piston rings seem to be the problem with the hog
Turbo Mini Forums

well after fitting the new set of mega pistons after the last cafuffle she has done 200 miles and guess what the smoking has came back on a fastish down run eg 3500 rpm to 2500 the put the acclerater down and the smoke would come out of the exhaust not lots but enough but would only do this when oil is hot eg over 70 deg.

so decided to strip her down for a check to make sure the lands havnt gone south again.

pulled all pistons out and all looked good.

so pulled a set of rings out and remeasured in the bores they were same as when i fitted from new so here goes and dont fall of your puter chair.

1st comp ring 22 thou
2nd comp ring 23 thou
oil con 51 thou


when i fitted these the first time round on the first set i thought they were some way a bit excessive the comp rings i can just about see the need but the oil control was some 38 thou to much.

all the otheres i have built have all been around the 12-14 thou gap.

i have measured the bores and pistons with a digi vernier but still cant see if the rebore was to much, i doubt it very much as the engineer company build race engines. but will take it to them to check it out though.

but even still some 40 thou to much on the oil control ring is some 20 thou to much much dia( if my maths serves me right) and i cant see that as the the pistons are a snug fit around the skirt so knock 20 thou off they certainly wouldnt go in.

i dont no it is certainly pissing me of now.

tried to ring neil at mini sport north ( not in)
gary at main shop ( very busy).

always looking for them bigger bunches of bannanas

Hogster, 0.040" too big on the gap is equivalent to 0.011" too much on the bore, looks like the oil rings are very worn or were 0.010 undersize to the bore to begin with.
Regards
Dave

my sentiments dave seem to big to start with bore isnt 11thou to big that i know as i have just measrued bottom skirt to bore clearance and is 2 thou at the back of the skirt so seem fine on bore size.

i recon the oil control rings are for a +20 bore and not +40 bore which would equate to the fiq.

but this is 2 sets now not just an odd set.

so something is amiss some were.

always looking for them bigger bunches of bannanas

oh and the first set had done 1000 miles and second only 200 miles

always looking for them bigger bunches of bannanas

Measure the piston across the pins just below the scraper ring, then measure the bore. If the difference is bigger than the piston clearance, the bore is too big.

This still relevent? though I wouldn't think so as the pistons were bought nearly 5 years ago, but mabie a similar problem has arisen at the suppy end.
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=125891

Just a possible line of enquiry.

Edited by minimole23 on 8th Dec, 2007.

sounds like minimole but we are talking 8 pistons worth here so thats some cock up

always looking for them bigger bunches of bannanas

this sounds exactly like what happened to me, my rings were 20 undersized, on start up it would smoke for thirty seconds and then stop, i would only be able to see smoke when i was on over run and then when i put my foot down a little puff would come out of the exhaust, took it all apart and sure enought rings were for 20 oversize bore and i had a 40 oversize bore, guess what big ring gaps same as you

"Can I legally marry people now that I am ordained in the Church of the SubGenius?" aka i know jack sh"t

i also make things

i love coming home to chrome

If it is indeed the wrong ring size, then yes the ring tension is too light.

Id still be checking the piston clearance though. Look at it this way, if the piston rocks excessivly in the bore, the rings will not be able to do their job properly

Has it bored slightly on the piss perhaps? Even a good machinist has the odd cockup. Only guessing...but something is amiss.
Aren't mega's similiar to omega rings?

is there an alternative ? total seal rings?

i need to replace mine on the rebuild and would rather use the best i can get

well reading the mini columns, old calver is liking his total seal rings...

sound worth a shot for sure.

Not had a problem with my 74mm total seal rings, I rate them.

http://www.performanceunlimited.co.uk

Edited by Sprocket on 8th Dec, 2007.