This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Aut. decompression device

O

Obmar

Joined Jun 2005
28 Posts | 0+
Värmland, Sweden
Hello! I have a FC550 -03.
How does the Aut. decompression device on the camshaft work. It says you must calibrate it with the camshaft when changing. How do I do that?
 
Obmar said:
Hello! I have a FC550 -03.
How does the Aut. decompression device on the camshaft work. It says you must calibrate it with the camshaft when changing. How do I do that?
Click to expand...

Hi Obmar,
The Auto-De-Comp unit consists of a small rotating eccentric lobe placed in the camshaft heel. Said lobe is intended to bump the exhaust valves open near TDC compression in order to ease cranking.

A weight and balance spring are affixed to the opposite end of said lobe via a shaft. During cranking rpm the De-Comp lobe pushes the exhaust valves open. Once running (most often above 800 - 1000 rpm) the weight over powers the spring allowing the lobe to rotate such that it no longer opens the exhaust valves.

If the spring and / or weight are incorrect the unit will either remain active after starting or fail to activate at all.

Indexing is another issue. If the shaft is not allowed to rotate far enough or too far the lobe lift value declines and insufficient bleed down is the result. The weight stop dictates the rotation limit.

Not to worry. Simply use the latest OEM components (spring / weight) for your particular year and model.

Hope this helps.

Sincerely,
Dale
 
Hope you don't mind me butting in on this topic with more questions!

Has anyone run their Husaberg with the auto-decompression removed? If so how does the engine respond to E-start and K-start with just the manual decompression pulled in?

Does your Husaberg run with the manual decompression pulled in? My XR 600 does the 2 Husaberg 650's I'm working on don't?

Ben
JBSracing
 
ben

i run mine without the auto de comp and have done for over a year now. i feed mine through the comp and then kick. it's easy but not necassarily quick.

although nobody ever seems to mention it, to me, the kickstart decomp never seems to work!

when the carb is set right the bike is a first time starter.

regards

Taffy
 
Hi Ben,
Depending upon camshaft selection, compression ratio and engine displacement I often do indeed remove both Auto De-Comp. devices.
(ie early model kick lever cable and camshaft bob weight unit)

Best Regards,
Dale
 
Photos in Gallery

In case you're interested, I have photos of the auto-decompressor mechanism in my gallery.

Husadawg 8)
 
I am going to hijack this thread....

I believe i have a problem with my auto decomp. Up until about 3 rides ago my 02fc470 always started off the button, hot or cold then the started motor began spinning after turning the motor over only once, I knew that my battery was old and figured that since the starter motor was spinning and not turning the motor that my starter clutch was shot also,

I have replaced both those items. I buttoned up the trans side and filled the bike with oil, adjusted the valves and the kick and manual decomp devices, and charged the new battery with a 3 stage charger. I wanted to see if my handywork would pay off and hit the "restart" button, (there is no fuel hooked up, as i dont want it to start, the radiator is not installed yet) the starter turns the motor over ONE time then stops. if i release the botton and hit it again it will turn it one time and stop. of corse if i pull in the manual decomp lever and hit the button the motor spins like there is no tomorrow. I know you are not supposed to do that, and i never really have i just wanted to see if it was the compression that was keeping the starter from turning the motor.

does it sound like the auto decomp device? I saw the pictures in husadawgs gallery but i am a bit confused as to what i need to look for or adjust.
 
answer if you will, always looking for more info... but i think i found the thread i am looking for....
 
It sounds like the auto decompression lobe is worn. As far as using the manual decompressor ...go ahead. I use it all of the time to get mine started. It seems my auto decomprssor has never worked from day one. Just one more thing on the list for me to check.
 
so the method of using the manual one is to just pull it in bit while cranking it?

this will bug since i hate it when things don't work like they used to....

hey json, why not make some of the larger threads with the most info in them sticky? for example this one starters & stators
 
As the autodecompression device is a wear item it seems to me that sprag failure could easily be misinterpreted for autodecompression device wear. If a "brick wall of compression" is hit, a somewhat worn sprag may not be able to hold and allow the starter to spin without turning the motor.

Now that you have a fresh sprag clutch the starter simply stops. I think you are correct in your assumptions Risky.
 
See i knew if I held my head to the screen long enough some of the brains of this group would seep through :D


edit: i guess if i was using my brain i would have checked there first when i noticed a problem.
 
So i pulled my freshly sealed rocker cover and inspected the auto decomp device, I can clearly see wear on th lobe, but nowhere near what i would expect would have to be there to eliminate the less than 1mm take up in the exhaust valve. there is just a hairs width of material missing at the wear spot on the auto decomp lobe. I take that it does not have to be much at all to produce said effect of a "concrete wall of compresion" or possibly i need to recheck my exhaust valves and make sure they are not to tight?
 
Measure from the valve spring retainer to some easily accessed portion of the head with a small metric rule, or better yet use a dial indicator, with the exhaust valves closed. Rotate the engine so the auto decompressor is on the rocker roller and remeasure. Should depress the valve. Manual doesn't state how far the valves should be depressed, but if memory serves me correct, guys in other posts were stating a bit less than one MM.
dan
 
risky1 said:
or possibly i need to recheck my exhaust valves and make sure they are not to tight?
Click to expand...

If the valves are too loose it will hinder the autodecompression device from working properly. A little tight on the exhaust will actually help with the lift.
 
Husabutt, it looks like you might be right!

prior to reading your post i was out in the garage, and decided to check my valves one more time since the wear on the auto decomp device does not look like enough to stop it from working.

well there i was with the trusty feeler gauge fishing around and it broke... so what am i going to do now?! well I guess it was time to try out the the 1/8 turn method so i did, and what do you know the bike turns over like a champ! no "brick wall of compression" like before. can't wait to get my radiator and get this thing fired up....

just confirming that when utilizing the 1/8 turn method, 1/8 turn equates to approx 3/4 of a side of the hex nut... correct?

because I really did not listen very well in autoshop in high school I don't know but is possible to have adjusted the valves on the exhaust stroke and still have it run? or even kick start? would that have caused the decomp device to not work? If it is possible... :oops: I think i may have done that and that is what fried my starter clutch....
 
Not only possible but probable. I also found the easiest way to set the valves is with the Motion Pro valve adjustment tool. It has a 10mm socket with a screwdrivdr in the middle of it with an indexed dial on the top. The 1/8 turn is the best! Do it twice with the motionpro tool and you will reach valve adjustment nirvana. Siince you have already worn out your sprague replace it and with valves adjusted properly it will start on the button more frequently but probably not for the first time in the morning.
 

Similar threads

S
2004 650 engine rebuild questions
Replies
8
Views
373
Samuel42
S
E
Bleeder Screw on Slave Cylinder won't open and needs to get replaced - Husaberg FE 390 2012
Replies
0
Views
251
eric.johnsson
E
P
Husaberg FC450 No start
Replies
0
Views
288
Putoze
P
A
Help with engine timing a 2005 FC550
Replies
21
Views
1K
Taffy
Taffy
T
Husaberg FE 450 viable in 2025?
Replies
1
Views
178
Goose916
Goose916

Register CTA

Register on Husaberg Forum! This sidebar will go away, and you will see fewer ads.

Recent Discussions

Recent Discussions