Register Login
Lamps by Post - For all your lighting needs
Reply
 
Thread Tools
Old 16-04-2018   #31
Join Date: Jun 2009
Posts: 663
Thanks: 52
Trader Rating: 0
United Kingdom 
Re: Damage to piston skirts

A hint of sunshine and I finally got outside and gave the worst piston from no 2 cylinder a bit of a soak in petrol. The 795cc engine was mothballed in 1985 and some oil poured into the bores that had now gone to the consistency of a very thick grease. The piston from no 1 is virtually unmarked but no 2 has 4 very distinct vertical bands of rubbing front and back of the piston. The bands do not seem to correspond to any feature inside the piston.
Attached Thumbnails
Click image for larger version

Name:	image.jpeg
Views:	10
Size:	1.62 MB
ID:	189970  
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

Toshi 975 is offline Reply With Quote Quote 
Old 16-04-2018   #32
Join Date: Jun 2009
Posts: 663
Thanks: 52
Trader Rating: 0
United Kingdom 
Re: Damage to piston skirts

The engine was said to have done less than 3,000 miles but I have every reason to believe that it would have been well thrashed in the time. In freeing off the rings on that piston, middle one still to go, the oil scraper ring came out in two pieces plus the spring inner piece. No 1 cylinder looks fine. I am wondering if the ring was broken on assembly and caused the damaged stripes in some way.
Attached Thumbnails
Click image for larger version

Name:	image.jpeg
Views:	9
Size:	1.87 MB
ID:	189971  
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

Toshi 975 is offline Reply With Quote Quote 
Old 16-04-2018   #33
Join Date: Dec 2014
Location: Ripon
Posts: 513
Thanks: 16
Trader Rating: 0
Bleeding Knuckles has donated!
United Kingdom 
Re: Damage to piston skirts

Hi Dave, the attached pics show the damage done to one of my new pistons with the corresponding vertical markings the third pic shows the same piston with the position of the marks. I can only surmise that the damage is due to overheating and I am investigating the exact piston to bore clearance used during rebore. I am aware that 'standard' oversize pistons should have a clearance of 0.020 to 0.040mm - 'Athena' use 0.06 to 0.08mm in their modification running at 10.3:1 C/R. With a bit of luck the Italian maker of my pistons should get back soon with the 'approved' clearance ?????
Ian.
Attached Thumbnails
Click image for larger version

Name:	IMG_20170808_112348.jpg
Views:	7
Size:	1.44 MB
ID:	189974   Click image for larger version

Name:	IMG_20170808_112354.jpg
Views:	8
Size:	1.09 MB
ID:	189975  

Click image for larger version

Name:	IMG_20180408_183827.jpg
Views:	8
Size:	1.61 MB
ID:	189976  
__________________
Si dice in Sicilia non c'e nulla di piu pericoloso di una Donna con fucile da caccia.

Abarth - Piccola ma Wicked
Bleeding Knuckles is offline Reply With Quote Quote 
Old 17-04-2018   #34
Join Date: Jan 2014
Location: Ireland
Posts: 700
Thanks: 87
Trader Rating: 0
Ireland 
Re: Damage to piston skirts

Quote Originally Posted by Toshi 975 View Post
A hint of sunshine and I finally got outside and gave the worst piston from no 2 cylinder a bit of a soak in petrol. The 795cc engine was mothballed in 1985 and some oil poured into the bores that had now gone to the consistency of a very thick grease. The piston from no 1 is virtually unmarked but no 2 has 4 very distinct vertical bands of rubbing front and back of the piston. The bands do not seem to correspond to any feature inside the piston.
Hi Dave,

Was No.2 cylinder the one that had no oil splash from the con. rod due to the oil hole being blocked by the fitting of the wrong bearing shell? I suspect the score marks on the piston skirt were as a result of lack of oil splash, not a broken ring. I've stripped many old well-worn Fiat engines, some have had broken oil control rings - none had bore damage or piston damage as a result - they just burned oil

Looking at No.2 piston, there appears to be a lot of carbon build-up on the ring lands (spaces between the ring groves) for an engine that supposedly only covered 3000 miles. Does No.1 piston look the same in this area?

It's possible, as you suggest, that the oil control ring was broken when engine was being assembled and this would likely allow too much oil to bypass the oil control ring resulting in excessive carbon build-up. If this was the case, it would probably result in some oil being burnt and some blue smoke from the exhaust.

Point of technical interest :- notice the expansion control slot in No.2 piston in the oil ring groove. This is to divert heat from the piston head away from the thrust faces of the piston skirt, thereby reducing expansion across them.

If the oil spray issue has been corrected, I think you could just clean everything up and reassemble with new rings - assuming that neither piston has collapsed across the skirt - if both piston measure the same I'd be satisfied. I've cleaned up worse damage to pistons in the past - they all worked and lasted just fine - ask if you want details on how-to, but it's not rocket science....

