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Old 12-19-2010, 06:57 PM   #1
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Default piston problems

I have 69 650a bsa and i cant seem to get a grip on which ring gos were. obviously the scraper is on the bottom but in which order do the others go. my manual tells me that one of the other rings should have a T mark on one side of it and that this one would be in the middle with the T facing up. But there is no T. I have noticed a difference in the pitch of the two remaining rings but cant tell witch is the face or in which order they go. Also these stander 40 overs are supposed to fit in any position according to manual.however i have noticed a big red dot on the inside of each piston dose this indecate a direction ie front, back,or left and right when setting on the bike that is. any help would be great as i don't remmeber how i took this apart its been a long time. thanks
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Old 12-20-2010, 01:09 AM   #2
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Default Re: piston problems

I typed out a nice reply, but type too slow and got logged out and now I'm tired from wasting my breath. Can you call who you bought the rings/pistons from?
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Old 12-20-2010, 05:26 AM   #3
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Default Re: piston problems

A lot of the rings you get for these things are made 'offshore'... if they aren't chromed, and are not marked, it doesn't matter which way you put them in. I have no idea what you mean by "pitch"....if there appears to be a taper, put it in the top groove facing up.
It doesn't matter which way you put the pistons in these engines ether, but just to be sure, always put any marks facing the front of the engine, if you can.
One more thing it is critical to do on these engines is to set proper crankshaft end float and make sure the little hole on lower part of the left connecting rod is facing toward the primary side of the crankcase.
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Old 12-20-2010, 08:12 AM   #4
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Default Re: piston problems

I do a copy/paste on posts over a paragraph before hitting submit; this saves the post in the event of a timeout.

As for the rings - what Goldy sez. The ring 'inflates' on the compression stroke, and you'll minimize leakdown with the taper up. Make sure you set the rings in 120 degree intervals.

Originally Posted by beaverbikes View Post
I typed out a nice reply, but type too slow and got logged out and now I'm tired from wasting my breath. Can you call who you bought the rings/pistons from?
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Old 12-20-2010, 09:47 AM   #5
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Default Re: piston problems


Read everything there and you will be ring educated. Rings will almost always be marked for "up" orientation if they are tapered. It is true sometimes tapered rings will be used in the top groove, but only to present a narrow edge for quick break-in, and they will always have a very shallow taper, sometimes so shallow you can't tell, hence the up marking. You will almost always find the tapered ring in the second groove though where it sees less pressure and functions more as a oil scraper to the oil ring. Technically it is also a compression ring ( the oil ring functions as a oil pump) the taper in the second ring also functions as a pressure release so the pressure between the top and second ring doesn't become so great as to unseat the top ring, therefore letting oil past (detonation) see anti detonation grooves in piston design!

Also, don't forget to stager the gaps so they don't line up and make sure you have enough gap.

Edit: Forgot, so none of the rings have a T on them. A dot means the same thing, one dot means top, two dots mean middle. Got any dots showing? Because BSA wants the taper in the second groove if only one piston ring has a dot I would put it there.

Taper Faced Ring:
Owing to the tapered running face the ring contacts the cylinder bore with its bottom outer edge. This shortens running-in and improves oil scraping. The gas forces acting initially at the running face provide a degree of pressure relief (especially when used in the top groove). Taper faced rings are chiefly installed in the second groove in passenger car gasoline and passenger car and truck diesel engines. In passenger car gasoline engines they are also used in the top groove.

Last edited by Lucky59; 12-20-2010 at 10:44 AM.
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