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Wössner piston for FC550 Y2002/compression/deck height

S

stephan

Joined Oct 2006
46 Posts | 3+
Helsinki, Finland
Hello

Most fairy tales start with once on a time.... For this forum probably more like I had lying on a shelf.... a Wössner piston part #8602DA with casting mark at the bottom W4108. I compared the pistons, too quickly yes, and installed the Wössner piston. The piston comes 0,3 mm above deck heigth and as I understood it should be about zero with a FC550. Took everything apart and compared the pistons again, the pin heigth is 0,3 mm less for the old piston. The casting mark at the bottom is also W4108 and on top a number 21201. Is the old piston a OEM and have other people experienced the same?
The con rod length is 123 mm, old and new. When ordering the 2002 (124 mm) part you'll receive the 2003 (123 mm) part, casting number 156). Is the thicker 2001 gasket a safe/good solution or better to purchase the OEM piston?

Regards,
Stephan
 
RE: Wössner piston for FC550 Y2002

you may have the perfect piston!

you too must check the squish exactly the same way as i prescribed in the other thread.

regards

Taffy
 
Hello,

Today I had time to check again this Wössner piston in combination with my engine. Officially Wössner doesn't produce a piston for the 550 2001-2003. Husaberg doesn't sell the 124 mm con rod and thicker cylinderhead gasket (# 200 321-01 470/550/650 (thick) -01) anymore (checked this with the Finnish importer). This means an OEM piston with a 2mm squish band as in the other thread about ElSnorro's engine rebuild or shave a little of this Wössner piston to achieve the correct deck height.
The squish I measured is 0,95 mm as could be expected with 1,25 mm for the compressed gasket minus 0,3 mm for the deck height. When the 2004 -2008 550 engines have a deck height of zero this means their squish is 1,25 (the compressed gasket only). Is a narrow squish band as 0,95 mm a problem?
Secondly I noticed that the cavity for the inlet valves is a little smaller, single angle at the back side, what probably has to do with the smaller inlet valves of the 2004-2008 engines. I'm going to use the torque cam shaft and this setup hasn't much room left for dancing. Probably have to machine them too to be save?
I would think that other people rebuilding/tuning the older 550's have run in the same dilemma.

Regards,
Stephan
 
i always check the valve into the piston with lots of plasticine around the back. over the years i've learnt that a valve often doesn't touch the bottom of the cut out but instead 'clips' the back edge. so i hand rotary file away a new angle. run a felt-tip along the rim/edge and create a 2mm line and then machine the piston by hand.

0.95mm squish is pretty much perfect. what i want to know is what is different about this piston to your OEM? it is how much higher? is it flat all over? then i can follow what you're saying?

regards

Taffy
 
Hi Taffy!

Both pistons are flat all over, the old and new (Wössner). The difference in height is the distance between top and the gudgeon pin. 13 mm for the old and 13,3 mm for the Wössner (this is why the deck height is +0,3 mm). I was worried about the squish band being too small. I have no idea if the old piston is OEM. Unfortunately I don't have the possibility to compare it with a new OEM piston. Maybe ElSnorro can tell his piston's height? But both pistons have the same casting mark at the bottom; W4108. An early Wössner?
The cups are easy to modify to prevent the valves from clipping the back edges and I'll take care for this.
When reading other threads about deck heights of -1/2 mm with 550 engines, I wonder about my old piston, did Husaberg install different pistons than selling as spare part? Is the 2004-2008 OEM 550 piston height different from the 2001-2003 OEM pistons?
For me there's a small mystery in this all.

Best regards,
Stephan
 
stephan said:
Hi Taffy!

Both pistons are flat all over, the old and new (Wössner). The difference in height is the distance between top and the gudgeon pin. 13 mm for the old and 13,3 mm for the Wössner (this is why the deck height is +0,3 mm). I was worried about the squish band being too small. I have no idea if the old piston is OEM. Unfortunately I don't have the possibility to compare it with a new OEM piston. Maybe ElSnorro can tell his piston's height? But both pistons have the same casting mark at the bottom; W4108. An early Wössner?
The cups are easy to modify to prevent the valves from clipping the back edges and I'll take care for this.
When reading other threads about deck heights of -1/2 mm with 550 engines, I wonder about my old piston, did Husaberg install different pistons than selling as spare part? Is the 2004-2008 OEM 550 piston height different from the 2001-2003 OEM pistons?
For me there's a small mystery in this all.

Best regards,
Stephan
Click to expand...

Will measure my piston heigt tonight.
 
i think if you two can start by tellng us the number on the box we can take this further. so need the numbers on the box....

i have a new in the box 100mm marked 8551DA and it is 12.7 to 12.75mm above the GP. the smaller figure is for when i push the GP up at the same time.

so now we have a 12.7, a 13. and a 13.3mm piston. woessner do several numbers so i'm sure we can work our way through these.....

regards

Taffy
 
Hi Taffy,

Wössner piston part #8602DA on the box and with casting mark at the bottom W4108. This is a 550 piston for 2004-2008. The piston you have is in the Wössner catalog mentioned twice, for 650/550 2003-2009 and 650 2000-2009. Is the piston you have the "ashtray" type or is it flat like the piston I have?
My old piston is probably the OEM because ElSnorro has exactly the same measurements and casting mark. But how can we explain the 2 mm squish band for his engine?

