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pistons???????
https://www.ausmini.com/forums/viewtopic.php?f=2&t=28376		 Page 1 of 2
Author:  Ziegech [ Wed Feb 21, 2007 3:07 pm ]
Post subject:  pistons???????
hi everyone my mini is a smoker and a bad one ive tried to tell her to quit but she just wont stop i had the cylinders all bored professionally at XXX and they supplied pistons with rings installed when i rebuilt her at the moment im trying these fancy stop smoke and stop leak fluids (last ditch effort) to try and avoid an engine rebuild what worries me is the fact that when i had the head off to fix an oil on clutch plate problem :roll: i noticed i could fit a 10 thow feeler gauge not wire actual gauge down the sides of my pistons is it possible they done a +.30 bore and given me a +.20 piston or something or did i need to rotate my piston rings more on installation? HELP im not an expert when it comes to the details but i have a decent basic knowledge any advice or ideas are much appreciated especailly as im starting uni next week and my car is smoking like a monkey :oops: thanks for all ur time and comments
Author:  DOZ [ Wed Feb 21, 2007 3:19 pm ]
Post subject: 
The pistons are smaller diameter at the top of the crown to avoid seizure when hot, the skirts are actually oval shaped and the diameter of the bore is based on the larger skirt size (this is perpendicular to the gudgeon pin). Unfortunately you can't easily measure this without taking the piston out of the bore

Assuming the rebore is aok and there are no issues with the new parts the only way oil would be getting into the cylinders is either a leaking head gasket or worn valve guides.

Regards

Daniel
Author:  AEG163job [ Wed Feb 21, 2007 3:28 pm ]
Post subject: 
Hmmm, I think you can forget using Nicorette patches :cry:
Seriously, 10 thou piston to bore clearance sounds excessive. I think it should be more like 3 on assembly.
Did you check the ring clearances in the bores?
A compression check firstly may give you some idea of problems with the rings. Also, it sounds like you may have a crankcase breather problem if oil is being forced out thru the primary gear onto the clutch. Perhaps excess oil is going down the valve guides as well.

Bad compression will mean a re-build most probably, assuming valves are OK. Is it blowing smoke on acceleration or just over-run?
Author:  sports850 [ Wed Feb 21, 2007 3:30 pm ]
Post subject: 
When does the mini smoke , when you first start it up and keeps going for a while getting better , particularly after sitting overnight , or all the time ? As DOZ said , valve guide seals can be a major cause of mini's smoking .
Author:  DOZ [ Wed Feb 21, 2007 3:33 pm ]
Post subject: 
I just measured a set of 1293 hepolite pistons and the crown is about 0.028" smaller in diameter than the skirt.

It would take a pretty foolish machine shop to machine the bore 10thou bigger than the pistons they've supplied. I have seen it done before though, even funnier was the machine shop that machined a block for stepped liners, without the step (nothing to stop the liner moving down in block).

Check the measurement of the bore with a vernier and check piston marking to determine the size of piston. This should show if they bored to the correct size.

Daniel
Author:  Ziegech [ Wed Feb 21, 2007 3:44 pm ]
Post subject: 
umm i put brand new old and new style valve guide rubbers(dont know exact name) and im pretty sure ive got decent pressure in the pistons and equal pressure through out all pistons ive got a brand new head gasket on and the clutch being oily was due to my "she"ll be right" attitude on a (what i found out to be) extremely worn primary gear ive got a rocker cover pipe running to below the air filter on one of a set of twin su 1 1/4s breather pipe on side covers is open to 10tho as apparently spec but still seems to wont to smoke. starting to consider those nicorete patchs thanks for ur help ill have a fiddle. would a shorter pipe off the rocker cover help at all? thank u all so much great help
Author:  DOZ [ Wed Feb 21, 2007 4:10 pm ]
Post subject: 
If you think the oil breather is causing the problem then remove/move it from the carbies. Check the spark plugs for oil signs, might only be one cyl.

Are you sure it's oil smoke and not power smoke (black). Power smoke from running rich?
Author:  Ziegech [ Wed Feb 21, 2007 4:20 pm ]
Post subject: 
ah that may be some of the problem no signs on the spark plug but no smoke when warm and idle white smoke with mid to low revs and black smoke over about 4 when not moving. might pull the colour tune kit out tonight my mixture will be out as my carb decided to try and pay a visit to the uni joints and walked down the back of the engine slowly without me knowing so mixture is all over the place thanks for all ur help
Author:  Ziegech [ Wed Feb 21, 2007 8:12 pm ]
Post subject: 
ok did a compression test got 160 160 165 165 pounds ? seems even maybe just buggered oil rings?
Author:  1018cc [ Wed Feb 21, 2007 9:12 pm ]
Post subject: 
I dunno but I'm with you - those kind of numbers seem good - but having said that what's your compression ratio?

If you compression ratio it rediculasly high those could in fact be low numbers but if your car still has a standard CR then those numbers are fine.
Author:  Ziegech [ Wed Feb 21, 2007 9:18 pm ]
Post subject: 
hmm i didnt shave it or anything and the pistons are standard i made another topic called oil cap i dont know if maybe im over pressurizing my rocker cover with a blocked breather of some kind on my oil cap or could it be my oil rings. i found a great way to stop the smoke tho i just close my eyes its the simplest solution i could find :D thanks again for ur time
Author:  1018cc [ Wed Feb 21, 2007 9:36 pm ]
Post subject: 
Well if it's still all the standard CR then those numbers are fine - they are high BUT most importantly there is only a small difference inbetween all of them.
Author:  My_Mini_Rocks [ Thu Feb 22, 2007 10:03 am ]
Post subject:  Pistons
Are you using hepolite pistons and rings?
If so...well that may answer your question...we have had heaps of customers 'blow smoke' after a rebore with hepolite brand.
We stoped using them 5yrs ago and have had smooth sailing ever since (now use the hypatec with hastings rings)
I think the problem is with the hepolite oil rings.
Author:  Ziegech [ Thu Feb 22, 2007 1:22 pm ]
Post subject: 
i have no idea what rpm gave me but thanks for the heads up
Author:  1360 LS [ Thu Feb 22, 2007 1:51 pm ]
Post subject:  Re: Pistons
My_Mini_Rocks wrote:
Are you using hepolite pistons and rings?
If so...well that may answer your question...we have had heaps of customers 'blow smoke' after a rebore with hepolite brand.
We stoped using them 5yrs ago and have had smooth sailing ever since (now use the hypatec with hastings rings)
I think the problem is with the hepolite oil rings.


I have heard of this before...... and where referred to me a heap-o-lite shyte ring wise not the pistons themselves.
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