Fitting compression releases

[MadMaxUK]

Does anybody manufacture a jig similar to the SE fixture for Twin Cams that can be used to fit compression releases into Evo heads? Or would anybody have an accurate diagram with angles etc to set the head up on a milling machine to do this?  Probably using the Goodson releases with 10mm x 1mm pitch thread .. Thanks!

[Don D]

I had to figure it out. Right behind the spark plug as close as you can get at 40° works for me. You need the shallow reach compression releases and just enough depth to clean the face at 3/4" or you break through the chamber. when drilling for the threads. Maybe someone will have a diagram and chime in, I have done so many I just make it happen. On the twin cam I changed the angle on the Jims jig so I don't have to go so deep into the head, closer to straight up. I also use the same jig modified to locate the stepped drills used to drill for the ACRs.

[Pirsch Fire Wagon]

I have looked for years for a JIG for the EVO's. Normally, I just send them off for installation. JIM's Tool is what I use on the Twin-Cams. Very nice.

[thumper 823]

From an observation POV, not as a flame-Would it not be better to install a proper cam?
A lot of us run around with over 225CCP and no release buttons.
This would seem to be better money spent?

[Don D]

Short answer with respect, no. Releases will prolong starter drive and flywheel life and the proper cam for the build can be used. Carbed EVO on pump gas are very happy at 195 CCP. Using a cam to compensate for too much static mechanical compression is not the best approach.

[Ohio HD]

A proper performance cam isn't designed to allow easy starting, (not speaking about S&S easy starts) it's to give the motor what it needs for the intended power and operation of the motor.

My 124" at a moderate compression of 11.3:1 gives a 190ccp cold crank pressure, cams close at 55°. No way this would turn over when hot or even easily cold without compression releases.

Harley went to auto compression release system in 2013 as the motor volume was becoming large enough to need them for more reliable hot starts.

[thumper 823]

I can say this I went from a DM 530 to a w8 with great results.
The wrong cam will certainly yield bad results esp with a Big CCP .

I might consider buttons but with double plugs it is all getting crowded in there.

[Ohio HD]

Manual compression releases go on the same side as the OEM plug, there isn't any issue with dual plugs. All you see in the chamber is an 0.062" hole drilled to allow compression bleed off.

[thumper 823]

Thanx, good to know..next time I pull the velcro fasteners off I will do it !

[MadMaxUK]

I had to figure it out. Right behind the spark plug as close as you can get at 40° works for me. You need the shallow reach compression releases and just enough depth to clean the face at 3/4" or you break through the chamber.

Great info there Don - thanks! Guess I'll have to get hold of a scrap casting and do the same. The releases that I use for TC's from Goodson have a thread length of 0.350". You go behind the plug though? Ohio's photo shows that it can be done right next to the plug and it still looks neat. Thanks for all the replies guys ...

[Don D]

There is room on the jims tool to colocate the drill bushing to go to the side at the spark plug angle but you will need a different length step drill. I remade the tool soon I can put the two cams at less steep angle, 15 deg, and now they stand much higher, less drilling to clean the hole. My jims tool also doubles as locate for the ACR step tools.

[Hillside Motorcycle]

We install them between the pushrods, holding the cylinder head in a fixture that I manufacture, that Goodson sells.
Doing another set this morning.
Easy peasy.

[Winston Wolf]

I tried to do this spot on my 88, but when we sonic tested it, there just wasn't enough meat there.  Had to go between the pushrods as mentioned above.  I found a long reach/short thread release from Vulcan that worked out well getting it out far enough not to burn your hands.

Manual compression releases go on the same side as the OEM plug, there isn't any issue with dual plugs. All you see in the chamber is an 0.062" hole drilled to allow compression bleed off.