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Author: Subject: piston ring bed in myths
bikecarbfred

posted on 22/3/19 at 06:51 AM Reply With Quote
piston ring bed in myths

please be gentle in replies.

rebuilt engine and ran for 15 minutes bedding in cam at 2k rpm.

apart from first first minute did not smoke a iota in the garage.

if i were to do a compression test and got seriously good compression does that mean the rings are bed in?

if yes , why do any more hard driving when not needed ?

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Mr Whippy

posted on 22/3/19 at 07:21 AM Reply With Quote
Just drive it, bedding in applies more to cams, rockers etc that often have a blasted finish when new

You'd get good compression with new rings right from the start. If your compression gauge can show the increase if any "bedding them in" produces it must have been made by NASA.

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cliftyhanger

posted on 22/3/19 at 07:56 AM Reply With Quote
I still think on a set of fresh rings and a hone, a bit of ring-bedding is required.Nothing like it used to be, but this may be worth a quick read:
https://www.enginebuildermag.com/2018/05/how-to-break-in-your-piston-rings-the-right-way/

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AdamR20

posted on 22/3/19 at 07:57 AM Reply With Quote
Hard driving creates more pressure in the cylinder, which forces the rings into the bores harder, which makes the two surfaces match better (ie. better sealing).

It's hard to get an accurate reading with home testers, yes you can check for consistency between each cylinder, but the value is very much a guide IMO.

The main improvement I found with hard running in was reduced oil consumption, all the MX5 race engines I've built use almost nothing at all (compared with a few hundred mils a race pre rebuild).

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rusty nuts

posted on 22/3/19 at 08:22 AM Reply With Quote
There was at one time a theory that oiling the rings when installing caused bore glaze that stopped the rings bedding in , I tend to lightly oil and drive fairly hard . Running in doesn’t seem to be required like it used to be due to be possibly due to better tolerances and lubrication?
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bikecarbfred

posted on 22/3/19 at 08:35 AM Reply With Quote
one final thing ive never really understood.

the rings can spin so what's the meaning of two surfaces mating together if the rings spin.

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flak monkey

posted on 22/3/19 at 08:44 AM Reply With Quote
The rings dont spin. Valves do, but piston rings do not.





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bikecarbfred

posted on 22/3/19 at 08:52 AM Reply With Quote
Interesting. they dont turn even with the lubrication.
okay. sure theres a few threads out there that contradict that.

but if they dont , then i can now understand the bedding in process fully.

well... in that case i hope i got the orientation of the three rings correct. sure they move abit when trying to insert them.



got from wikipidea

"However, while the engine is running, the rings will tend to rotate around the piston and not remain in the position as fitted. Many rings will then stick in one spot at random and remain there for the life of the engine."

[Edited on 22/3/19 by bikecarbfred]

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CosKev3

posted on 22/3/19 at 09:31 AM Reply With Quote
quote:
Originally posted by bikecarbfred
Interesting. they dont turn even with the lubrication.
okay. sure theres a few threads out there that contradict that.

but if they dont , then i can now understand the bedding in process fully.

well... in that case i hope i got the orientation of the three rings correct. sure they move abit when trying to insert them.



got from wikipidea

"However, while the engine is running, the rings will tend to rotate around the piston and not remain in the position as fitted. Many rings will then stick in one spot at random and remain there for the life of the engine."

[Edited on 22/3/19 by bikecarbfred]


Wikipedia

The reason you fit the rings with the gaps at thirds apart is so they aren't all in line.
The rings are easy to spin around when not compressed in the cylinder,but as above they won't turn much at all,if any,once in the cylinder and engine is used.
Ref running in make sure you use the engine as much on over run as you can

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coyoteboy

posted on 22/3/19 at 09:53 AM Reply With Quote
Rings are not constrained by anything unless a pin is used (rare). I'd wager there's zero point staggering the rings.

Jung, S., and Jin, J., “Monitoring of Rotational Movements of Two Piston Rings in a Cylinder Using Radioisotopes”, Journal of the Korean Nuclear Society; vol 31(4); ISSN 0372-7327, August 1999


[Edited on 22/3/19 by coyoteboy]





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Mr Whippy

posted on 22/3/19 at 09:59 AM Reply With Quote
there's also no mechanism or profile that would cause rings to spin. When you install rings you are meant to position the gap for each ring at 180 degs from the last to reduce the gas flow path. If the rings rotated that would be completely pointless.
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Mr Whippy

posted on 22/3/19 at 11:49 AM Reply With Quote
quote:
Originally posted by coyoteboy
Rings are not constrained by anything unless a pin is used (rare). I'd wager there's zero point staggering the rings.

Jung, S., and Jin, J., “Monitoring of Rotational Movements of Two Piston Rings in a Cylinder Using Radioisotopes”, Journal of the Korean Nuclear Society; vol 31(4); ISSN 0372-7327, August 1999


[Edited on 22/3/19 by coyoteboy]


On some 2-stroke engines there is a pin to prevent the ring rotating over time or during a bad rebuild and the gap catching on a port and snapping.

I suppose the vibration of them banging back and forwards could cause rotation till oil burning in the groves locks them in place anyway. I'm sure it varies a lot between engines and engine design.

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CosKev3

posted on 22/3/19 at 12:37 PM Reply With Quote
quote:
Originally posted by coyoteboy
Rings are not constrained by anything unless a pin is used (rare). I'd wager there's zero point staggering the rings.

