Technical Damage to piston skirts

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Technical Damage to piston skirts

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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 :eek: ) 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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Hi Ian,

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.

Hi Al, Thanks for the decode :devil::devil: I'm happy with the result - it's very frustrating when there is an apparent lack of information that should be freely available as my engine man says that the pistons came in a scruffy box with no information ???? (n)(n) You then have to pester the Italian maker for details - are we in the EU or what ????:eek::eek: Thanks for the tip regarding the piston, no worries as I purchased another new set to fit as the damaged piston (number 2 bore - front) was oval after the event so no go as far as refitting!! I do now have one spare (y)(y) Yes the cooler and fan should keep things under control, but I wonder as other modified cars seem to have huge coolers??
The thermostat flap functions well and the hot air will just vent to atmosphere as the heater is not fitted. I might just consider a CHT gauge (cylinder head temperature) of some sort, but that would be an extra mod. The oil temp gauge does work well too. I'm just going to take the time of careful running in and monitor the temp - I will be using Mobil 1 10w 60 too as they say - every little helps!!!:slayer::slayer:
Ian.
 
Use feeler gauges between your piston and bore to establish the clearance.
From memory , without rings fitted, place piston in bore upside down , find the blade that is a stiffish (technical term) sliding fit between the thrust face of piston and bore at its tightest point.

Ps pistons are often manufactured slightly oval plus the vertical sides are not parallel. This is in an attempt to control different expansions at different points due to temperature variations throughout the piston while engine running.
 
Hi Ian,






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.

Hi Al, you are correct the type of CHT gauge you mention is still available on Ebay for air-cooled VW vans etc priced at £46 for a 3 meter cable fitting (y)(y)
It will indicate from -200 to +1300 degC !! with a 14mm ring fitting to go under the spark plug (y)(y) Best place or not????
Now all this is fine, But does anyone know the Temperature of 500/126/panda 30 cylinder heads ????????? and what are the limits ????? I need to know this if the thing is going to be of any use!!!:rolleyes::rolleyes::rolleyes:
Ian.
 
I've looked through the few tech. books I have here, most are stored elsewhere. I found some temp. figures for internal engine components but nothing for outside temps. I'd guess putting the CHT sensor (thermocouple?) under the spark plug would possible show 200 -250C max?

Inside the engine, the spark plug insulator nose runs at 350 - 850C max.
Piston head temp. can exceed 300C.
Exhaust valve head can be 800C or more.

Cylinder temps in the vicinity of the spark plug, typically are 60C at end of intake stroke, 350C at point of ignition, max. values of 3000C and end of power stroke 1100C. But these are not relevant to measurements taken on the outside of the cylinder head. Plus you've got the effect of the air-cooling fan, cooling fins and in the case of your engine, the oil cooler.

If you have access to one of the 'point and measure' infrared temperature measuring devices as used nowadays to check for heat loss in the home (afaik they read up to 350C?), you might try this on various parts of the engine - interesting to see what temp. the little cast iron exhaust manifolds run at - this might give a better indication of what's happening in the engine (exhaust gas temp). There are also inexpensive clip on temp. gauges for stove pipes (e.g wood burning stoves) that measure up to 500C? and some dearer multimeters come with a temp. measuring probe or an infrared measuring facility?

None of these methods are going to tell you what temp. your pistons are running at, or what the piston to bore clearance is with the engine hot. And without knowing what the temp should be at the point being measured, it seems a bit pointless. Your plan to just keep an eye on things as you carefully run-in the rebuilt engine is probably just as good -no point in over-complicating things!

Regards,

AL.
 
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