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------- I have heard back from CPS. Below is the content of the message -
Hallo,
my boss says>:
1° Liner 0,10 cents
2° liner 0,12
regards
Francesca
CPS s.r.l.
Now I'm not good with the Italian lingo, but I take the message to say - Early 126 cylinder 0.010mm and the later 126 cylinder 0.012mm ???????????????????
If this is so I believe that my piston to bore clearance is WAY too tight, (these pistons must expand a lot!!!!) but I shall confirm if these figures were used during the rebore anyway.
Ian.
Hi Ian,
I don't speak Italian but have sometimes had to figure out what Fiat technical info. in Italian meant in English when no English version was available.
I would interpret the above message as:-
Step No.1 - Bore cylinder so that piston to bore clearance is 0.10mm
Step No.2 - Hone cylinder so that piston to bore clearance is 0.12mm
which would agree with your Engineer's figures and those indicated by 'jackwhoo'.
If you intend to re-use these pistons and the existing bore size, I would urge you to remove some metal at the 4 damaged areas by filing/ sanding/ linishing or some other means.
In previous posts I've mentioned that some pistons use cast-in 'struts' to control expansion. Other pistons have a horizontal slot just below the head of the piston or in the oil ring groove to control expansion by limiting heat transfer. If your pistons are machined from a billet, they won't have expansion control struts and might not have the expansion control slots either (some people think they weaken a piston). But there's seems to be a lot of material around the gudgeon pin bosses in your current pistons and I suspect this may be pushing the piston skirt outwards at the 4 points of damage as the piston heats up.
I even mentioned ( for anyone who might be interested) a text book that contains a lot of info on piston design features including the complex shape of a piston (it's neither perfectly circular or perfectly cylindrical ) and how it changes shape as it heats up, plus lots of other info.
You mentioned you were going to keep an eye on engine temp. in future and that you have an oil cooler fan and would fit a different temp switch. I'm wondering if you've checked the engine thermostat for correct operation?
I'm guessing you probably have an oil temp. gauge fitted but there used to be temp. gauges and pick-ups available for air-cooled engines - the pick-up often took the form of a thick washer that could be fitted under e.g. a cylinder head bolt. This would provide a good indication of cylinder temp. and act as an early warning system.They're probably still available for air-cooled VW's. Of course, you might already have something similar or better already fitted?
Good luck with the next engine reassembly!
AL.
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