Jung, S., and Jin, J., “Monitoring of Rotational Movements of Two Piston Rings in a Cylinder Using Radioisotopes”, Journal of the Korean Nuclear Society; vol 31(4); ISSN 0372-7327, August 1999


[Edited on 22/3/19 by coyoteboy]


So all the engines I've stripped it must just have been luck the ring gaps were near enough at thirds to each other then!

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Mr Whippy

posted on 22/3/19 at 12:45 PM Reply With Quote
Yeah but look at the source.

Korean engines though, probably a few mm of slop in those groves....





[Edited on 22/3/19 by Mr Whippy]

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flak monkey

posted on 22/3/19 at 12:47 PM Reply With Quote
quote:
Originally posted by bikecarbfred
Interesting. they dont turn even with the lubrication.
okay. sure theres a few threads out there that contradict that.

but if they dont , then i can now understand the bedding in process fully.

well... in that case i hope i got the orientation of the three rings correct. sure they move abit when trying to insert them.



got from wikipidea

"However, while the engine is running, the rings will tend to rotate around the piston and not remain in the position as fitted. Many rings will then stick in one spot at random and remain there for the life of the engine."

[Edited on 22/3/19 by bikecarbfred]


Can say from experience that in almost all conventional car engines the piston rings will never rotate in the bores. I have rebuilt a few of my own engines and the gaps have been exactly where they were when I originally built them. Never seen one move.

There is no rotational force which is applied in a running engine which would cause them to shift (which in itself would require considerable force).





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bikecarbfred

posted on 22/3/19 at 02:29 PM Reply With Quote
quote:
Originally posted by flak monkey
quote:
Originally posted by bikecarbfred
Interesting. they dont turn even with the lubrication.
okay. sure theres a few threads out there that contradict that.

but if they dont , then i can now understand the bedding in process fully.

well... in that case i hope i got the orientation of the three rings correct. sure they move abit when trying to insert them.



got from wikipidea

"However, while the engine is running, the rings will tend to rotate around the piston and not remain in the position as fitted. Many rings will then stick in one spot at random and remain there for the life of the engine."

[Edited on 22/3/19 by bikecarbfred]


Can say from experience that in almost all conventional car engines the piston rings will never rotate in the bores. I have rebuilt a few of my own engines and the gaps have been exactly where they were when I originally built them. Never seen one move.

There is no rotational force which is applied in a running engine which would cause them to shift (which in itself would require considerable force).


thank you guys

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snapper

posted on 22/3/19 at 10:27 PM Reply With Quote
This is what Dave Baker if Puma racing advises after you have done the static bedding in of a cam.

bed the piston rings in. To do this requires several brief applications of full throttle in a high gear to generate high cylinder pressures and force the rings against the bore walls. Put the car into 4th or 5th at 1500 to 2000 rpm and apply full throttle for about 10 seconds. Coast along for 30 seconds to dissipate any heat generated and repeat. Do this ten times. It should take about 10 minutes and maybe 5 miles if you don't have too many other cars up your chuff trying to get past.

By now you've already worn off more than 90% of the high spots on the various bits that contact each other. However friction levels inside the engine are still fairly high compared to what they'll eventually settle down to. The next stage is to gradually build up throttle usage and rpm limits. This can take place much faster than many people realise. Drive for 50 to 100 miles with gradually increasing throttle usage and rpm. By the end of this time you should be using full throttle and high rpm for brief Periods.
99% of the high spots are now worn off after 100 miles and it's time to change the oil and filter again. Use a high quality non synthetic oil. You can leave this in for either another 1000 miles or until your normal oil change interval. At that point swap to your long term oil which might be a fully synthetic if the engine and your pocket warrants it. The engine should be happy to take pretty much whatever you can throw at it after 100 miles





I eat to survive
I drink to forget
I breath to wee my ex wife off (and now my ex partner)

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coyoteboy

posted on 23/3/19 at 02:14 AM Reply With Quote
quote:


There is no rotational force which is applied in a running engine which would cause them to shift (which in itself would require considerable force).


No direct force, but plenty of vibration and twist in directions other than the reciprocal motion. Its a well established fact, so I'm not going to bother arguing it further!





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mark chandler

posted on 23/3/19 at 11:06 AM Reply With Quote
I go with Dave Vizard on this, the rings rotate at different speeds depending upon where they are located on the piston, some two strokes have pins to stop the ring turning as you risk the end catching on a port, obviously does not apply on a 4 stroke.
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SPYDER

posted on 23/3/19 at 06:58 PM Reply With Quote
According to Wiseco the rings rotate. But what do they know?
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flak monkey

posted on 23/3/19 at 07:10 PM Reply With Quote
Happy to be wrong on this one. Just saying I've never seen ring gaps anywhere other than I put them when I have stripped engines i built. Maybe just coincidence, who knows..?





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bikecarbfred

posted on 23/3/19 at 09:30 PM Reply With Quote
see.... if the rings rotate... then what's the next myth... piston ring bedding in.

i bet the rings bed in after a few minutes lol if they rotate what's the point of two surfaces mating when there going to spin anyway.

i noticed my smoke went away after a minute, i bet at that point the rings are bed in.

if the rings never spun then i can understand that 3rd n 4th gear full throttle acceleration but the fact if they do turn defeats the purpose.

think about it. the amount of lubrication , slipper oil, their bound to move.

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