4 replies to this topic

[andyb16fun]

Good evening everybody,

I have a question regarding the amount of lateral movement that is acceptable in an A+ series?  I have a 1988 vintage 1275cc Metro GTA A+ series engine in a mini.  It's one I have had moth balled for about 12 years.  I started it the other day and it was kind of smokey.  I thought the valve stem oil seals were to blame and have just stripped the head off.  I noticed that cylinder 1 was a bit oily.  I put my fingers on top of the piston and pushed it back and forth and found there was some latterl movement within the bore. 

I took a video of it here  Can anyone tell me if the amount I have is normal?

Cheers,

Andy.

 

[tiger99]

It does seem quite a lot, but it would be useful to get a feeler in the gap and measure it, then do the same half way down the bore. There will be piston to bore clearances specified somewhere. Ok, you can only measure at the very top of the piston, because of the rings, but it may give something more definite to go on. Otherwise, piston at bottom of stroke, and internal micrometer at top and middle, will tell you a lot.

 

The movement is usually worse front to back than side to side, because the thrust side of the piston is on the front, facing the front of the car, on the power stroke, rod pushing crank down and backwards.

Edited by tiger99, 08 February 2014 - 11:45 PM.

[andyb16fun]

Cheers Tiger99, I shall do just that and see how I get on. 

Andy.

[andyb16fun]

Checked and I have about 0.30mm, not good when the max suggested is 0.072mm as far as I have found.  Time for a rebore me thinks!

Andy.

[carbon]

Andy,

 

The 0.072mm clearance (about 3 thou in old money) you mention is measured at the base of the piston at right angles to the gudgeon pin axis. Nothing to do with the clearance between piston crown and cylinder wall.

 

The diametrical clearance at the top of any piston is much greater than at the bottom - if it was not so then the engine would sieze as soon it was made to work hard due to the higher temperature at the crown of the piston.

 

Would suggest that you clean all of the carbon off the top of the inside from all 4 bores, then try the 'fingernail test'. What you're looking for is any significant wear lip about 6mm down from the top of the bore, where the top piston ring is at tdc.

 

Also worth checking the crown-bore clearances on all 4 bores, see if there are any significant differences.