Best regards,
Stephan
 
the piston is still flat gentlemen ok? i have written to the italian at the factory asking that they make a replica of the ashgtray piston but he didn't even reply. i asked for the price to commision 100 of them. no reply.

here is a link to the husaberg pistons gpage. there is a misprint stephan in that they meant to say FC, FE 550 from 2003 but they dropped the 650 in there. later it is as you say under all 650 models.

they also have the 100mm piston for the 600 fer chrissakes and they have already mentioned the 570. i didn't think the 570 had a 100mm bore but i guess it must have....

when i get 100mm pistons i can change the code i order and right now manxberg / keiran has minimal squish and i can see how in the future i may be able to help with this.

elsonnorra/stephan
if you clean up your old piston crown you'll see the manufacturing code indented lightly i think - please have a look.

this is the email address of toni pirocci: [email protected]

but i have given up with him, a complete ****** if ever i met one so i suggest going to the international rep: [email protected]

they need to clean up their site and we want ashtray pistons!

regards

Taffy
 
stephan said:
Hello,

Husaberg doesn't sell the 124 mm con rod and thicker cylinderhead gasket (# 200 321-01 470/550/650 (thick) -01) anymore (checked this with the Finnish importer).

Regards,
Stephan
Click to expand...

according to my supplier, there is no problem getting this rod. maybe £226.40 is enough to stop you though!

you never know stephan, my name on your bike and we might be able to do something for you!

regards

Taffy
 
Hi Taffy.

Originally I ordered the 124 mm rod, part # 210 191-01, following the owner's doc and some threads the 2001-2002 550 engines have the 124 mm rod. But when opening the box I found the 123 mm rod with casting mark 156. The same rod, length & mark, was installed in my engine and also in ElSnorro's. If your supplier has this rod on the shelf, is it possible if he could measure it's length and/or has it a different part number?
ElSnorro mentioned a free play about 1 mm with his rod, this could be the reason he measured a wider squish band. I measured the squish band with the rod replaced already. Both our old pistons are the same and probably OEM.
This far we know that with the 123 mm rod and a stock piston for the 550 2001-2003 the deck height will be about zero. And with the Wössner piston part # 8602DA the deck height is + 0,3 mm resulting in a narrower squish band ( 0,95 mm) and the cups have to be reshaped at the back sides.

I searched for more information about the purpose of the squish band and generally a narrow squish band is indeed preferred to force the mixture to the combustion chamber. A flat piston or dome shaped piston split generally the opinions. A flat piston seems to give a more responsive but less flexible engine. Is there any benefit with the "ashtray" shaped piston except that it's possible to machine a few mm of the top safely. I know these pistons from diesel engines but they are normally heavier than flat pistons.

Best regards,
Stephan
 
Off course...
I didn't thought of that when I measured squish, my big end is bad, so my squish will be bigger than normal..

God im feeling stupid now :p
Thanks for the heads up stephan!
 
Hi ElSnorro,

Don't worry, took me too some time to work this out after you mentioned your piston height. I was really wondering how it was possible we measured different squish bands with the same pistons and rods. :?

Best regards,
Stephan
 
stephan said:
Hi ElSnorro,

Don't worry, took me too some time to work this out after you mentioned your piston height. I was really wondering how it was possible we measured different squish bands with the same pistons and rods. :?

Best regards,
Stephan
Click to expand...

by the way my this was on top of my piston:
21201-2
Maybe the 2nd size of the 100mm piston?
 
Hi ElSnorro

My old piston has only 21201 stamped on it. The oversize pistons are in the part list from year 2004 and I could see from your images that the cups are large as in my old piston. Would be interesting to compare the pistons we have with a new original Husaberg piston. But for now I'll stick with this modified Wössner. When the engine gets too limited in its power band I'll try to get a different gasket or order an original piston. I'm using this engine in a MX-sidecar and some extra punch at the bottom is never bad.

Best regards,
Stephan
 
ok

i've had a word with david larsson and basically the finnish importer is right, although the part number is still ok, it's only because it's for the later - and shorter - rod. so you're out of luck!

so all those with too much squish should, IMHO, go out and buy the 2006 100mm piston. not cheap but you will get a better bike. look at the advantages

shorter and lighter rod, better combustion path, reduced lead on the ignition advance, more power.

regards

Taffy
 
Taffy said:
ok

i've had a word with david larsson and basically the finnish importer is right, although the part number is still ok, it's only because it's for the later - and shorter - rod. so you're out of luck!

so all those with too much squish should, IMHO, go out and buy the 2006 100mm piston. not cheap but you will get a better bike. look at the advantages

shorter and lighter rod, better combustion path, reduced lead on the ignition advance, more power.

regards

Taffy
Click to expand...

Ok Taffy thanks for the info.
Send you an email :)
 
i have elsnorro's new OEM 100mm piston sitting here. it is a quality peice of kit i have to say and i've measured it all up.

the deck height above the gudgeon pin is 14.3mm, squish band is 6mm, depth of dish is 1.9mm, comp ring = 1.17mm thick, oil ring 2.3mm thick.

this will transform your 2.05mm gap into the perfect 1mm!

i can feel the power already!

please let us know the realtime compression ratio when you measure it elsnorro!

i have a customer who this week SM'd a 550 with the Wossner 470 HC piston in it. reckons it has gained in 4th, 5th, 6th but with more torque??? you can't argue with his feelings that it's a lot quicker but you may question his evaluation of where it made it's power. BTW, a Higher comp is meant to really aid torque the most but that's all relative to what it was when you started. a 7:1 compression increased would simply help everywhere!

john: any chance you could go back to your very first post in this thread and change the thread title? something about compression/deck height???

regards

Taffy
 

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