I can't remember if you intended fitting new pistons or not, but regardless, unless you're going to hone the cylinder bores, check that there's no wear lip
starting to form near the top of the cyl. bores as this can damage new rings.
This is unlikely to have happened in 3000 miles of use but worth checking.
(there are also special 'ridge-dodger' top rings which have a small step to avoid contact with any wear lip, available from specialist suppliers if needed)

Al.
__________________
If what I write is helpful please click on the 'thanks' button, (smiley face on lower right).

Last edited by F123C; 17-04-2018 at 02:47.
F123C is offline Reply With Quote Quote 
Old 17-04-2018   #35
Join Date: Jan 2014
Location: Ireland
Posts: 700
Thanks: 87
Trader Rating: 0
Ireland 
Re: Damage to piston skirts

Quote Originally Posted by Bleeding Knuckles View Post
---------------------------
------------------------------------------------
---------------------------------
-------------------- With a bit of luck the Italian maker of my pistons should get back soon with the 'approved' clearance ?????
Ian.
The answer is probably on it's way to you right now, in a Mail bag, on a slow boat, from China

AL.
__________________
If what I write is helpful please click on the 'thanks' button, (smiley face on lower right).

Last edited by F123C; 17-04-2018 at 02:53.
F123C is offline Reply With Quote Quote 
Old 17-04-2018   #36
Join Date: Jan 2014
Location: Ireland
Posts: 700
Thanks: 87
Trader Rating: 0
Ireland 
Re: Damage to piston skirts

Quote Originally Posted by Bleeding Knuckles View Post
Hi Dave, the attached pics show the damage done to one of my new pistons with the corresponding vertical markings the third pic shows the same piston with the position of the marks. I can only surmise that the damage is due to overheating and I am investigating the exact piston to bore clearance used during rebore. I am aware that 'standard' oversize pistons should have a clearance of 0.020 to 0.040mm - 'Athena' use 0.06 to 0.08mm in their modification running at 10.3:1 C/R. With a bit of luck the Italian maker of my pistons should get back soon with the 'approved' clearance ?????
Ian.
Hi Ian,

Your pics are very interesting.....

No marks on piston skirts across thrust faces so piston to bore clearance is probably just fine.
Piston on left - milled from a solid billet - too much mass of material across gudgeon pin bosses compared to a standard cast piston. I think this is where the problem lies.

If this was my engine :- I wouldn't increase piston to bore clearance.
I'd remove the piston rings, file all torn/scraped material away (4 lines on piston) plus a bit extra for clearance (or luck!), clean up the ring grooves using a needle file just enough so rings are free, clean up any marks on the cylinder bores and ......

Reassemble the engine using the old gaskets (I don't like wasting gasket sets). Run engine for 2-300 miles. Strip engine, check how things are faring re. piston clearance etc. If everything is now ok, reassemble with new gaskets and enjoy the car for the summer.

Remember, whenever an engine is modified, things don't always work out the first time. Sometimes, it takes a few cycles of build/try/strip to find cause of problem/reassemble, to get things just right. Don't lose heart

AL.
Thanks Bleeding Knuckles thanked for this post
__________________
If what I write is helpful please click on the 'thanks' button, (smiley face on lower right).

Last edited by F123C; 17-04-2018 at 03:17.
F123C is offline Reply With Quote Quote 
Old 17-04-2018   #37
Join Date: Dec 2014
Location: Ripon
Posts: 513
Thanks: 16
Trader Rating: 0
Bleeding Knuckles has donated!
United Kingdom 
Re: Damage to piston skirts

Quote Originally Posted by F123C View Post
Hi Ian,

Your pics are very interesting.....

No marks on piston skirts across thrust faces so piston to bore clearance is probably just fine.
Piston on left - milled from a solid billet - too much mass of material across gudgeon pin bosses compared to a standard cast piston. I think this is where the problem lies.

If this was my engine :- I wouldn't increase piston to bore clearance.
I'd remove the piston rings, file all torn/scraped material away (4 lines on piston) plus a bit extra for clearance (or luck!), clean up the ring grooves using a needle file just enough so rings are free, clean up any marks on the cylinder bores and ......

Reassemble the engine using the old gaskets (I don't like wasting gasket sets). Run engine for 2-300 miles. Strip engine, check how things are faring re. piston clearance etc. If everything is now ok, reassemble with new gaskets and enjoy the car for the summer.

Remember, whenever an engine is modified, things don't always work out the first time. Sometimes, it takes a few cycles of build/try/strip to find cause of problem/reassemble, to get things just right. Don't lose heart

AL.
Greetings Al, I note what you say thanks and lo and behold 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.
Thanks jackwhoo thanked for this post
__________________
Si dice in Sicilia non c'e nulla di piu pericoloso di una Donna con fucile da caccia.

