Piston ring gaps orientation

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scooby

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I'm working on assembling my howell v4 and was wondering what orientation relative to each other should the 3 rings gaps be when installing the piston in the cylinder?
 

rklopp

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FWIW I stagger the gaps 0-180-0. Conceptually, that gives the longest path for gas to sneak through all three gaps. Maybe just as effective as tossing a lucky penny in the fountain.
 

djswain1

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Standard practice on full size engines is to space the ring gaps evenly, so 120deg with three rings. Most engine workshop manuals are particular about the installation position but as Tornitore says they do rotate position when in use anyway. Lubricate the rings in the grooves well before installing the pistons.
Cheers, Dave.
 

tornitore45

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Just to limit my blanket statement above.
Some 2 stroke engine have anti-rotation pins, to avoid being snagged passing by the ports.

I suppose that for microscopic reason in the ring/groove geometry and in the chamber pressure distribution a ring has less resistance to rotate in one direction than the other. Pressure in the gap will move the ring toward the least resistance.

Orienting may make one feel better, or possibly help in starting a new engine but the proof of the pudding is in disassembling the engine after several hours of operation.
 
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Mechanicboy

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I'm working at car shop. Most common to set all 3 piston ring gap 120 degree or 4 ring 180 degree degree ring gap when mount the piston into the cylinder with 2 rings in 45 degree off-set from 2 other rings, let us say the two rings 180 degree then next 45 degree off-set then 2 rings 180 degree.

2 stroke engine has pin in the ring groove to prevent the ring is rotating and snag into the port in the cylinder.

Some 2 stroke engines do not have the pin in the groove to prevent the ring is rotating if the ports has a lot small ports in the cylinder and the rule is same as 4 stroke engine where the piston ring gap is positioned.
 

Brian Rupnow

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Three positions at 120 degrees does the trick.--And, DO NOT have a ring gap in line with the wrist pin. That last bit about not being aligned with the wrist pin is very important. I have found that out by trial and error.---Brian
 

scooby

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thanks for all the replies

Brian, if I under stand you correctly, top ring would be at 12, 2nd ring at 4, and last ring at 8 o'clock
 
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jeez.....i love how wild a tangent the simplest questions go on here , now , coming from a practicing mechanic of more than 30 yrs , i just want to set the 'piston ring gap story ' straight , now remember this is in relation to commercially produced engines be it car , motorcycle , mower , stationary etc. (home made little motors may follow some made-up wisdom of which im not aware , but the afore mentioned 'real' motors follow strict ring-gap-rules if one wants it to work , 2 stroke ring are 'pegged' as stated , to prevent interference (failure) with port edges , 4 strokes (working on the most common format of 2 compression rings & 2 oil control rings with a sprung back-up ). ring gaps are staggered to reduce/eliminate blow-by , comp. rings gaps opposite each other , at a 45 across gugeon if one was looking down on top of piston (so as to avoid thrust side of piston bearing on gap/s , barrel ground pistons are tighter in this direction too , avoid gugeon sides too as barrel ground pistons are looser in ths direction) ive tried explaining off-set piston pins previously-fell on deaf ears (it exists on all commercial pistons in spite of this), piston thrust & ovalic wear of the bore(though slight)prevent any meaningful rotation of these rings , be rather low comp. if they didnt ,likewise oil control rings same orientation but 180 off-set to the compression ring above it ,then 180 to each other , these ring have a spring pushing them out to the bore so same reason as above to not rotate (especially in relation to each other , be a huge smoke generating machine otherwise , dont worry ive seen the consequence of improper ring assembly & its not pretty),please refer any ring manufacturer & any engine repair/assembly manual to confirm this , manual will show diagram/s and a similar reasoning to above
 

Steamchick

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Basically, reading all the above, everyone has got it right.
But what most mechanics don't realise, although some know and have experienced this, the rotation of rings does happen (except as you explained for pegged rings on 2 strokes, and oval pistons like the Honda and other specials). The proof is during long term endurance testing of engines, that I experienced in Engine Design at a well known manufacturer. In a 200 hour test, there were a series of spikes in the oil trace in the exhaust. Each spike on the trace is related to an incidence of ring groove alignment, where the ring grooves leave an un-wiped line of oil on the bore that is exposed to the combustion, and the vaporised oil is detected in the exhaust detector. The detector data is integrated over a 200 hour test to give an "overall oil consumption" - which forms part of the Engineering of the service interval and oil check intervals in service documentation. Actual oil consumption is also checked by measuring the drained oil volume at the end of test, compared to initial fill.
Some of the necessary additives in oils are harmful to exhaust treatment catalysts, so obviously the whole package has to be thoroughly measured, checked, evaluated and engineered to provide the customer with an adequately durable finished vehicle.
Yet there are always instances where the consumer will use a product outside of the constraints considered by the Engineers, but >99.7% of the products work as expected.
Please don't knock the Engineers for what they do, as they have far more information, historical and test data, knowledge and expertise available than the user's and service mechanics can ever have.
Cheers,
K2
 

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