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May 16th, 2017, 09:35 AM   #1
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Question Replacement piston for FS650 '08 (628cc)

Hello!

I suspect to have broken a piston ring. I have oil dripping from the exhaust port and when I rev the bike after leaving it on idle for a while a lot of whitish smoke comes from the exhaust.

I need help on deciding what piston to get for the bike.

I have read here that the Wössner piston for 650 (8551DA) is only to be used with 82mm stroke engines. Should there be power loss / other complications using this with my engine type?

Someone said that the Wössner piston for FE570 '09 (8737DA) might be a good fit for the 628cc husa. Can someone confirm or deny that?

Prox is an option too I guess. Haven't really had positive experiences with their products so far.. (Used them in a 125cc 2-stroke, maybe those are different?)

OEM is OEM. Will fit and last although be really expensive for me (2-3 times the other options)


Thank you for your time and answers in advance!
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May 16th, 2017, 09:59 AM   #2
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White smoke is generally a coolant burning issue but you did say white-ish. Check the reed valve near and under the clutch basket as sometimes a piece of grit will lodge itself between the pedal and seat causing it to remain open. Oil will back-flow into the crankshaft cavity causing an excessively high oil level in turn causing excessive oil burning. Overfilling with oil can also have an impact on oil burning especially if the reed valve has been compromised. Fill with oil when cold to just above the bottom of the sight glass.

The reed valve is not a high wear item but can and does wear. You can check out member bushmechanic's thread something to the effect of a mongrel engine build wherein he adds an aluminum stiffener on top of the reed pedal.
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Last edited by husabutt; May 16th, 2017 at 10:32 AM.
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May 16th, 2017, 10:26 AM   #3
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Thank you for the answer. I'll definitely look into those things first. I would have suspected coolant also but oil in the exhaust is a clear tell.
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May 16th, 2017, 10:56 AM   #4
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I Haven't done any stiffening of The reed petal.

I am using a wossner 570 piston in my 628

It's not ideal but it does work.

Alternatively there is the Ktm 560 /540 piston check wossner catalog for specs I did a thread on dbw about all the dimensions etc

Prox no good I Broke one pretty quick
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May 16th, 2017, 11:02 AM   #5
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Originally Posted by bushmechanic View Post
I Haven't done any stiffening of The reed petal.
What was the purpose of adding the metal overlay on top of the composite reed?
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May 16th, 2017, 11:47 AM   #6
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Originally Posted by bushmechanic View Post
I am using a wossner 570 piston in my 628

It's not ideal but it does work.

Alternatively there is the Ktm 560 /540 piston check wossner catalog for specs I did a thread on dbw about all the dimensions etc
Thank you for your answer. I think I got this idea from your old messages.

Do you think that the 570 piston is better compared to the 644cc wössner?

Also would you care to elaborate on "not ideal". Combustion chamber just is not ideal? I don't need it to be perfect, just reliable and ok power.
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May 16th, 2017, 11:58 AM   #7
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Originally Posted by husabutt View Post
What was the purpose of adding the metal overlay on top of the composite reed?

It's an oem part so nothing added at all.

What I did do was add a second reed valve over the hole up near the cam chain to increase crankcase vacuum without running the rockers in the same vacuum since a vacuum destroyes oil mist
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May 16th, 2017, 12:13 PM   #8
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The valves on the 570 are closer to the edge of the bore so the valve pockets are different both In location and size depth etc.

I put mine in backwards and with the stock cam the valve pockets were just ok.

The squish band area is also smaller on the 570 piston. It's the same depth ie same as the head gasket thickness as the pistons are the same height. Compression ratios the same too.
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May 18th, 2017, 08:46 AM   #9
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Problem solved!
Solution: Swapped the filter mesh to my new breather hose from the old broken one.. + new air filter and less engine oil. TY for saving me €€€!
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May 18th, 2017, 10:13 AM   #10
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Originally Posted by Finland744 View Post
Problem solved!
Solution: Swapped the filter mesh to my new breather hose from the old broken one.. + new air filter and less engine oil. TY for saving me €€€!
When they went to a dual breather spigot setup on the rocker cover in,04-05, the one that was added (I think the rear one) just severely throws oil out. Presumably due to its proximity to the timing chain.

Don't overfill with oil. Keep it just barely visible on the sight glass when cold. It just encourages the motor to blow out more oil through the breather system.

Last edited by husabutt; May 18th, 2017 at 10:16 AM.
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