Starters & Stators??

Scully, I just checked my valve travel with a small steel rule. It measures about 1mm.

As you may have read in the past, the decomp lobe protrudes out of the cam by 0.7 - 0.75mm, it actuates the exhaust valve momentarily while the piston is on the compression stroke. Its generally a pain to measure hence my suggestion to just measure the travel at the valve.

As I mentioned previously, remove the exhaust valve inspection cover and stator cover. With a 17mm socket, rotate the crank while watching the exhaust valve. When the timing marks on the flywheel are around 10 or 11 o'clock you will see the exhaust valve open and close over a fairly short duration. Its the travel in the valve you want to measure.
You can stand the end of a steel rule on the edge of the inspection hole opening to hold it steady.

Its a quick check and will hopefully rule one potential cause of your problem out.

Good luck.

Scully said:

Yuasa YTZ7S dimensions are 113mm X 79mm X 105mm so this means that it will not fit our Bergs?? As the old batteries are 71mm wide not 79mm? I suppose we need the 04 model battery box?

Click to expand...

Scully, the YTZ7S drops straight in. I put one in my bike about 9 months ago. The battery dealer is correct, Yuasa don't bring the battery into Australia.

Your options are.
1) Buy the battery from your Husaberg dealer.
2) I have heard that the WR450 uses the same battery but they give it a proprietary part number. You could get the battery from a Yamaha dealer but to be sure, take your old battery along with you and compare the size.

Sounds like the Yamaha battery won't fit. My battery box is the same as yours so it looks like your only option on the YTZ7S is the Berg dealer.

First check for the 1mm valve movement per the previous post, if it doesn't have the travel then...........

You don't need to remove the head. Its a matter of removing the valve cover (note where the different length bolts go) then undo the cam chain and lift the cam out. Very straight forward.

My cam chain had a joining link in it, don't know if this is standard but have a look as it makes the job very easy.
First you have to remove the mid section of the exhaust, then remove the centre bolt/spring on the cam chain tensioner and then unbolt the cam chain tensioner.

Mark the timing sprocket tooth that lines up with the joining link then carefully remove the link. While keping a little tension on the chain so it doesn't come of the bottom sprocket, I threaded some thin wire through the chain at each end and tied it to the bike.

To measure the decomp, rotate it so that it protrudes above the cam, it should protrude by at least 0.7mm.

If it is below 0.7mm you can probably get more out of it by adding a dab of weld to the inside of the arm where it contacts the cam. You should be able to see where the weld was placed originally as this is the normal procedure for adjusting the decomp. Aim for a lift of 0.75-0.8mm.
Please don't try for a higher lift as it wont work on the 02 model!!!

If the lobe is badly worn you should replace the decomp device, expect to pay around $125. Even with the new decomp you will probably have to add/grind weld to get the correct lift.

After the cam chain is refitted, to install the cam chain tensioner, leave the centre bolt/spring out. Lift the little pawl and push the tensioner all the way into the body. Then bolt the tension onto the head and then fit the centre bolt/spring.

When refitting the valve cover (after cleaning it up) use a thin silicon sealant such as white 3-Bond. Thick sealants like Silastic can prevent the cover seating all the way down reducing the grip on the cam bearings.

If I have forgotten something I am sure someone will let us know.

I hope this helps.

Twisty
You mentioned not to go over 0.8mm lobe height on the '02 model. What is the best height for the pre2001 bikes - aka a '98 600?

I'd also add to NOT use Loctite 515 Master Gasket, or any other anaerobic sealant like it, on gasket faces that you want to mate accurately such as the rocker cover. It always props the two surfaces 0.005" to 0.010" apart, preventing the bearings being locked in place correctly. I use Permatex Aviation No.4 - a bitumen-like gasket compound.

Scully, glad to hear you are getting on top of the problem.

1) Trust me, the YTZ7S will fit. Don't worry about the extra 8mm.

