I'd like everyone to know that this is my bias opionion, and have never owned a system from accu-products, but having a family business of building performance engines for over 35 years
www.millarengines.com, careful consideration of how i was going to approach the decompressor regarding durability, engine wear, tuneability, and ease of install, I put it in the head.
downside of accu:
-Altho the accu style works theres a few things i've got against it. It offers an area for the compression to escape past the rings, which is also heat, and fatigue to the ringset.
-Its a dammn big hole to poke in your cyl. Its a big clumsey valve, sure its likely durable, possible rebuildable, but find someting to plug that hole when the valve is leaking comression
-The modification to the cyl limits the owner to using the 89+ jug.
-It is a big open hole, and exposed mechanism located close to the dust and grime, how often have you had to wash the top of the head when cleaning the bike?
-The valve face exposed to the cyl occupies an area large enough to relieve cylinder pressure, but in only the first 1/3? of the stroke
Both instilations require passing thru the waterjacket, the accu style is larger. The head install of the harley stlye actually only interferes with the waterjacket for 2/3 of the .750 dia plug, and only passes thru water for .180" Head hotspotting is not a factor.
upside of my install:
-I feel that mounting the valve in the cheapest, most expendable compenent of the entire engine is deffinately a bonus.
-Hey you dont like it, put a 10mm plug in it and forget its there.
-Its up, out of the way, in possibly the cleanest area of the bike
-It is also actuated at the bars with any manufacturers hot start lever, oem, or aftermarket.
-It requires only .110" of movement to open the valve
-Its instiallation has absolutely no affect on ring wear, ring tempature, or rewarding the crankcase continuously with compression past the rings.
-You need to replace the valve, hey don't go to the phone, If you cant find the 2nd one that came as spare with the instilation, go to your husqvarna dealer and get the identical part (ok the color of the knob may be different model to model, but dimensions is exact). Its used in the large cc chainsaws. $28.00 to $38.00 canadian each depending on the dealer
-with these small valves in big harley applications, I have maybee failed one in 200, only after many many uses, and only the ability to click down is whats failed, this is irrelevant when you're holding it diwn with a lever anyways.
-the head is shipped with a hole from the relief chamber to the head chamber that is small enough to comfortably decompress a stock 500, and unlike an accu style, this hole can be enlarged to tune the amount of decomresson to match increased cyl pressure from either head work, port changes, or deck changes.
-the install is only affecting an area .125" at maximum recommended size in the head chamber, which leaves access to machining in the chamber identical to that of an unmodified one.