What piston for my 550?

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HusaDave

Joined
Mar 31, 2005
Messages
26
Location
Karlshamn, Sweden
Hi everybody,

during the last race this weekend my Berg saw it fit to drop the decomp-weight into the cylinder (don't ask me how it got there, a complete mystery!), rendering the piston and valves useless.

So my question is this; are there any benfits in using, say, the 470-piston instead of the 550-piston? I'm opting for a Wössner or Athena. Is one lighter than the other etc etc bla bla bla? :lol:

So, what should I go for? Thinking of going for 32mm exhaust instead of 30. Is there any gain in power? Worth the effort? A lot is already done to the bike in tearms of tuning, but there is always a need for more.. :evil:

Also installing new bearings of course and removing that darn counter-balancer to get the wide crank bearings. Did this to teammate's 650 with great results!

Best Regards
/Dave
 
I think Athena's piston's are made by Wossner. I know the Athena piston I put in my KTM 520 was actually a Wossner.
 
Doesn't the 470 piston have a compression dome which is lacking in the 550 piston (or does the 470 have a flat top piston and a dished piston for the 550)? If so, the compression ratio would increase significantly if the 470 piston was used in the 550.
 
Hello again,

and thanks for your replies. I have a dealer who sells both Wössner and Athena pistons. The Athena are a bit pricier. Are they really the same?

I have also heard that the 470 piston has slightly more compression the the 550 ditto. Can anyone confirm? And does that translate into the aftermarket ones or are they all of the same shape?

Interested in knowing if the 32mm valves give more performance, probably have to change seats as well.

Best regards,

Dave
 
Hello,

I changed my exh valves 31,5mm ,which gives 2Hp + from 4000Tpm's to top Rpm's.

Pm Dale Lineaweaver,he knows more about it.

it is certainly worth the money,so Go for it.


Greetings Madero
 
Sounds good! Will probably go for it, have pm:ed Dale to hear what he thinks.

/Dave
 
i have the 35/27 head and that had a 8mm difference which i knew to be too much so i took a pair of 30 exhausts and turned down to 29mm for safety - good improvement. you'll find a report on it in 'taff's racing season 2005' from about last july.

so a 37 to 32 is not a bad idea at all. i used some filler to make the ports smaller at the splitting point (just into the head) and again there was a power increase.

i prefer the bike WITH the counter balancer in and if i pull it apart next weekend for the new woessner - it'll have the CB re-fitted!

it's true that the OEM 470 piston gives the highest compression of the three (470-550-650).

what do you mean 'don't ask how the CB got there!" WE'RE ASKING!!!!!!!!!

regards

Taffy
 
Thanks for the reply, Taffy. I'm set on putting in new 30mm valves with porting to match. According to all accounts there is a noticeable difference!

I do prefer the bike without the CB, so it will go. The 650 engine we stripped the CB from only had positive sideeffects after the work. So I'm hoping the Wössner piston I ordered will be a light one. Was recommended by Lineaweaver to go for the flat piston as opposed to the domed 470 and skim off the head instead.

And it wasn't the CB that ended up in the cylinder, it was the decomp weight from the camshaft. I just can't grasp how the darned thing could travel from the upper head into the barrel. Any ideas?

Regards,
Dave
 
Re: The Journey

HusaDave said:
I just can't grasp how the darned thing could travel from the upper head into the barrel. Any ideas?
Click to expand...

The de-comp weight was ejected from the spinning camshaft passing through the valve cover breather, air box, carburetor, inlet valves and finally coming to rest atop your piston. :wink:

Dale
 
That sounds probable, if it wasn't for the fact that I have a rerouted breather into a catchtank! Ex-works bike.

Still a mystery...
:?

Regards
Dave
 
HusaDave said:
That sounds probable, if it wasn't for the fact that I have a rerouted breather into a catchtank! Ex-works bike.

Still a mystery...
:?

Regards
Dave
Click to expand...

Then I would need to go with black magic and bad Karma.
Piss anyone off lately?
 
Hehe, actually sounds most probable so far... :lol:

There is no physical way for the weight from the head into the cylinder, but the fact remains, it was sat atop the piston upon removal of the head.

I won't bother trying to figure it out anymore, just rejoice the fact that the engine will never again suffer from the above mentioned junk on the camshaft.

Hmm... come to think of it, I may have pissed some people off by winning a Husaberg colored expensive helmet after the first race of the weekend... :evil: :evil: :twisted: :D
 

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