Author Topic: Revolving piston rings?  (Read 393 times)

Offline BSA Biker

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Revolving piston rings?
« on: 11.09. 2018 11:50 »
Hi, just got back from a very short ride on the A7SS.

A while ago I changed over the pistons back to 7.25:1 comp. from 6.6:1. Long story.

But when I first took it out there was more smoke than it should be from oil being burnt after a rebuild. So biting the bullet, the other day I stripped the engine down again and found that the piston rings on the L/H cylinder side had turned on themselves until they had the gaps in line. Thinking at the time that perhaps I hadn't set them up correctly I reset them and fitted all back together again.

Lots of smoke on starting but this morning I was going to go for a decent ride, only did 4 miles as the smoke was as bad as before.

Will strip it down again and this time change over the rings, but any suggestions as to why it should be doing this. The pistons are old new stock with what looks like original rings in with them in the boxes.

As this will be done again on Thursday any info you might have would be appreciated.

Online Greybeard

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Re: Revolving piston rings?
« Reply #1 on: 11.09. 2018 12:18 »
I thought rings tended to rotate. There is nothing to locate them after all.

Online RichardL

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Re: Revolving piston rings?
« Reply #2 on: 11.09. 2018 12:48 »
Wondering what your idea of "lots of smoke" is. A video might clarify. I think you  might get "some" smoke from aligned rings but not billows. To me, it sounds like a different issue. Apparently, you changed pistons and kept the same rings. Maybe this is OK, but I'm sure new rings and a fresh hone would be better. I'd like to hear from others on this.

Richard L.
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Online berger

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Re: Revolving piston rings?
« Reply #3 on: 11.09. 2018 13:50 »
clean your bores up take piston rings off pistons , slightly smear marking blue {engineers blue} around the none worn part {bottom } of cylinders put a ring in and use a piston to push the ring out of the top of the cylinder and inspect the rings for how much blue they pick up. be spareing with the blue you only need a small amount, when mine was chucking smoke out I used this method and found the rings were no good  *rant*. so they went in the bin and I fitted gandinis  *loveit* test on the none worn part at the bottom of barrel

Online RDfella

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Re: Revolving piston rings?
« Reply #4 on: 12.09. 2018 12:41 »
Greybeard - yes, unless pegged 2stroke rings, they do rotate. The rotational speed is related to engine revs. at roughly 1:1000 - ie at 7,000rpm the ring rotates around 7rpm.
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Offline BSA Biker

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Re: Revolving piston rings?
« Reply #5 on: 12.09. 2018 20:26 »
Hi all, thank you for your comments, tomorrow I intend to strip it down again and check, but will change the rings anyway.

Yes I understand that they would revolve but not that they would line up and stay on that position, aligned gaps. The pistons and rings were both what looked like new old stock, certainly both the piston boxes and the rings packaging paper looked very old -  60+ years. But who knows.

Will keep you posted.

Offline BSA_54A10

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Re: Revolving piston rings?
« Reply #6 on: 13.09. 2018 13:09 »
Rings that rotate too freely are generally too thin.
So measure the ring gap in the groove .
Bike Beesa
Trevor

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Re: Revolving piston rings?
« Reply #7 on: 13.09. 2018 15:29 »
Spent the morning stripping down once again. Used the last of my spare gaskets now, so will have to buy some more when back in the UK.

With the head off there was enough oil to start an oil well!. tried the ring test and things were not good so put the old, not done much mileage rings from another set of pistons which were okay before and all was okay again after quick test run to bed things in. Will later reset the tappets again and then go for a proper spin.

Thank you all for the info and help.

Morgan