Abarth - Piccola ma Wicked
Bleeding Knuckles is offline Reply With Quote Quote 
Old 17-04-2018   #38
Join Date: Apr 2017
Posts: 1,783
Thanks: 123
Trader Rating: 0
United Kingdom 
Re: Damage to piston skirts

I'm thinking that should be 0.10 mm to 0.12 mm
Which is approx 0.004 inch to 0.005 inch
Or to put it another way 4 to 5 thousands of and inch.
That's pretty close to the Athena kit figures.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides


Last edited by jackwhoo; 17-04-2018 at 13:52.
jackwhoo is offline Reply With Quote Quote 
Old 17-04-2018   #39
Join Date: Dec 2014
Location: Ripon
Posts: 513
Thanks: 16
Trader Rating: 0
Bleeding Knuckles has donated!
United Kingdom 
Re: Damage to piston skirts

Quote Originally Posted by jackwhoo View Post
I'm thinking that should be 0.10 mm to 0.12 mm
Which is approx 0.004 inch to 0.005 inch
Or to put it another way 4 to 5 thousands of and inch.
That's pretty close to the Athena kit figures.
Thanks JW, never did get decimal points correct

Ian.
__________________
Si dice in Sicilia non c'e nulla di piu pericoloso di una Donna con fucile da caccia.

Abarth - Piccola ma Wicked
Bleeding Knuckles is offline Reply With Quote Quote 
Old 17-04-2018   #40
Join Date: Dec 2014
Location: Ripon
Posts: 513
Thanks: 16
Trader Rating: 0
Bleeding Knuckles has donated!
United Kingdom 
Re: Damage to piston skirts

Have just heard from the engineer who did the work for the rebore, he states that the cylinders would have had a 4 thou piston clearance and as the cylinders have been rehoned after the last piston damage that would make it very slightly more than 4 thou. So my cylinders do have the correct piston to bore clearance!!!! I now have to pay attention to Cooling, Timing and fuel grade. My oil cooler fan switch is being changed for one that will start the fan sooner (87DegC) and run until (77DegC)
Hey Ho back to running in (after rebuild - again!)
Ian.
__________________
Si dice in Sicilia non c'e nulla di piu pericoloso di una Donna con fucile da caccia.

Abarth - Piccola ma Wicked
Bleeding Knuckles is offline Reply With Quote Quote 
Old 18-04-2018   #41
Join Date: Jan 2014
Location: Ireland
Posts: 700
Thanks: 87
Trader Rating: 0
Ireland 
Re: Damage to piston skirts

Quote Originally Posted by Bleeding Knuckles View Post
-------------------
------- 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.
Thanks Bleeding Knuckles thanked for this post
__________________
If what I write is helpful please click on the 'thanks' button, (smiley face on lower right).

Last edited by F123C; 18-04-2018 at 08:15.
F123C is offline Reply With Quote Quote 
Old 18-04-2018   #42
Join Date: Dec 2014
Location: Ripon
Posts: 513
Thanks: 16
Trader Rating: 0
Bleeding Knuckles has donated!
United Kingdom 
Re: Damage to piston skirts

Quote Originally Posted by F123C View Post
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 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 ???? You then have to pester the Italian maker for details - are we in the EU or what ???? 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 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!!!
Ian.
Likes F123C liked this post
__________________
Si dice in Sicilia non c'e nulla di piu pericoloso di una Donna con fucile da caccia.

Abarth - Piccola ma Wicked
Bleeding Knuckles is offline Reply With Quote Quote 
Old 18-04-2018   #43
Join Date: Apr 2017
Posts: 1,783
Thanks: 123
Trader Rating: 0
United Kingdom 
Re: Damage to piston skirts

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.
Likes F123C liked this post
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

jackwhoo is offline Reply With Quote Quote 
Old 18-04-2018   #44
Join Date: Dec 2014
Location: Ripon
Posts: 513
Thanks: 16
Trader Rating: 0
Bleeding Knuckles has donated!
United Kingdom 
Re: Damage to piston skirts

Quote Originally Posted by F123C View Post
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
It will indicate from -200 to +1300 degC !! with a 14mm ring fitting to go under the spark plug 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!!!
Ian.
__________________
Si dice in Sicilia non c'e nulla di piu pericoloso di una Donna con fucile da caccia.

Abarth - Piccola ma Wicked
Bleeding Knuckles is offline Reply With Quote Quote 
Old 19-04-2018   #45
Join Date: Jan 2014
Location: Ireland
Posts: 700
Thanks: 87
Trader Rating: 0
Ireland 
Re: Damage to piston skirts

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.
__________________
If what I write is helpful please click on the 'thanks' button, (smiley face on lower right).
F123C is offline Reply With Quote Quote 
Reply
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump
Similar Threads
Thread Thread Starter Forum Replies Last Post
(T) Piston damage grapeman Punto (Mk2/2b) 18 20-06-2015 22:42
(G) multipla 1.6 piston damage Deejwatson Multipla 4 03-09-2013 16:48
(T) Punto 1.1 Fire engine, Piston damage Simples31 Punto (Mk1) 9 05-10-2011 22:52
(T) Piston damage, what has casued this? ralphnz Uno 4 02-12-2008 17:14
how can i repair this? (damage on plastic skirts) beau Bodyshop 8 09-03-2006 01:15