


OK, got it! Not familiar with the Vulcan releases, but you made it perfectly clear how you tuned it. So there you go Douglas, Gary's got you pointed in the right direction I think. Hope it goes well, and keep us posted. Pretty interesting thread actually.

-JW

[garyajaz]

oh douglas.
one other thing. your ignition system should be looked over .
that mag system is not the best thing for starting and a lot of start problems from those days are due to the mag.
let us know how things work out.

[iamdouglas1]

Hey guys
Gary, I get what your talking about now with adjusting the orifice sizes on each c release and I'll certainly keep it in mind when it comes time to install in my heads.

The pictures help a lot.

Thanks again and I've just begun to compile several questions the The Team. See ya JW.

Doug

[iamdouglas1]

Oh yeah
On that ignition system Gary. I'm definitely springing for a Joe Hunt magneto.

Thanks again