Piston rings

[hilton484]

Ok so basically I ordered some for the cg10 and they refunded after a few emails as they didnt have them in stock at best parts store so I had anpther look on ebay and the one that were the right year said they were fpr 72.5mm bore iirc not the 71 that the haynes manual says coildnt find any that were the right size but then I found some on ebay with the wrong yr (said for 83-93) and wrong engone code ma10 I think it was but the right size bore so I just ordered them yesterday taking a £50 gamble

They arrived today which was quicker than expected so ive took number 4 pistons rings off to compare. The top 2 are both very similar but a wider gap at the split so ill check them dimensions with haynes but I think they will be good but the oil scraper is a different design.

Only slight as the sizes seem to match up but the waves go in and out (along the radius of the piston) wheras the standard ones go up and down (cam to crank)

Cant see the scraper making much difference as it doesnt have to seal it but will it be ok to use? I imagine it has some benefits or somat, possibly less likely to get clogged with crud?

What you reckon peeps

 

[pollyp]

orientation of the spring wave doesn't matter, it still performs the same.

more important to check all the clearances are within the original spec and that the spring is pushing the oil rings against the bore with adequate force/drag cos there's no combustion pressure to help it.

too little = oil control issue, slow oil ring bed-in
too stiff = high drag, rapid oil ring wear

 

[hilton484]

Thanks paul thats good news, I am a little concerened about the gap being bigger as I would have thought tho old one would be bigger from stretching after wear but ill check all the dimensions against the haynes book to see how they shape up. The width and thickness match up (well by eye) but ill mic them up when I go in.

An just reread your post and realised you meant the specs for oil ring lol but ill mic that up too

 

[hilton484]

Measured old v new and there all pritty close but some little diffebce and decided it close enough to give it a test fit and check the gaps and then make final decision.

 

[frank]

what are the end gaps hilton ? and coilpack rings are different eh

 

[hilton484]

As they are or after pushing in and removing.

Also I read thats how you check it but couldnt help but think that they would unspring when I take em back out? Ill give it a go later on

 

[frank]

the ring gap when inserted squarely in the bore mate

 

[pollyp]

how I measured & gapped mine

 

[hilton484]

thanks guys

frank as soon as i saw that pic i had a headslap moment, i remember reading the same bit of haynes book and understanding it as that but misread it this time for some reason as put it on the piston

and i like the little grinding jig you've made there pollyp, like how youve got everything to hand and layed out neat and clear, something i strugle with ive got better generally from work and 5s stuff etc but mainly struggle for space atm, using tub and resealable food bags atm

the results are anyway
oil rings are perfect, and so is the second ring
but top ring is too thick for the groove and gap is too small.

its .33 thicker than the ring that came off and i havent cleaned the pistons up or honed yet so i wont adjust it till ive done all of that and coming to rebuild but think ill just rub both side on some fine wet and dry, and ill make a grinder like that to adjust the gap. was .25mm when i checked it so want to be double that but i think it should be all good to use.
happy to crack on getting the filthy bugger looking spanking decided what the hell after seeing a nice gold painted engine and order (and recieved) some chrome vht, should be interesting was gonna do the gearbox too but the matt black cans arrived too so im gonna do the geabox case with that

 

[hilton484]

*using multiple tubs not got everything all crammed in one bucket

 

[frank]

shaving .33mm off the sides of the rings will take forever hilton ! and you will lose the important gas sealing profile of the ring.
opening the groove in the piston is the option i took a while back, and that .25mm gap is what i set for the top one

 

[pollyp]

first I'd advise to measure the clearances after it's all cleaned n re-honed.
this ensures that no dirt, crud etc gives false readings. measure several times to validate the value.

also after re-honing, remember that after break-in, the rings & bores would have worn in a fraction and the end gaps will have expanded abit.
you can decide either to intentionally gap it slightly tighter than the spec min gap so hopefully after break-in it'll be exactly at/just above the perfect min gap but risk the two ends getting too tight if pushed too hot during break-in.
or gap it exactly at min gap and know that it'll expand slightly after break-in (I chose this safe option).

after I bedded my forged piston rings the gaps expanded up to:
top = 0.025mm
2nd = 0.127mm
upper oil ring = 0.102mm
lower oil ring = 0.102mm
http://micra.org.uk/threads/pollymobiles-rebuild.35251/page-92#post-624126

haynes says top ring gaps should be 0.2 - 0.3mm so ur 0.25mm gap (before honing?) is within spec. read it after honing.

I agree with frank bout the thickness issue.
sanding down the rings by hand will not guarantee a perfectly flat and smooth face nor a even thickness all around, all of which are essential to a good seal against the piston ring groove, and will take forever to accurately remove that amount and repeatedly checking the thickness all along the ring.

the most effective options as frank pointed is to either machine the piston ring groove to match the new rings (seperate piston from rod & lathe the grooves)
or source another 71mm top ring that'll hopefully suit the original piston ring groove (source rings, wait for it, fit & check clearances hoping it's correct)

the standard piston rings are part# 1203399B20
http://nissan4u.com/parts/micra/er_...n_and_crankshaft_and_flywheel/illustration_2/

prob not easy to trace just the top rings alone (nissan dealers only sell em as whole set)
this one I think is a wholesale type place, dunno
http://www.yoyoparts.com/oem/6103338/isuzu-1203399b20.html

on ebay there's a 71x1.5x2.80mm ring for older micra's
http://www.ebay.co.uk/itm/NISSSAN-M...INGS-SET-/271148389765?_trksid=p2054897.l4275