Compression Release

[HrcRacing]

I've been doing some searching/reading on the subject of decompression aids. On cr500riders.com, I found a thread from Bearorso who has an auto decompresser, AJ's version, ACCU-Products and even some who have used a Harley unit. At 45 and with my knees/back, all very interesting and something I'd like to pursue.

If anyway has tried one of these, I have a few questions for you guys:

1) With manual units, how do you use them? I know that you pull the lever and kick but do you let it run for a second then release the lever or what? My only decompression experience is the auto versions on the CRF450's.

2) Has anyone in the states replicated Bearorso's auto unit and, if so, can you post pics and part numbers (or where you bought the parts)?

3) Same question with the Harley decompresser.

Any information/input is greatly appreciated.

Thank you.

Auto-decompression thread: http://cr500riders.com/cgi/yabb/YaBB.pl ... 013783/2#2

[AlisoBob]

I have used the S/H unit firsthand. While is functions, the bracketry ( What A/J refers to as his "Reverse RockerArm" and overall engineering leaves a little to be desired in my opinion. The bleed hole is in the head, exposed to the forces of combustion.

By contrast, the of the other methods bleed pressure out the side of the jug, below the position of the rings during combustion.

Are you sure your jug has the factory de-compression scallops? I would even try enlarging them first to see if that aids in starting before trying any other methods.

[britincali]

Why do you need one?

[HrcRacing]

I have used the S/H unit firsthand. While is functions, the bracketry ( What A/J refers to as his "Reverse RockerArm" and overall engineering leaves a little to be desired in my opinion. The bleed hole is in the head, exposed to the forces of combustion.

By contrast, the of the other methods bleed pressure out the side of the jug, below the position of the rings during combustion.

Are you sure your jug has the factory de-compression scallops? I would even try enlarging them first to see if that aids in starting before trying any other methods.

Yeah, the auto decompression valve in the link I provided is also mounted in the head. The ACCU-Products version mounts in the back of the cylinder where the older style cylinders had a hose mounted.

I'll be sure to keep the scallops when I have the cylinder bored and try it like that first.

Thanks Bob.

Why do you need one?

For the same reason I use a jack to lift my truck instead of doing it by hand - it's a "bit" easier. J/K

I've had back surgery and have some arthritis in my knees. I think it was ACCU-Products that claimed it was like kicking over a 125.

Can't think of a reason why I wouldn't want that for my body, not to mention the kickstarter mechanism, etc.

[Ported&Polished]

You might consider buying a new electric starter bike like a crf100 or whatever. I hear they are just right for women and others that are old and weak.

[HrcRacing]

You might consider buying a new electric starter bike like a crf100 or whatever. I hear they are just right for women and others that are old and weak.

I get the humor but, here's a thought, you might want to actually add something to a conversation from time to time.

[Mik329]

You might consider buying a new electric starter bike like a crf100 or whatever. I hear they are just right for women and others that are old and weak.

I get the humor but, here's a thought, you might want to actually add something to a conversation from time to time.

Seems that kind of sarcasim comes up all the time with this subject. Please keep me advised on what you end up with as I've had almost a dozen knee surgeries and would love to make starting a bit easier. Don't let the being a puss comments get to you .... my guess is maybe 1/3 of the guys who own these bikes can actually use the power they produce....

[HrcRacing]

You might consider buying a new electric starter bike like a crf100 or whatever. I hear they are just right for women and others that are old and weak.

I get the humor but, here's a thought, you might want to actually add something to a conversation from time to time.

Seems that kind of sarcasim comes up all the time with this subject. Please keep me advised on what you end up with as I've had almost a dozen knee surgeries and would love to make starting a bit easier. Don't let the being a puss comments get to you .... my guess is maybe 1/3 of the guys who own these bikes can actually use the power they produce....

I'll definitely keep you posted. At first, I'm going to try it with the decompression scallops and see how that does. If it's a problem, I'll be trying something else for sure.

[100hp honda]

i dont know dude but i doubt scallops will help if you had back surgery and such. my shit is stock at .010 over and it was alot of compression. usually it fires in a few kicks but 1 time i think i flooded it and it took about 12 kicks, and i havent had no surgery and it was dificult. i know mine is every bit of 165psi atleast, maybe more and it has good scallops and it will give the strongest guy a work out if you dont get it fired within a few kicks

[Roostius_Maximus]

the prooven harley decompressor that aj uses is extremely dependable

[AlisoBob]

AJ should buy the bracketry from Harley too then.

[Roostius_Maximus]

I agree, that linkage is a little backwoods

[aloha450x]

ill post5 this for roost. sweet stuff right here. he said it was 10deg out and bike was cold. you can hear him open the decomp while it is running. it's the clicking sound. http://cid-76dd2330685afe13.skydrive.li ... 00086b.WMV

[ou812]

My , I personnally don't like the head mounted one for various reasons. If I were to do it I would go with the rear mounted Accu style one as it does not effect the head or any changes one may latter want to make to the head. Also the bonus to the accu style one is you have the mini lever on your bars, so what does this allow? well you now have and engine brake lever which when pulled on long steep down hill sections give you the same kind of engine braking like on a 4 banger. And ya they do kick over much like a strong 125

[aloha450x]

he has a lever. you can here him open and close it. he uses a hotstart lever. i think it is cool

[AlisoBob]

My , I personnally don't like the head mounted one for various reasons. If I were to do it I would go with the rear mounted Accu style one as it does not effect the head or any changes one may latter want to make to the head.

X2

[Roostius_Maximus]

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.