2) Regarding the weld. My bike has 3 bolts. 2 hold the sprocket onto the cam, the third is the stop bolt for the decomp. The decomp rests against this bolt during normal running, ie while the decomp isn't engaged. If this is the bolt you are refering to, adding weld wont help.
When the engine is at rest, the decomp is engaged by the spring, at this point the inside curve of the decomp arm is resting against the cam. Its at this point where the inside of the arm touches the cam that you need to add weld.

If the lobe is badly worn its probably worth fitting a new one. I have heard of guys adding weld to the lobe but that makes me nervous. The lobe takes a pounding and you don't want a piece of weld breaking off and doing major damage just to save 120 odd bucks.

Good luck Dale, hope this helps.

Brad said:

Twisty
You mentioned not to go over 0.8mm lobe height on the '02 model. What is the best height for the pre2001 bikes - aka a '98 600?

Click to expand...

Brad,
Here is the background for comming up with the 0.8mm.

When it came time to replace my decomp I read the old threads here on UHE. A few of the guys were raving about the improved starting by increasing the autodecomp lift to 1mm so that is what I aimed for. (I actually had about 0.95mm)

When I fitted the decomp, the bike would usually start well but other times the engine would do half a turn and lock. What I found was that the cam follower bearing was smacking into the decomp lobe and rotating it back out of the way. In effect it was like have no autodecomp at all and the engine would just stop spinning on the compression stroke.

I couldn't understand why it had worked for the other guys so I started going through the gallery of guys that had gone for the 1mm lift. I found they all had pre 2001 bikes and from the pictures the lobe appeared to be more rounded.

Now I don't know when the decomp lobe profile actually changed but I do know that the new decomp lobe wont work properly when the lift gets somewhere above 0.9mm.

To answer your original question, I suspect your bike would work fine and possibly start better with the 1mm lift.

I think I mentioned it previously but the factory spec for the lift is 0.75mm

Guys,
Don't know if you have seen this in the gallery but check it out.

Autodecomp Pictures

They show the older style decomp cam lobe. I would like to know why they changed it as the older style looks a lot more durable.

scully

i hear ya on the weld idea and you appear to be right. i bought a used cam off scoot about 6 months ago and i got the auto decomp with it. in the inside of the curved bit was a blob of weld-about 1mm wide and it was obvious that this was how someone had dealt with it.

my record is that i welded a blob on the actual lobe and then had it ground down and shaped. the trouble is that the contact point moves from the leading edge to the dome in the middle. so instead of the roller "keeping the decomps head down" and in the decomp position it allows it to roll back and it doesn't decomp anymore.

that's why you get a two-speed starter motor. so i have converted mine completely back to manual decomp and nothing else. so as you can guess i've no extra rotational mass. i will be in charge of when and if it starts-i hope!

another thing to remember that hasn't been mentioned (i did on this subject when doing the weld mod) is that if the auto decomp used to bump at the leading edge of the 'bump', by welding a lobe that looks like a humped back bridge you are infact making the bump back near the middle.

aha! i hear you say, so what! but that's about 40 degrees at the crankshaft. 40d and we should be working to within 5-10d of the orignal auto decomp. 40d? jeez!

working on it all today so i can let you know of the decomp, battery fit, the lot.

PS why a new thread? all the info is HERE!

Taffy

iwa swith ya until the last coupla words aussie and then ya lost me! too many tubes methinks!

the inner curve of the decomp swing arm. weld there! that'll keep the front edge of the decomp up. not only that but that face will become broader as it wears and therefore LESS liable to wear.

as to manual decomp; well you should have had one cable from the back of the kickstart housing, then you have the one we are presently on about-the auto decomp and then finally you should have a cable from the magura juice clutch over the bars and down vertically to the right of the engine. here is a boomerang shaped piece of shiny metal that pivots in the head. the cable attaches to this and upon you pulling it a bar pushes the exhaust rocker arm down and stops the valves seating.

please go look at a workshop manual in the downloads or if you have your own.

i started the bike once today and have a little task to redo which i won't bore you with. i never make mistakes now remember that!!!!!!!!!!!!

fuller picture at a later date.

hope this helps and er....lay off the beer scully!

Taffy